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Packard 54600A - 100MHz -2 channel £750Hewlett Packard 54610A - 500MHz - 2 channel £1850Hewlett Packard 54502A - 400MHz-400 MS/s 2 channel £1800Hitachi V152N212N222N302BN302FN353FN550BN650F from £125Hitachi VI 100A - 100MHZ - 4 channel £900Intron 2020 - 20MHz. Dual channel D.S.O. (new) £450lwatstu SS 5710/SS 5702 - from £125Kikusui COS 5100 - 100MHz - Dual channel £350Lecroy 9354M 500MHz - 2 Gs/s - 4 channel £6000Lecroy 9314L 300MHz - 4 channels £3000Meguro MSO 1270A - 20MHz - D.S.O. (new) £450Philips PM3094 - 200MHz - 4 channel £1750Philips 3295A - 400MHz - Dual channel £1600Philips PM3392 - 200MHz - 200Ms/s - 4 channel £1995Philips PM3070 - 100MHz - 2 channel - cursor readout £750Tektronix 465 - 100MHZ - Dual channel £350Tektronix 464/466 - 100MHZ - (with AN. storage) £350Tektronix 475/475A - 200MHz/250MHz - from £450Tektronix 468 - 100MHZ - D.S.O. £650Tektronix 2213/2215 - 60MHz - Dual channel £350Tektronix 2220 - 60MHZ - Dual channel D.S.0 £995Tektronix 2235 - 100MHZ - Dual channel £600Tektronix 2221 - 60MHz - Dual channel D.S.O £995Tektronix 2245A - 100MHZ - 4 channel £900Tektronix 2440 - 300MHz/500 MS/s D.S.O. £2450Tektronix 2445A/2445B - 150MHz - 4 channel £1000Tektronix 2445 - 150MHZ - 4 channel + DMM £1200Tektronix TAS 475 - 100MHZ - 4 channel £995Tektronix 7000 Series (100MHZ to 500MHZ) from £200Tektronix 7104 - 1GHz Real Time - with 7A29 x2, 7610 and 71315 from £2500Tektronix 2465/2465A/2465B - 300MHz/350MHz 4 channel from £1250Tektronix 2430/2430A - Digital storage - 150MHz from £1250Tektronix 2467B - 400MHz -4 channel high writing speed £4750Tektronix TDS 310 50MHz DSO - 2 channel £750Tektronix TDS 320 100MHz 2 channel £850Tektronix TDS 340A 100MHz DSO - 2 channel £1250Tektronix 544A 500MHz 4 channel £4950

SPECTRUM ANALYSERSAndo AC 8211 - 1.7GHz £1500Avcom PSA-65A - 2 to 1000MHz £850Anritsu MS 6108 10KHz - 2GHz - as new £3500Advantest/TAKEDA RIKEN - 4132 - 100KHz - 1000MHz £1500Hewlett Packard 8756A/8757A Scaler Network Analyser from £1000Hewlett Packard 853A Mainframe + 8559A Spec. An. (0.01 to 21GHz) £2750Hewlett Packard 182T Mainframe + 8559A Spec. An. (0.01 to 21GHz) £2250Hewlett Packard 8568A (100Hz - 1500MHz) Spectrum Analyser £3500Hewlett Packard 85688 - 100Hz - 1500MHz £5250Hewlett Packard 8567A - 100Hz - 1500MHz £3995Hewlett Packard 8752A - Network Analyser (1.3GHz) £5995Hewlett Packard 8754A - Network Analyser 4MHz-1300MHz £1500Hewlett Packard 8591E 9KHz-1.8GHz £4250Hewlett Packard 3561A Dynamic signal analyser £3995Hewlett Packard 35660A Dynamic signal analyser £3250IFR A7550 - 10KHz-1GHz - Portable £1950Meguro - MSA 4901 - 30MHz - Spec.Analyser £700Meguro - MSA 4912 -1MHz - IGHZ Spec.Analyser £995Tektronix 2712 Spec. Analyser (9kHz - 1.8GHz) £3750Wandel & Goltermann TSA-1 system analyser (100Hz-180MHz) £2750Wiltron 6409 - 10-2000MHz R/F Analyser £1750

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83 COMMENTNo laughing matter

84 NEWS UK firms excluded from European R&D Flexible organic LED research Memory and logic fault -tolerance news Power switching and logic combined Digital broadcasts on AM a step nearer UK telecoms operators avoiding xDSL

90 BIOMETRICSAND BEYONDSteve Bush reports on new biometrictechnology that is now cheap enough to

allow banks and health authorities toidentify people quickly and reliably.

92 PHASE -LINEARSUB -BASS BOOSTERSmall, enclosed sub -woofer cabinets canpotentially produce more realistic soundthan their big -box counterparts, but theyfail to do so because of phase shifting inthe electronic equaliser, arguesGraham Maynard. Here, Grahampresents a general-purpose sub -bassbooster with phase -linear performance.

99 AN IDEAL TRANSISTORWith the aim of helping you producemore effective analogue designs,Bryan Hart explains how it is possible todevelop a set of 'ideal' transistor models.This second article deals with dynamicmodels.

102 USING FUZZY LOGICUsing conventional software methods todesign fuzzy logic circuits leads tounnecessary complexity.Douglas Clarkson looks at alternativeways of implementing it.

108 HANDS ON INTERNETCyril Bateman reports on novelapproaches to power measurement -including PIC circuits and new chips thatreplace the electro-mechanics in domesticpower meters.

114 ACCURATEMILLI -OHM METERWith a most sensitive range of 0 to150m0, David Ponting's low-cost andself-contained milli -ohm meter measureslow resistances without injecting a largecurrent into the resistor under test. Themeter can be used to locate solder bridgesand PCB shorts as well as measuringresistances.

119 NEW PRODUCTSNew product outlines, editedby Richard Wilson

130 SPEAKERS' CORNER"All of the problems associated withdesigning a dome loudspeaker can besolved by relegating it to the function of adust cap in the middle of a cone", arguesJohn Watkinson.

132 ANALYSING THEDIFFERENTIALAMPLIFIERLionel Gay presents a precise analysis ofthe emitter -coupled differential amplifier.

134 CIRCUIT IDEAS Digital metal detector Generating 00K, PSK and FSK Versatile test oscillator Ideal rectifier works at video speed Novel audio level indicator CMOS logic frequency tripler Improved lead -acid charger

147 CURRENT CONVEYORSGiuseppe Ferri et al present a guide tocurrent conveyors in three parts, the firstof which gives you a brief history of thisfrequently overlooked circuitconfiguration.

152 WEB DIRECTIONSUseful web addresses for theelectronics designer

156 LETTERSPhase shifter for headphones, A ministerfor electronics? Curve tracing, X-raycomments, Better buffers rebuffed.

March issue on sale 1 February

Non -conformal

coating

Cover photography Mark Swallow

Unusually, David Ponting'saccurate milliohm meter - shownhere measuring a 50m52 1%resistor - does not involve drivinga high current through theresistance. Turn to page 114 tofind out how it works.

Reflection path Dome

Surround

Coil

Magnet

If you've just invested in anexpensive hi-fi incorporating domeloudspeakers, please avoid page 130.

SPECIAL OFFERDevelop fast ISP 8051s foraround £50, save £25,see page 144

Organic LEDs that canbe printed onto aflexible polymer layerhave many uses,particularly if they canbe produced in matrixform. Steve Bushreports on the currentstate-of-the-art onpage 86.

February 2001 ELECTRONICS WORLD 81

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3 BIPOLAR TRANSISTOR: Powe Output Stage.

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VCEO =VCPO =100V

1.331 611 I lin pto

Stored Dotal Volu

Multiply each digit

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value and add.

x x

8 7

72 0 24 ac power = Vce(ims) x Ic(rrn)) =11.55W

Divide total by 11, remainder becomes the

Modulo 1

power =icc x

.rnplifier efficiency ( ni=;?1,c: pprweer, x 100 = 19.24

Operator key entry = 55443322

(5x3)+(5x 7) * (4 e 6) + (4 5) + (3 rt + )3 x 31 +12 x 21 + (2 x 1) = 146

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Acceleration a (miss)

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No laughing matterLately this magazine's leader columns have takena depressing and even hectoring turn pointing

out the inadequacies in the way that UK plc andBritain.com are managed. Far be for me to breakthe trend, although this month's sermon (or is itharangue?) does at least target a different failing.

First of all, though, a word of praise.Technologists - the kind of people who read thismagazine and turn electronic concepts in to reality- can take a bow. They are the people whoconsistently come up with new ideas and deliverworking products and services, often within budgetand timescale. Well done!

It's funny then - in an un-funny way - that manybusiness leaders are far less adept in exploitingthose developments, particularly in the field ofelectronic business. There's overwhelmingevidence that e -business is set to revolutionisesupply chains as online market -makers begin todemonstrate savings arising from using the Internetto make purchases. Survival, profitability andopportunities for future cost savings and growth alldepend on its adoption, with trading on the Internetdelivering greater market penetration, increasedresponsiveness to customers, more flexibility andlower costs.

It's a concept already adopted by businesses inthe USA and a message that British business woulddo well to heed, according to the EngineeringCouncil, which issued a rousing wake-up call toUK plc in December.

Many valuable insights arose from this top-levelforum, in particular that UK businesses would dowell to accept, as the Americans do, that change isthe only constant in modern business. The moral isto embrace this 'change culture' with theenthusiasm and vigour of US businesses.

It is better to take the risk and invest intransacting either directly with customers orthrough e -marketplaces, than not to take the riskand exclude any chance of business -to -businesssuccess.

While uptake of e -business offers many benefits,it also entails significant challenges. Many of thesechallenges are a mixture of technological, culturaland legal issues, all of which should be seen in thecontext of the business they are designed tosupport. Serving that business and its customersmust be the key objective.

The biggest threat of e -business will be thatarising from inaction - being left behind - whengiven the opportunity to take part in what maybecome a key e -market place for a relevantindustry sector.

Many of those who best understand the speed andimpact of e -business are young. Many of those whomake the strategic decision to invest in exploiting

e -business are experienced and probably not soyoung. This is one issue in which the experiencedcould benefit from being mentored by the young.

Engineers with change -management skills arewell placed to manage programmes to develop andimplement e -business systems.

Crucial to success in e -business is the customer -supplier interface. Much more effort must be madehere. "Customers are overwhelmed and confusedabout adopting e -business for their needs,"declared David Smith of ICL to forum delegates."E -business solutions are not a straight replacementfor existing systems and processes, although manypurport to be that. If e -business solutions are to besuccessful then traditional methods and processesneed to be forsaken to allow a new operation toemerge."

Considerable improvement is needed also forwebsites, often used as the portal to e -businessactivity. Simple is best here, even though far toomany websites exist purely as a monument to theextreme virtuosity of their designers or thecorporate vanity of the organisations thatcommissioned them.

"There are 20 million sites on the Web and nearlyall of them are awful," declared American websitedesign and usability guru Jakob Nielsen, on a visitto London a week previously. "When peopledesign websites, they rely too much on their ownperceptions of style and aesthetics, without givingenough thought to how the average user, diallingup on a slow connection and lacking thesophisticated aesthetic sensibilities of a designprofessional, will explore the site. As a result," hecontinues, "users lose interest trying to fight theirway through the artistic graphics to find what theyreally want and immediately develop a jaundicedperception of sites that fail to come up with thegoods.

"If a site has not delivered the desiredinformation within a few seconds, one click andthey're off to a competitor - meaning lost profits tothe website owner."

Those who bear no responsibility for theseshortcomings may smirk, but it's no laughingmatter. They may argue too that their motivationfor reading this magazine is to learn about newtechnologies in electronics and how to apply them- not to be harangued on the incompetence of theirmarketing colleagues.

All the same, the issue is highly relevant, sincetechnologists will starve if their employers fail tosell the products they create. For each and everyperson who earns a living from electronics, thewriting is on the wall: embrace e -business or be leftbehind at the mercy of your competitors.

Andrew Emmerson

Electronics World is published monthly. By post, current issue £2.65,back issues (if available). Orders, payments and general correspondenceto 1514, Electronics World, Quadrant House, The Quadrant,Sutton, Surrey SM2 SAS. Tlx:892984 REED BP G. Cheques shouldbe made payable to Reed Business Information LtdNewstrade: Distributed by Markelforce (UK) Ltd, 247 Tottenham CourtRood London WI P OAU, tel. 020 7907 7777.Subscriptions: Quadrant Subscription Services, Oakfield HousePerrymount Road, Haywards Heath, Sussex RH16 3DH. Telephone01444 445566. Please notify change of address.Subscription rates 1 year UK £36.00 2 years £58.00 3 years £72.00.Europe/Eu 1 year £51.00 2 years £82.00 3 years £103.00ROW 1 year £61.00 2 years £98.00 3 years £123

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Reed Business Information Ltd 1997 ISSN 0959 8332


Iti!DATEPan European R&D initiative:UK firms excluded because of DTI rulesBritish electronics firms are to be cutout of a new pan-European researchinitiative because of rules imposedby the UK Department of Trade andIndustry (DTI). Exclusion will affectUK companies' competitiveness.

MEDEA (Microelectronics forEuropean Development andApplications) has been extendedfor another eight years under thetitle `MEDEA+'. MEDEA+ wasaccepted as a Eureka project inJune, and approved its first 18R&D projects toward's the end of2000.

More projects in the rt4bnprogramme are expected to beapproved throughout December.

"The UK is not participating inMEDEA+," said MEDEAchairman Dr Jurgen Knorr, "but itis considering the situation andmaybe they'll come to a decision tojoin later on."

Participation by UK companiesis restricted under DTI rules whichtotally ban big companies fromjoining, and make it onerous forsmall companies to participate. TheDTI's attitude persists, despite thefact that one of the biggest recentUK technology successes -Bookham Technology - got muchof its early funding from aEuropean research project.

In the original MEDEA, a total

of 9400 man-years of research wascompleted. The French accountedfor 3512 man-years, the Dutch for1839, the Germans for 1614, theBelgians for 1056, the Italians for1111, the Finns for 89, the Swedesfor 31, and the British for 16.

MEDEA has had some notablepast successes such as GSM,xDSL, automotive and smartcardtechnologies in all of whichEuropean companies are worldleaders.

Companies in the UnitedKingdom complain that by beingexcluded, they get to exploit theresults of R&D later thancompanies in mainland Europe.

Telecoms operators are avoiding xDSL technologyTelecoms network operators arefinding they prefer to install the15 -year -old ISDN technology forupgrading telephone lines, ratherthan the latest, and much morepowerful, xDSL technology.

"ISDN is how the telcos canstabilise revenues," said ChristianWolff, v -p and general manager ofInfineon Technologies' carrieraccess division, speaking atElectronica 2000 last November .

"ISDN provides two channels,and allows voice calls. It is veryeasy to install and subscribers gettwo numbers," he added.

This means that telecomsoperators or telcos can still getlucrative, time -monitored voicerevenues rather than having thosewiped out by xDSL technologywhich allows voice over InternetProtocol (VOID) calls which aremost conveniently paid for by a flatfee for 'always on', broadbandInternet connection.

"ADSL has the flat -fee problem.ISDN is more strategic for telcos,"said Wolff. So attractive do UStelcos find the ISDN alternative,that they are marketing it overthere as IDSL'.

Wolff is finding particularlylucrative markets for ISDN chip -sets in China. "China installs 30

million new analogue lines a year.ISDN is a solid business which fillsthe fabs and creates a stablerevenue flow."

Nonetheless, Wolff does notbelieve that telcos can resistbroadband xDSL for ever. "I can'timagine the network will stayanalogue, it has to be upgraded todigital. If the telcos don't installbroadband then cable modem willtake over and they'll lose outanyway."

Wolff added: "Infmeon's xDSLstrategy is to solve the deploymentissues so people can install

DSLAM' s (DSL access modules)more quickly. We will introducesuch products early next year."

Infineon's new DSLAMs will be`multi service access platforms'which include ADSL and theexisting telephone network, knownas POTS, in one box and so reducethe number of connections.

"The POTS splitter is includedin the chip -set," said Wolff, "andADSL is integrated with it, it's justlike installing a new analogue line.The vision is to enable massdeployment."

David Manners

Touch -screen feature added to flat loudspeakersFlat speaker specialist NXT is adding a touch -screen capability to its loudspeakers.

Called TouchSound, it fits in front of an LCD or any other flat screen, just like SoundVu, thefirm's loudspeaker -in -a -screen system.

"SoundVu has little exciters to resonate the panel. If we also feed an ultrasonic signalthrough these exciters we know exactly what to expect at the receiver," said a spokespersonfor the company.

When a finger or pen presses on the screen, it disrupts the complex pattern of resonantmodes on the screen. The sound at the receiver changes, and NXT has figured how to calculatethe position.

But does it affect the sound when the screen is pressed?"In theory yes, in practice no. You can't even hear any difference," said the spokesperson. He

claimed the resolution and accuracy are as good as other touchscreen technologies usingcapacitive or resistive techniques.

84 February 2001 ELECTRONICS WORLD

The science lab in a PCExperiments Ideas for DrDAQ

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UPDATE

Five layers of highdensity dielectriccould be the key

to long life fororganic LED

displays.

Si02

Path cleared for digital AM broadcastThe way is clear for digital radio tomove onto the AM wavebandsfollowing the ITU' s adoption of aworldwide standard on digital soundbroadcasting.

The standard adopted wassubmitted by the DRM (DigitalRadio Mondiale) consortium whichhas been working towards digitalbroadcasting in the AM bands below30MHz since 1998.

Digital AM will operate alongside

the Eureka 147 digital audiobroadcasting (DAB) standard butwill be unable to offer the dataservices of DAB. This should lead tocheaper sets.

"With digital AM, you'rerestricted in bandwidth and you'renot going to be able to do muchmore than convert what you've gotto digital," said Peter Florence,managing director of RadioScape."But it does take it into the digital

age so you should get improvementsin audio quality which will besignificant."

Software house RadioScape hasbeen tracking the progress of digitalAM and has already carried outpreliminary work on it.

The final digital AM standard isexpected to be available towards theend of 2001. Pilot transmissions willstart in 2002 with the official launchin 2003.

Organic LEDs on flexible plastic substrates:possible, but not easyThe Society for Information Display(SID) 2000 UK conference was heldat the Electronic InformationDisplays show held at London'sDocklands in November 2000.

Mike Weaver of US -basedUniversal Display Corporation spokeon the state-of-the-art for flexibleorganic LED displays (OLEDS).

In a down-to-earth presentation,he described the solutions thecompany has found to some of theproblems of producing workable

or -----.

Non-conformalcoating

+75nm

'Baird TV' might catch on yetRemarkably, a demonstration of this 70 year -oldtechnology may show a way forward for mobilevideophones. The Narrow Bandwidth TelevisionAssociation, a historian society, was showing a 32 -linevertically -scanned 3:2 'door' format head and shouldersmovie of someone talking. The 48 x 32 pixel movingmonochrome image was perfectly recognisable andonly requires a 12.5kbit/s uncompressed data stream.The image is clear, apparently, because the human brainis exceptionally good at filling in the missing data whenfaces are transmitted. No other images were shown onthis display, but its maker said that perceived qualitysuffers when the subject is not a face.

OLEDs on plastic films.Display lifetime is a big issue with

OLED material, not only from theinherent emissive lifetime of thematerials, but from poisoning.

Unfortunately, the chief poisonsare water and oxygen. Apparentlyany exposure makes short work ofdestroying the OLED.

Glass and metals effectively blockwater and oxygen, but plasticsubstrates, "look like a sieve towater", according to Weaver.

To get over water and oxygeningress without compromisingflexibility, the company hasdeveloped a coating called Barix.

This consists of a series of layersof a dense transparent dielectric -aluminium and silicon oxides weregiven as examples - separated bysurface levelling layers ofnon -conformal coating.

To keep the dielectric layers freefrom leaky pin -holes and grainboundaries, thickness is restricted toless than 70nm per layer.

This means around five layers tokeep out moisture and air for the10000 hour planned operating life ofthe displays - 5000 hours is theaverage life of a car apparently.

Existing measurement equipmentis an order of magnitude tooinsensitive to measure thepermeability of the Barix structure,which Weaver estimates to be under10-6g/m2/day.

"The best way to measurepermeability at the moment to tobuild the display," said Weaver.Plastic has a permeability of up to1g/m2/day.

Current life of the company'sprototype flexible OLEDs, measuredby accelerated life testing, is 1000hours. This is limited, he claims, bythe display material rather than

ingress as far as anyone can tell. "Bymid -2001 we may be up there, to10 000 hours," he said.

The Holy Grail of OLED researchis an active matrix display on plastic,and constructing the matrix iscausing headaches. Basically thesubstrate is damaged at 70°C andpolysilicon is processed at 400°C.

There are two approaches to asolution according to Weaver. Thefirst is an alternative plastic. Amaterial called PEE is being workedon by the plastics industry whichcould be processed at up to 500°C.Meanwhile, work by Lucent andPhilips may produce organic ratherthan polysilicon transistors whichwill be processed at lowtemperature.

Whatever the substrate, conductortechnology now seems available toget power to the OLEDs, which arelow -voltage, high -current devices.

Steve Bush

LCD backroundenhancerDuPont has developed a holographicreflector material that increases thevisual impact of standard`watch -type' black -on whitereflective LCDs.

The film is self-adhesive andreplaces the reflective metal diffusernormally employed.

Displays with this backing have a`brighter' more eye-catchingbackground than those with a metaldiffuser and either a blue, gold, greenor red sheen - depending on the filmchosen.

It works by 'bunching' reflectedambient light at approximately 90° tothe display.

86 ELECTRONICS WORLD February 2001

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UPDATE

Cambridge start-up finds a way tocombine high -voltage switching circuitswith CMOS logicA spin-off from CambridgeUniversity claims to have developeda technique for integrating high -voltage power -switching circuitsalongside standard CMOS logic.

Called Cambridge Semiconductor,the start-up plans to begin prototypeproduction of its invention. Thisinvention is the result of ten yearsresearch in the University'sDepartment of Engineering.

Combining logic and high -voltageswitching circuits is one of the bestroutes to reducing powerconsumption of consumer goods.

"Power ICs will allow us toefficiently integrate powerelectronics into a standard CMOS

process," said Professor GehanAmaratunga, who heads up the newcompany.

The circuits can cope withvoltages up to 600 or 700V, "whichis what is required for mainsconnected power management",Amaratunga said. Able to handlecurrents of up to 1.5A, the devicesare aimed at goods under 1kW.

These sorts of levels have onlybeen achieved by one or perhapstwo other companies, includingHitachi in Japan.

Typical circuits implemented bythe chips would be mains AC -to -DCconversion, control circuitry,followed by efficient inversion back

to AC to drive a motor."The whole thrust is to get away

from the single phase AC motor,"Amaratunga said.

The firm reckons any devicesupplied with mains electricitycould benefit from the technology -including PCs and vacuum cleaners.Today's vacuum cleaners forexample are around 50 per centefficient, but they could be mademore than 90 per cent efficientusing power ICs.

Cambridge Semiconductor hasreceived a £250000 investmentfrom the University's ChallengeFund.

Richard Ball Electronics Weekly

Space -borne error detection landsin French design houseSingle event upsets (SEUs) and softerrors have been a feature of space -borne electronics for many years.However, we are reaching the pointwhere SEUs - which can causecatastrophic failure of a system - areappearing in earth -bound systems,due to decreasing feature sizes.

iRoC Technologies, a design housebased in Grenoble, France, hasdeveloped a technique for addingfault tolerant circuitry which it hasapplied to a 32 -bit Risc processor.

Most SEUs are caused by cosmicradiation - neutrons - flipping a bitinside a circuit by raising the localvoltage above the threshold for ahigh. Other soft errors includetemporary logic delays causingglitches and races.

iRoC reckons that three-quarters ofSEUs are the result of reduced Vddand noise margin - consequences of

750GHz logic uses niobiumLogic operating speeds of more than 750GHz havealready been achieved experimentally insuperconducting niobium, according to a report in theIEEE's Spectrum magazine. Rapid single flux quantum(RSFQ) logic, as it is called, works with the presence orabsence of a magnetic flux quanta that representsinformation bits. The report predicts the feasibility ofcommercial 100GHz superconducting ICs within thenext five years.

smaller geometries. At 0.13µm, saysthe firm, the soft error rate is oneevery few hours, while at 0.101.im it'sas many as one every couple ofminutes.

While memory can be checkedthrough standard error -correctionschemes, logic has no such fallback.

The aerospace solution ofreplicating logic several times over isjust not suitable for modernelectronics, especially in our pricesensitive consumer world.

iRoC's technology is called a`transient fault tolerant architecture',a collection of circuits distributedacross an IC. It is implemented at theregister transfer level of design.

"The extra circuitry on the logicdetects the transient," explained DrMichael Nicolaidis, chief technicalofficer at iRoC.

He claims the circuits are able toprotect almost all logic and memory,with over 98 per cent coverage of thechip. Performance is unaffected andthe whole process fits within astandard cell approach to design.

According to Nicolaidis, the extracircuitry adds around 17 per cent tothe die size, a significantly betterfigure than duplicating or eventriplicating logic.

To prove its point, iRoC has builtthe ROC S81, a 32 -bit processorbased on the Sparc architecture.

It is manufactured bySTMicroelectronics using a 0.25tim

process and runs at 100MHz. It isclaimed to be immune to SEUs.

The firm also has a collection ofEDA tools, including Shielder whichenables insertion of the test circuits. Itfits into a standard chip design flow.

Richard Ball

"We are creating aterrible disaster" claimsSTM's CEOThe earth cannot cope with thecurrent pace of economic growth,Pasquale Pistorio, CEO ofSTMicroelectronics told anElectronica 2000 gathering.

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The problem cannot just be leftto governments. "Companies andindividuals should take the initia-tive," said Pistorio.

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"ST will have zero CO' equiva-lent emissions by 2010, by whenwe will be neutral to the environ-ment," said Pistorio.


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UPDATE

Biometrics and beyondBiometrics used to be the territoryof seventies James Bond filmsor sci-fi books populated with

silver -suited types who could only getthrough doors by having their retinasscanned.

Now, the computing power neededfor processing the biometric algorithmsand the sensors for capturing thephysical data are becoming cheapenough to be used by banks and healthauthorities and to be integrated intomobile phones and smart cards.

Beyond the basic technology,however, biometrics poses somedifficult issues in terms of dataprotection, privacy and even humanrights.

The commercial use of biometrics ismainly about data security as moreservices and data become Internet -accessible by a growing number ofgadgets.

As the web enables stranger -to -stranger transactions, there's a need toauthenticate who's on the other end ofthe line. "Access and convenience arethe important drivers coupled withquestions as to the long termssustainability of the multiplePIN/password model," says AlineCoutts from the Nationwide BuildingSociety.

The Nationwide has just completed a6 month pilot study on speakerrecognition as part of a wider EuropeanCommunity project called Picasso thathas worthy aims to help people livingin remote areas have access to the sameinformation and services as peopleliving in urban areas. (Other partnersinclude Union Bank of Switzerland,University of Numegan, Perceptive,KPN Research and Vocalis.)

There is a growing range of

hardware and software forimplementing biometrics. There areseveral companies who make low costsilicon fingerprint sensors includingInfineon, Polaroid, STMicroelectronicsand Veridicom. These chips are basedon capacitive or image sensingtechniques and are being integratedinto computer mice for logging ontocorporate networks and smart cards.

Infineon promises to have flexiblecapacitive fingerprint sensors that areonly 4011m thick by the end of nextyear specifically for smart cardapplications.

hiScan, the company with the solepatent for using for the iris as abiometric, has just formed apartnership with Panasonic for a PCaccess device based on iris recognition.hiScan is also talking to automotivemanufacturers on immobilisationapplications.

Paul Stanborough aconsultant for hiScanreckons that irisrecognition could be cost-effectively added to everymobile phone. "You justneed a bit of software andthe ability to grab animage. CMOS imagesensors would be the wayforward because theydon't use much power."CMOS sensors couldalternatively be used forverifying the user's facialfeatures.

According to GrahamTownsend, technical director ofSTMicroelectronics' CMOS imagesensing division, the advantage ofusing optical sensing technology is thatyou are not limited by silicon size:"You have a lensing system that coversthe sensor to enable an image to betaken that is much larger than thesurface area of the chip.

"The state of the art is an opticalarea of 3 by 2.5mm. You can add abasic sensor to a system for under $10.Once you've got a CMOS imagesensor integrated into your phone, itcan be used for a host of cameraapplications including adding somesort of biometric."Problems, problemsHuman beings and the regulatoryenvironment are the difficult variablesin the biometric equation. If you live inthe Yemen you probably won't bat an

eyelid about the scary national IDscheme where everyone gets a swipe -card with a barcode that holds theirfingerprint code and the details arekept on a central database.

In Europe or the USA, this wouldcause a national outcry about humanrights and civil liberties.

It's all about personal biometric data(called the biometric template). Is itheld by the person who owns it or on acentral database? And if held centrally,how will it be safeguarded and whatelse might it be used for?

A recent story in the SundayIndependent about a UK scheme tocombat rising credit card fraud sumsup the issues nicely. The schemerequires shoppers to leave a realthumbprint on the back of their chequeor credit card slip so when there hasbeen a fraudulent transaction, policecan check it on a national fingerprintdatabase.

"What it means is that it leaves a lotof personal information sitting aroundon cheques and there is a hugepotential for abuse, said DeborahClark, director public affairs for thecivil rights organisation, Liberty. Shefears that the scheme could lead tofingerprint scans replacing signaturesas the means of security identificationwhich in turn could lead to a nationalidentity scheme via the back door.

"It is the tip of the iceberg. If thepolice have access to these recordsthere is a crime that has beencommitted, then that is one thing. Butif the banks were holding databases offingerprints, that is a completelydifferent matter," says Clark.

Marek Rejman Green of BT suggestssegmenting biometric templates as away of addressing concerns aboutidentity theft and privacy. In this way,the bits come together only at the timeof a network transaction rather like ajigsaw puzzle.

No one holds the entire template andit circumvents problems of someoneintercepting your biometric and youthen requiring... er... a new finger oreye or face?

And biometrics change over time.The voice, for example, is affected bythe psycho -physiological state of aperson and alters with age and illness.So, if you've got a cold and are in badmood, then presumably you might bedenied access to your bank account.

Steve Bush Electronics Weekly


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There is a trend towards small,closed sub -woofer cabinetsused in conjunction withelectronic boost to compensatefor the speaker's low -frequencyroll off. But although suchsystems can potentiallyproduce more realistic soundthan their big -boxcounterparts, they fail to do sobecause of phase shifting in theequaliser, argues GrahamMaynard. Here, Grahampresents a general-purposesub -bass booster with linearphase performance.

Hi-fi; stereo; semiconductors;digital; each of these milestoneaudio developments has

contributed towards the accuracy,miniaturisation and power ofaffordable music reproduction systems.

However, and in spite of suchtechnical developments, today's low -distortion tuners, CDs, and 20-20 flatamplifiers cannot ensure that we willenjoy 'fully realistic' soundreproduction. This is because theiraudio outputs are still used to drivepermanent -magnet loudspeakers inmuch the same way as they wereduring the twilight years of the classicvalve era.

I have no wish to denigrate anyquality audio system, whether solid orhollow state. Most can generally beadjusted to perform well, but no matterhow low their distortion, they cannotproperly replicate lower bass soundwaves with a flat 20Hz to 20kHz hi-firesponse. This is because;

loudspeaker transduction efficiencyfalls with reducing frequency

socially acceptable playback levelsmake some low -frequency boostnecessary to compensate for thenatural fall -off in human hearingabilities.

Equaliser effectsYou can use graphic equalisers andelectronic crossovers feedingindependently adjustable multi -channelamplifiers that drive separate bass, midand treble loudspeakers to constructthe most impressive of sound systems.Yet no matter how you adjust thecontrols to counter loudspeaker andhearing deficiencies, fully realisticreproduction remains frustratinglyelusive.

This lack of fidelity is due to thefrequency -selective -amplitudecorrections for the natural roll -offs thatoccur within the audio spectrum. Thesecorrections lead to our hearingbecoming subjected to frequency -variable phase changes and time delaysthat affect waveform coherence andtransient delivery.

Phase changes are why, for example,a little necessary bass boost from aBaxandall tone control or equaliserslider can sound okay. However, the

greater amounts of amplitudecorrection that we might ultimatelywish to correctly apply at lowerlistening levels, actually soundsomewhat off-putting. A 'loudness'control is little better, and if one isused in addition to bass boost then thesound becomes atrociously soft andboomy.

Purists might use headphones, orstick to a flat amplifier response thatthey know does not alter signal phaseor waveform coherence. Then, afterselecting the best loudspeakerequipment that they can afford, theysimply accept the natural lowfrequency roll -off that they can donothing about.

Fortunately for experienced ears, flatamplification has little effect on thereproduction of choral works and themusicality of classical string and windinstruments. Yet, while it is the musicand not the sound system that we listento, it occasionally becomes obviousthat some recordings have been madevia studio equipment that had itself notbeen running fully flat!

RealismFor most listeners however, flatamplification and conventionalloudspeakers will lead to aconsiderable loss of realism atplayback. This is especially so whenattempting to reproduce electronic andpercussion instruments, full orchestraand open air performances, or the deeplows 'ambience' of larger auditoriawhere longer wavelengths have had thefreedom to develop a `spatial' soundthat has been 'characterised' by thebuilding itself.

You might not be able to hear 10Hz,but infra -sound beats and standingwave sensations are physicallyobserved when we attend live classicaland pop music performances. Thesebecome essential components of ourlearned experience.

When playback is carrying thesubliminal harmonic and mixedsignatures of such deep lows but theirbody -vibrating fundamentals aremissing, then we cognitively realisethat reproduction lacks the full set ofcharacteristics that are essential tomatch our known experience, and thusto create the illusion of 'being there.'


Good recording equipment does

transfer infra -sound frequencies tomasters. When these are not filteredout prior to the disc printing run,then good CD players and systemscan be made to reproduce them. Thismight be a tiny part of the sensoryspectrum, and it is not alwaysrecorded, but it does remain veryimportant: If you feel that the basscurrently reproduced byconventional audio systems is notseriously compromised, then take alisten to known good music testtracks when played back throughquality headphones.

Existing bass equalisersMany active bass -equaliser circuitshave already appeared in electronicspublications. Most are additional in -line stages, though some use thepower amplifier's negative feedbackloop.

Those that start to roll off around20Hz, or that incorporate a tuned -feedback loop to achieve their boost,make me cringe as I imagine thenature of the bass sound that wouldbe reproduced.

With any frequency -selectiveamplitude adjustment or turnover,whether it be passive, electronic orloudspeaker in origin, there isalways a phase change about andbeyond its turnover frequency. Ifsignal phase changes occur in the 15to 100Hz range then low bass soundwaves that initially had acoincidental starting point canrecombine differently at playbackand make an instrument sound as ifit has been physically altered.

Occasionally, combinations ofloudspeaker and equalisationcharacteristics so badly affect thesound that fundamental tones canrun into quadrature with their ownrange of reproduced harmonics.Alternatively, they can become outof phase at frequencies that are nottoo far above and below whatbecomes an effective resonant 'Q'like turnover well within the audiospectrum.

When an amplifier or aloudspeaker amplitude responsestarts to roll off at, say, 20Hz, it isgenerally capable of good

reproduction above 40Hz.However, even though normal

musical sounds seldom havefundamentals below 30Hz,reproduction can still be shown to bephase shifted and thus harmonicallydistorted. This is because a smalldeficit in the amplitude of a low -frequency fundamental introduces alarger level of distortion with respectto its entire family of harmonicovertones than would be the case ifonly a few of the upper orders hadbeen similarly altered.

It is true that crossover networksalso cause phase changes. Usuallythough, the aim here is to counter thereproduced shift in one drivenchannel with an equal but oppositeeffect in its continuing partner.

Why is phase important?At the low -frequency limit of humanhearing, where no other driver takesover, such phase distortions generatewhat we commonly term as aloudspeaker or system 'footprint'.

It has been said that we are lesscapable of noticing distortion at lowfrequencies, but I wonder what thereference has been. I also wonderwhether this conclusion has beendrawn while listening viaconventional loudspeakers andamplifiers that start to roll off at20Hz.

When phase changes occur, arange of frequency -related timedelays develop. Previouslyaccompanying wave componentsbecome separated at playback; i.e.they become displaced in time.

The resultant sound quite literallyloses its coherence. Occasionally,the harmonic 'voice' of a bassinstrument can be perceived beforethe peak of the first half cycle of itsfundamental note. It is as if the bassloudspeaker cone is operating fromfarther and farther away withincreasingly lower frequency.

There is thus a most definite needto maintain an overall flat phaseresponse at all audible frequencies.Also, the associated amplitudelinearity needs to extend to as farbelow hearing as is stably possible,without risking equipmentreliability.

Filters that alter amplitudeintroduce phase related effects thatextend out to two or three times, alsoto a half or a third of their nominalturnover frequency. Because of this,I personally consider that anamplitude roll -off should not beallowed above 5 to 7Hz foramplifiers and loudspeakers that areexpected to perform linearly down tothe lower limit of human hearing.

From a constructional viewpoint,minimising bass -driver and cabinetderived phase shifts below 100Hzthen preclude the use of baffles.They also preclude large, ported orlabyrinth cabinets and low -frequency auxiliary bass radiatorsthat look like heavily conedloudspeakers without magnets.

These preclusions apply evenwhen any of these options is drivenvia a specially -designed activeequaliser element that maintains anoverall flat audio response via thatparticular system. This is becauseair -column and mechanicalresonances become independent ofsignal input once they have beenexited. Resonant displacement canbe controlled only via physicaldamping and/or motional feedback.

Yet the solution is simple.

The solution to the phaseproblemTake a rigidly -coned long -throwdriver motor, mounted within oragainst a small airtight enclosure.When crossed over and usedresistively only at those frequenciesthat are below the new relatively -highresonant frequency, it will be morephase linear, more reliable and morecompact than the conventionalcabinets that we have come to accept.

However, a power transient inducedresonance within such a compactcabinet that is fed by a poorlydamping LC crossover can beunpleasantly distinct when comparedto larger and conventional cabinets.As a result, an electronic crossoverwith a directly damping amplifier tovoice coil connection becomesessential.

Also, the use of any resistor -capacitor type signal equalisationthen merely introduces other separate


AUDIO DESIGN

Fig. 1. Using asmall cabinet,

incorporating arigid -conedspeaker and

mounted against awall, offers many

benefits overtraditional bassenclosures. The

drawback is thatsuch a speaker

needs considerablymore power asfrequency falls.

This filter providesboost rising to20c18 at 15Hz.

Fig. 2. Sub -bassamplitude and

phasecharacteristics forthe filter in Fig. 1,

and the 'e -bass'circuit. The browntraces result from

Fig. 1 while thegreen traces are

the 'e -bass' circuitoutput

characteristics.

but additional phase changes and/or arumbly single note overhang effect.An electronically resonant circuit thatgenerates necessary sub -bass boosthas the same effect.

These distortions are as if the driveritself had been made very large, beenmounted in a much larger enclosure,or had itself become under -damped.Thus the mechanical phase problemsdue to a loudspeaker being mountedin a conventional cabinet coulderroneously be replaced by newlyintroduced electronic ones that soundequally undesirable.

You simply cannot reproduce arecording of clean and tight soundingbass on any system that is itself notclean and tightly damped in everyregard; that means electronically,electro-dynamically, and physically.

EqualisationOf course the above suggestedcompact loudspeaker solution is alsoseriously inefficient at generatingsub -bass frequency sound -waves.

A considerable boost to signalamplitude becomes necessary at15Hz with respect to 100Hz -approximately 20dB. At 15Hz, this20dB boost then places seriousdemands upon amplifiers and drivers.A handling requirement of 100W at15Hz becomes necessary tocomplement 1W at 1kHz.

Figure 1 shows a passive multi-stage resistor -capacitor filter networkcapable of providing the necessaryboost. Its simulated amplitude

30.00

-020.00-

° 10.00-

0.00

response is the brown trace in theupper half of Fig. 2.

Also note however, that the phaseresponse examination in the lowerhalf of Fig. 2 reveals a considerableturnover lag at all audible bassfrequencies. You will observe thissame phase lag on any normalcombination of active or passiveequaliser circuits that act with respectto ground to provide the same slopeof sub -bass increase.

This degree of phase shift runs bassinstrument fundamentals intoquadrature with the rest of theircharacterising harmonics, and rendersboosted sub -bass reproduction woollybeyond tolerance.

During the summer of '98, Idevised and test auditioned manydifferent circuit architectures thatwere each individually capable ofgenerating the same 20dB ofamplitude boost at 15Hz. All weremeasured to check that theirequalisation mirrored, and thereforecompensated for, the natural roll -offof a dynamic loudspeaker workingagainst a compact airtight enclosure.This meant a response that wouldhold 12dB per octave down to 10Hz.

In spite of their identical audioamplitude responses, each circuitsounded different. Some were grosslyunacceptable due to phase distortion.

Then I realised that my dual -traceoscilloscope could be used to displaythe output waveform against signalgenerator input. This would allow meto observe any phase shifts thataccompanied gain directly.

Eventually, I achieved a correctlow -frequency amplitude boostcharacteristic. It always deliveredoutput in the correct sense persinewave half cycle. This means thatit delivered zero crossing ac voltageinput and output transitions that werein phase at all audible frequencies.

10

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-100 0010

100

Frequency [Hz]

1k

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100

Frequency [Hz]

1k

I had heard, measured and dislikedthe more usual bass -frequency lagthat results from filters similar to theone shown in Fig. 1. After muchexperimentation and repeated trials,my desire to counter this distortionresulted in the development of myfinal circuit, Fig. 3.

Both green traces in Fig. 2 show themuch flatter but still boosted è -bass'response that I achieved andmeasured with conventional testequipment.

Circuit detailsIn Fig. 3, Tri forms a low -Q 5Hzinput filter. This is necessary toreduce infra -sound playbackfluctuations. These can be caused bydigital -audio bias and gain levelsettlement data, that should not be -but nevertheless occasionally is -imprinted upon some CDs.

This filter has a negligible effect onamplitude at audio frequencies,though it does introduce theunavoidably increasing phase leadthat comes in below 15Hz. See tracesà' in Figs 4.

All mid -high audio frequencies aretwice phase reversed - first at Tr1collector, traces 'b', and then again atTr3 collector, traces TransistorTr3' s output, buffered by Tr4, is thusshifted back to being fully in phasewith Tri's base input, yet withoutdelay.

Bass frequencies are separatelytaken from the emitter of Tr', tracesà', with respect to the 180° phaseshifted signal at the collector of Tr1,traces 'b'. Sub -bass frequencies atTr2' s emitter, traces 'c', thus developan intermediate and frequency -dependent phase lead with respect tothe higher frequencies at Tri'scollector. The intermediate leadcounters the typical lag of the browntrace in Fig. 2. This lag is caused bythe passive resistor -capacitor high cutand thus sub -bass boosting networksacting on both Tr1 and Tr3 collectorswith respect to ground.

The outcome at the emitter of Tr4,is that all audio frequencies nowremain in phase with the input. Bassfrequencies have received a12dB/octave characteristic boost to+20dB at 15Hz, with respect to100Hz and above.

Audio output at Tr4 emitter is fullyin phase with the signal at input. As aresult, a simple potentiometerarrangement between it and the firststage, Vr3, is all that is necessary totap off any desired level of phase -linear sub -bass boost between flat and+20dB at 15Hz with respect to100Hz.

The greater the level of boost, then


AUDIO DESIGN

LEFT

INPUT

RIGHT

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1k

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Fig. 3. Although more complex than the filter of Fig. 1, this 'e -bass' compensation circuit provides a much more faithful phaseresponse, resulting in much -enhanced fidelity at sub-100Hz frequencies. A 5Hz input filter removes sub -sonic effects of CDgain and level settlement data that shouldn't occur - but sometimes does.

obviously the more thatpotentiometer Vri might need to bebacked off, to prevent sub -basspower -amplifier overdriving.

During listening tests, it becameobvious to me that some CDs hadbeen produced using equipment thathad not maintained a flat phaseresponse at sub -bass frequencies.Because of this, I introduced a thirdpotentiometer.

Additionally, some unusedequaliser phase shifting abilityremained available between Tri andTr2. So this potentiometer couldprove useful in compensating forother undesirable loudspeaker andcrossover shifts

I chose a component value thatwould allow a fully variable, butindependent, sub -bass shift ofbetween +60 and -20° at 25Hz. Thusphase was adjustable relative tounequalised audio that was beingreproduced separately by the mainbass -mid -treble component drivers.The result was a uniquely useful anduser -controllable range of phasevariation!

Initially, up to -60° had beenavailable, but just as with ordinarybass controls, this amount of lagnever sounded acceptable. Zerodegrees is dead centre on the100k12 potentiometer. This alsoturns out to be the most commonposition set by ear.

Transistor Tr4 bootstraps Tr3 stablydown to 7Hz. This optimises stagegain without any need for lowimpedance components at Tr3emitter.

Components Tr6,7,8 form a simpletwo -stage, self biasing 2V rms outputamplifier. This amplifier countersequalisation circuit losses whenrunning flat.

Power supplyTransistor Try isolates the equaliserfilter from supply -rail ripples. Thusthe entire circuit eliminatesloudspeaker thumping at power -up.

Key ais bis cd e

Keyam a bc de

100 00-

0 00-75;or

-100.00-

-200.00

This is something that op -ampcircuitry cannot easily do.

An electronic on/off switch ifformed by Tr9 and Trio. This enablesremote dc control from a pre -amp or

10 100

Frequency [Hz]

1k

10 100

Frequency [Hz]

1k

LEFT

OUTPUT

RIGHT

LOGIC

CONTROL

0 = OFF

1 = ON

Fig. 4. Signalamplitude andphasecharacteristics atpoints within the'e -bass' equalisercircuit.


AUDIO DESIGN

head unit. These controllingtransistors and their associatedcomponents can be omitted. If theyare, diodes D2 and D3 will need to bepowered directly from a mainamplifier supply or via a separatelyswitched rail.

This class -A constant -current circuitrequires a single, positive, 11V to 16Vdc supply at about 25mA. Fed via D2and D3, it is tolerant of momentarypsu interruptions, ripples and power -audio induced supply rail voltage dipswhen running from a commonnedsupply or car battery.

Diodes D2 and D3 could beconnected to a raw a.c. supply. Wherethe equaliser must be installed at theend of long cable runs, a separatelypowered dc -to -dc converter might beconsidered. This would be insertedbetween the diodes plus the signalearth line, and Tr9 plus the powerearth line.

Adding a converter in this waywould isolate audio circuitry from DCrails. I have not experienced anysupply rail or common earth problemswith prototypes, mainly due to thesharp roll off below 5Hz.

Remote controlDuring the design phase, I connectedVri,2,3 so that they could be controlledremotely from the listening position. Iused a six metre screened multicorecable for this. No instability,interference or induced hum pickupproblems were encountered.

My thanks to Andy Collinson atwww.mitedu.freeserve.co.uk for theuse of his TINA simulator program togenerate the above amplitude andphase graphs directly from my finalcircuit. Andy's simulations confirmexactly my own longhandmeasurements made on 1998prototypes.

In Fig. 4, amplitude trace 'e' showsa sharp turnover between the12dB/oct boost and the 20dB/oct cutbelow 5Hz; this sharpness is achievedover several stages and thus is notresonant.

Also note that phase trace `e' inFig. 4 shows the overall phasedeviation between input and outputnot exceeding ±13° down to 20Hz -figures that hold for the zero boosttrace 'a' phase line: Can anyconventionally cabinettedloudspeaker do better?

RealisationThe most significant test bed for thisequaliser has been my son's 50Hzelectronically crossed over sub -basschannel.

This crossover feeds a US -madeRockford Fosgate 100+100W 40

amplifier that maintains output downto 5Hz. It drives a Rockford Fosgate15in diameter double 412 voice coilbass unit. The woofer is mounted in asealed enclosure whose volumewithout the driver mounted is 2.3ft3.

With one amplifier channel pervoice coil, I observed a muchsuperior cone control. Thecombination is capable of displacingup to one litre of air per half cycle;that is two litres peak to peak!

As this amplifier is capable ofhandling down to 10 per channel, Itried it in a bridged configurationwith the voice coils in parallel toform a 20 load. The bridged set-upfunctioned exactly as expected;unnecessarily powerful with audibledegradation in cone driving accuracyand damping.

An equalised power of 200W ofcannot set any sound -pressure recordswhen driving a compact sub -bassloudspeaker, but it is notably morerealistic. The low frequencies ofbeating bowed cellos properlyresound, and kick drums cleanly andtonefully kick air rather than thud-boomphing as if not a drum at all.

Also, reproductions from CDrender. more life -like stage and theatrehall acoustic ambiences. This aspectis hard to describe, it creates theillusion that your hearing is extendedfar beyond loudspeakers and thelistening room.

Open-air recordings actuallybecome more 'open'. Distant soundsclearly sound distant. This is becausethey are not modified by those nimblybass loudspeaker colourations that wehave become so used to, and whichwe can hear being differently exitedon different systems as a result of airdisturbance on a source microphone.

Positive clippingAnother positive attribute of theseparately -powered sub -bass channelis that when a sub -bass amplifier runsinto clipping, the rest of the audiosystem remains unaffected. Thusmomentary sub -bass overdriving doesnot distort other bass -mid -treble'output.

With a clean clipping sub -bassamplifier it can be determined that aninsufficiency has occurred without ithaving had any mind catchinglydeleterious effect upon listeningpleasure. This is simply not the casewith an inadvertently clipping main orwhole bass amplifier, the effects ofwhich can totally capture yourattention and ruin our enjoyment for along time after the momentarydistortion has occurred.

This equaliser has proven effectivewith long -throw bass drivers as small

as 8 inches in diameter. However, Itrust that anyone who seriouslyattempts to produce realistic resultswill use a minimum single 12in, ortwin 10in drivers. In the case of thetwin drivers, one will face inwards,the other outwards and they will bewired oppositely.

Such sub -bass speakers shouldpossess a genuinely continuous powerrating of at least 100W. Also, thedriving amplifier should clip cleanlyand itself be capable of a continuousminimum 100W rms output. Itsamplitude response should hold flatdown to at least 5Hz so that its phaseresponse will remain flat through theaudible spectrum.

7Hz turn -overTo ensure that reproduction phasechanges do not occur at normallyaudible frequencies, this equaliser'slow -frequency boost has been set toturn over at 7Hz. This is similar to anormally specified half -power point.It is also the frequency at which theoverall loudspeaker drive is allowedto fall away from a 12dB/oct boostcharacteristic. In other words, 7Hz isthe frequency at which the equaliserand amplifier are no longer expectedto provide increasing output withfalling frequency.

Fortunately, there are few genuinelymusical signals that require powerbelow 30Hz. As a result, a risingpower output is seldom necessarydown to 7Hz. The 100W at 15Hz tomatch 1W at 1kHz really should bemore than sufficient for loud sub -bassreproduction - even with modernsynthesised instruments.

Nor should we forget that all ofthese turnovers, whether from flat toboost or cut, or from boost or cut toflat, alter the phase response for afactor of two to three beyond anynominal turnover frequency. Thus the7Hz roll -off introduces a phaseadvance that adds to the input filterbelow 17Hz. Had the gaincharacteristic merely been allowed tosatisfy the accepted 20Hzspecification limit, then all audiblesub -bass frequencies could havebecome phase distorted.

I have tested this circuit for severalmonths with a 2.5Hz-input filterturnover, and 5Hz for the boost roll -off. The phase integrity was within±20° down to 15Hz before the high-pass leading phase characteristicscame in. But the resulting higher gainat infra -sound frequencies then overemphasised previously unnoticed CDflutter errors. Although inaudible,these errors did pressurise thelistening room and introduce anunnecessary risk of additional non -


AUDIO DESIGN

linearity product generation.Turnovers points of 5 and 7Hz were

eventually deemed the sensiblecompromise between what waspossible with good CDs, and whatwas realistically acceptable andpractical on an everyday basis .

With 100 to 200W of continuousamplifier drive and an equivalentlyrated low -impedance sub -bass motorthat is properly sealed against acompact and adequately rigid airtightenclosure, the cone simply cannotover travel. Air pressure in thecabinet prevents it from doing so.

Here, I must emphasise that conestiffness and cabinet rigidity areessential. Normal driver cones orcabinets having sides that flex whenyou stand on them can leave a sub -bass system not necessarilyvulnerable to, but capable of,occasionally producing a mostunpleasant and whip cracking likerelease of sound energy.

Do not use a woofer for sub -bass ifits entire cone does not move as apiston when it is pushed at a singlepoint just inside the surrounding edgesuspension; the cone must not beflexible.

With high supply rail voltages andlow -frequency, high -power outputs,the SOAR limitations of theamplifier's output the devicesbecome challenged. To overcome thisproblem, speakers with dual voicecoils as low as 1.45/ have alreadybeen manufactured in the US.

Drivers and enclosuresIn recent years, loudspeakermanufacturers have reduced bassdriver coil impedances considerably.This enables longer -wavelength airdisplacements to be generated withless risk of failure of the poweramplifier's output devices.

To reveal the qualities andweaknesses of your own system, Irecommend the highly competentSheffield Labs Audiophile Referencetest tracks that are supplied withrecording plans in booklet form.These are compiled on theInternational Auto Sound ChallengeAssociation competition CDs, alsofrom the US. Check out thespecialised links to manufacturers atwww.iasca.com

For sub -bass loudspeakerconstruction, a simple starting pointis to mount the chosen wooferexternally against - not inside - analready sealed, thick walled cube.This cube should be lined and half -loosely filled with natural fibrewadding. It should have internal sidedimensions that equal the chassis'outside diameter. Of course, one

internal side dimension could bedoubled if the depth is halved and thewadding is placed in line with thedriver cone.

There are many 'per -chassis'Theile-Small parameter calculationsthat could be made. I would not wishto dissuade you from satisfyingyourself about a cabinet'sperformance. However, calculatedresults could lead to one making anenclosure that is too large and hencenot resistive enough for the12dB/octave characteristic to besafely and smoothly applied.

When used singly, loudspeakersthat are intended for sub -bassreproduction actually run morecleanly if they are mounted on to analready constructed cabinet facinginwards. This is because air flowthrough a tapered magnet vent isbetter able to cool the voice coil. As abonus, harmonics that develop at thecentre of the cone are less able toradiate directly. It is as if thecrossover has an additional pole at noextra cost.

Component choicesI did not use any especially closetolerance components when makingand testing prototypes. Resistors weresub -miniature 2% types. Allminiature capacitors up to 10µF wereselected within 10% of their ratedvalue.

For neatness I used multiples ofminiature 470µF radials to make upthe larger electrolytic values. Initialdc testing was completed by checkingthat approximately half of the supplyvoltage developed at the collectors ofTr4 and Tr8 after dc bias levels hadbeen allowed to settle.

All audio systems are different. Asa result, the sub -bass crossoverfrequency will need to be determinedby ear while simultaneously adjustingthe equaliser potentiometers and anyexisting tone controls to level out anoverall bass sound. This is not asdifficult as might sound. Good resultscan be quickly achieved, but don'twrongly use maximum or impressivelevels of boost, and don't use toohigh a crossover frequency.

Being realisticThis circuit maintains a tolerably flatphase response at all audiofrequencies. However, it is no betterat generating a low -frequencyamplitude boost at the instant itoccurs in real time than are any of theother frequency selective amplitudeadjusting networks already in use.Here I am referring to theineffectiveness of capacitors below aturnover frequency, and thus to the

leading phase response that normallycomes in below 30Hz.

Thankfully our brains appear toprocess waveforms on an averagingbasis. When audible amplitude andphase responses are correct, we aremuch less distracted by the relativelyfew transient induced errors that hereare now below the range of humanhearing.

I am being entirely open herebecause most listeners are amazed bythis equaliser's improvement to sub -bass sound when the significant phaseshifts occur below 15Hz. Either weput up with larger loudspeakers andtheir audible weaknesses, or weaccept equalised audio withoccasional infra -sound phase errorsthat are much less noticeable.

An overall flat amplitude with flatphase sub -bass response actuallysounds different from what ispresently accepted as being 'normal'on conventional systems! Of courseVr1_3 can be used to adjust theequaliser output towards a moredirect and flat response if somesource material already seems to bebass heavy or phase shifted. Mediumboost with a leading phase can beapplied if hardcore 'dance' playbackis required.

Some discs sound disappointing.This led me to ask what types ofloudspeakers are used in some of theproduction suites used monitor ourprospective purchases.

I wonder if producers watch out forflutter errors that becomepermanently imprinted on their CDstamping masters after all dynamicand digital compression procedureshave been completed, but before theygo into production. These lowfrequency flutterings are to CDs whatrecorded rumbles were to some oldvinyl discs.

Occasionally, cone movement canoccur due to level compression orbadly biased circuitry reacting tovoice and solo instrument tones whenno bass is being reproduced. The vastmajority of CDs do play satisfactorilythough.

FinallyAs far as I am aware, this is the first'phase linear' sub -bass equalisercircuit to be published. It was born ofmy unwillingness to accept bassphase distortion on everyday systems

The system has undergone repeatedlong term listening tests. These testshave been carried out with adetermined empiricism and anenthusiastic disregard for any timethat was necessary for developmentor evaluation.

I have not written about the many


AUDIO DESIGN

previous designs that werecompleted, discarded, orsuperseded. Nor have I mentionedthose that produced the sameresults but needed 1% capacitors,or which were less stable whendriven with transients, etc.

A number of in car entertainmententhusiasts have listened to mysystem. They have been amazed atthe much greater level oflow -frequency output that can becorrectly reproduced using aloudspeaker enclosure similar insize to the ones they are alreadyusing.

Like other Electronics Worldreaders through the decades, I havehad many opportunities to readabout amplitude and phaserelationships in audio articles.Soon after embarking upon thisproject, I was encouraged by theappearance of John Watkinson's`Speakers' Corner' series.

John's writing sustained mydetermination to produce a circuitthat would not generate the phaseshifts that are normally introducedby amplitude equalisation whendriving a compact and resistively

loaded low frequency loudspeaker,which is otherwise much morephase linear in its own right.

I regard John's articles as beingessential reading for anyone whohas an interest in this form of bassreproduction; especially theOctober 1998 notes.

It is also worth mentioning thatdirectly -driven resistiveloudspeaker enclosures thatoperate below their resonantfrequency do not hit amplifieroutput stages with the samemomentary - and transistorpopping - dynamic impedance dipsthat conventional loudspeakerssystems do.

I am not claiming that thisequaliser is the best or only wayforward, but it does genuinelypromote our striving for ever morerealistic sound reproduction. I lookforward to seeing other phasecorrection related circuits or lettersappearing in future EW pages.

The circuit is straightforward andinexpensive. It is easy to insert itbetween an electronic crossoverand a sub -bass amplifier. It mayeven be used as the basis for an

additional and stand alone centralsub -bass channel for use withalready existing stereo systems. Inthis way, the original system mightcorrectly be run flat.

Good sounding cinema, disco andprofessional loudspeakers need nolonger be so large. Manufacturerscould easily integrate an equaliserwith an electronic crossover andsub -bass driving amplifier, to make20Hz from 1 ft3 the domestic norm.Solid-state sub -bass can also be anexcellent partner for tube amplifiedhi-fi. Many possibilities exist.

Phase linearly equalised sub -basschannels inconspicuously add depthto the sound stage in a surprisingway that cannot be appreciated untilexperienced. All 'normal' systemsthen seem lacking, even when goodand expensive reproducingequipment is already in use.

We cannot miss what we have notheard from our own CDs, but thatis not a reason for doing nothing.Modern developments in amplifierand loudspeaker technologiesalready make the 'e -bass' approacha practical possibility. So come on- get your soldering iron out.

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With the aim of helping youproduce more effectiveanalogue designs, Bryan Hartexplains how it is possible todevelop a set of 'ideal'transistor models that suitparticular 'families' ofapplications. This secondarticle deals with dynamicmodels, leading off with thecharge -control model. The firstcovered static models.

An ideal transistorpioneered by Sparkes,1,2 the charge -control model isapplicable to dynamic switching conditions. In Fig. 1,its essential elements for VBc<O are shown superim-

posed on a schematic cross-section of the device in order toindicate the regions that they refer to.

The lettering denotes instantaneous values. Parametersdefining the model may be unfamiliar to some of you, so Iwill outline them here.

Network element SB represents a storage cell for a basecharge, of magnitude qB. This charge controls the transportcurrent iD via the relationship,

_ qB1:. - (1)`

TT

In this equation, TT is the mean transit time of minority car-riers crossing the base from the emitter to the collector.

By way of analogy, think of the relationship between theflow rate, quantity and transit time of a fluid in a pipebetween two planes perpendicular to the flow. There is nopotential difference across SB. This is because the injectioninto the base, via the base contact, of a majority -carriercharge (qB) causes an equal and opposite charge of minoritycarriers to be drawn in from the emitter region to maintainbase charge neutrality. In this respect SB resembles an infinitecapacitance, and the capacitive association is reflected in itssymbolic representation as a capacitor, albeit with curvedplates. Thus, SB requires a current,

dqa

dt

only when the charge is changing.Recombination of minority carriers entering the base from

the emitter, and vice -versa, causes discharge of SB. This istaken into account by the parallel current generator,

qB

B

Here, TB is the overall minority carrier lifetime.Under dynamic conditions,

thiBqe'e = -dt TB

This equation resembles that relating the rate at which thequantity of water, qB, is changing in a bath when it is beingfilled from a tap, iB, and the water is leaking away at a rate,

qB

zB

through an ill-fitting plug.Base -emitter voltage drop VIE is associated with the injec-

tion of charge qB into the base and is modelled by the diodeDE for which,

(2)

V = V, loge tD = VT log., IT (3)IS

As mentioned in the case of DC operation, parameter Isdepends only on the properties of the base region. Parasiticelements CIE, CJC and rx are included in the model of Fig.2. Junction -transition capacitances CTE and CJC are averaged

C

Depletion layer

V JE Depletion layer

BaseiD = CIB

Fig. 1. Essentialelements in thecharge -controlBIT model for abase -collectorvoltage of lessthan zero.


COMPONENTS

r,

Fig. 2. Modifiedversion of Fig.1,

taking into accountparasitic elements.

VG

-0.5V

Fig. 3. A current -switching pulse -

generator.

over their operating voltage ranges.The base bulk resistance rx is usually ignored in DC cal-

culations. This is because the potential difference across it isnegligible compared with VIE. It is included in this modelsince it can affect the rate at which qB can be injected, as inthe example described below.

Under DC conditions a base current /B is only needed tomaintain the base charge constant at a value QB=/cTT, andequation 2 gives QB=/BTB.

From the two expressions for QB, the common -emitter cur-rent gainft is given by,

I TC B

IB Tr

As an example of the use of the model in Fig. 2, consider thecircuit in Fig. 3. This shows the basic form of a scheme thatI developed for producing two short -duration time -coincidentrectangular voltage pulses of opposite polarity following theapplication of a voltage step 2VG, which is 1V in thiscase. This is balanced about earth and supplied from a pulsegenerator having an output resistance RG, which is 500.

The circuit has a long-tailed pair switch comprising Q1,2and tail current generator I. It also has a pulse -formingcable, with one-way delay time td and a characteristic resis-tance RG of 500, that is correctly terminated at each end.

Initially, Q2 passes the full tail current but this is switchedto Qi when the pulse edge arrives. A voltage change of10(R0/2) results at each collector. This voltage change ceas-es after the cable delay time td. When R0 is 500, td innanoseconds is around three times the cable length in metres.

Crucial to the design is an estimate of the switchover time,tt, of the long tailed pair. This determines the minimumlength of cable that can be used if the output pulses at the

C

C jc

C JE

9B

TB9B

+5V o

5052 co -ax.

(4)

= 9B

,1,10 = 5mA

1 OVo

TB

L

collectors of Qi, Q2 are to have flat tops.In the model of Fig. 4, only those parts necessary to find ti

are shown. Recombination is ignored since it is anticipatedthat tt is much greater than TB - an assumption that is subse-quently justified.

During the switchover process,

1B(Rc+2rx)=Vc-vJEI-vJE2) (5)

Using equation 3 shows that iD1liD2 is less than 0.01 whenv.tEr-vJE2 is -5 VT. This condition is taken as the start of thetransition, which ends when viEi-v JE2 is +SVT, corre-sponding to i Di+ im>0.99.

The mean value of the right hand side of equation 5 is VGso the mean base current, 1B(,11,), during the switchover pro-cess is,

ViB(mean) = (6)RG+ 2r,

This serves to remove a charge QT from the base of Q2whilst establishing a charge of equal magnitude in the base ofQ.

QT=034-Qm+ arc (7)

where QB is loTT; QTE iS (AVJE), which is Cm (5VT);

Qic = C A(AV= C jc[517T + 1,13-1

t=,QrB(mean)

Suppose Qi, and Q2 each have the following representativevalues:

rx=500C JE=C JD=2pF

Hence,

(8)

rT=0.2nsfl=100.

Substituting this data in equations 6 to 8 shows that,

ti=0.6ns (9)

Since tt is much less than TB (93T7-20ns), neglecting therecombination is justified.

Each collector has a time constant, CL(R0+2), associatedwith it. Here, CL is the stray capacitance. Assuming that CLis 5pF, this means a 10% to 90% transition time of 0.275ns.Combining this with tt in an rms sense, appropriate to cas-caded systems, gives overall voltage transition times less than0.7ns

The long-tailed pair offers the fastest known method ofcontrolled BJT switching. This is because the control signalswing can be at its minimum value and the circuit can oper-ate out of saturation.

Saturating circuits require a BJT model2 that is a modifiedform of that in Fig. 2 but its use is not always necessary.Excess carrier -storage effects can be largely eliminated usinga Schottky clamping diode in parallel with the base collectorjunction.

The hybrid -1c small signal modelFor small -signal wide -band and tuned amplifier design, anappropriate BJT model is the hybrid-rc, introduced byGiacoletto3.

From the charge -control model, it can be deduced by con-sidering incremental changes about fixed bias levels, IB, ID,etc. Thus,

qB=QBA-qbic=ic+ic

b


COMPONENTS

v JE=VJE+v

In these relationships, qj, is SQB, and hence is is much lessthan QB, etc.

Equations 1 and 2 now become,

i (1B

Tr

and,

dqb qblb= - -dt

Differentiating equation 3, and rearranging, gives,

qb= gv = cT= CdvVr VT

Here Cd, which is,

/c

is defined as the base emitter diffusion capacitance.From Equations 10 and 12,

ac. =46=

g,,,vTT

been used successfully in the design of amplifiers for high-speed optical transmission systems.

ConclusionsI have shown that the hybrid -7c model is deducible from thecharge -control model by considering incremental changes: inother words, by replacing qB by qb, etc. Similarly, DC mod-els are obtained from the charge model by assuming qB to beconstant.

Relevant inter -relationships are summarised in Fig. 6.Apparently, the charge control model can be regarded as the`big daddy' of a family of ideal models.

References1. Beaufoy R & Sparkes JJ, 'The junction transistor as a charge

controlled device', ATE Journal, p. 317 et seq., 1957.2. Sparkes JJ, 'Junction transistors', Pergamon Press, 1966.3. Giacoletto LJ, 'Study of pnp alloy junction transistors from

d.c. through medium frequencies', RCA Review, 15, p. 506et seq., 1954.

jC2) = constant

(13)C jc

RG rx

iC1

'.4JC

Q

VJE1

\Iy'C2

VJE2

CJ

11

where,

/,gb, =

VT

is defined as the mutual conductance, or as `transconduc-tance' .

Also, the use of equations 12 and 4 gives,

qb QB)v c V (14)TB \STT \SITT

where,

rn = TV p

Ic g,

Equation 11 can now be rewritten as,

dv v= Cd - - (15)dt r

The hybrid -7c model in Fig. 5 is based on a graphicalinterpretation of equations 13 and 15 together with the addi-tion of the elements rx, CJE and CJE. By definition,Cx=Cd+CJE and CK=Cp. The model parameters are eithercalculable from the bias and temperature conditions, orobtainable from terminal measurements. Thus, for a givencollector current, Co- Cp can be found from the frequencydependence of the short circuit common -emitter small -sig-nal current gain. By itself, capacitance Cp, can be deter-mined using a capacitance meter.

Element r0, not so far discussed, is included to accountexplicitly for the implicit dependence of Is, and hence gni,on the voltage factor,

VCE

V,

mentioned previously. Normally VA is much greater thanVcE, hence,

VAro = -IC

Note that r, is independent of VcE because f3 depends on thesame voltage factor as gm.

Among its widespread applications, the hybrid -7c model has

rxB

constantcurrent

C0

Tc-Tcd

(CJE+Cd) =CT,

QJC1, Cjc

SB2 R°QB

CJE

IIQJE

rx iB

Fig. 4. A model ofthe circuit in Fig.3 for calculatinglong-tailed pairswitchover time.

A

Voro

Fig. 5. The hybrid-ir BITmodel, derived from Fig. 2.

( Large signal dynamic model: qb = f(t)(Beaufoy and Sparkes)

Static models: qb constant

Ideal exponential models(Ebers-Moll: Gummel-Poon)

Ideal piecewise-linear models(degenerate form of above)

Fig. 6 A family -tree of ideal models.

Static models: qb = f(t) or f(w)

Hybrid-pi model (Giacoletto)

LF model(degenerate form of hybrid-pi)


Using conventionalsoftware methods todesign fuzzy logic circuitsleads to unnecessarycomplexity.Douglas Clarkson looks atalternative ways ofimplementing fuzzy logic.

What is fuzzy logic?According to Rudolf Graf's 'ModernDictionary of Electronics':

"Fuzzy logic - 1. A branch oflogic that uses degrees of mem-bership in sets rather than a stricttrue/false membership.2. A kind of logic using graded orqualified statements rather thanones that are strictly true or false.The results of fuzzy reasoning arenot as definite as those derived bystrict logic, but they cover a larg-er field of discourse.3. A method of handling impreci-sion or uncertainty that attachesvarious measures of credibility topropositions. A form of logic usedin some expert systems and otherartificial intelligence applications.

Fuzzy sets - Sets that do not havea crisply defined membership, butrather allow objects to have gradesof membership from 0 to 1."

Usinguzzlogic

Fuzzy logic has come a long way since itwas discovered in 1965 by Lotfi Zodehin the USA. After being initially taken

up by the Japanese, it was rediscovered inAmerica, perhaps because the Japanese hadhad so much success with it.

In this first article, I outline the concept offuzzy logic. In a second article I will bedescribing how to implement a basic fuzzy -logic unit.

This pair of articles will show you how todesign a system with various analogueinputs, and how to process these inputs usingfuzzy rules to create an analogue output. Youwill see that if conventional software meth-ods are used to do this, then the resultingelectronic circuit can become unnecessarilycomplex.

As I will show though, using a slightly dif-ferent model can make it much easier toimplement fuzzy logic.

Fuzzy -logic basicsPerhaps a better name for fuzzy logic wouldbe 'continuous' logic, as Fig. 1 indicates.

Take, for example, a pneumatic monitoringsystem that provides the pressure indications`low', `ok' and 'high'. These are essentiallyBoolean in structure. Whatever the pressure,

only one function can be true. If the realpressure is at the threshold between the `ok'and 'high' indications for example, there isambiguity.

Fuzzy logic on the other hand embraces theconcept of cross -over behaviour. In fuzzylogic, you can consider separate fuzzy logicfunctions. In this example, the functions aretriangular in shape, rising to maximum valueof 1, as in Fig. 1d). These functions .arecalled membership functions.

The whole point of a fuzzy controller is tohave a series of such 'crisp' inputs, such astemperature, pressure, current, speed, etc.,and derive appropriate 'crisp' outputs to con-trol the system using fuzzy logic.

A balancing actIn Fig. 2, the position of a ball bearing isbeing maintained as centrally as possible ona see -saw guide. A geared -down DC motorcan tilt the see -saw either way, depending onthe value of drive voltage V.

A potentiometer indicates the shaft's posi-tion, producing an output voltage V,,. As theball bearing moves along the slide, it changesthe resistance of a second sensing circuit sothat the system can detect the bearing's posi-tion using a bridge circuit.


DIGITAL DESIGN

LowA

1

0

1

0

1

0

a) Boolean

OK

b) Boolean

High

c) Boolean

d) Fuzzy

PO P1 P2 P3

Fig. 1. Expression of states of a system in Boolean and fuzzylogic. 'Continuous logic' might be a better term than fuzzylogic.

Between the see -saw guide's end stops, the ball bearingcan move freely. The problem is to develop fuzzy logic thatwill try to keep the unit horizontal, ideally with the ball bear-ing close to the centre position.

Figure 3 defines a series of conventional membershipfunctions. The angle of the system is described by functionsAR, AZ and AL while its position is described by PL, PZand PR. The value of drive motor voltage is described byfunctions VNEG, NEG, ZERO, POS and VPOS.

While it is possible to identify up to nine rules that fullydefine the system, the system can be run with five rules asindicated in Fig. 4.

Table 1 indicates how the separate components of themembership functions behave for specific values of an inputparameter. Such inputs are termed 'crisp' inputs.

For given values of ANGLE and POSITION crisp inputs,it is necessary to determine which - if any - rules apply. Ifyou select values for which rules 3, 4 and 5 apply, then theprocess of calculation is indicated in Fig. 5.

In rule 5, the membership value of AR based on the inputvalue of 12° is 0.35.

Similarly the membership value of function PR with inputvalue of 3 is 0.5. What is required at this stage is to performsome function based on this pair of values that will give ameasure of how much significance should be carried to theoutput function.

The most widely used approach is to take the minimum ofthese two values and to select the set of values in the hashedarea of function VNEG. In a similar way, a value of 0.25 forthe function ZERO based on rule 3 can be selected, based onintersection of AR/PZ of 0.4/0.25. Now this value for func-tion ZERO can be applied to the output -function ZEROvalue.

Defuzzification -a processIf you combine, for example, two zones of the output func-

Potentiometer

Controlboard

Ball bearing

_Guide

DC motor

Fig. 2. Simple system of 'balancing act'of a ball bearing being balanced by aDC motor and a feedback system todetect the position of the ball.

AAA Position (cm)

-1 0 1 9

Motor drive(V)

-3.0 -2.0 -1.0 0 1.0 2.0 3.0

Fig. 3. Conventional membership functions of 'balancing act'example.

Table 1. Values of membership functions for 'crisp' inputvalues of ANGLE AL, AZ and AR.Crisp ANGLEvalue

Membership valueAL AZ AR

43 0 0 0.1

18 0 0.1 0.658 0 0.6 0.15-2 0 0.9 0

-11 0.3 0.45 0-39 0.3 0 0

Rule 1: If AL and PL then MOT = V pos

Rule 2: If AL and PZ then MOT = Pos

Rule 3: If AZ and PZ then MOT = Zero

Rule 4: If AR and PZ then MOT = Neg

Rule 5: If AR and PR then MOT = Vneg

Fig. 4. Rules for 'balancing act' together with indication ofpositions of ball bearing and angle of motor, etc.


DIGITAL DESIGN

Fig. 5. Details ofderivation ofconventional

intersection valuesof active rules for

'balancing act'.

x1 0

x0

x2 o

x3 0

x2 0-1 I

-4 H-

-45° -20° -5° 0° 5° 20°

12°

0.4 0.35

45' Angle (°)

PL PZPR

-9 -1 0 1

D-

r

-x

3

0.5 0.25

9u Position (cm)

Rule 3: AZ/PN 0.4/0.25 = 0.25 ZeroRule 4: AR/PZ 0.35/0.25 = 0.25 NegRule 5: AR/PR 0.35/0.5 = 0.35 Vneg

-3.0 -2.0 -1.0 0 1.0 2.0 3.0 Motor drive(V)

y10

yo

y2*

y3o

X -X

-x + x2

6y - y1

0-=--f=1-

ABEIII

LD

Fig. 8. 8. Circuit

implementation of selectionof output value from amembership functionsindicated in Fig. 7.

ox0

S

C D E

III

-L

-y + y2

Pos

41111111111111111111111,

(a)

Output function

Zero (b)

CM

A

A1111111111111111111'

Output function

(c)

Output function

Fig. 6. General aspects of defuzzification

F1

1 x x2

F2

y1 y2 y y3

Fig. 7. Typical membership functions.

Table 2. Function selection for circuit implementation of Fig. 8.A B C D E xo yo1 0 - 0 x -x1 -

0 1 - 0 -x+x2 -

1 0 0 y -y10 1 0 -y+y2

- - 1 0 0

oy0

S

Lion NEG and ZERO, you can more closelyidentify the area of the combined output.

The problem now is to derive a single`crisp' value of the output function MOTOR-a process known as defuzzification. Whilemany methods are available, the most com-mon one is known as the centroid, or centreof mass, approach.


DIGITAL DESIGN

In a simplistic approach, Fig. 6, imagine that line AB is thecentroid. If you now imagine the hashed areas being cut outof cardboard, then line AB is the point at which the weight ofcardboard on either side of it would be equal.

Many other methods can be used. If the output is consid-ered to be a set of discrete points at U(ux) and value ux, thenthe centroid value can be considered to be,

CMOuI)uI + U(u2)U2 + U(U3)U3...

+ U3-...

This centre of mass calculation takes quite a bit of digitalcomputing power to solve though, which can slow thingsdown. An analogue solution, however, may even be faster.Provided that you do not have a zero on the denominator, ananalogue division can be provided by an electronic circuitsolution using analogue multipliers.

Implementing membership functionsIn the example in Fig. 7, function F1 has discrete valuesbetween xl, x2 and x3 and with variable input x. Similarly,the function F2 operates between y 1, y2 and y3 and withinput y. Simplified membership functions required are givenin Table 2.

Figure 8 outlines how this function table can be imple-mented in an electronic circuit to select the output value ofeach membership function. The logic of A, B, C, D and E is

used to select the output using quad SPST CMOS analogueswitches. Where any rule fails, E is logic 1 and a zero isselected for both xo and yo.

The next stage of the rule processing requires the inter-section of the two values xo and yo derived for F1 and F2.

Fig. 9. Circuit for intersection:minimum of X0 and YO.

min (x0,y0)

This is generally taken as the minimum of the two values. Soyou need to design a circuit element that will select the min-imum of the two voltage values.

Figure 9 outlines how this minimum function can beimplemented.

At this stage, with the circuit of Fig. 9 processing the out-put from Fig. 8, the output value of a single specific rule hasbeen determined.

The next stage requires this value to be transformed into anoutput value function, taking into consideration all the rulesthat may be active. At this point, things are getting complex,yet we are only at the stage of resolving only part of the 'out-put contribution' of a single rule.

In a second article, Douglas looks further at the complexityissue and describes practical circuitry.

Further readingFuzzy Controllers: Leonid Reznik, Newnes, 1997.

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106

VISA 'S YEARS


Is the fine pitch of surface mount ICs causing you problems withprototyping? If so, here's the answer...

Om -Adapt surface -mount to through -hole convertersThe Om -Adapt Series is a range of products that allow surface mountdevices to be used easily for prototyping and one -offs. They are intendedfor use during circuit development.

These miniature adaptor PCBs have solder pads that take today's ultra -

fine pitch SMD components, effectively turning these connections into amore usable array of 0.1 in -spaced holes. These through holes allow fordirect wiring. Alternatively, they take single -in -line or dual -in -line pinheaders, PCB mount socket headers/or even wire -wrap pins. The adaptorPCB can then be directly used in breadboards or development pin boards.

The one -one tracking also allows ease of circuit probing during designand testing.

Each Om -Adapt in the series is designed to be able to accommodate arange of different sized devices, to reduce the stockholding in development labs, and by offering the PCBswithout connectors, a significant cost saving can beachieved together with increased flexibility of use.

Omega Research is producing a range of smallPCBs patterned to take various sizes of SMDpackages and pad formats that turn the SMD partinto a 0.1in pitch through -hole device. Called Om -Adapt, these adaptors are available for the followingSMD packages:

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Measuring true powerIn his previous internet investigations,Cyril Bateman searched for conven-tional power measurementtechniques. Here he reports on somemore novel approaches, including PICcircuits and new chips that provide analternative to the electro-mechanicalsystem in your domestic power meter.

Fig. 1. An alternative method for multiplying voltageand current involves the LM3812 current sensing IC.This easy -to -build circuit avoids the cost andcomplications found using conventional multipliers.It was designed by I. Kotowski and A. Johnston ofNational Semiconductors.

IdiscuSsed several circuits formeasuring circuit power in mylast internet article. Some

involved measuring RMS voltageacross a known resistor. Otherscomputed the power consumedaccording to the product of circuitvoltage and current.

Multipliers were used in thecircuits involving computation. Butother methods can be equally valid.The following circuit is perhaps themost novel of those I found in myInternet searches.

National's LM3812 integratedcircuit is intended to monitorcurrent levels and produce a duty -cycle output proportional to thecurrent being monitored.) Thiscircuit can be used to produce anovel, low-cost power meter.

Using the duty cycle output togate the input voltage effectively

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provides a multiplication functionbut without using a dedicatedmultiplier circuit. A low-pass filterthen provides a voltage outputproportional to the power level.

While this approach soundsconvoluted, it is easy to implement- and it doesn't cost much either.

In the circuit shown, the outputvoltage represents the input power,divided by ten to keep the output inrange.2 This circuit claims betterthan 3% accuracy with currents to±7A and voltages from 2 to 5.25V,Fig. 1.

Another simple low-cost powermeter uses the non-linear behaviourof a quad optisolator to act ratherlike a Gilbert cell and perform theneeded multiplication. It alsoprovides mains voltage isolation.This concept was originated in amuch earlier 1994 design by W.Woodward, who also provides thisupdated circuit, Fig. 2.3

The optoisolator multiplier outputis a current, drawn from C1, that isproportional to the true instanta-neous power delivered to the load.This current is then converted to afrequency in Al and A2 to producean output at A2 pin 7 from 0 to1200Hz. With the componentsshown, 1Hz represents 1W.

Using a copper -wire senseresistor with its temperature


COMMUNICATIONS

Fig. 2. A low cost and simple AC power meter, designed byW. Stephen Woodward, University of North Carolina. Take care toprotect the optoisolators from temperature fluctuations and draughts.

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This use of a quad optoisolatorintrigued me, so I explored further.I was unable to find the originalWoodward article on internetthough. Searching for it howeverled me directly to my next circuit,which uses the optoisolator sensortogether with a PIC to provide adigital readout.

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A PIC power meterA number of AC mains powermeter designs have been based onlow-cost PIC microcontrollers.Most use conventional methods toextract the voltage and currentinformation.

This award winning circuit on theother hand, designed by Rick May,uses a quad optoisolator. Based onWoodward's circuit, the isolatorgenerates an analogue voltageproportional to the power consumedby a load.

While not perhaps the mostaccurate power measurementmethod, the non-linear behaviour of

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the optoisolators permits anextremely simple, low cost andhand-held design. Instantaneous andaverage power up to 1200W aredisplayed, as well as kilowatt hoursof consumption.

The essential power -to -voltageconversion using the quad optoiso-lators can be seen in the upper leftthird of the diagram. The remainingcircuits convert this voltage into thedesired output using the ADC0831a -to -d converter with a PIC16C61,Fig. 3.

A five -page discussion of thiscircuit, together with the sourcecode for the software routines used,

More informationA. Cookie CentralB. JunkBustersC. Webwasher AGD. Internet Explorer "Open Cookie Jar"1. National Semiconductor LM3812M2. Power Meter uses low-cost multiplier3. Simple Digital AC Wattmeter4. A PIC-Based AC Power Meter5. WattHour-Meter Reference Design

6. 31/2 -digit DVM IC measures power factor7. Single Phase Bi-Directional Power/Energy IC8. Designing a Watt -Hour Energy Meter Based on the AD7750

http://www.cookiecentral.comhttp://www.junkbusters.comhttp://www.webwasher.comhttp://www.peacefire.org/security/iecookieshttp://www.national.comhttp://www.ednmag.com/ednmag/reg/1999/122399/designideas.htmhttp://www.ednmag.com/ednmag/reg/1997/041497/designideas.htmhttp://www.circuitcellar.com/Pastissues/articles/MAY96/rick-96.pdfhttp://www.microchip.com/Download/

Appnotes/Category/rDevices/30452a.PDFhttp://www.ednmag.com/reg/1994/042894/09di3.htmhttp://www.cirrus.comhttp://www.analog.com


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Fig. 3. This award winning circuit isbased on W. S. Woodward'soptoisolator multipliers. A PIC16C61 drives a digital read-out.

can be downloaded from the CircuitCellar website.4

In direct contrast to the simplicityof Rick May's circuit is a detailedreference design for a watt-hourmeter using a PIC16C924. You canfind this on MicrochipTechnology's site.5

Its schematic circuit spreads overfive pages. To save space I havechosen to show only the AC mainsto analogue -and -digital interfaceschematic. As you can see, this usesa transformer as the current inputbut a resistive divider for thevoltage input.

To correct the input phase differ-ences, a CR circuit of a lkL2 resistorand three parallel capacitorstotalling 0.378µF is used, Fig. 4.

The resistive voltage dividerincorporates carefully -specifiedhigh -voltage 1ML1 resistors fromPhilips. In the interests of safety,these should not be substituted bylower rated components, whichcould be prone to flashover betweenelement spirals.

Bugs or cookies?

Whenever the internet is accessed, eachuser leaves behind usage trails, recordedin log files on his or her computer andthe various internet computers used.

More significant however are thoseattached to the many adverts commonlyfound on most web pages. These advertsnot only slow down your web access.Many extract personal details from your

Elk Olt Vow fie lommunkaloo Ltelp 1,1nIts

; Boolmarka4

Internet Explorer "Open CookieJar"Cookies stored by IE for Windows can be Toad by any Web site

Bennett Heselton, hAnnP/Ificne....frre,Jame McC9965 imew/g7P,79.&,,,t55/11/2000

News 91,919aeLltusetilliELToes.I.CliNtalllashdetILliet um. h'ILeolastedimidlliattoaaEaslwthrmmtese,ma

Soo 4612.ueSt-Hrtt-ot-moNtes security hole (0900) atutizmailLs.:LimvaL

HOD', 'stoalth altachmenr demo 55590 (4/27/00),Esiti1IllkuNesolatosatu8noLu..trjnot FWAOIPI laveSorsor s000me hole (5/5/00) caloit,No.ate.

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Any Web sire that uses cookies to authenticate users or dote private information -including Amazon. core, Hotlfail, Yahoo MaiL DoubleClick, HP3.cora, NYTimes.comand thousands of others - could have cookies exposed by Internet Explorer andintercepted by a third -parry Web site.

Update 5/11/2100: Mictosoft has released a patch that will fix thisvulnerability in Internet Explorer:

lama Done Jaen.461Vis

Fig. A. If you access Internet usingInternet Explorer with any version ofWindows or NT operating systems, leavingyour 'cookies' uncontrolled could allowyour private data to become public.

computer while tracking your progress.This can happen even without 'clicking'on the advert: simply visiting the hostpage often suffices. Your details can besold -on. At best this results in youreceiving many unsolicited e -mails.

One way your private data can beextracted is by 'cookies'A. These wereoriginally intended to travel onlybetween the web host and yourcomputer. A cookie was a temporaryrecord of your access to a site so that,for example, if you were making an on-line purchase, it would retain yourneeds, allowing you to browse furtherbefore completing the sale.

Web pages often use components froma number of different servers, especiallyfor adverts. Any server providing suchcontent can install a cookie on yourmachine, to track your presence orextract information. Consequentlywithout visiting the advert site, your datacan be known.

The Windows 98 registration wizardinserts unique ID numbers that identifyyou, your computer and certain softwareinstallations, into cookies without askingyour consent. Each time you visit theMicrosoft site, this information can beaccessed. According to PC Magazine,the ActiveX control has a bug thatallows any Web site to retrieve yourregistration information.

The easiest way to restrict cookie

access is to completely disable cookiefunctions in your browser. But this willprevent you accessing a great many safeand desirable web pages. For some timeI have set my machine to automaticallyaccept only those cookies that will bereturned only to the originating site. Mybrowser then seeks my permission for allother cookies. This method of 'cookie'control works, but it can be a nuisance.

Today I examined the 'cookies' files ofmy four browsers on OS/2 andWindows98. I was concerned to find myname, e-mail address and other detailsheld in various cookies as plain text -not encrypted in any way. How muchlarger and detailed might these files behad I not tried to control cookies?

A better approach may be to installcookie -management software. This cancontrol cookie access and even preventthe downloading of adverts, thusaccelerating web page access. I havenow downloaded copies of 'Junkbuster'Band 'WebWasherc and will watch theireffect with interest.

Using Netscape, you will find your'cookies' in a file called cookies.txt inthe Netscape directory. For InternetExplorer, look in Windows \cookies.

Internet Explorer for Windows 95, 98,NT and 2000 can also be tricked intoreleasing your cookies to third -partysites. Microsoft has issued a patch torectify thisD.

1 1 0 ELECTRONICS WORLD February 2001

COMMUNICATIONS

L

P2

AC outputtp load

R2

36/NOA,_111_

TMT2 R1

04010LB

Mr Teccor5

C6A Philips100n, 500V 1M,1%,1/4W

AC6-- 5043EDL input

= BUSS Z1

25OVAC

V420LA10P1 AGC-12

420VAC-cfC10A.001p500V

T2MagnaTekCSE187-L

IA 2A

5

RI \r-20,1/8W

R31k0

1k0

R6 IC13 R10MOC3042

Av A((

ZeroCrossingDetector

I 470

To IC4 -10 RA4

R333.83k

J

3

3,

1

R4178.7k

a

R351k0

2

+8V0

C5

7 7IC2 S

AD620

R2566k5

C19

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1/2 LM3932

+8V

IC5

-8V

+8V

R134k7 Digital Voltage Sense

D11 To IC4 - 5 RG7

C23 R2770.011.1 10k

D10 Analog Voltage SenseRAO

R262k2

C22

Input Balanced/ Unbalanced Sense LineTo IC4 - 11, RA5

Fig. 4. AC mains/current/voltageinterface schematics as used inthe watthour meter reference,

designed by Microchip.

C28

R36a 2112

1k0

.2211

7.1 .005p

iv R141k

+8V0

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Power factorComplementary to the measurementof AC power is the power factor ofyour load. Knowing the powerfactor helps you to decide whethercompensation capacitors are neededto attain a near unity power factor.

One of the simplest circuits Ifound uses only three ICs togetherwith an ICL7106 DVM chip. Itallows you to determine the powerfactor of an inductive load in therange 0.85 to 1 with 0.1% resolu-tion and 1% accuracy.6 To measurepower factor, the meter has to solvethe equation V,cosoV,.

For safety, the meter is batterypowered and uses current andvoltage transformers to isolate andinterface with the mains supply.The voltage waveform is rectifiedin a precision rectifier, then aver-aged in a long time -constant CRcircuit to derive the mean voltage or

The load current waveform isamplified and converted to abalanced drive voltage. This is usedto drive a synchronous rectifierwhich samples the voltage coinci-

R38100k J2

AC mainsO 0

To load

R56k2

1k

7

IC2AD620

4G.,14

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To R29

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1/2 LM393

'1'

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R16 Digital Current Sense4k7 D12

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To U4-6, RA1/AN1

C217 -8V.1p

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ICia324

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324

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324

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339

IC2

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47k

47k

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IC3

4016

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=31,3

1M Vincose

REF Hi

IC4

ICL7105

REF LO

COMM

IN LO

IN Hi

Fig. 5. Perhaps the simplest possible circuit devised for measuring the power factor of yourmains -loading circuits.

Todisplay


COMMUNICATIONS

Fig. 6. Using adedicated mains

energy meter chipto measure the

powerconsumption of

your load.

Fig. 7. Make-up ofthe Cirrus Logic

CS5460 singlephase bi-

directional 'powermeter on a chip'

integrated circuit.

Rf1

4001.1-1Rf1

Ra

b

x

PSU 1--C)+5VMOV

220V

RcWit 0 V2+

Cf2

Rf2

11

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-L o REFIN

I 0 REFOUT

1 0 V2-Cf2

VDD F1

AD7750 F2

FOOT

REVP

G1

ACDC

FS

S2

AGND DGND

dent with the phase of the loadcurrent. Output of this synchronousdetector is also similarly averaged,deriving V,cos0.

Dividing these two voltages iseasily performed using an ICL7106DVM chip in ratio mode. With Vinput to the 'Ref Hi' input andV,cos0 to 'In Hi', the ICL7106automatically divides V,cos0 by V,to display the measured powerfactor, Fig. 5.

Measuring AC mains supplyThe most common power meter isthe billing meter attached to everyhome. To date, these have relied on

S1

0 0 0 5 1 4 7

100implkWhr

3200imp/kWhr

+5V

XTAL- 3.5795MHz

j_

33pF

33pF

electro-mechanical methods tomeasure your power consumption.Such meters are expensive to makeand may lack accuracy.

Recent integrated -circuit designshave targeted this market, resultingin single chip solutions capable ofdriving either electronic or mechani-cal readouts, Fig. 6.

Both Cirrus Logic and AnalogDevices offer dedicated ICs. Theseclaim 0.1% and 0.2% readingaccuracy respectively over a 1000:1dynamic range. Other manufacturersmay also have similar devices.

Not surprisingly, both makersdemonstrate solutions that provide a

variety of useful outputs besides themass market's need for kW/h. Thesecircuits can be used to measureRMS voltage, current and instanta-neous power. Both makers'approaches provide outputs able tointerface to a mechanical counterand an on -chip serial interface to acomputer, Fig. 7.

Those of you interested in thistopic will find a good introductionto the practical application of thesecircuits by downloading two appli-cation notes. These areCS546ORD.PDF from Cirrus logic?and AN-545.PDF from AnalogDevices8.

IIN+ 0

IIN -0

VIN +O

VIN -0

VREFIN + 0 P.

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PGAX10,X50 4th Order

Modulator

2nd Order

Modulator

VoltageReference

0VA -

PowerMonitor

PFMON

DigitalFilter

Digitalfilter

SystemClock

High PassFilter

PowerCalculation

Engine(Energy

I x VIRMS, VRMS)

High passFilter

/KClock

Generator

Watch DogTimer

SerialInterface

E to F

0 /CS4 0 SDI

00 SDO

0 SCLK

00 /INT

*0/EDIR

*0/EOUT

CalibrationSRAM

6XIN XOUT CPUCLK

0DGND


TiePieScope HS801 PORTABLE MOST

ABRITARY WAVEFORM GENERATOR -STORAGE OSCILLOSCOPE -

SPECTRUM ANALYZER-MULTIMETER-

TRANSIENT RECORDER -

The HS801: the first 100 Mega samplesper second measuring instrument thatconsists of a MOST (Multimeter,Oscilloscope, Spectrum analyzer andTransient recorder) and an AWG (abritarywaveform generator). This new MOSTportable and compact measuringinstrument can solve almost everymeasurement problem. With theintegrated AWG you can generate everysignal you want.

The versatile software has a user -definedtoolbar with which over 50 instrumentsettings quick and easy can beaccessed. An intelligent auto setupallows the inexperienced user to performmeasurements immediately. Through theuse of a setting file, the user has thepossibility to save an instrument setupand recall it at a later moment. The setuptime of the instrument is hereby reducedto a minimum.

When a quick indication of the inputsignal is required, a simple click on theauto setup button will immediately give agood overview of the signal. The autosetup function ensures a proper setup ofthe time base, the trigger levels and theinput sensitivities.

401.141111111111mm

The sophisticated cursor read outs have21 possible read outs. Besides the usualread outs, like voltage and time, alsoquantities like rise time and frequencyare displayed.

Measured signals and instrumentsettings can be saved on disk.Thisenables the creation of a library ofmeasured signals. Text balloons can beadded to a signal, for special comments.The (colour) print outs can be suppliedwith three common text lines (e.g.company info) en three lines withmeasurement specific information.

The HS801 has an 8 bit resolution and amaximum sampling speed of 100 MHz.The input range is 0.1 volt full scale to 80volt full scale. The record length is32K/64K samples. The AWG has a 10 bitresolution and a sample speed of 25MHz.The HS801 is connected to theparallel printer port of a computer.

The minimum system requirement is aPC with a 486 processor and 8 MbyteRAM available. The software runs inWindows 3.xx / 95 / 98 or Windows NTand DOS 3.3 or higher.

TiePie engineering (UK), 28 StephensonRoad, Industrial Estate, St. Ives,Cambridgeshire, PE17 4WJ, UKTel: 01480-460028; Fax: 01480-460340

TiePie engineering (NL),Koperslagersstraat 37, 8601 WL SNEEKThe NetherlandsTel: +31 515 415 416; Fax +31 515 418 819

Web: http://www.tiepie.n1 Jit3CIRCLE NO. 113 ON REPLY CARD

Accurate milli -ohm meterWith a most sensitive range of 0 to 150mi2, David Ponting's

low-cost and self-contained milli -ohm meter measures lowresistances without injecting a large current into the resistorunder test. The meter can be used to locate solder bridges

and PCB shorts as well as measuring resistances. Having alinear output, the circuit can drive a standard DVM displaymodule, simplifying the design.

Iwas designing a circuit that neededan analogue ammeter capable ofreading up to 2A DC. To save

money, I decided that I would use ameter with a full scale deflection of100mA, which I had to hand.

An accurate wire shunt was neededacross the meter. It was not toodifficult to calculate that with aninternal resistance of 31(Q, thevoltage drop across the meter wouldbe 0.3V for full-scale deflection. So

+15V

NC-

-15V

2

5

IC1

4

AD534

10

1 3 7

0

c247n

SET SETFRED- AMPLI-UENCY TUDE

10k1 Ok 03

R3 10k

TL071MULTI'TURN - RJRN,T1

MA- IG2- -

-15V

DI

1N4148

RIM

C31p 3311

R2

4k7

1%

the shunt needed to drop the samevoltage at very nearly 2A. Hence itsresistance had to be 0.155.

If the resistance were 0.160, themeter used would read 107 and if itwere 0.140 the meter would read 93.This represents an unacceptable errorof ±7%. Clearly, the accuracy of theshunt resistance is very important.

So I looked around to see if therewere any off-the-peg resistancemeters that would measure to 0.252

8

TEST POINT

S1A

+15V 15V

10ki I

R7 IM

IC5A

with some degree of accuracy. Mostdigital multi -meters have a lowestscale of 200.052 and have a resolutionof 100m0. This is nowhere near goodenough. In any case, leads andcrocodile -clips or test points alreadyprovide errors of the order of IQ.

Beyond these multi -meters I foundno low resistance measuring devicesthat could be said to be within thefinancial reach of the averageelectronics enthusiast.

8

- IC5 =AD708

+15V

1511

1610

15

11p

1G4 R4 100k R6 100k18 13 7

AD63020

17

,

14-8 11

+15V

15V

C.8

IC5B

R800k

Fig. 1. Unlike manylow -resistance measuringschemes, this one does notinvolve injecting a highcurrent into the resistancebeing measured. It getsround the need for highcurrent by synchronouslydemodulating the voltagedrop across the unknownresistor. Test current isabout 1 mA.

5k

ULTI-TURN

Le20OrnVmeter

module

© 9-12V

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INSTRUMENTATION & TEST

Was it possible to make somethingthat would do the trick? I searchedaround and found some circuits thatgot close, but all of those I foundinitially relied on injecting highcurrents into the unknown resistancein order to produce a large enoughvoltage -drop to be accuratelymeasured.

High current would not matter inthe resistance I was trying todetermine in my meter -shunt, butmaking an accurate high -amperagepower supply just to measure lowresistance seemed excessive.

Then I found Analog Devices'Application Note number AN -306. Itdescribes - albeit in scant outline -acircuit that will measure very smallresistances without using highcurrents.

My circuit is an extension of thisapplication note. It results in thepractical realisation of an accuratemilli -ohm meter.

Meter specificationsThe meter has four ranges covering150m52, 1.552, 1552 and 15051. Allthe scales are linear.

On its most sensitive range themeter will measure accurately andrepeatably down to lma It alsogives a pretty good indication of thenext decimal place, hundredths ofmicro -ohms.

Current through the resistanceunder test is fixed at 1 mA, so mostdevices can be connected withoutdamage. For example, the resistanceacross the closed contacts of a low -current switch or relay can safely bemeasured at the kind of current theywill be expected to carry.

Figure 1 is the complete circuitdiagram. Reading this from left toright, the first section of the circuit isbuilt around AD534. This is aninternally trimmed, precision -multiplier chip. Connected as shown,this IC functions as a sine -waveoscillator. Multi -turn potentiometerP1 allows precise adjustment of theoutput frequency. Potentiometer P2sets the output amplitude. Op -amp/C2, which is used here as a voltage -following buffer, can be almost anygood -quality type.

With the proper adjustment of P1and P2, a 10V peak, 1kHz signal isinjected through both R3 - the onlyprecision resistor in the design - andRt, the resistance under test.

Voltage across Rt is detected andamplified by precision

Mainsinput

Bridge2

9

I C9L---1.11111116v

220p11 voltsfloating

Power supply. Because the meter's current consumption is low, it is possible touse a 15-0-15V transformer to produce the two 15V rails. A separate floatingsupply is needed for the 200mV meter module.

10V PKAT 1kHzCARRIER

GENERATOR

+V.0

COMO

ve

10k

10

1 PF 10k

If .Niv

tikA

AN

7 116 1

21CI AD630

14

13 100k

1 pF

100k

0.1 pF 0.1 pF "1-+

0.1IFT 0.1p,

instrumentation amplifier, AD524.The output is further amplified byIC5A, one of a pair of ultra -low -offsetvoltage op -amps in the AD708.

Now the signal feeds pins 1 and 16of AD630, a balanced modulator/de-modulator chip. The 630 demodulatesthe signal and passes it to the secondhalf of /C5, which forms a low-passfilter. This filtering is necessary toattenuate those random drifts, noiseand offsets not connected with themeasurement of Rb.

Pin 7 of /C5 outputs a voltage

7

12

1 F

ICy

AD708 0 Vow.

Circuit from Analog Devices' application note AN306,entitled 'Synchronous system measures Thesynchronous demodulator circuit is said to measure low-level resistance while rejecting uncorrelated disturbancessuch as noise, drift and offsets. Reprinted from EDN, thenote is by Moshe Gerstenhaber and Mark Murphey.

directly proportional to the resistanceof R. This voltage is scaled by R8 andP3 and can be read directly as milli -ohms on either the 200mV scale of adigital multi -meter, or on thefundamental range of a dedicatedvoltmeter module.

Why use an expensiveoscillator IC?You may think it a little extravagantin a simple design like this to use asomewhat expensive IC like theAD534 to do nothing more than



I couldn't get holdof a DIL version of

the AD534multiplier so Iadapted a OIL

socket to take theTO100 package.

PCB filesWe may be ableto supply ProteusCAD files for theohm -meter'sPCB. If you areinterested, [email protected] usingthe words 'ohmmeter' in thesubject heading.

produce a simple sine wave. Theexact frequency of 1kHz isunimportant and the absolute purityof the sine wave is not reallyrequired.

In fact, the circuit shown around theAD534 does produce a pretty puresine wave and does so at a very stablefrequency. But its crucial contributionin the oscillator circuit is that itsoutput amplitude is very stable.

Looking at the rest of the circuitdiagram, the AD524 is switched sothat pins 3 and 11 are joined. Withoutany external resistors, thisconjunction produces a precise

amplification factor of 1000.Similarly, a factor of 100 is achievedby joining pins 3 and 12, and a factorof 10 when connecting 3 and 13.

Further, if pin 3 is left unconnected,the amplification factor is unity, andhence the four positions of Sipprovide the separate ranges of themilli -ohm meter. If a dedicated200mV meter module is used, pole Bon Si is used to place the decimalpoint at the correct position in thedisplay.

Four -terminal measurementsAs with all attempts to measure lowresistance, this design uses the 'four -wire' approach, which involves a pairof wires going to each end of theresistance being measured.

Ideally then, separate wires should

go from IC3 pin 2 and from ground,while a second pair should go fromIC3 pin 1 and from R3. On my PCB,these four connections are paired offas close as possible to the terminalsthat take the component to be tested.

The meter measures any resistancebeyond the point where the pairsmeet. This means that the connectingterminals used to secure the ends ofthe component under test must makeas good a contact as possible with thepads on the PCB.

Any connection terminals usedmust have as low a resistance aspossible and must screw down firmlyon the contacts of the componentbeing measured. The ones I usedwere each made from a'/,in brassbolts with brass nuts. I even usedlarge spring washers to ensure goodcontact with the PCB.

Any single wires used between theterminals and a component under testmust be as short as possible and verythick. Crocodile clips used at theirends must be strong -spring -loadedand have sharp teeth to producemaximum electrical contact.

Power supply requirementsFigure 2 shows a suitable powersupply. It is fairly standard. Becausethe circuit draws only a small current,it is possible to use a 15-0-15V,100mA transformer to supply the±15V rails, even though the

regulators and rectifiers cause voltagedrops.

I was fortunate in that thetransformer I found for this circuithad an auxiliary 6V winding. Whenfull -wave rectified and wellsmoothed, this winding did not need aregulator to provide the 9 to 12Vfloating supply needed to drive thevoltmeter module.

It is possible to implement thecircuit on a single -sided board.Double -sided board is better thoughas it allows lower groundingresistance. Where possible, the legsof components should be soldered toboth sides of the board so that all thecopper -fill becomes a single andsubstantial ground.

It is good practice to set each multi -turn potentiometer to its mid -pointbefore soldering it. Doing this willensure that the circuit - particularlythe oscillator section - will at leastfunction when the board is firstpowered up, even if the calibration isinaccurate.

Setting up and calibratingThis will measure low resistancevalues to high precision. Betweenswitch -on and warm up though, thereis a small drift. Before you calibrate,it or use it for precise measurements,wait about 15 minutes. Warm-up driftis at most about 0.25%.

After warm-up, connect a counteror oscilloscope between the test pointand ground. Adjust potentiometer P1until you measure 1kHz. Replace thecounter with a digital multimeter setto read AC volts and adjust P2 ascarefully as possible for a reading of6.37V. This odd figure is derivedfrom 10(2/E), the mean value of a10V peak, sinusoidal input.

Beg, borrow or steal a 1% or betterresistor whose value is in the range0.1 to 0.150. It is worth some effortto get hold of a suitable referenceresistor but close parallel soldering often 152 1% resistors is good enough.

Set range switch S1 to its mostsensitive setting and screw down, astightly as possible, your standardresistor to the meter's terminals.Then, in the case of a 0.10 standard,adjust P3 so that the 200mV meterreads 100.0.

And that is it. All the other rangesare automatically adjusted.

You will soon notice that if theterminals are left open -circuit, themeter will read somewhere around1900 on all ranges. In other words,



beyond the end of each useable scale,the output voltage is compressed.

It is difficult to generalise about anexact value at which the meter beginsto become inaccurate. On the displaymodule I used though, which reads upto 1999, I have found all readings upto 1500 are accurate. Above that, it issafer to switch to the next range.

Measurement tipsGetting good contact with theresistance under test is veryimportant. Even with all theprecautions that I took, a copper barmeasuring 5 by 10 by 30mm screweddirectly across the terminals stillresulted in a measurement of 0.6m0.Consequently, I subtract somethingof the order of 0.6 from readings.

If you need to measure componentsthat do not lend themselves to beingattached via screw terminals, itwould be better to lay out your PCBso that pins 1 and 2 of IC3 float withrespect to the terminals and groundplanes. Then four separate wires canbe brought out, two directly frompins 1 and 2, and two more directlyfrom the R3 terminal and the groundplane.

Each wire should terminate in astrong crocodile -clip. Whenmeasuring, the wires should beattached in pairs - pin 2/ground andpin 1/R3 - to the ends of thecomponent.

After taking the measurement, allfour connecting wires should bejoined together and another readingrecorded. This second readingprovides the error factor that willneed to be taken away from thereading of measured resistance.

Other usesHaving completed the final design, Ifind myself using it far more than Iexpected. For example, I found Icould check the accuracy of thecurrent reading on my bench powersupply.

It uses a 0.10 nominal resistance ina power line to measure the voltagedrop and hence the current flow. ButI found the resistance to besignificantly higher than 0.152.

Shorting the resistor with an old100 speaker potentiometer, I wasable to adjust the combinedresistance to a rather more precise0.10052.

I have also measured variouscontact resistances of 'closed'switches and found how inaccurate it

On the left is the milli -ohm meterwith the copper shunt showing areading of 0.6mS2. Right is a 50,770,t 1% resistor being measured.Subtract the 0.6m0 residual and thereading becomes 49.9tna

is to say that 'this point is directlyconnected to that point via theswitch' !

And of course I measured theresistances of various odd bits of wireI found on my bench, just theordinary kind of hook-up wire oneuses to connect sections of anamplifier, for example. Suddenly thereason for hum via earth loopsbecame very much moreunderstandable.

There is one very important use forsuch a low resistance meter. You allknow how easy it is to leave solderbridges across adjacent tracks on aprinted circuit board duringprototyping. And you also know howdifficult it is to find them.

The resistance meter easily allowsthe tracing of such bridges. Usingpreferably the four -wire system,simply join one set of meter leads toone track and slide the joined secondpair along the other. The measuredresistance reaches a minimum at theposition of the short.

The same effect can be achievedusing the terminals and two short,thick leads but the sensitivity is not sohigh.

ComponentsResistors

R1,7

R2

R3

R4,6,8

R5

P1,2

P3

Capacitors

C1,4-6

C2

C3

C7,8

C9

C10,11

1M

4k7

10k, 1%

100k

10k

10k, multi -turn potentiometers

5k, multi -turn potentiometer.

1p

47n

33n

330p, 35V220p,16V100n

DiodesDl 1N4148

Bridge1,2 1A, 100V (piv)

Integrated circuitsIC1 AD534(JH)

IC2 TL071

IC3 AD524AD

IC4 AD630W1

IC5 AD708JN

IC6 78L15

IC7 79L15

February 2001 ELECTRONICS WORLD 1 1 7

Available exclusively fromElectronics World

Pandora's drumsUnique and atmospheriq music recordedin the early 1900s - the pays before 78s.

ruse this coupon to order your copy oflPandora's drums

Please send me CD(s) at £11.99 eachincluding VAT plus £1.50 carriage per order UK,or £3.00 overseas for which I enclose:

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Amazing music21 tracks -72 minutes ofrecordings made between1900 and 1929. Theseelectronically derivedreproductions are no worsethan - and in many casesbetter than - reproductions ofearly 78rev/min recordings -some are stunning...

All tracks on this CD were recordedon DAT from cylinders produced inthe early 1900s. Considering the ageof the cylinders, and the recordingtechniques available at the time, thesetracks are of remarkable quality,having been carefully replayed usingmodern electronic technology byhistorian Joe Pengelly.

Track1 Washington Post March, Band, 19092 Good Old Summertime, The American Quartet 19043 Marriage Bells, Bells & xylophone duet, Burckhardt & Daab

with orchestra, 19134. The Volunteer Organist, Peter Dawson, 19135. Dialogue For Three, Flute, Oboe and Clarinet, 19136. The Toymaker's Dream, Foxtrot, vocal, B.A. Rolfe and his

orchestra, 19297 As I Sat Upon My Dear Old Mother's Knee, Will Oakland, 19138 Light As A Feather. Bells solo, Charles Daab with orchestra,

19129 On Her Pic -Pic -Piccolo, Billy Williams, 191310 Polka Des English's, Artist unknown, 190011 Somebody's Coming To My House, Walter Van Brunt, 191312 Bonny Scotland Medley, Xylophone solo, Charles Daab with

orchestra, 191413 Doin' the Raccoon. Billy Murray, 192914 Luce Mia! Francesco Daddi, 191315 The Olio Minstrel, 2nd part, 191316 Peg 0' My Heart, Walter Van Brunt, 191317 Auf Dem Mississippi, Johann Strauss orchestra, 191318 I'm Looking For A Sweetheart And I Think You'll Do, Ada

Jones & Billy Murray, 191319 Intermezzo, Violin solo, Stroud Haxton, 191020 A Juanita, Abrego and Picazo, 191321 All Alone, Ada Jones, 1911

118 J Total playing time 72.0921 tracks - 72 minutes of music.

Published by Electronics World. All recordings reproduced by Joe Pengelly.

PRODUCTSPlease quote Electronics World when seeking further information

Magnetics offer powerfeed in LANsPulse has launched a series of10/100 -base -TX local areanetworking (LAN) magneticmodules which it claims willeliminate the AC powerrequirements for IP (InternetProtocol) telephones and otherlow -power Ethernet devices.Capable of feeding up to350mA on to standard LANcabling, the H2005A andH2006A dual -port modulesallow for enough power to drivemany different applicationsover LAN cabling. Theseinclude IP phones, remotesensors, building thermostats,and wireless LAN accesspoints. There are two partnumbers in the series. TheH2005A, designed for switchapplications, providesmaximum EMI suppressionwhile facilitating power feedand return on LAN cabling. TheH2006A is a more compactmodule for space -restrictedapplications such as IP phones,said the company. Each IEEE802.3 -compliant part is housedin an IC grade, transfer -moulded package, suitable forconvection and infrared reflowsoldering at temperatures up to235°C. The new LANmagnetics are currentlyavailable in tubes or tape andreel packaging and arecompatible with most high-speed pick -and -place assemblyequipment. Details are listed indata sheet H327.PulseTel: 01483 401 700Web: www.pulseeng.corn

Enhanced BGArework systemMetcal has enhanced its ballgrid array (BGA) reworksystem. This system isavailable in two models - theCSP-3500 designed for smallerchip scale rework, and the

BGA-3590 with high-poweredunder -board heating forthermally demanding PCBs.The main system enhancementis the addition of an improvedimaging camera that providesbetter definition when workingon fine pitch components. Aprism feature allows users to

simultaneously look at thetopside of the PCB and asuperimposed image of thecomponent underside. Theimages can then be accuratelyaligned in the X, Y and Thetaaxis. In addition, the improvedvision system includesfacilities for either solder pasteor flux application without theneed to remove the PCB fromthe machine. Otherenhancements includesimplified system controls,which are now accessible fromthe front of the machine, andimproved board handling. Infact the under -board supporthas been completelyredesigned to ensure easyadjustment and firm supportwithout the risk of damage tothe PCB.MetcalTel: 023 8048 9100Web: www.metcal.com

LDO consumes 650nAindependent of loadA low -dropout (LDO) regulatorfeaturing a low 650nA groundcurrent has been designed byMicrel Semiconductor for usein battery -powered devices.Capable of driving a 10mAload, the MIC5231 is availablein the company's proprietaryIttyBitty SOT -23 package.Aimed at power sensitiveapplications, this micropowerLDO uses the firm's FCap

Current -sensing motor drive IC claims to halve shutdown timeInternational Rectifier has introduced the IR2172 linearcurrent sensing IC with built-in over -current shutdown.Suitable for motor drive applications, the device isclaimed to eliminate external current sensing protectioncircuits. It is rated at 600V, for 230V three-phase ACinverter or brushless DC industrial motor drives used inconveyor belts and similar applications. The device hasa 1.51.ts over -current shutdown feature, with a wired -ORconnection capability direct to the microprocessor orDSP. Conventional linear current -sensing opto- or Halleffect -based systems have typical shutdown times ofthree to four microseconds. Motor drive circuits usingopto or Hall effect sensors require two externalcomparators and a level -shift operational amplifier toachieve the same functions, says the supplier. Themotor driver comes in two industry -standard, compactpackage outlines: SO -8 and 8 -pin DIP. The monolithichigh -voltage IC construction is designed to eliminateoptical or mechanical links between the current sensorsand motor drive output circuits, and increases reliabilitywhile shrinking circuit size as much as 75 per cent,compared to circuits using Hall effect or opto-basedcouplers.International RectifierTel: 0208 8645 8001Web: www.irf.com

February 2001 ELECTRONICS WORLD

NEW PRODUCT

Please quote Electronics World when seeking further information

design, which is optimised forstability with low-cost ceramicor tantalum capacitors, or withno capacitor at all. Featuresincludes two per cent initialaccuracy, no need for an outputcapacitor, enable input, fixedoutput voltages: 2.75, 3.0, 3.3and 5.0V, an input voltagerange of 3.5 to 12V and atemperature range from -40 to85°C.Micrel SemiconductorTel: 01635 524455Web: www.micrel.co.uk

Switching IC for widevarying loadsUltimate Renaissance has madeavailable the STR-G6551integrated off-line switching IC.The device operates in fixedoff -time mode with a maximumfrequency of 60kHz. The STR-G6551 features a 9R...3- - -,s(on)avalanche rated 650V, 158mJFET and includes over voltageprotection, under voltagelockout and thermal shutdowncircuitry. It is available in a5 -pin isolated TO -220 package.Ultimate RenaissanceTel: 01793 439310Web: www.ur-home.com

Reference clock withstress compensationGeneral Hybrid has developed aprimary reference clock, theAlpha 1, for Quartzlock'sCosmo double oven -controlledcrystal oscillators. The circuit,which incorporates a stress -compensated quartz crystal, isthe main element in the

rubidium frequency standards,GPS and quartz oscillatorsmade by Quartzlock. The circuitis based on an aluminiumnitride substrate that has athermal expansion similar tosilicon. Applications includetelecoms, metrology, radiotransmitter referencing,calibration and navigation.General HybridTel: 01295 256363Web: www.ukgeneralhybrid.com

Pipes shed light oninfra -red devicesHero Electronics is introducingSignal Construct light pipes foruse with infra -red devices.Conventional and surface

mount types are available. Forarrays of devices such as IRLEDs, photodiodes orphototransistors, vertical andhorizontal pipe arrangementsare available with between threeand ten light guides in a unit.For single devices, such asremote control receivers,straight bulkhead mountingpipes are the main option, butflexible pipes are available.Applications include set -topboxes, measurement systemsand remote control transmitters.Hero ElectronicsTel: 01525 405015Web: www.heroelec.co.uk

SBC for medical andPOS applicationsAdvantech has introduced anEBX single board computer.The PCM-9550F/M's PentiumMMX 266MHz processor, EBXform factor, digital I/0 andmultimedia features make it asuitable embedded platform formedical and POS applications.

Power consumption is typically3A at 5V and it operateswithout a fan in temperatures upto 60°C. The EBX form factorprovides an embedded layoutand PCI bus for expansionmodules such as 100Mbit/sEthernet or fax -modem. Eightdigital inputs (TTL levelsignals) and eight digitaloutputs are provided. There arefour com ports with +5 or +12Vcontrolled by jumper select.There is also cash drawersupport.AdvantechTel: 01908 304800Web: www.advantech.com

3.3V VCXO comes with±100x10-6 pull rangeEpson has introduced the VG-4231CA voltage controlledcrystal oscillator with a pullrange of ±100x10-6. TheVCXO is for use in networkingand ADSL equipment anddigital set -top boxes. There isan optional extended range from

to Charm10eDit AD

USART10 MBPS

SSP-rSP1

Piet8CX58.

. -Timers (4)Captures (2)PWAls (2)

EMA112M1qq,

cakTrtirtimOu.sori(3)..R4.4.45le 1!Autaife-r2)

PIC micros combine 10 Mips CPUwith 32kbyte program memoryMicrochip's PIC18C658 and PIC18C858microcontrollers combine a 10Mips CPUcore with 32kbyte OTP program memory,1536byte user RAM and a controller areanetwork 2.0B active peripheral interface.The intelligent CAN interface lets complexcontrol algorithms and network interfaces beexecuted on the same microcontrollermaking them suitable for automotive andindustrial control systems. The CANinterface contains a double -buffered receiverwith two priority levels, six full acceptancefilters and two acceptance masks. Threetransmit buffers are available forapplication -specific prioritisation.MicrochipTel: 0118 921 5858Web: www.microchip.com


SMUT'AMPLIFIERS

Amplifier Research 1W1000 1GHz 1W Amplifier

HP 70621A /H50 100KHz to 2.9GHz Pre -Amp Module

CALIBRATORS

Fluke 5220A Transconductance Amplifier

COMPONENT ANALYSERS

HP 4141B DC Source/monitor

HP 4145B Component AnalyserHP 4191A-002 1GHz Impedance Analyser

HP 4192A 13MHz Impedance Analyser

DATACOMMS

Microtest Penta Scanner Cat 5 Cable Tester

Fluke DSP100 Cat 5 Cable Tester

Fluke DSP4000 Cat 5/5e/6 Cable Tester

ELECTRICAL NOISE

HP 346B 18GHz Noise Source

HP 8970B Noise Figure Meter

EMC

R&S EB 100 Miniport Receiver 20-1000MHz

R&S EPZ 100 Mini Panoramic Display

R&S HE 100 1GHz Active Directional Antenna

FREQUENCY COUNTERS

EIP 548A 26.5 GHz Counter

HP 5350B 20GHz Frequency Counter

Counter Power Meter

Philips PM6654C/526 1.5GHz/2ns GPIB Counter Timer

FUNCTION GENERATORS

HP 33120A 15MHz Function/Arbitary Waveform Gen

HP 3325B 21MHz Function Generator

Philips PM5193 50MHz Function Generator

LOGIC ANALYSERS

HP 16500B Logic Analyser Mainframe

HP 1650A 80 Channel Logic Analyser

HP 16510B 80 Channel Logic Analyser Card

HP 16530A DSO Timebase Card

HP 16531A 400MS/S DSO CardHP 16550A Timing Analysis ModuleHP 16555A Tming Analysis Module

HP 1662A 68 Channel Logic Analyzer

HP 1670A 136 Channel Logic AnalyserHP 1671D 102 Channel Logic Analyser

NETWORK ANALYSERS

HP 4195A Network / Spectrum Analyser

HP 85046A 3GHz S Parameter Test Set Ohm)

HP 8753B 3GHz Vector Network Analyser

HP 8753C 3GHz Vector Network Analyser

OPTICAL FIBRE TEST

Anritsu MW0972B 1310/1550nm SM Plug-in

Anritsu MW9070B OTDR Mainframe

OSCILLOSCOPES

HP54603B 2 Channel 60MHz Digitizing Scope

HP 70700A /H25 20MS/S Digitiser Module

FREEFree Palm m100shipped with every

order over £10k

JEST EQUIPMENT Quality second user testequipment bought and soldAll purchases backed with

ito full one-year warranty and110 technical support

Philips PM3055 2 Chan 60MHz Analogue Scope

1850 Philips PM3295/40 2 Chan 350MHz Scope with GPIB

1500 Philips PM3295A/40 2 Chan 400MHz Scope with GPIB

Tektronix 2445A 200MHz 4 Channel Analogue Scope

Tektronix 2465N10 350MHz Analog Scope

Tektronix 24658 400MHz 4 Channel Analogue ScopeTektronix TM501/AM503/A6302 Current Probe System

.

2350

350

1250

1500

1500

1950

2750

1800

"10200 Tektronix 1A54bb z Channel uumriz Analogue Scope toy11950 Tektronix TDS350 200MHz 2 Channel Digitising Scope 1850

6500 Tektronix TDS380 400MHz 2 Channel Digitising Scope 2500

5500 Tektronix TDS380P 400MHz 2 Channel DSO with Printer 2950

Tektronix TDS420 4 Channel 150MHz Digitising Scope 2950

Tektronix TDS52013 2 Channel 500MHz Digitising Scope 6500

POWER METERS

HP 436A RF Power Meter with option 022

HP 437B RF Power Meter

HP 438A Dual Channel RF Power Meter

HP 70100A 100KHz to 50GHz Power Meter Module

Various HP 848x Power Sensors (from)

1650 Various Marconi 69xx RF Power Sensors (from)

1650 Marconi 6960A Power Meter

2650 Wandel & Goltermann OLP-2 Optical Power Meter

POWER SUPPLIES

1150 HP 6282A / 005 / 028 10V 10A DC Power Supply

8500 HP 6284A 005/028 20V/3A DC Power Supply

HP E3615A 20V/3A DC Power Supply

HP E3631A 25V 5A DC PSU

Hunting Hivolt Series 250 50kV, 5mA Power Supply3750

1250

1150

2200

2600

5000

1650

975

3500

1750

1200

1250

1400

1000

1200

1950

1900

4600

6900

9950

10500

8750

5750 HP 8596E 12.8GHz Spectrum Analyser

11950 HP 8901A 1.3GHz Modulation Analyser

HP 89038 20Hz To 100KHz Audio Analyser

Tektronix 492-02 21GHz Spectrum Analyser

Lindos LA100 Audio Analyser (inc. LA101 & LA102)3500

2500

850

1000

SIGNAL GENERATORS

Advantest R4262 4.5GHz Signal Generator 16500

HP 8642A /001 1GHz High Performance Signal Gen 2500

_0 a co so lb WILDLII woo

le IBM IN IP Olt MI tlt,11,, IN so acsIN MI IN al 1111 maw

ItILILivrrr

750

1250

1950

1000

395

350

750

900

150

150

195

650

975

PULSE GENERATORS

HP 8082A Pulse Generator 850

RF SWEEP GENERATORS

Wavetek 2001 1.4GHz Sweep Generator 1300

SIGNAL & SPECTRUM ANALYSERS

Advantest R41318 3.5GHz Spectrum Analyser 3950

Advantest R4131D 3.5GHz Spectrum Analyser 4500

Advantest R9211A 100KHz Dual Channel FFT Analyser 3750

Anritsu MS26018 2.2GHz Spectrum Analyser 5500

Anritsu MS2612A 4.6GHz Spectrum Analyser 6500

Anritsu MS6108 2GHz Spectrum Analyser 2650

Anritsu MS612A 50Hz to 5.5GHz Spectrum Analyser 6500

HP 3561A 100KHz Dynamic Signal Analyser 3250

HP 3562A 2 -Channel 100KHz Dynamic Signal Analyser 4500

HP 35660A 102.5KHz Dynamic Signal Analyser 2950

HP 35665A 102.4KHz Dynamic Signal Analyser 9750

HP 3585A 40MHz Spectrum Analyser 4500

HP 70000 22GHz Spectrum Analyser System 14500

HP 70000 2.9GHz Spectrum Analyser c/w Tracking Gen 13500

HP 8560A 2.9GHz Spectrum Analyser 10500

HP 8561A 1KHz-6.5GHz Spectrum Analyser 10850

HP 85628 22GHz Spectrum Analyser 17500

HP 8591A / 021 1.8GHz Spectrum Analyser 4650

HP 8592A /021 Spectrum Analyser 9500

HP AcCrIA 22GHz Spectrum Analyser losnn

HP 8648B 2GHz Signal Generator 3650

HP 8656B /001 1GHz Synthesised Signal Gen 1150

HP 8657B 2GHz Signal Generator 4250

HP 8673C 0.05-18.6GHz Synthesised Signal Generator 19800

HP 8673G 26GHz Synthesised CW Signal Generator 5400

Marconi 2017 1GHz Low Noise Signal Generator 1000

Marconi 2019A 1GHz Signal Generator 1000

O-^" ' ' ""DU

6950

6950

14500

Marconi zuzz 1GHz Signal Generator

Marconi 2031 2.7GHz Signal Generator

R&S SMH 2GHz Signal Generator

R&S SMHU58 4.32GHz Signal Generator

TELECOMS

Anritsu MD0623C 2MBPS CEPT Interface for MD6420A 3000

Anritsu MD6420A Data Transmission Analyser 3500

Anritsu MP1520B PDH Analyser 4300

Anritsu MS371A PCM Frame Analyser 4500

HP 37717C SDH/PDH/ATM Analyser (various configs) 13800

HP 37732A / 005 8MBPS Telecoms/Datacoms Analyser 7950

HP 3788N001 2MBPS Error Performance Analyser

HP 4934A / 001 Tims Test Set With Battery Pack

Marconi Triton Signalling Test Set

Marconi 2840A Handheld 2MBPS BERT Tester

Trend Aurora Duet Handheld ISDN Tester

TTC Fireberd 6000 c/w Jitter (interfaces available)

W&G PFA-35 2MBPS Communications Tester

Wandel & Goltermann DST -1 E&M Signalling Tester

Wandel & Goltermann PA -20 PCM Analyser

Wandel & Goltermann PCM23 Voice Freq PCM Tester

TV & VIDEO

CA100 Colour Analyser with CA -Al 0 Measuring Probe

Fluke 54200 /M01 TV Signal Generator

HP Calan 2010 Sweep/Ingress Analyser

Philips PM5415TNS TV Pattern Generator

Tektronix 1781R Video Measurement Set

Tektronix TSG271 TV Generator

Tektronix VM700A / 01/11/1C Video Measurement Set

0 c.

2950

3200

8500

1950

3950

4950

4950

1250

2500

2750

2650

4950

1950

1950

4500

2750

11750

WIRELESS

HP 11757A / 70/140MHz Multipath Fading Simulator 4500

HP 83220A /022 PCS/DCS1800 Test Set 3950

HP 83220E PCS/DCS1800 MS Test Set 3500

HP 8920A 1GHz Radio Comms Test Set (Many configs) 3950

HP 8920A /2/3/4/5 1GHz Radio Comms Test Set

HP 89208 Radio Comms Test Set (Many configs)

HP 8922M GSM Test Set

Marconi 2955 Radio Comms Test Set

Marconi 29558 Radio Comms Test SetMarrnni 2965A Radio Communications Test Set

19500 Racal 6103 /001/002 GSM/DCS Test Set c/w SMS/Fax

1250 R&S CMTxx Radio Test Set - Various Models (from)

2750 R&S CTS55 Digital Radio Tester

4500 Schlumberger 4015 1GHz Radio Comms Test Set

2750 Schlumberger 4031 Radio Comms Test Set

Schlumberger 4922 Radio Code Analyser

Schlumberger 4039 960MHz Radio Comms Test Set

Wavetek 4032 GSM Test Set

4950

12500

9500

1950

3500sgsn

9750

2250

4250

4950

2750

250

1250

9500

See our extensive online catalogue at www.TestEquipmentHQ.com Flexible commercial solutions available on all products.

Prices shown are in LUK and are exclusive of VAT. Free carriage to UKmainland addresses. This is just a selection of equipment we haveavailable. If you don't see what you want, please call. All items suppliedfully tested and refurbished with one year warranty. All manuals &accessories required for normal operation included. Certificate ofConformance supplied as standard, Certificate of calibration available atadditional cost. Test Equipment Solutions terms apply. E&OE.

01753 59 6000fax: 01753 59 6001www.TestEquipmentHQ.come-mail [email protected]

5 y4CIRCLE NO. 114 ON REPLY CARD

NEW PRODUCT


-40 to +85°C; standard rangeis -20 to +70°C.It operates at 3.3V and uses aCMOS IC inside with anoutput enable function. Besidesthe ADSL-frequency of35.328MHz, it is availablefrom 16 to 41MHz and comesin a 7 by 5mm ceramicpackage.Epson ElectronicsTel: 00 49 89 14005 277Web: www.epson-electronics.de

Micro interfaces on0.635mm pitchSamtec has introduced matchedimpedance micro interfaces inthe MIT and MIS series on0.635mm pitch with 38, 76,114, 152, 190, 228 and 266I/Os and a discrete groundplane with through -hole leadson 2.54mm pitch. They aretested for 50 and 750 systemsfor impedance, VSWR,attenuation, crosstalk,

propagation delay and rise timeat frequencies from 10MHz to1GHz. Spacings betweenboards can be 5, 8 or 11mm.There is a choice of full surfacemount, micro pitch interfacesfor quiet and high speedapplications, including 0.4mmpitch with 80 I/Os (QTF andQSF series), 0.5mm pitch withup to 300 U0s (QTH andQSH), 0.635mm pitch with upto 250 I/Os (QTS and QSS)and 0.8mm pitch with up to200 I/Os (QTE and QSE).SamtecTel: 01236 739292Web: www.samtec.com

Pushbutton operatespassenger door panelEAO has introduced apassenger door operating panelfor use in refurbishing rollingstock. The door operatingpushbutton panel has switchesflush mounted or fitted withbezels. Bezels and actuators

The Distributor with20,000 hard -to -find lines

EX STOCK!!!Semiconductors

We have one of the largest ranges of discrete parts in theUK, both new and obsolete types and, if we do not have it in

stock, we can usually source it for you.Call or fax for our latest Semiconductor stock list.

Computer productsWe carry in stock everything to make a Personal Computer.

CPUs - Memory - Motherboards - Cards - Scanners -Modems - Sound Cards - Speakers - All types of Drives -

Cases - PSUs - Monitors etc

Components & equipmentCall or fax for our latest Semiconductor stock list.

Capacitors - Resistors - Connectors - Potentiometers -Cables - Batteries - Speakers - Amplifiers - Lamps -

Microphones - Fans - Power supplies - Transformers -Buzzers - Sirens - Fuses and Holders - LEDs - LCDs -Relays - PA Systems - Tools - Test Equipment - etc

See our web site. Non -trade customers, send £9.80 tothe sales office for a complete suite of catalogues.

Semiconductor Supplies International Ltd

Dawson House, 128 - 130 Carshalton Road,Sutton, Surrey, England, UK. SM1 4TW020-8643 1126 (Sales and Technical Queries)Fax: 020-8643 3937 (For International use +4420)e-mail: [email protected] Web: ssi-uk.com

are available in variouscolours, and the pressel areacan be supplied with raisedsymbols or engraved torequirements.EAO GroupTel: 01444 236000Web: www.eao-group.corn

Debugging support forH8/2664F MicroHitachi has released the E I OTon -chip debugging tool thatprovides debugging support forthe H8/3664F 16 -bit flashmicrocontroller. The device hasa five -pin interface thatprovides access to the on -chipdebug system, letting the userset breakpoints on -chip andaccess an on -chip software tracefacility. It is available in PCIand PCMCIA versions, and canbe used in development and thefinal production version. Thefive pins comprise three I/0pins with NMI and resetfunctions. The tool provides the

user with a hardware breakpointon address and data, three -levelbranch trace, single stepping atC and assembly level, and theability to download applicationsand program on -chip flash. TheHDI source level debuggergives the user high leveldebugging in C with C level,mixed or assembly level displayoptions. It can also run user

180W converter suits 19in racksThe 180W P -series DC/DC converter from Power -Onemeasures 4TE wide and is suitable for I9in. rack systems. Itprovides single, dual, triple or quadruple outputs with voltagesfrom 3.3 to 24V. Input voltage range is 16 to 150V DC acrossfive models and they are protected against surges andtransients occurring on the source line. The fully enclosed,black coated aluminium case includes an H15 or H1552 typeconnector and acts as heatsink and RFI shield. The unitsincorporate input and output filtering, over -temperatureprotection and input over and undervoltage lock -out. Each canbe used as a modular power supply or as a part of a distributedpower supply system.Power OneTel: 00 49 7666 931 962Web: www.power-one. corn

ELECTRONICS WORLD February 2001

SMALL SELECTION ONLY LISTED - EXPORT TRADE AND QUANTITY DISCOUNTS - RING US FOR YOUR REQUIREMENTS WHICH MAY BE IN STOCK

HP New Colour Spectrum Analysers LAST FEW ONLYHP141T+ 8552B IF + 8553B RF -1KHZ -110Mc/s - £500.HP141T+ 85528 IF + 85548 RF -100KHz -1250M - £600.HP141T+ 8552B IF + 8556A RF - 20Hz-300KHz - £400.HP141T+ 8552B IF + 8555A 10 MC/S-18GHzS - £1000.HP8443A Tracking Gen Counter 100KHz-110Mc/s - E200HP8445B Tracking Preselector DC to 18GHz - £250.HP8444A Tracking Generator 5-1300Mc/s - £450.HP8444A OPT 059 Tracking Gen 5-1500Mc/s - £650.HP35601A Spectrum Anz Interface - £300.HP8970A Noise Figure Meter + 346B Noise Head - £3k.HP8755A+B+C Scalar Network Anz PI - £250 + MF 180C -Heads 11664 Extra - £150 each.HP3709B Constellation ANZ £1,000.HP11715A AM -FM Test Source - £350.FARNELL TVS70MKII PU 0-70V 10 amps - £150.MARCONI 6500 Network Scaler Anz - £500. Heads availableto 40GHz many types in stock.Mixers are available forANZs to 60GHz.Marconi TF2374 Zero Loss Probe - E200.Racal/Dena 2101 Microwave Counter - 10Hz-20GHz - withbook as new Elk.Racal/Dana 9303 True RMS Levelmeter + Head - £450.TEKA6902A also A6902B Isolator - £300-E400.TEK CT -5 High Current Transformer Probe - £250.HP Frequency comb generator type 8406 - £40HP Sweep Oscillators type 8690 A+B + pluto 18GHz also 18-40GHz.HP Network Analyser type 8407- 110Mc/s - £500 - E1000.HP 8410 -A -B -C Network AnaGHz - plus most or units and8411a -8412-83A14-8418-8740-874From £16Racal/Dom 9301A-9 millivoltmeter - 1stock £250-£400.Racal/Dago- ulation Meter Type 9009-90081.5GHz - 5 50 - 9009A £350.Ma L Bridge type TF2700 - £150.Marc ni Microwave 6600A 1 sweep osc., mainf6650PI -18-26.5 GHz or 6651 PI - 26.5-40GH£600. MF only E250.Gould J3B test oscillator + manuaBarr & Stroud Variable filterjF3 0.low pass - £150, otherRacal/Dana 9300 RHP 8750A storage noMarconi mod metersRacal/Dana counters -9

stocE25

r E400 viit lead + S.A. or N, AOt E250 - TF2305 - £1, 1

05-9906-9915-9916-9917-9

GHz or 18d in thi up -

42-8743

pass +

50Mc/s-3GHz - £100 - £400 - all fitted with FX standards.HP180TR. HP181T, HP182T mainframes £300 - £500.HP432A-435A or B -436A -power meters + powerheads to60GHz - E150 - £1750 - spare heads available.HP3586A or C selective level meter - £500.HP86222A+B Sweep PI -01-2.4GHz + ATT £1000-E1go:HP86290A+B Sweep PI -2 - 18GHz - £1000 -HP8620C Mainframe - £250. IEEE £35

-511

HP3455/3456A Digital voltmeter -E400HP8165A Programmable signal sou

HP5370A Universal time interval couHP5335A Universal counter - 200Mc/sTEKTRONIX 577 Curve tracer + adaptors - £900.TEKTRONIX 1502/1503 TDR cable test set - £400.HP8699B Sweep PI YIG oscillator .01 - 4GHz -£300.8690BMF-£250. Both £500.Dummy Loads & Power att up to 2.5 kilowatts FX up to18GHz - microwave parts new and ex equipt - relays -attenuators - switches - waveguides - Yigs - SMA - APC7plugs - adaptors etc. qty. in stock.B&K Items in stock - ask for list.Power Supplies Heavy duty + bench in stWeir - Thurlby - Racal etc. Ask for list,stock, all types to 400 amp -100HP8405A Vector voltmeter - I

HP8508A Vector voltme £2

LIGHT AND OPTICALAnritsu ML93A & Optical er Meter - £250.Anritsu ML93B & Optical Ind Power Meter - £350.Power Sensors for above MAMA - MA98A - MA913A -Battery Pack MZ95A.Anritsu MW97A Pulse Echo Tester.PI available - MH914C 1.3 - MH915B 1.3 - MH913B 0.85 -MH925A 1.3 - MH929A 1.55 - MH925A 1.3GI - MH914C 1.3SM- £500 + one PI.Anritsu MW98A Time Domain Reflector.PI available - MH914C 1.3 MH915B 1.3 - MH913B 0.85 -MH925A 1.3 - MH929A 1.55 - MH925A 1.3GI - MH914C 1.3SM- 000 + one P.I.Anritsu MZ100A E/O Converter.+ MG912B (LD 1.351 Light Source + MG92B (LD 0.851Light Source £350.Anritsu MZ118A 0/E Converter.+MH922A 0.8 0/E unit + MH923 A1.3 0/E unit £350.Anritsu ML96B Power Meter & Charger £450.Anritsu MN95B Variable Att. 1300 £100.Photo Dyne 1950 XR Continuous Att. 1300 - 1500 £100.Photo Dyne 1800 FA. Att £100.Cossor-Raytheon 108L Optical Cable Fault Locator0-1000M 0-10kM £200.TEK P6701 Optical Converter 700 MC/S-850 £250.

TEK OF150 Fibre Optic TDR - £750.HP81512A Head 150MC/S 950-1700 £250.HP84801A Fibre Power Sensor 600-1200 £250.HP81588 ATT OPT 002+011 1300-1550 E300.HP81519A RX DC-400MC/S 550-950 £250.STC OFR10 Reflectometer - E250.STC OFSK15 Machine jointing + eye magnifier - £250.

MISCELLANEOUS ITEMSHP 4261 LCR meter - £650.HP 4274 FX LCR meter - £1,500.HP 3488 Switch Control Unit + PI Boards -HP 75000 VXI Bus Controllers + E1326HP 83220A GSM DCS/PCS 1805-1with 8922A - £2,000.HP 1630-1631-1650 LogiHP 8754A Network£1,500.HP 8754£2,000.HP 83505.9-12.4GHHP MICRO£400.HP PREAMPLIFIER 84HP PREAMPLIFIERHP POWER LIFI

HP PRE Ar.

HP 3574£400.MARC'2305 Mo

RCONI 2610 -hueMARCONI 893B AF Powe£350MARCMARRange 411RACAL 1°792 COMMUlate model with k ligRACAL 177 UNIC

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400KHZ to 110 MC/S. 3.5k.

WE KEEP IN STOCK HP and other ma es of RF Frequencydoublers which when fitted to the RF output socket of aS/Generator doubles the output frequency EG.50-1300MC/Sto 50-2600MC/S price from £250 - £450 each.

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£2,000.m anz.1.10

SPECTRUM ANALYZERSHP 3580A 5HZ-50KHZ - E750.HP 3582A Dual 0.2HZ-25.5KHZ - E1,500.HP 3585A 20HZ-40MC/S - £3,500.HP 3588A 10HZ-150MC/S - E7,500.HP 8568A 100HZ-1.5GHZ - £3,500.HP 85688 100HZ-1.5GHZ - £4,500.HP 8590B 9KC/S-1.8GHZ - £4,500.HP 8569B 10MC/S10.01-22GHZ)- £3,500.HP 3581A Signal Analyzer 15HZ-50KHZ - £400.TEK492 50KHZ-21GHZ OPT 2 - £2,500.TEK492P 50KHZ-21GHZ OPT 1-2-3 - £3,500.TEK492AP 50KHZ-21GHZ OPT 1-2-3 - £4,000.TEK492BP 50KHZ-21GHZ - £3,000-E4,000.TEK495 100KHZ-1.8GHZ - £2,000.HP 8557A 0.01MC/S-350MC/S - £500 + MF1807 or 180C -£150 -182T -f500.HP 85588 0.01-1500MC/S - E750 - MF180T or 180C -£150-182T-f500.

HP 8559A 0.01-21GHZ -£1,000 - T or 180C -050 -182T - £500.HP 8901A AM FM Modul AN O.

HP 89018 AM FM atHP 89038 Ayilia.AnHP 89036 ArlaMARCONI 2970 SPECIVI ANALYZERS - HIGH QUALITY -DIGITAL GTORASg- 30HZ-110MC/S Large qty to clear as

e from all sold as is from pile complete or addsic testing and adjustment - callers preferred -wn from over sixty units - discount on qtys of

e.

EARLY MODEL GREY - horizontal alloy cooling fins - £200.B LATE MODEL GREY - vertical alloy cooling fins - MOO.

LATE MODEL BROWN - as above Hew only) - £500.

1,750.

ILLOSCOPES465-465B 1

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s - £250-£300.es - E200.

C + 2 probes - £300-E350.A-2224-2225-2235-2236-2245-60-

C/S + 2 probes - £450.h 150MC/S + 2 probes - £600.

B 4ch 150MC/S + 2 probes - E750.TEK 468 D.S.O. 100MC/S + 2 probes - £500.TEK 485 350MC/S + 2 probes - £550.TEK 2465 4ch-300MC/S - E1,150.

465A 4ch-350MC/S -£1,550.ACT 4ch-350MC/S - 1,750.

0.2230 -100MC.0.2430 15

S.O. 2430AK D.S 0.2440 -

TEK T S 475-495 1

robes - £1,000.probes -£1,250.

/S probes - £1,750.+ bes - £2,000.OM -4 ch + 2 probes - £900-

IS"2 probes - E250.

storage + 2 probes - £200.722A - 1725A - 275MC/S + 2 probes - £300-£400.

- 100MC/S storage - large screen -£250.1745A - 1746A - 100MC/S - large screen - £35

HP54100A - 1GHz digitizing - £500.HP 00A - 50MC/S digitizing - £500.

1A - 100MC/S digitizing -£50- 1GHZ digitizing -

AVE CO351D Au

EIP 371EIP 45

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Hz-18GHz - £850.300MC/S-18GHz - E700.

545 Mi as1 equency Counter - 10Hz-18GHz -£1K.P 548A Mi ave Frequency Counter - 10HZ-26.5GHz

575 Microwave Source Locking - 10Hz-18GHz - £1.2K.588 Microwa ulse Counter - 300MC/S-26.5GHz -

£1.4KSD Z-24GHZ -SMA Socket - E800.SD HZ-18GHZ -N Socket - E700.SD 6 ter 800MC/S-18GHz - MAO.SD 62 ounter 20Hz-26GHz -£1.2K.

D 62 Micro Counter 20Hz-4.5GHz - £400.535 Micro Counter OPT 010-005-46GHz - new in box -c.

HP5340A Micro Counter 10HZ-18GHz - Nixey - £500.HP5342A Micro Counter 10HZ-18-24GHz -£800-£1K - OPTS001-002-003-005-011 available.HP5342A + 5344S Source Synchronizer - £1.5K.HP5345A 500MC/S 11 Digit LED Readout - £400.HP5345A + 5354A Plugin - 4GHz - £700.

P5345A + 5355A Plugin with 5356A 18GHz Head - £1K.P5385A 1GHz 5386A -5386A 3GHz Counter - £1K-E2K.

Racal/Dana Counter 1991-160MC/S - £200.Racal/Dana Counter 1992-1.3GHz -£600.Racal/Dana Counter 9921-3GHz - £350.

SIGNAL GENERATORSHP8640A - AM -FM 0 5-512-1024MC/S - £200-£400.HP8640B - Phase locked - AM-FM-0.5-512-1024MC/S - £500-£1.2K. Opts 1-2-3 available.HP8654A -8 AM -FM 10MC/S-520MC/S - £300.HP8656A SYN AM -FM 0.1-990MC/S - £900.HP8656B SYN AM -FM 0.1-990MC/S -£1.5K.HP8657A SYN AM -FM 0.1-1040MC/S - £2K.HP8657B SYN AM -FM 0.1-2060MC/S - £3K.HP8660C SYN AM-FM-PM-0.01-1300MC/S-2600MC/S - £2K.HP8660D SYN AM-FM-PM-0.01-1300MC/S-2600MC/S - £3K.HP8673D SYN AM -FM -PM -0.01-26.5 GHz - El 2K.HP3312A Function Generator AM -FM 13MC/S-Dual - £300.HP3314A Function Generator AM-FM-VC0-20MC/S -£600.HP3325A SYN Function Generator 21MC/S - E800.HP3325B SYN Function Generator 21MC/S - £2K.HP8673-B SYN AM -FM -PH 2-26.5 GHz - £6.5K.HP3326A SYN 2CH Function Generator 13MC/S-IEEE - £1.4K.HP3336A-B-C SYN Func/Level Gen 21MC/S - £400-£300-E500.Racal/Dana 9081 SYN S/G AM-FM-PH-5-520MC/S - £300.Racal/Dana 9082 SYN S/G AM-FM-PH-1.5-520MC/S - £400.Racal/Dana 9084 SYN S/G AM-FM-PH-.001-104MC/S - £300.Racal/Dana 9087 SYN S/G AM-FM-PH-.001-1300MC/S -£1K.Anritsu MG3601A SYN AM -FM 0 1-1040MC/S - E1.2K.

ITEMS BOUGHT FROM HM GOVERNMENT BEING SURPLUS. PRICE IS EX WORKS. SAE FOR ENQUIRIES. PHONE FOR APPOINTMENT OR FOR DEMONSTRATION OF ANY ITEMS, AVAILABILITY ORPRICE CHANGE.VAT AND CARRIAGE EXTRA. ITEMS MARKED TESTED HAVE 30 DAY WARRANTY. WANTED: TEST EQUIPMENT -VALVES -PLUGS AND SOCKETS-SYNCROS-TRANSMITTING AND RECEIVING EQUIPMENT ETC.

Johns Radio, Whitehall Works, 84 Whitehall Road East, Birkenshaw, Bradford BD11 2ER. Tel: (01274) 684007. Fax: 651160

CIRCLE NO. 115 ON REPLY CARD123

NEW PRODUCT


code in real-time and singlestep, with step -over, step intoand step out of functions. HDIprovides a register display,three level branch trace, C levelwatch -points and a memorywindow.HitachiTel: 01628 585163Web: www.Hitachi.co.jp

Half -pitch DIP switchhas 1.5mm profileOmron's A6H half -pitchsurface mount DIP switch has a1.5mm profile, making itsuitable for space sensitiveapplications where occasionalor installation -specific settingchanges are required, such as insecurity and vendingequipment. It can be reflowsoldered and is available in fourand eight pole versions, with asix pole version planned.

Measuring 4.5mm wide, and6.31, 8.85 and 11.39 mm longfor four, six and eight polemodels respectively, it willswitch 25mA at 24V DC andprovides 100%2 insulationresistance. Available with tapeseal for immerse cleaning andon embossed tape reels forautomatic pick -and -placeprocesses, the switch canoperate at -20 to +70°C withzero icing or condensation.OmronTel: 020 8450 4646Web: www.omron.co.uk

Sun SPARC clustersystem launchI-Bus/Phoenix has launched theG2077 NEBS tested Sun Sparccluster system, which is aCompactPCl platform equippedwith two independent systemboards, Sun MicrosystemsCP1500 SBCs, configured as a

cluster server.The system comes fullyintegrated with dual hot -swap,Intraserver ITI-8241C-S quadEthernet, dual Ultra -2 SCSI and4MB video board, 10 userexpansion slots, as well as SunCluster 2.2 or Veritas HAFoundation Suite installed.I -Bus PhoenixTel: 023 9242 4800Web: www.sales@ibus .co.uk

Memory products withdual -bank flashSilicon Storage Technology hasintroduced four ComboMemoryproducts that incorporate adual -bank flash memoryarchitecture and allow forconcurrent operations betweenthe two internal flash memorybanks and the SRAM. Theycontain 16Mbit flash and 2 or4Mbit SRAM. Housed in an 8

by 10mm BGA package withstacked -die technology, thedevices are for mobile wirelesscommunications applicationssuch as Bluetooth and WAP-enabled mobile phones andInternet -based PDAs. The datacan be read from either bankwhile an erase or programoperation is in progress in theopposite bank. The flashmemory is partitioned into 4and 12Mbit banks with top orbottom sector protection optionsfor storing boot codes andconfiguration data.Silicon Storage TechnologyTel: 01628 585163Web: www.ssti.com

Line interface hybridssupport ISDN S chipsAdvanced Power Componentshas released line interfacehybrids to support InfineonISDN S interface chips. The

Data recovery up to 2.5Gbit/sMicrel Semiconductor has developed a clock and data recoveryIC that combines onboard clock synthesis with operation from28Mbit/s to 2.5Gbit/s. The AnyRate SY87702L can recoverdata from serial streams running at any rate up to OC-48. Thedevice can handle commonly used communications speeds andprotocols including OC-3 STM-1, 0C-12 STM-4, OC-48STM-16, Fast Ethernet, Gigabit Ethernet, FDDI, Escon, fibrechannel, 2x fibre channel, Infiniband and digital video ratesoutlined in SMPTE 259 and 292. It also supports proprietaryrates.Micrel SemiconductorTel: 0207 823 3224Web: www.micrel.com

hybrids contain the interfacecomponents required betweenthe chip and the telephoneconnector port, including lineisolation and secondaryprotection. The Infineontransceivers operate on a 3.3Vsupply. There are three packagestyles for the hybrids. Thestandard sized APC14131Eprovides 1500V supplementaryisolation. The APC8305 minihybrid and PCMCIA-heightAPC8403 provide basicisolation. They are verifiedagainst the requirements oflayer one testing.APCTel: 01634 290588Web: www.apc-plc.com

200V integrated SMPSin TO -262 packagingInternational Rectifier hasintroduced a 200V integratedswitched mode power supply ICin a TO -262 package. TheIR4007 is a DC -to -DCconverter control IC with anavalanche -characterised Mosfetbuilt-in. The device can handlemomentary transient voltagesabove its rated breakdownvoltage as long as they do notexceed the specified avalancheenergy limit of 100mJ. It has

proprietary input and outputfeedback circuits. Topologiesinclude 48V in, 3.3V outputflyback converters up to 5A.Two operating modes are built-in - quasi -resonant mode andpulse ratio control mode. Inquasi -resonant mode thetransformer primary inductanceand an additional capacitorprovide a resonant signal totrigger the Mosfet when thedrain -source voltage is at aminimum, reducing powerdissipation.International RectifierTel: 0208 645 8001Web: www.irf.com

40 MHz comms chipCypress has introduced a40MHz intelligent controlcommunications processor forLonworks control networks.Each device contains three 8 -bit


PHONE020 86841166

LANGREX SUPPLIES LTDDISTRIBUTORS OF ELECTRONIC VALVES FAX

TUBES AND SEMICONDUCTORS AND I.C.S. 020 86841 MAYO ROAD CROYDON SURREY CR0 2QP 3056

24 HOUR EXPRESS MAIL ORDER SERVICE ON STOCK ITEMSemail: langrex@aoLcom

£ p KT66 Special 20.00 5Z4GT 3.00 6U8A 1.50AZ31 8.00 KT88 Special 20.00 6AQ5 2.00 6V6G 10.00

CL33 15.00 N78 8.00 6AR5 6.00 6V6GT 6.00E88CC 8.50 0A2 3.00 6AS7G 7.50 6X4 3.00E180F 3.50 OB2 3.00 6AU5GT 4.00 6X5GT 3.00E810F 20.00 0C3 3.00 6AU6 2.00 12AT7 3.00EABC80 4.00 OD3 3.00 6AW8A 4.00 12AU7 3.50EB91 1.50 PCF80 2.00 6B4G 22.00 12AX7 5.00EBF80 1.50 PCL82 2.00 6BA6 1.50 12AX7A 7.50EBF89 1.50 PCL85/805 2.50 6BE6 1.50 12AX7WA 6.00EBL31 25.00 PCL86 2.50 6BH6 2.00 12BA6 2.00ECC33 12.00 PD500 8.00 6B07A 2.00 1213E6 2.00ECC35 12.00 PL36 3.00 6BR7 4.00 12BH7 10.00ECC81 3.00 PL81 2.00 6BR8 4,00 12BY7A 7.00ECC82 5.00 PL504 3.00 6BW6 4.00 12DW7 15.00ECC83 3.00 PL508 3.00 6BW7 3.00 12E1 10.00

ECC85 5.00 PL509/519 10.00 6BX7GT 7.50 13E1 85.000ECC88 6.00 PL802 4.00 6BZ6 3.00 572B 27.50ECC808 15.00 PY500A 3.00 6C4 2.00 805 45.00ECF80 1.50 PY800/801 1.50 6CB8A 3.00 807 7.50ECH35 3.50 00V02-6 12.00 6DC6G 5.00 811A 10.00ECH42 3.50 00V03-10 5.00 6CL6 3.00 812A 55.00ECH81 3.00 Q0V03-20A 10.00 6CG7 7.50 813 27.50ECL82 5.00 00V06 -40A 12.00 6CH6 3.00 833A 85.00ECL86 5.00 U19 8.00 6CW4 6.00 866A 20.00ECLL800 25.00 UABC80 1.60 6005 17.50 872A 30.00EF37A 3.50 UCH42 5.50 6DQ6B 10.00 931A 25.00EF39 2.75 UCL82 2.00 6F6G 8.00 2050A 12.50EF40 4.00 UCL83 2.00 6FQ7 7.50 5687WB 6.00EF86 5.00 UF89 4.00 6GK6 4.00 5751 6.00EF91 2.00 UL41 12.00 6J5G 6.00 5763 8.00EF183/4 2.00 UL84 3.00 6J5M 4.00 5814A 5.00EL33 15.00 UY41 4.00 6J7 3.00 5842 12.00

EL34 5.00 UY85 2.00 6JB6A 27.50 6072A 6.00EL34G 5.00 VR105/30 3.00 6JE6C 27.50 6080 6.00EL36 5.00 VR150/30 3.00 6JS8C 27.50 6146B 15.00

EL41 3.50 Z759 10.00 6K6GT 4.00 6201 8.50EL84 2.25 Z803U 15.00 6L6G 15.00 6336A 35.00EL95 2.00 2021 3.50 6L6GC 17.50 6550A 25.00EL360 15.00 3828 12.00 6L6WGB 10.00 68836 15.00EL509/519 7.50 4CX250B 45.00 607 3.00 7025 7.50EM34 25.00 5R4GY 7.50 6SA7 3.00 7027A 26.00EM81/4/7 5.00 5U4G 10.00 6SC7 3.00 7360 26.00EN91 7.50 5U4GB 10.00 6SG7 3.00 7581A 15.00

EZ80/EZ81 5.00 5V4G 5.00 6SJ7 3.00 7586 15.00GZ32 8.50 5Y3GT 2.50 6SK7 3.00 7587 20.00GZ33/37 15.00 5Z3 5.00 6SL7GT 5.00 Prices correct whenKT61 15.00 5Z4G 6.00 6SN7GT 7.50 going to press.

OPEN TO CALLERS MON-FRI 9AM-4PM. CLOSED SATURDAYThis is a selection from our stock of over 6,000 types. Please enquire for types not listed.

Obsolete items are our speciality. Valves are new mainly original British or American brands.Terms CWO/min order £10 for credit cards.

VISA P&P 1-3 valves £2.00. 4-5 valves £3.00MINNEY Add 17.5% VAT to total including P&P 4111::


WATCH SLIDES ON TVMAKE VIDEOS OFYOUR SLIDESDIGITISE YOURSLIDES(using a video capture card)

"Liesgang diatv" automatic slide viewer with built in high quality colour TV camera. It hasa composite video output to a phono plug (SCART & BNC adaptors are available). Theyare in very good condition with few signs of use. For further details see www.diatv.co.uk

£91.91+ vat = £108.00Board cameras all with 512x582 pixels 8.5mm 1/3 inch sensor and composite video out.All need to be housed in your own enclosure and have fragile exposed surface mountparts. They all require a power supply of between 10 and 12v DC 150mA.47MIR size 60x36x27mm with 6 infra red LEDs (gives the same illumination as a smalltorch but is not visible to the human eye) £37.00 + vat = £43.4830MP size 32x32x14mm spy camera with a fixed focus pin hole lens for hiding behind avery small hole £35.00 + vat = £41.134OMC size 39x38x27mm camera for 'C' mount lens these give a much sharper imagethan with the smaller lenses £32.00 + vat = £37.60

Economy C mount lenses all fixed focus & fixed irisVSL1220F 12mm F1.6 12x15 degrees viewing angle £15.97 + vat = £18.76

VSL4022F 4mm F1.22 63x47 degrees viewing angle £17.65 + vat = £20.74



Better quality C Mount lensesVSL1614F 16mm F1.6 30x24 degrees viewing angle £26.43 + vat = £31.06

VWL813M 8mm F1.3 with iris 56x42 degrees viewing angle £77.45 + vat = £91.00

1206 surface mount resistors E12 values 10 ohm to 1M ohm 100 of 1 value £1.00 + vat1000 of 1 value £5.00 + vat

866 battery pack originally intended to be used with an orbitelmobile telephone it contains 10 1.6Ah sub C batteries(42x22dia the size usually used in cordless screwdrivers etc.)the pack is new and unused and can be broken open quiteeasily £7.46+vat = £8.77

Please add 1.66 + vat = £1.95 postage & packing per orde,

JPG ELECTRONICS276-278 Chatsworth Road, Chesterfield, S40 2BH.

Tel 01246 211202 Fax 01246 550959 MastercardNisa/SwitchCallers welcome 9:30 a.m .to 5:30 p.m. Monday to Saturday

1st


Standalone Data LoggersLow-cost standalone data capture solution

T -Logger 44.99 +VatMicro power standalone singlechannel temperature logger

X -Logger 69.99 +VatMicro power standalone voltagelogger with 1 temperature and 3voltages channels

Initialised by a PC via a RS232 portCatch data and store the values into its on -board memoryfor future retrievalData can be downloaded into a PC and viewed thoughExcel or other spreadsheet packagesWin 95/98 driver for initialisation and downloadUltra -low power consumptionSensors available for X -logger: temperature, humidity, lightintensity, etc. Other Standalone Loggers

Standalone Event Loggers (record occurrence of events)Standalone Data Loggers with memory up to 8 Mega byte.Intec designs standalone data loggers to your specification

I storm15:=1L- I

Intec Associates Limited11 Sandpiper Drive, Stockport,

Tel: +44 (0)161 477 5855E-mail: ma i I intec-group co. uk

www.intec-group.co.ukCheshire, SK3 8111.. UK

Fax: -r441 (0)161 477 5755Ter ER 1111


PPM520 pin DIL Peak Programme Meter

PROFESSIONAL MEASUREMENT OF AUDIO LEVEL

Consumption 3mA.

Mother Board MB1

Fully meets BS5428-9

* PPM10 In -Vision PPM and Chart Recorder * Advanced ActiveAerial 4kHz-30MHz * Stabilizer frequency shift units for howlreduction * Stereo Variable Emphasis Limiter * PPM9, PPM5hybrid and PPM8 IEC/DIN -50/+6dB drives andmovements * Broadcast Monitor Receiver 150kHz-30MHz *

SURREY ELECTRONICS LTDThe Forge, Lucks Green, Cranleigh GU6 7BG

ATelephone: 01483 275997 Fax: 01483 276477 w


NEW PRODUCT


CPUs, onboard memory, 11general purpose I/0 pins and acomplete, interoperableimplementation of the AnsiEIA709.1-A-1999 controlnetwork protocol standard. TheCY7C53120E4 is for embeddedInternet systems that remotelymonitor and control electricaldevices through onlineconnections. It integrates4kbyte of onboard E2PROMand is made using a 0.35µmsilicon oxide, nitride oxidesilicon process.Cypress SemiconductorTel: 01707 378700Web: www.cypress.com

Microcontroller peaksat 50MipsDallas Semiconductor hasannounced the DS89C4208051 -compatiblemicrocontroller with peakprocessing speeds of one

machine instruction per clockcycle, or 50Mips, at a maximumclock speed of 50MHz. It has16kbyte of flash memory thatallows programming in any ofthree modes - in -system, in -application or standard parallelprogramming. The device is pinand instruction -set compatiblewith existing 8051 -basedsystems.Dallas SemiconductorTel: 00 1 972 371 3832Web: www.dalsemi.com

Flexible connectorspitch at 2.54mmRobinson Nugent hasannounced the FPC 5 series offlexible printed circuitconnectors on straight (verticalentry) or right angle (side entry)mounting. With a contact pitchof 2.54mm and pin counts fromthree to 21, they are tin platedphosphor bronze and rated at

A. The contacts are housed ina UL rated PBT body and havean operating range of -40 to+105°C. The flex circuitinterface wipes on the contactsremoving debris and oxidationon the contact surface. Alsoavailable is a 1.25mm pitch sideentry version.Robinson NugentTel: 01227 794495Web: www.robinsonnugent.com

SBC supports AMD's133MHz Elan 520 CPUThe Microspace PC/104MSM586SV single boardcomputer from Digital -Logicsupports an AMD 133MHzElan 520 CPU, 10/100BaseTEthernet network interface,SXGA 69000 graphicscontroller and PCI video datapath. Interfaces include

Servicing Audio and Hi-Fi EquipmentReturn to Jackie Lowe, Room L514, Quadrant House,The Quadrant, Sutton, Surrey, SM2 5AS

Please supply the following title:

Servicing Audio and Hi-fi EquipmentTotal

Name

Address

Postcode

Telephone

Method of payment (please circle)

Access/Mastercard/Visa/Cheque/POCheques should be made payable toReed Business Information

Credit card no

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Signed

`Its readers will benefit from its wealthof easily assimilated information, andrepairs hitherto thought impossible willspeedily become routine. And the firstmay well cover its purchase price.Congratulations on a comprehensive,well -written and lucid work' ElectronicsInformer.

`Interesting, entertaining and useful forboth practitioners and teachers. Allround a satisfying book which deservesto be considered as a tool rather than anornament collecting dust on the shelf.'Skillset Newsletter

Service engineers and technicianshave come to regard this book asessential to their work. As a bench -sidecompanion and guide it has no equal.Its purpose is to ease and speed up theprocesses of fault diagnosis, repair andtesting of all classes of home audioequipment: receivers, amplifiers, recorders and playback machines.The mechanics and electronics of domestic audio are examined byNick Beer in a down-to-earth and practical way, concentrating onwhat goes wrong, how to track down problems, and how to solvethem.

A symptom index and comprehensive manufacturer and supplierguide allow quick access to specific advice and suggestions.

The third edition is bang up to date with the latest technology-DVD,CD Recordable, PC audio systems. There is also new material on PAequipment.

* Essential benchcompanion for allservice engineers.

. New technology suchas DVD and expandedmaterial on MiniDiskwill ensure anothersuccessful launch to thisnew edition

UK Price: £32.00 Europe £34.00 ROW £64.50

* * Price includes delivery and packing **


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RAM VALVE"A h7EPAID &AUDIO

'ItiAdOOK

Valve Radio and AudioRepair Handbook

* A practical manual for collectors, owners, dealers andservice engineers * Essential information for all radio andaudio enthusiasts * Valve technology is a hot topic

This book is not only an essential read for every professional working withantique radio and gramophone equipment, but also dealers, collectors andvalve technology enthusiasts the world over. The emphasis is firmly on thepracticalities of repairing and restoring, so technical content is kept to aminimum, and always explained in a way that can be followed by readerswith no background in electronics. Those who have a good grounding inelectronics, but wish to learn more about the practical aspects, will benefitfrom the emphasis given to hands-on repair work, covering mechanical aswell as electrical aspects of servicing. Repair techniques are alsoillustrated throughout.This book is an expanded and updated version of Chas Miller's classicPractical Handbook of Valve Radio Repair. Full coverage of valveamplifiers will add to its appeal to all audio enthusiasts who appreciate thesound quality of valve equipment.

Contents: INCLUDES: Electricity and magnetism;Voltage, current, resistance and Ohm's Law; Real liferesistors; Condensers; Tuning; Valves; Principles oftransmission and reception; Practical receiver design;Mains valves and power supplies; Special features ofsuperhets; Battery and mains battery portablereceivers; Automobile receivers; Frequencymodulation; Tools for servicing radio receivers; Safetyprecautions; Fault finding; Repairing power supplystages; Finding faults on output stages; Faults ondetector/AVC/AF amplifier stages; Finding faults on IFamplifiers; Faults on frequency -changer circuits;Repairing American 'midget' receivers; Repairing faultson automobile radios; Repairing battery operatedreceivers; Repairing FM and AM/FM receivers; Publicaddress and high fidelity amplifiers.


** Price includes delivery and packing **

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Valve Radio and Audio Repair Handbook

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keyboard and mouse, four serialRS232Cs and a floppy diskport. The board also has an IDEhard disk connection and aprinter interface. Featuresinclude disk -on -chip 2000 slot,watchdog and E2PROM andIrDA support.Digital -LogicTel: 00 41 32 681 58 00Web: www.digitallogic.ch

Prescaler performsdivide -by -two functionSiGe Microsystems hasintroduced the D602 prescalerperforming a divide -by -twofunction for frequencysynthesisers up to 6GHz.Consuming 16mA from a 3Vsupply, it has a residual phasenoise performance of-145dBc/Hz at 1 kHz offset.Power -down mode, reducessupply current to less than100nA and input sensitivity istypically -27dBm. Applicationsinclude local multipointdistribution systems, satellitesand 5GHz WLANs.SiGe MicrosystemsTel: 01223 597806Web: www.sige.com

WAN switch doublesthe bandwidthA wide area network (WAN)access switching chipannounced by MitelSemiconductor, the MT90866switches up to 4096 by 2432channels, twice the bandwidthof alternative designs, claimsthe company. The devicemanages voice, data and videotraffic in large-scale carrier -class equipment that bridgesinformation on packet -baseddata networks to the circuit -switched public telephonenetwork. When different typesof packet -based and circuit -switched traffic converge onto

the network infrastructure, theresult can be delay, jitter, echoand data loss - conditions thatdegrade quality of service.According to Mitel, its switchincorporates a phase lockedloop (PLL), a block of circuitrythat minimises these effects byoptimising system timing andsynchronisation. It is aspecialised 3V time divisionmultiplex (TDM) timeslotinterface that supports voice,data and video traffic. Thedevice incorporates threeswitching functions into asingle product: 4096 by 2432channels between backplaneand the local streams, 2432 by2432 channels among localstreams, and 2048 by 2048channels among backplanestreams.Mitel SemiconductorTel: 01793 518528'Web: www.mitel.com

Wirewound inductorsfrom 3.3nH to 4.7pHNIC has introduced wire -wound SMT inductors forhandheld devices, telecoms,high -frequency and wirelessdesigns. Available in D (0805)and C (1008) sizes, the NIN-Hunits have inductance valuesfrom 3.3nH to 4.7pH withcurrent ratings up to 1.0A.Inductance tolerances of 20 and10 per cent are available, whileminimum Q factor is up to 65and minimum self -resonantfrequency up to 6GHz.Maximum DC resistance can bedown to 0.0852 and maximumDC current up to 600mA.Operating range is -40 to+125°C and they come inembossed plastic tape packagesfor automatic pick -and -place. NIC EurotechTel. 01280 813737Web: www.niccomp.corn


Self on AudioDouglas Self

The cream of 20 years of Electronics Worldarticles (focusing on recent material)

A unique collection of design insights andprojects - essential for all audio designers,amateur and professional alike.

Scientific electronics based on empirical data

Douglas Self has been writing for ElectronicsWorld and Wireless World over the past 20years, offering cutting -edge insights intoscientific methods of electronics design.

This book is a collection of the essentialElectronics World articles, covering twenty yearsof amplifier technology but with a very strongbias towards more recent material. The articlesinclude self -build projects as well as designideas and guidance for the professional audiodesigner. The result is a unique collection ofdesign insights and projects - essential for allaudio designers, whether amateur orprofessional.

Contents: Introduction; PRE -AMPLIFIERS: Anadvanced preamplifier MRPI;High-performance preamp MRP4; Precisionpreamp MRP10; Moving -coil head amp;Preamp '96 I; Preamp '96 ll; "Overload Matters"(RIAA overload); Balancedline inputs and outputs, part 1; Balanced lineinputs and outputs, part 2;POWER AMPLIFIERS: FETs less linear thanBJTs; Distortion in power amplifiers1-8; Distortion residuals; Trimodal part 1, 2;Load -invariant power ampINVAR.DOC; Common -emitter amps; Two -stageamplifiers; SPEAKERS: Excessspeaker currents; Class distinction (ampclassification); Relay control;Power partition diagrams; Audio power analysis.

Douglas Self has dedicated himself todemystifying amplifier design and establishingempirical design techniques based on electronicdesign principles and experimental data. Hisrigorous and thoroughly practical approach hasestablished him as a leading authority onamplifier design.

Readership: Audio electronics enthusiasts;Professional amplifier designers;Power amp usersPaperbackPages: 416pp


Return to Jackie Lowe, Room L514, Quadrant House,The Quadrant, Sutton, Surrey, SM2 5AS


SELF AUDIO

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February 2001 ELECTRONICS WORLD I29

Fig. 1. Basicconstruction of a

dome tweeter.Such speakers

invariably have asolid centre piece

that reflects soundfrom the back of

the dome.

Areader from Sweden e -mailedto ask what I meant by theterm 'dome sound'. And by

the time I had finished thinking whatto say, I had quite a lot of material.

There is more to buildingloudspeakers than assembling acollection of parts. In order to obtainhigh quality, the parts have to worktogether as a coherent system.

The full frequency range high -quality moving -coil drive unit is animpossibility. That leaves us with theneed for at least two drive units in apractical speaker.

I have argued at length that one ofthe critical aspects of loudspeakerdesign is to obtain an inaudiblecrossover so that the existence of twodrive units is not revealed in thesound. Inaudible crossover is aperformance related term. This

Reflection path Dome

Surround

Magnet

Coil

exolo0"All of the problems associated withdesigning a dome loudspeaker can besolved by relegating it to the function of adust cap in the middle of a cone",argues John Watkinson.

means that the crossover networkmust separate the original wide -bandwaveform into two sub -bands as amirror of the way the sound from thetwo drive units will add back togetheracoustically.

When designing a real speaker, thedesigner has to balance the strengthsand weaknesses of availablecomponents in such a way that thestrengths are revealed and theweaknesses are concealed oreliminated. The design process is anart form. It requires a degree ofcompromise so that the resultingspeaker has a balanced performancein various domains with no obviousflaws.

The dome's inherentlimitationsThe problem with the dome tweeter isthat it severely limits the scope of thespeaker designer to make designtrade-offs. These limits are not due toany lack of attention to quality, butare inherent in the dome design.

Figure 1 shows a typical dometweeter. The coil is attached to theperimeter of the dome, the whole ofwhich is suspended by a flexiblesurround.

Figure 2 reveals one of the myths

111.11111111110M111.ro.

of the dome. In a) is an ideal soundradiator. It is a sphere that cansomehow change its radius as afunction of the audio waveform. Iwould dearly love to know how to dothis, but for the moment no-oneknows how.

Now the dome looks superficiallysimilar, because it is a section of asphere, but there the similarity ends.Figure 2b) shows that the entirespherical section simply moves fromside to side along a single axis.Acoustically this is totally differentfrom 2a). The dome is not a sphericalradiator

Looks can be deceiving. It isphysics and performance that matterthough - not appearance. Forexample, few people realise that theold air-cooled Volkswagen microbushad a better drag coefficient than theE -type Jaguar.

How the dome worksIn order to determine how a domeworks, it is necessary to treat thesurface as an infinite number of pointradiators and then to integrate thecontributions from each at thelistening point. For the time being, Iwill assume that the dome is rigid.

Figure 3a) shows that the


AUDIO DESIGN

difference in path length between thecentre and the perimeter causes anaperture effect. When the height ofthe dome is half a wavelength, therewill be significant cancellation.Figure 3b) shows that if the dome isconcave, exactly the same response isobtained.

Practical domes are made smallenough and shallow enough so thatthe first null is outside the audioband. Within these limits the actualshape of the dome is irrelevant as itcould be convex, concave or flatwithout affecting the frequencyresponse. In fact the dome shape isused for rigidity, and to fool thegullible.

Considering off -axis sound, therigid dome also suffers an apertureeffect. Figure 4 shows that there willbe a response drop when the pathlength difference from the two sidesof the dome approaches half awavelength. This is classical beamingfrom a radiator of finite area.

The only solution to obtainradiation over a reasonable angle isto keep the dome small in diameter.A typical figure is 19mm. A radiatoras small as 19mm will have a highfundamental resonance, and the smalldiaphragm area will limit the volumevelocity that can be obtained.

All of these factors together meanthat the dome tweeter isfundamentally a narrow -band device.If the dome is made larger, it willhave more volume velocity and alower resonance, allowing it to beused at lower frequency. But thegreater size will lower the frequencyof the first null and make thebeaming worse.

The designer of a two-way speakerhaving a dome tweeter is basicallystuck with an impossible choice ofcrossover frequency in the 1.5 to2kHz region. The woofer will beasked to operate at frequencies whereits diaphragm is far too large and itwill beam.

Figure 5a) shows the result. Atlow frequencies the woofer isomnidirectional. As frequency risesthe woofer gets more and moredirectional until at the crossover thewide directivity of the tweeter takesover. Off -axis, the frequencyresponse is like a dog's hind leg andthe reverberant field will becoloured.

Figure 5 also shows the frequencyand power responses of almost anysmall two-way speaker with a dometweeter. The frequency responseusually shows a small dip at the

crossover where the designer istrying to make the crossoverfrequency as low as possible. Thepower response shows a huge dip atthe crossover.

Effectively a huge chunk of thespectrum is missing in thereverberant field. This gives the

(a)

(a)

Path length difference

s, Sphere ofvaryingradius

4k,*Listeningpoint (b)

Listeningpoint

Fig. 3. Whether the dome is convex, as in a), or concave as in b) makes nodifference to its performance.

listener the impression that the audiohas literally been cut in half. Somuch for the inaudible crossover!

In practice, domes can't be rigidbecause vibrations can travel rightacross the dome and bounce off theother side. The palliative here is thesoft dome which is made from alossy material. The resultant problemis that at high frequencies the centreof the dome decouples as in Fig. 4b),leaving an annular radiator which hasappalling directivity.

Fig. 5. At a), the excessive beaming of thewoofer at a high crossover frequencycauses a large dip in the power response,b). This is audible.

(a)

Woofer at LF

Finally, most domes have solidcentre -pole pieces. Sound radiatedfrom the back of the dome bouncesoff the pole piece and passes throughthe soft dome as shown in Fig. 1.This causes time smear and combfiltering in the frequency response.

All of the problems of a dome canbe solved by relegating it to thefunction of a dust cap in the middleof a cone, but then it wouldn't lookright to someone who is judging byappearances. Perhaps the solution isto colour the cone black and leave thedome a bright colour.

Path lengthdifference

off axis

(a)

(b)

, , Sphereff.> moving

in onedimension

Fig. 2. The myth of thedome. The idealmotion of a), wherethe diaphragmexpands andcontracts, is simplynot met. You can seefrom diagram b) thatthe diaphragm movesin one dimensiononly.

(b)

Radiation fromperimeter

Fig. 4. From a), you can see that the dome must be as smallas possible in order to minimise directivity problems.Diagram b) shows how the dome centre decouples at highfrequencies.

(b)

Wooferjust belowcrossover

Level

Power

Domejust abovecrossover

Frequency

Frequency


Analysing thedifferential amplifierLionel Gay presents a theoretically exact analysis of theemitter -coupled differential amplifier.

The emitter -coupled differential amplifier evolvedfrom the cathode -coupled differential amplifier andthe behaviour of the circuit is well known. See, for

example, Slaughter's paper, published in 1956'.No approximations are made in the analysis that follows.

As a result, it is applicable to any circuit that incorporatesa pair of identical active two -port devices that are definedby their identical hybrid parameters. In addition, theanalysis can be readily modified to take account of a pairof non -identical active devices.

Consider Fig. 1, where Vi, Vol , and V02 denote signalpotentials. Assuming that Tr1 and Tr2 have identical hparameters, the task is to set up expressions for Voi/Vi,V02/Vi, the input resistance R1, and the two output resis-

Fig. 1. Theemitter -coupled

differential amplifier.

R9

O

E

RP

C

ov

R3

K

ov

:lout

E

B

Fig. 2. Equivalentcircuit of theemitter -coupleddifferential

foi amplifier.OV

ov

tances Rol and R02.In order to calculate V01/V;, it is helpful to draw the

equivalent circuit of Fig. 2. Next, set up expressions forRJ, RK, and hence V01/V, RN, and In order to do so, youcan make use of the equations listed in Appendix X ofreference 2.

Assuming that the signal frequency is low so that the hparameters are real, it follows that,

hib + D(R, + R7)+ R7(1+ hi - h + hR5)=

1+ ho,(R, +R,)

where,

D = hthh - h,,h,

Given the common -emitter h parameters, the other twosets of h parameters can be calculated. See, for example,Table A8.1 on page 480 of reference 2.

RK = R3+R4+ R6+ Rj

R,(R6 + RI)

and,

Vol _ -R2(hf, - h,R,)

V, - D(R2 + R,)+ R,(1+ hf, -h,, +121?2)

Here, Ri is the parallel combination of RI and RN. So,

R - R' RNov R, + R,

and,D(122 + R,)+ R,(1+ - h + h,R2)

RN =1+ + RK)

In order to set up an expression for Vo2+Vi, draw theequivalent circuit shown in Fig. 3, where /1, /2, 13, and /4denote signal currents.

VO2 -1.4R5 -ktR5 R5 /4 13 /2V. V I, RN RN 13 12 1,

14 hib h,R,13- 1+ h,(R, + R7)

ov 12 R, + R6+ R,


and,

/2 - k8R,

1+ + R2)

So,

V02 - h,R4(hf, - h,R2)

where,

Y, = +R6 + Rj)(1+ + R7))(1+ h,(RK +R2))

R01 is the parallel combination of RP and R2,see Fig. 2, sothat,

Rp R2

Rol = \Rp + R2)

where,

+)X(1+1k,81?,)+

R,(1- h)(1+ hf,)+ Rs)Rp=

Y2

and where,

Y2 = Dh, + 114 R,R +R, + R8

Resistance R02 is the parallel combination of RT and R5,Fig. 3, so that,

RO2 =+

R,RT

where,

(kb + RA)(1+ hthR7)+ R7(1- h)(1+ hfl,)RT=

D + h(RA + R7)

RA(R, + RQ)RA

+ + hock) + R2(1 - + h ft)

RQR, + Rs

=

Where,Y3

Y3 = D + ho,(RR +R2R, Rs

With reference to Fig. 2 , where I. and /, denote signalcurrents, the mutual conductance of the circuit is, bydefinition, given by grni=lout÷ViSince,

= -1 R-2V

,

R2

/ou1 A,

I ,RN RN

Where, At denotes current gain,

A, =hfr - h"12,

1+ hAJR2 + Ric)

With reference to Fig. 3,

V02

-

where,

14

g m2 =1,R,

References1. Slaughter, D W, 'The Emitter -Coupled Differential

Amplifier,' IRE Transactions - Circuit Theory; March, 1956,pp. 51 to 53.

2. 'Physical Principles and Applications of Junction Transistors'by J. H. Simpson and R. S. Richards, pub. Clarendon Press,Oxford, 1962.

Computed resultsHere is the input data for a BBC -Basic programthat the author used to make some calculations.Also shown is the resulting output data.

Input data:Riohm=75R1/ohm=1.2E4R2/ohm=k4/ohm=R5/ohm=1.0E3R3/ohm=R6/ohm=R7/ohm=4.7haohm=1.05E3h=240E-6ke=200hoe.ohm=110E-6.Note that '.' is used to signify either a decimalpoint, as in '1.0E3', etc., or a full -stop, or themultiply operator, as in 'hoe.ohm'.

Output data:V01/V; =-48.66V02/ Vi=48.16R01/ohm=981.6R02/ohm=983.4

.ohm=4.866E-2.This data excludes hib, hk, etc.

R9

RN

B

v,

RK

E=2

-0-

0 V 0 V

R

ov

R

13i E

Fig. 3. Equivalent circuit of the emitter -coupleddifferential amplifier modified to allow an anexpression for V02+vi to be set up.

---RT

0C 14

ov

V02

Tl ov

February 2001 ELECTRONICS WORLD I ; ;

!til IDEAS

Searchcoil

Fact: most circuit ideas sent toElectronics World get publishedThe best circuit ideas are ones that save time or money, or stimulate the thought process. This includesthe odd solution looking for a problem - provided it has a degree of ingenuity.

Your submissions are judged mainly on their originality and usefulness. Interesting modifications toexisting circuits are strong contenders too - provided that you clearly acknowledge the circuit youhave modified. Never send us anything that you believe has been published before though.

Don't forget to say why you think your idea is worthy.Clear hand-written notes on paper are a minimum requirement: disks with separate drawing and text

files in a popular form are best - but please label the disk clearly.

Digital metal detector provides visual indicationThis BFO-based metal detector

uses a 1MHz crystal reference inconjunction with a search coiloscillator, operating at the samenominal frequency.

The squarewave reference andsearch signals are mixed by /Cob toproduce the detected beatfrequency. /C2 generates afrequency of about 500Hz for

f...*12.J Winner

R1

22M

1MHz

C1

_20p

1

IC1c

C2

100p1I

C3

I20p

0

22k

VCI4-40p

2

i2lR32k

VC2

Vcc = 5V

1213

display driving. The detected anddisplay signals are combinedthrough IC3 and NAND gates, andfed to U4 and /C7 to drive LEDs D1

through D10.With VC1 and VC2 suitably

adjusted, it will be possible in theno metal situation to set P1 so thatall LEDs are OFF, even in theproximity of ground. If the search

Vcc

Vcc

14

IC3555

4

5

11 8 9 12

R4

10k

P1

30k

D11

1N91

D121N914

R5

50k

IC2

555

C4

I68n

head is moved over a metal object,e.g. ferromagnetic, the LEDs willlight sequentially.

If the metal is non -ferromagnetic.The LEDs will light sequentially inthe opposite direction.Saheed Mansoory AlgalandisTabrizIranD91

12

IC6d 11

7400

2

4

5

IC6b

7400

9

IC6c

9

8 10

IC a

IC6b

IC6c

4-40p L1 is 80 turns of No 26 wire, 8in diameterPower supply connections to ICs are not shown

VCC

2

Vcc

12'

3

IC ca

IC5d

VCC

IC8

7442

12

15

13

9

14

10

15

16

14

IC77475

3

11

6 2

9 12

7400

IC47490 VC C

0

I2 3

Digital metal detector provides visual indicationand distinguishes between ferrous andnon-ferrous metals.

13 i7

(D91)


PASSIVE COMPONENTSFOR CIRCUIT DESIGNPassive Components forCircuit Design is a uniqueintroduction to this key areaof analog electronicsdesigned for technicianengineers and anyoneinvolved in circuit design.The coverage encompassesall component types capableof power amplification:resistors, capacitors,transformers, solenoids,motors and transducers. Thebehaviour of the componentsis explored along with thedifferent types available andthe principles of circuitdesign. Tolerances, stability,variation with temperature,reliability and manufacturingstandards are all covered.Reading this book willimprove your skills incomponent selection andanalog circuit design. Theseare essential skills not onlyfor the analog designer, butfor all circuit designers,professional or amateur.

Contents: Preface;Fundamentals; Fixedresistors; Variable resistors,potentiometers and diodes;Capacitors; Inductors andinductive components;Inductive devices;Transducing components;SMT; Hardware; Index

Readership: Technicianengineers, circuit designers,advanced hobbyistsPages: 304ppPrice: UK £22.00Europe £24.00ROW £26.00

is el rt)ttic ProjectsI row the

ELECTRONIC PROJECTSFROM THE NEXTDIMENSIONFor years paranormalscientists have explored thedetection and documentationof spirits, auras, ESP,hypnosis, and many morephenomena throughelectronics. ElectronicProjects from the NextDimension provides usefulinformation on buildingpractical circuits andprojects, and applying theknowledge to uniqueexperiments in theparanormal field. The authorwrites about dozens ofinexpensive projects to helpelectronics hobbyists searchfor and document their ownanswers about instrumentaltranscommunication (ITC),the electronic voicephenomenon (EVP), andparanormal experimentsinvolving ESP, auras, andKirlian photography.

Although paranormalstudies are consideredesoteric, Electronic Projectsfrom the Next Dimensionteaches the technical skillsneeded to make devices thatcan be used in manydifferent kinds ofexperiments. Each sectionindicates how the circuit canbe used in paranormalexperiments with suggestionsabout procedures and howto analyze the results.

Contents: White noisegenerators for use ininstrumentaltranscommunication (ITC)and electronic voicephenomenon (EVP)experiments; Practicalcircuits for imageexperimentation, such as a

wireless sparkling imagegenerator, horizontal bargenerator, brontophic sound,magnetic field generator,high -voltage generators(Kirlian Machine's I & II);Paranormal skillsexperiments withtemperature change,polygraph, electro-shock,random number generation,UFO detection, and ghost -finding.Readership: Hobbyists,Electronics EnthusiastsPages: 256ppPrice: UK £22.00Europe £24.00ROW £26.00

BASIC AC CIRCUITSThis is the step-by-stepapproach for beginners. Thisself -paced individualizedlearning tool coversconcepts, terms, and themathematics required tounderstand AC circuitproblems. It has beendesigned to improve analysistechniques for prediction andcontrol development.

Readership: Beginnersmeeting AC circuits for thefirst time: students;techniciansPages: 92l ppPrice: UK £27.00Europe £29.00ROW £31.00

Post your completed order form to: -Jackie Lowe, Room L514, Quadrant House,The Quadrant, Sutton, Surrey, SM2 5AS

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CIRCUIT IDEAS

Generating amplitude, frequency andphase -shift keying signalsA mplitude-shift keying, frequency- I.

rAshift keying and phase -shiftkeying signals can all be produced bythis circuit. It operates as follows:

With switches S2 and S3 opened,the circuit produces frequency -shift keying signal under controlof switch SI.

R1 Ra R3 R4 and C: are selectedaccording to the frequencies of operation

A, any suitable opaerational amplifier can be used

(D87)

Circuit producing phaseor frequency -shiftkeying, or on -off keying.

2. With switches Si and S3 opened,the circuit produces phase -shiftkeying signal under control ofswitch S2.

3. With switches Si and S2 opened,the circuit produces on -off keyingsignal under control of switch S3.

On -off keying is a special case ofamplitude -shift keying where thesignal is keyed entirely off or on. Ifswitches Si, S2 and S3 are monolithicanalogue switches, the circuit isdigitally controllable.Muhammad Taher Abuelma'attiDharanSaudi ArabiaD87

Versatile test oscillatorA feature of this instrument, a

rAvariant of the Franldinoscillator, is that the tank circuitinductor is untapped. It can thusbe used with a wide range ofinductors resonating at frequen-cies up to 100MHz.

The active load provided byPFET 2N3820, with its typicalpinch -off voltage of 1.5V,provides the maintaining amplifi-er with a high dynamic outputimpedance. This minimisesloading on the tuned circuit.

Potentiometer P1 is set formaximum amplitude of oscilla-tion, while P2 adjusts the amountof regeneration.

With the regeneration set to justprovide oscillation, as monitoredby the expanded scale indicator,

Testitem

FranklinOscillator

0.111

0.1p

250R

1k8 270R

0220k

0.5mA

BF245ABF245A 0.1µ

P25 BF245A

33klk -A/VVV-

the circuit forms a sensitiveabsorption wavemeter. As a dip oscillator, dipsup to the eleventh overtone can be observed.

The unit can be used as a signal generator, diposcillator, absorption wavemeter, field strengthindicator etc. Comparative measurements of coiland capacitor Q factor and crystal activity arepossible.

An RF output for connection to a sensitivefrequency counter is provided. Phase noise isgenerally so good that the one hertz digitindication will not vary.Wim de RuyterOudkarspelThe Netherlands

Shunt meterby trial and error

10k

10k 10T

DC in

0

0 1k2DC out

0.1µ I

0.1p

220k

Matchedtriplettriplet

Vp -1.3Veach

10µ

470R

+9V(D89)

This versatile low -noiseoscillator has a varietyof uses.

0.1u

+9V

0

RF out

Expanded scale indicator1k1 47k 10T

10k

220k

+9V

CA31604k7

0.5mA

I36 ELECTRONICS WORLD February 2001

Ideal rectifier works at video speedRectification by diodes has its advantages such as size and cost.There are applications though that require very precise splitting

and control of the waveform. This is achieved by the circuit shown.High-speed comparator LM106 is used to detect the point at

(D94)

+7V

16

-7V

5 VOUT

Gnd

which the input waveform goes below OV. At that instant, theoutput of the comparator goes low, forcing the 4053 to switch to thegrounded input. Voltage V, then follows this input; thus clippingthe negative half of the input waveform.

Complex waveforms may begenerated if the voltage at thegrounded input of the 4053 isderived from a potentiometer.To achieve a good response athigh frequencies, decoupleboth ICs and the power supply.

A single ground point andshort tracks are essential.K P CummingsNottinghamD94

A

Precision half waverectifier works atvideo speeds.

£50 Winner

1

Ten year index:new updatepfilAll I lUtAS

apacitor, Bipolar capacitorapacitors, dark secrets ofar immobiliserar intruder alarmar radio loop aerialassette motor controllerlipper provides flat -top outputlipper, Symmetrical audiooaxial-cable testerolour-bar generator (NTSC)ommunications link, single -wireompact-disc player into scanomparator, High input -voltageomparitor extends alarm systemomparitor, simple twelve -bitompass helps the blindompass, Audibleonnection, Two -wire power/signalontinuit tester, im roved

drol tern E ItrI1J1 I

1:11 '3:1 1:1:111

CONTROL SYSTEM SIMULATORGeorge Varkey

January 1990, p28

A simple electronic simulator forproducing a Simple Harmonic Motion(SHM) test for use in testingcontrol systems,

ww.softcopy.co.uk

Photo copies of Electronics World articles from backissues are available at a flat rate of £3.50 perarticle, £1 per circuit idea, excluding postage.

Hard copy Electronics World indexIndexes on paper for volumes 100,101, and 102are available at £2 each, excluding postage.

Hard copies and floppy -diskdatabases both availableWhether as a PC data base or as hard copy, SoftCopycan supply a complete index of Electronics World articlesgoing back over the past nine years.

The computerised index of Electronics World magazinecovers the nine years from 1988 to 1996, volumes 94 to102 inclusive and is available now. It contains almost2000 references to articles. circuit ideas and applications- including a synopsis for each.

The EW index data base is easy to use and very fast. It

runs on any IBM or compatible PC with 512K ram and ahard disk.

The disk -based index price is still only £20 inclusive.Please specify whether you need 5.25in, 3.5in DD or3.5in HD format.Existing users can obtain an upgrade for £15 by quotingtheir serial number with their order.

Ordering detailsThe EW index data base price of £20 includes UK postageand VAT. Add an extra £1 for overseas EC orders or £5for non -EC overseas ordersPostal charges on hard copy indexes and on photocopiesare 50p UK, £1 for the rest of the EC or £2 worldwide.For enquires about photocopies etc please send an sae toSoftCopy Ltd. Send your orders to SoftCopy Ltd,1 Vineries Close, Cheltenham GL53 ONU.Cheques payable to SoftCopy Ltd, please allow 28 daysfor delivery.

e-mail at [email protected], tel 01242 241455

February 2001 ELECTRONICS WORLD 1 iT

The definitive biography of thecentury's godfather of invention -from

the pre-eminent Edison scholar "Israel'smeticulous research and refusal to shy

away from the dodgier aspects ofEdison's personality offers a fresh

glimpse into the life of the inventor."-New Scientist

"Remarkable."- Nature

"An authoritative look into Edison'sworking methods, here leavened by

enough personal detail to give theachievements shape." -Publishers

Weekly

"Israel's book should go a long waytoward taking Edison out of the

shadows and placing him in the properlight." Atlanta Journal -Constitution

"Exhaustively researched, with strongemphasis on Edison's methods and

achievements."-Kirkus Reviews

The conventional story of ThomasEdison reads more like myth thanhistory: With only three months of

formal education, a hardworking youngman overcomes the odds and becomesone of the greatest inventors in history.

But the portrait that emerges fromEdison: A Life of Invention reveals a

man of genius and astonishing foresightwhose career was actually a product of

his fast -changing era. In this peerlessbiography, Paul Israel exposes for the

first time the man behind the inventions,expertly situating his subject within a

thoroughly realized portrait of aburgeoning country on the brink of

massive change. Informed by Israel'sunprecedented access to workshop

diaries, notebooks, letters, and morethan five million pages of archives, this

definitive biography brings freshinsights to a singularly influential and

triumphant career in science.13c6

Post your completed order form to: -

Jackie Lowe, Room L514, QuadrantThe Quadrant, Sutton, Surrey, SM2 5AS

Fax your completed order form to 020 8652 8111UK Price: £15.00 Europe £17.00 ROW £19.00Price includes delivery

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CIRCUITS IDEAS

£70 Winner

Audio level indication by tri-colour ledA single tri-colour LED is used here

r1to convey an idea of audio signallevel. It is relatively simple andinexpensive, and is particularlyattractive in cases where front panelspace is at a premium. It is much lesscumbersome than a full blownbargraph, and far more informativethan a simple 'overload' LED.

At low signal levels, the LEDglows green, with varying intensityaccording to the amplitude. As thesignal level increases, the colourchanges through amber, then finallyto red.The circuit is based on quad op -ampICI. I used the LF347, but otherdevices would no doubt work just aswell.

Op -amp ICIb is configured asprecision half wave rectifier, theoutput of which charges C4. Attackand decay rates are determinedlargely by R5 and R4 respectively.Input sensitivity is determined by R3.These parameters are characterisedfor speech signals at a nominal 0dBlevel.

Op -amp /Cia simply buffers the

R1+15U0.----=

1OR cti C2

capacitor from the following stages.These require a low -impedancesource.

Output of /C1, is a voltage propor-tional to the green segment current. Atlow levels, D4 does not conduct, andthe output simply follows the input.Above /34's 'knee' point, the non -inverting input is clamped, invertingaction takes over, and the output startsto fall again. This is the 'amber' phaseof the circuit's operation.

The output of ICId is a voltageproportional to the red segmentcurrent. This remains at zero until thesignal level increases sufficiently toallow D3 to conduct. Beyond thispoint, the output rises in line with theincrease in signal. A point is reachedwhere the green segment current hasdiminished to zero, and only redsegment current flows.

Both transistors are in a common -base configuration. The base biasvoltage is set at approximately -Vbeby R12/D5 so that the emitters form`virtual -earth' inputs. Voltage outputsof /Clad appear across resistorsR10,11. The resulting currents flow via

the transistors to the common -cathode tri-colour LED. This arrange-ment eliminates any need to compen-sate for the LED segment forwardvoltages. Furthermore, the relativelyheavy LED currents flow `rail -to -rail', and not via the ground return.

The LED segment currents aremodulated smoothly, rather thanbeing switched as is the case in abargraph. Demands on the powersupply are therefore reduced, andsimple decoupling suffices - asprovided by RI, R2 and C6. Multipleindicator circuit blocks can share thissupply, and also the -Vbe bias volt-age.

Local HF decoupling for the IC isessential. This is provided by ceramiccapacitors C2,3.

With no signal applied, a smallresidual current flows, resulting in avery faint glow from the LED. Thisshould not be a problem in practice.Graham BoothAuditel LtdAmershamBucksE51

olOn

Cl R3

I /P0 -01:1-1-1--4--100n 27k

OU

+

R4I=220k

RS--I=1

1k

02

r±i C4

1p

R6lkS

-I-- OU

R9

R747k

1 k S

IC1 04LF347 4U7

R11330R

IR10

P1-LBC327 /

Using a three -colour LED toindicate audiosignal level givesallows you totake asses levelsat -a -glance. Also,an LED takesmuch less spacethan a panelmeter.

L P2

/ BC327

cn C6NE 1000p

DS-A- No CsLA 100p

R2-15UN--1=1

1OR

C310n LD1

HUIP4000

R12- 2k2

Dr UBE

Di NOU

ALL SIGNAL DIODES ARE 1N4148 OR EGUIUALENT

I.> NU

_ TO OTHERCHANNELS


CIRCUIT IDEAS

£50

15.E111

DBIVGI

FILT

-10.0B

Winner

CMOS tripler needs no adjustmentHaving a low output impedanceand high input impedance,

advanced-CMOS logic is useful fornon-linear signal processing.

In this example a low -impedancesquare -wave is generated from a10MHz source using one advanced-CMOS logic gate. A bandpass fitterthen extracts the third harmonic while

43.88e 58.66 FRED-MHZ 106.0

Input 10n33R .33pH 82p

10MHz5V pk-pk

100k 33p100p

providing voltage gain by impedancetransformation.

A second -order 'coil -saving'elliptic design provides adequateselectivity without adjustment, andgives good rejection at thefundamental and fifth harmonic. Asecond gate then squares up andbuffers the output.

In a square wave, the thirdharmonic is only 7.44dB lower inamplitude than the input. The filtergives about 10dB of voltage gain, soeven with circuit losses there is noshortage of signal to operate thesecond gate. High signal levelscombined with LC filtering shouldensure that the output has low noise.

The plot shows a simulation of thefilter response allowing 2011 ofsource resistance and 4.5pF of loadcapacitance, typical of an AC gate.The idea can be adapted to work atdifferent frequencies.

At low frequencies though, Schmitt

47p

1150p

Output30MHz

5V pk-pk

(D93)

trigger gates should be used to avoidself -oscillation during signaltransitions. At higher frequencies,more attention may need to be paid tothe effect of the receiving gatecapacitance.

The circuit was built with twosections of a 74AC00 quad 2 -inputNAND gate each with one inputwired high. It worked without furtheradjustment.I N WellsSt AlbansD93

Apologies, but we are unableto announce the winner of theNational Instruments Labviewkit until next month. Making adecision is proving more diffi-cult than we expected! Ed.

Frequency tripler takes advantage ofnon-linear characteristics of advanced-CMOS logic.

Improved lead -acid battery chargerImproved battery charger handles

sealed and standard lead -acidbatteries and the new carbon -

fibre types.

13.7V16V DC standby

charge

To

battery

0

NC

1k

Setchargecut-off

330R

16V min.o(D90)

LM317

240

k set referencevoltage

1k

3.9V

L

1 N4001

Thelead -acid battery charger shown on

page 830 of the October 1999 issuewill not give a 100% full charge to a flatbattery, if set up as described, using afully charged battery (12.6V or more) asthe reference voltage. This is because oncharge, a final voltage of 15.6V isrequired to guarantee 100% capacity.

My modified circuit shown addressesthis problem. It also changes the batteryover to a trickle charge regime onreaching full charge.

An adjustable regulator output is alsoshown, permitting the charging ofstandard lead -acid batteries (15.6V),sealed types (15V), the new Elecsolcarbon -fibre battery (14.5V) or even 6Vbatteries.Andrew BirdBurntwoodStaffordshireD90


DIGITAL DESIGN

8051 -type controllersinclude ISP

New 8051 -type controllers are appearing that lend themselves to

in -circuit programming and reprogramming - drastically reducing

development time for those of you without a full-blown emulator. The one

described here has a separate loader ROM so none of the 64K application

ROM is lost. Both ROM areas are reprogrammable flash memories.

Wtnbond's W78E516microcontroller is an8051 derivative that can

be programmed in situ. This is alsothe first 8051 -based device toprovide two separate on -board flashROMs. One is a 64k block ofapplication ROM, referred to asAPROM, while the other is a loaderROM of 4k, called LDROM.

Either ROM can program the otherwithout external programmingvoltages or hardware. And, becauseboth ROMs are blank when thedevices are manufactured, softwaredevelopers are free to implementtheir own loader program rather thanbeing tied to a specific serial typeinterface.

Normally, these devices aresupplied either blank or pre-programmed with a boot loader thatallows the APROM to beprogrammed by a serial connectionto a PC. Because either ROM canprogram the other, developers canprogram the device with applicationcode, then program the LDROMwith a bespoke boot loader program.

Source code for the LDROM isfreely available from FlintDistribution. This code may be

Registers used for in -system programming.Register name: SFRCNBit Name Function7 Reserved6 WFWIN Selects the ROM for In -circuit programming - 0=APROM, 1=LDROM5 OEN ROM Output enable4 CEN ROM Chip enable3,2,1,0 CTRL[3:0] Flash control signals (See below)

Mode WFWIN CTRL[3:0] OEN CEN SFRAH, SFRAL SFRFDErase APROM 0 0010 1 0 - X

Program APROM 0 0001 1 0 Address in Data inRead APROM 0 0000 0 0 Address in Data OutErase LDROM 1 0010 1 0 X

Program LDROM 1 0001 1 0 Address in Data inRead LDROM 1 0000 0 0 Address in Data out

Register name: CHPCONBit Name Function7 SWRESET Reading as logic 1 indicates that the device is in FO4KBOOT mode. MCU

will perform a software reset if this and FBOOTSL and FPROGEN are set6 - Reserved5 - Reserved4 ENAUXRAM 1: Enable on -chip 256 byte auxiliary RAM

0: Disable on -chip 256 byte auxiliary RAM3 0 Must be zero2 0 Must be zero1 FBOOTSL 1: Loader program is in LDROM, APROM can be reprogrammed

0: Loader program is in APROM, LDROM can be reprogrammed0 FPROGEN 1: ISP function enabled

0: ISP function disabled*F04KMODE


DIGITAL DESIGN

modified and reprogrammed into theLDROM either via the APROM orusing a standard device programmer.

In -system programmingISP functions available on theW78E516 are erase, read and write,and 'act on the alternative ROM tothat currently selected'. Access isthrough four registers. Three areaddress pointers, namely SFRAHand SFRAL, SFRFD. Thesecontains data read from or written toflash. The fourth is the controlregister SFRCN, which selects ISPmode.

Erase is accomplished by a singlecommand. All functions are carriedout independently of the CPU, whilethe device is in 'idle' mode.

Once the controlling registers areprogrammed, the device is put intoidle mode. While in idle mode, theCPU clock is disabled but

peripherals and interrupt logicremain active.

Usually a timer generates aninterrupt after a predefined time,based on how long the ISP functiontakes to execute. This interruptreturns the CPU to active mode sothat the device can continue ISPservices or normal operation.

During normal operation, theW78E516 boots from APROM,jumping to the LDROM undersoftware control when required. It isalso possible to force the device toboot from the 4k LDROM viahardware. This mode has anassociated flag known asFO4KBOOT.

An FO4KBOOT flag allows thesystem to distinguish betweennormal or forced execution ofLDROM code. Forced executionmight occur for example if a reset isinstigated while there is no set

Start

Reset control regs.MOV CHPENR,#78HMOV CHPENR,#59HMOV CHPCON,#03H

Set timer to 1.5p.sand enable

interrupt

Start timer andenter IDLE modeCPU will rebootfrom LDROM on

timer interrupt

Go

Normaloperation

End

Procedure forswitching programexecution from theAPROM to theLDROM.

condition, or while waiting for ahardware reset if set.

The FO4KBOOT flag can alsotrigger a hardware test routine withinan application.

Development environmentThere's support for the W78E516'sin -system programmability - andother 8051 type devices - in theform of a development platformavailable from Flint Distribution.This platform is based on hardwarethat connects to the standard 40 -pinDIL 8051 socket. The hardwareallows code to be downloaded to thedevice and executed in situ.

At the heart of the system is aW78E516 programmed with a bootloader. It runs from an 11.0592MHzcrystal and connects to the PC via aserial interface. A PC applicationallows users to select a `.bin' fileand download it to the device whilein FO4KBOOT mode.

The program first erases theAPROM, and then programs andverifies the device with the selectedfile. In this way the APROM can befully utilised by the programmer.There is no overhead of a monitorprogram or operating system.

File size checking is also provided,to ensure that the file is no greaterthan 64k and data are verified duringfile transfer.

HardwareThe system was designed for usewith bread -boarded prototypes.Because of this, a standard 8005X40 -pin DIL pin -out is provided. Thisprovides compatibility with standarddevices and with third -party adaptersfor conversion to PLCC or QFPfootprint.

A key factor in the hardwaredesign is that as many I/O lines aspossible are kept free for use.Because the PLCC version of thedevice has an extra four -bit port, thisis used to drive an LED. This LEDindicates that the boot loader isrunning and therefore the device iswaiting for code to be downloadedto the APROM.

The port is also used to invokeFO4KBOOT mode. The only othertwo I/O lines used for the ISPfunction are RXD and TXD.Connecting these ports to DIPswitches allows users to choosebetween connection to the board'sRS232 driver during programdownload; or to the pins of the 40 -pin DIL header when programs are


DIGITAL DESIGN

running and require serialcommunications.

The system further allows controlof the /EA input, used to switchbetween external and internal dataaccess. All bus control signals arealso available, giving maximumflexibility in expanded memoryapplications.

The only pins that are not availableto the developer are the reset andoscillator pins. Most of the device

resources remain available to theuser.

A number of new ISP devices arebecoming available from Winbond,such as a low -voltage version of theW78E516 and the W78LE58, againa low voltage device which featuresa 32k APROM and 4k LDROM.Either of these devices can be usedwith the ISP kit, and may be orderedseparately.

When coupled with a public -

domain 8051 assembler or Ccompiler, the result is an extremelylow cost 8051 development system,where maximum MCU resources areaccessible to the developer, andsoftware overheads are kept to aminimum.

For more information on the ISPkit and to download the associatedprograms, please visit the Flintwebsite, www.flint.co.uk.

Offer over page

LDROM timer ISR.Stop timer anddisable timer

interrupt

V

0

Reset CHPCON reg.MOV CHPENR,#78HMOV CHPENR,#59HMOV CHPCON,#03H

Set timer to 15msfor erase. Enable

timer interrupt

V

Issue commandfor erasing APROMMOV SFRCN,#22H

Start timer andenter IDLE mode

for erasing

APROM erased afterwakeup for idle mode

on timer interrupt.

Program

Procedure forin -circuitprogramming theapplication ROMfrom the LDROMloader ROM.

v No

Set timer to 50us forbyte programming.

Enable timer interrupt

Get next byte ofdata to program(I/O, UART, etc.)

Issue command forprogramming APROM

MOV SFRAH, #ADD_HiMOV SFRAL, #ADD_Lo

MOV SFRFD, #DATAMOV SFRCN, #21 H

Software reset andreboot fromAPROM

MOV CHPENR,#78HMOV CHPENR,#59HMOV CHPCON,#83H

0

YesV

Hardware reset requiredto boot from APROM.Software reset is not

possible inFO4KBOOT mode

)Terminator

ELECTRONICS WORLD February 2001 143

DIGITAL DESIGN

Reader offerBuy your in -circuit programming development kit for just £60 - save £25Until 31 March 2001, Flint Distribution is offering the new W78E516 in -circuitprogramming development kit to Electronics World readers for just £60 includingVAT and postage - a saving of £25 over the normal selling price without VAT.Simply mention that you are an Electronics World reader when you order.

At the heart of this developmentplatform is a W78E516 controllerrunning from an 11.0592MHzcrystal and pre-programmed withboot loader.

The loader, contained in aseparate flash memory calledLDROM allows the controller'sAPROM application memory areato be programmed via a serialconnection to a PC. No monitorprogram or operating system isneeded in the controller so theAPROM can be fully utilised by thedevelopers.

The target device plugs into astandard 805C5X 40 -pin DILsocket, which is also compatible

with third -party adapters for conversion to PLCC footprint. Devices can alsbe removed and programmed with a range of alternative programmersincluding systems from Dataman, Needhams, BP Microsystems and MPQ.A PC application is included to allow binary code to be downloaded to

the device by forcing it to boot from LDROM rather than APROM. File sizeis automatically checked to ensure that APROM space is not exceeded,and data verification is incorporated to ensure reliable downloading.

ecause either ROM can program the other, developers are free toprogram the device with application code, which can in turn program theLDROM with a bespoke boot loader programme. LDROM source code isfreely available from Flint, allowing any amount of development ormodification.

The kit includes: in -circuit programmable evaluation board with W78E516 microcontroller serial cable for interfacing the board with your PC DOS software for downloading object code to the target board Windows software for downloading code to the target board

Developers can use the ISP kit with new 8051 microcontrollers in theWinbond family, such as low -voltage versions and the W78LE58, whichprovides 32k APROM and 4k LDROM, also with low -voltage capability.

For further details, please contact Flint Distribution at Walker Road,Bardon Hill, Coalville, Leicestershire, LE67 1 TU. Tel 01530 510333 or seethe website www.flint.co.uk.


;lir I. °I1

Post your completed order form to: -

Jackie Lowe, Room L514, Quadrant House,

The Quadrant, Sutton, Surrey, SM2 5AS

Phone your credit card order: 020 8652 3614

Fax your completed order form to 020 8652 8111


Paperback price includes delivery

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i

his book is the definitive study of the life andworks of one of Britain's most importantinventors who, due to a cruel set of

circumstances, has all but been overlooked byhistory.Alan Dower Blumlein led an extraordinary life in

which his inventive output rate easily surpassed thatof Edison, but whose early death during the darkestdays of World War Two led to a shroud of secrecywhich has covered his life and achievements eversince.

His 1931 Patent for a Binaural Recording Systemwas so revolutionary that most of his contemporariesregarded it as more than 20 years ahead of itstime. Even years after his death, the full magnitudeof its detail had not been fully utilized. Among his128 patents are the principal electronic circuitscritical to the development of the world's firstelectronic television system. During his short workinglife, Blumlein produced patent after patent breakingentirely new ground in electronic and audioengineering.

During the Second World War, Alan Blumlein wasdeeply engaged in the very secret work of radardevelopment and contributed enormously to thesystem eventually to become 'H2S' - blind -bombingradar. Tragically, during an experimental H2S flightin June 1942, the Halifax bomber in which Blumleinand several colleagues were flying, crashed and allaboard were killed. He was just days short of histhirty-ninth birthday.

For many years there have been rumours about abiography of Alan Blumlein, yet none has beenforthcoming. This is the world's first study of a manwhose achievements should rank among those ofthe greatest Britain has produced. This bookprovides detailed knowledge of every one of hispatents and the process behind them, while givingan in-depth study of the life and times of this quiteextraordinary man.

ContentsEarliest daysTelegraphy and telephonyThe audio patentsTelevisionEMI and the Television CommissionThe high- definition television periodFrom television to radarThe story of radar developmentH2S - The coming of centimetric radarThe loss of Halifax V9977LegacyTo Goodrich Castle and beyond

14-s

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VVithout an engineering degree, a pile ofmoney, or an infinite amount of time, therevised 289 -page Interfacing with C is worthserious consideration by anyone interested incontrolling equipment via the PC. Featuringextra chapters on Z transforms, audioprocessing and standard programmingstructures, the new Interfacing with C will beespecialy useful to students and engineersinterested in ports, transducer interfacing,analogue -to -digital conversion, convolution,digital filters, Fourier transforms and Kalmanfiltering. Full of tried and tested interfacingroutines.Price £14.99.

Listings on disk - over 50k of C source codededicated to interfacing. This 3.5in PC formatdisk includes all the listings mentioned in thebook Interfacing with C. Note that this is anupgraded disk containing the originalInterfacing with C routines rewritten for TurboC++ Ver.3Price £15, or £7.50 when purchased with theabove book.

Especialy useful for students, the originalInterfacing with C, written for Microsoft CVersion 5.1, is still available at the price of£7.50. Phone 0181 652 3614 for bulkpurchase price.

Post your completed order form to: -Jackie Lowe, Electronics World, Room L333,Quadrant House, The Quadrant, Sutton, Surrey, SM2 5AS

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144,

Introduction to

o

\77,}EF

Giuseppe Ferri et al present a guide to current conveyors inthree parts, the first of which gives you a brief history ofthis frequently overlooked circuit configuration.

In the autumn of 1966,A.S.Sedra, working on hisMaster's thesis', had to design a

voltage -controlled waveformgenerator. He implemented acurrent -controlled oscillator, so hehad the additional task ofconverting the voltage to current.

At that time, the best knownsolution to convert a voltage to acurrent was to take a p -n -p bipolarjunction transistor with its base

grounded and connect its emittervia a resistor to the controlvoltage. But that solutionpresented several drawbacks. Thefinite base -emitter voltage causeda large offset in the voltage -to -frequency conversion. Moreover itdepended on temperature and onthe flowing current, worsening thestability and linearity of the entirecircuit.

To improve the current -to -

voltage conversion, Sedra came upwith the circuit of Fig. 1. This wasthe first type current conveyor, orconvertor, 1-3 and it was given theabbreviation CCI, where the 'I' isthe Roman numeral '1'.

Both X and Y are output nodes.If you look closely at Fig. 1, youwill see that the current in Tr3,which is approximately ix, is`copied' by the dual -outputcurrent mirror formed by Tr3_5.

Giuseppe Ferriand PierpaoloDe Laurentiis,are with theUniversity diL'Aquila,L'Aquila, Italyand GiovanniStochino is withEricsson LabItaly SpA, inRome.

Fig. 1. Firstimplementation ofcurrent conveyor, CCI.Here, ix=iy=iz. Fig. 2. Symbol of a

first -generation currentconveyor, or CCI.

Fig. 3. CMOSimplementation

of a CCI workingin Class AB

mode.


ANALOGUE DESIGN

So, ix=iy=iz. Moreover, as thesame current is flowing in Tri andTr2, their base -emitter voltageswill be same too. This means thatvy=vx, regardless of the values ofVy and 1y.

In mathematical terms, the CCI,whose symbol is given in Fig. 2, isan active device described by thefollowing matrix relationship,

iy 0 1 0 v1

vX = 1 0 0 ix

iz _0 1 0 vx

This type of current conveyor isparticularly useful whenevercurrents at very low impedanceshave to be measured. This is whythe current is duplicated withunity gain on high -impedanceterminal Z.

Historically, the CCI has formeda useful alternative to oscilloscopecurrent probes based on Hall effectdevices. They have allowedmeasurements over a range of 0 to100MHz to be made at inputimpedances of less than 1Q.

Note that the performance of thecircuit of Fig. 1 can be improved.For example, more elaboratecurrent mirrors can be added, ascan operating capabilities. Thecomplementary version of thecircuit could also be considered.Here, each transistor would bereplaced by its opposite polaritycounterpart and the negativesupply replaced with a positiveone.

It is also possible to connect twocomplementary current conveyorsto come up with a currentconveyor capable of AB operation.When the CCI works in Class AB,it can be biased from low dccurrent values. It can also processcurrent signals having magnitudelarger than the bias current I, withreduced harmonic distortion.

Fig. 3. Shows a CMOSimplementation of the Class -ABCCI. A typical supply would be3.3V.

Second -generation currentconveyorsIn 1970 two years later than theCCI invention, Sedra and Smithproposed an extension of theiroriginal circuit2. They called it the

(a)

Ix

(b)

):

zo.

izZ

Fig. 4. In a) is the CCII+ while b) shows the complementary CCU-.

Current mirror

Current mirror

Fig. 5. Internal block structure of the CC1101.

lz =

z

Fig. 6. This positive current -conveyor, abbreviated to COI+, usescomplementary MOS devices to provide better voltage -followerperformance.


ANALOGUE DESIGN

second -generation currentconveyor, or CCII. This novelcircuit was a more versatiledevice. We will be concentratingmostly on this second -generationin this article and its twosuccessors.

The idea of Sedra and Smith wasto make the input impedance onthe terminal Y infinite, i.e. wehave the following idealbehaviour,

0 0

v,c= 1 0

iZ 0 ±1 0 [idThus we have iy=0, Vx=Vy, that isto make the impedance on terminalX zero, iZ=±iy. This makes theoutput impedance on terminal Zinfinite.

The `±' sign means that thecurrent supplied to X can beconveyed to Z with either positive(CCII+) or negative (CCII-)polarity. Figure 4 shows thecircuit symbols used for the CCII+and CCII- respectively.

Generally speaking, the currentconveyor can be considered a`double follower' in that it canform a voltages or current follower.

The main advantages of thecurrent conveyor approach is thatthe traditional closed -loop gainband -width conflict of negativefeedback voltage op -amp isavoided. The benefits of negativefeedback - noise reduction,improvements of input and outputimpedances, etc. - are not available.However, a wider bandwidth athigh gain levels is inherent.

When the current conveyor wasintroduced, the semiconductorindustry was absorbed with thedevelopment of monolithic op -amps. However, a lot of paperswere published on the conveyor'stheory and applications, showingthat the traditional op -amp has noclear benefits over a current -conveyor.

Because of their combinedvoltage and current bufferingaction, current conveyors may beused to synthesise a great numberof analogue circuit functions. Theycan also reduce the number ofcomponents needed to implementthe circuits3-7, as you will see fromthe Table on the right.

Table 1. Basic topologies using current conveyors, demonstrating that many analogue functions can beimplemented with fewer components relative to traditional op -amp solutions.

Functional element SchematicMathematicalexpression

Current buffer lout = lin

Y

X

(yr I+Z

lout

V

Voltage -controlledcurrent source

lout = Vin/RVino Y

R CCII+X Z

I out

Curent-controlledvoltage source

Vout

Vou, = Rlinin

CCII+X Z

YCCII+

X Z

V R

v

1r

Current amplifier

I;

lout = lioR2/191

Y

ccii+X Z

i

R R1

V

Voltage amplifier Vont - VinR2IR1

Vin y YCCII+

X

ZCCII+

X Z

R1

V

VastR2

V

V

Negative -impedanceconverter

(current controlled)

Zio = ZTY

CCII+X Z

IZTv

Negative -impedanceconverter

(voltage controlled)

Zio = ZTZ,,v_i,

(

YCCII+

X Z

ZT

V

Table continued over page...


ANALOGUE DESIGN

Table continued from previous page

Functional element Schematic Mathematicalexpression

Current differentiator

C

dl,,,lout = RC

dt

lil

YCC11+

x zIOLA

R

V

Current integrator

n

C

lout =RC f 60) dt? Y

CCII+X z

lout

R

V

Differentialvoltage -to -current

converter

Vlout = --L'

R

YCCII+

Xlout

Z

n R

YCCII+

x1

z out

Instrumentation amplifier VoutR

=Vin' =Rt

YYCCII+

X ZCCII+

X Z

yin !MI2VR2

Y ZCCII+

xv

Fig. 7. Negative current -conveyor, or COI-, using

complementary transistors.

First commercialconveyor chipsThe first monolithic commercialcurrent -conveyor was the CCII01,developed by LTP Electronics.Figure 5 shows its simplifiedschematic. This device, capable ofworking from ±5V up to ±15Vsupplies, it features an equivalentslew -rate of 2000V/Lis and a100MHz bandwidth3.

A commercial CCII is thePA630A 8925, produced byPhototronics.

In order to perform a betterfollowing action from a voltageview -point, it is possible to taketwo complementary transistors inthe negative feedback loop of anop -amp. This technique has beendemonstrated to work well withCMOS technology.

An example of CCII+ is given inFig. 7. Here, the op -amp can berealised as a standard two -stageamplifier. In order to implement aCCII-, only two current mirrorsneed to be added, as in Fig. 7.

References1. K.C.Smith, A.Sedra: 'The

current -conveyor- a new circuitbuilding block', IEEE Proc. 56,1968, pp. 1386-1369.

2. A. Sedra, K. Smith, 'A Second -Generation Current Conveyor andIts Applications', IEEE Trans. onCircuit Theory, CT -17, pp. 132-133, February 1970.

3. A. Sedra, G. Roberts, F. Gohh,`The Current Conveyor: History,Progress and New Results', IEEProc. Part G, Vol.137, No 2, pp.78-87, April 1990.

4. J. Lidgey, C. Toumazou, 'Currentamps from voltage op -amps',Electronics World, July 1990,from p. 568.

5. I. Hickman, 'Current conveyorICs' Electronics World, May1994, p. 402.

6. M.T. Abuelma'atti, N.A.Humood, 'Current -conveyor sine -wave oscillator,' ElectronicsWorld, March 1988, p. 282.

7. F.J. Lidgey, K. Hayatleh, 'Arecurrent -conveyors finally comingof age?', Electronics World, April2000 pp. 322-324.


RS446 keyfeatures...

Up to 2 milecoverage radiusScans main andsubchannels

Eight channels, eachwith 38 sub channels

Backlit display fornight time use

Unique call function Headphone and mic

sockets allowdiscrete use

Battery statusindicator

Auto battery savefeature

Keypad lock -out

Personal voice communications without a licence over atwo mile radius for £75, exclusive.

Reader offerA pair of two-way PMRradios for just £75*RS 446 personal mobile radio...To celebrate its launch, new test and instrumentation company Tecstar isoffering Electronics World readers two RS446 personal mobile radios for just£75 excluding VAT and carriage.

Capable of transmitting and receiving voice over a distance of up to two miles,depending on terrain, the PMR 446 needs no licence. It offers eight channels,scanning - and with CTCSS up to 304 channel combinations.

A backlit liquid -crystal display shows volume level, channel number, sub -channel number, battery level and transmit/receive or channel busy. A uniquecall feature enables the user to alert the person they wish to contact.

Transmission distance is up to 2 miles. The radio has an accessory socket foran external headphone, earpiece or vox-microphone/headphone combination. Akeypad lock and battery save feature are also standard.

The unit measures only 120 by 50 by 20mm and weighs less than 150 grams -including batteries. It is supplied complete with instructions and belt/mountingclip.

Compact, lightweight and low cost, the RS446 wireless personal -communications hand set has a wide range of applications. These include fetes,events and rallies. Builders on building sites could benefit from these radios, ascould exhibitors at exhibitions and staff at warehouses, winter activities, sportsevents, maintenance departments, schools and care homes. Of course you canalso use the RS446 just to keep contact with someone locally. The uses arealmost limitless.

Send a cheques or postal orders to Tecstar Electronics Limited, 1 NuffieldRoad, St Ives, Huntingdon Cambridgeshire PE27 3LX.Tel 01480 399499, fax 01480 399503, e mail [email protected]

Order couponPlease send me RS446 personal mobile radios, for which I enclose:

For pairs of RS446 radios at £75 per pair

Plus VAT at 17.5%, or £13.13 per pair

Plus £6 UK postage per order, or £14 overseas

Total

Fill in your name and address and post this coupon together with a chequefor the total amount above payable to Tecstar to the address below.

Name

Address

Post code

Signature

Send cheques, postal orders etc to Tecstar Electronics Limited, 1Nuffield Road, St Ives, Huntingdon Cambridgeshire PE27 3LX.Tel 01480 399499, fax 01480 399503, e mail [email protected]

*excludes carriage and VAT tSi

What is CTCSSCTCSS - or'continuous -tonecontrolled squelchsystem' - allows subchannels of the mainchannels to be used.There are 38 subchannels to each mainchannel. Usingsubchannelsdecreases thelikelihood thatsomeone else will beusing the samefrequency.

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Studying electronics or computing or justwant to keep up-to-date in an easy andenjoyable way, then this fully interactivesoftware is for you.

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Feller (UK) Ltd. manufacture Fullyapproved cordsets (Moulded mainsplugs and connectors) and PowerSupply Cables for all industrialCountries to National and InternationalStandards

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Flash supply low cost AVR ISPprogrammers (£39), MINI -ICE starterkits (from £69), Portable Easy -ICEemulators (from £199), ICE Adapters& 'C' compilers for any ATMEL AVR,MCS51, Dallas, Hitachi H8microcontroller. Download FLASHNEWS now, Watch out for SpecialOffers'. ARE YOU developing code ina Flash?

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Kiea Trading Company is the sole agent ofGoot products, We specialise in supplyingthe soldering and desoldering productrange manfactured by Goot Japan for theUK market. Goot uses advancedproduction technology to manufacturehigh quality soldering iron products forindustrial, professional and generalpurpose use.

HSPS LTD

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FILTER DESIGNER - Advanced analog anddigital filter design software for the PC. -Standard and Professional versions.- Freedownload of Evaluation version.

152ELECTRONICS WORLD February 2001

To reserve your web site space contact Pat Bunce

Tel: 020 8652 8339 Fax: 020 8,46a) IQ'

HTB ELEKTRONIK

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We are selling second-hand test &measurement equipment and accessoriesfor over 10 years,from all leadingmanufactures.

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U.S. Military Surplus meters, plug -ins,test sets, oscilloscopes, power supplies,signal generators, spectrum analyzers andradio components from Tektronix, HewlettPackard, Sony, Phillips and more!

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LPRS markets low power radiotransmitters, receivers and transceivermodules manufactured by ourselves,Radiometrix, Circuit Designs, RDT andMicrel. Applications for telemetry,video and remote control.

MATTHEY MICROFILTERS

http://www.microfilters.net

0 MattheYA/lkittifterse

30 years experience in the design andmanufacture of high quality passive filtersand delay lines. Used in Broadcast,Telecommunications, Medical,Multimedia, and Computer industries.

MATRIX MULTIMEDIA LTDwww.matrixmultimedia.co.ukme-natb,rnoimedia..

Matrix MJItimedia publishes a number ofhighly in eractive CD ROMs for learningelectronics including: Completeelectronics course, Analogue filter design,and PlCmicro(R) microcontrollerprogramming (C and assembly).

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http://www.newnespress.comOver 300 books and information packages

for those working with electronics andengineering technology:Visit our site for afree catalogue and downloads.

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Suppliers and repairers of MOBILE RADIOequipmentSALES

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Huge stocks of used radios and sparesPye Philips Simoco Icom KenwoodStandard Cleartone Maxon Yaesu KeyMidland.WE CAN PROGRAM ANYTHING24hr Service

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"SMD prototyping adapters. Unique,flexible, low cost adapters to allow benchworking with SM devices. Range suitsmost devices down to 0.5mm pitch."

PCA:PHILIP COLLINS &

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PCA manufactures Radphone 2000DXremote control systems for shortwavebroadcasters and government agencieswanting worldwide control ofcommunications receivers andtransceivers from any tone phone.

POLY -FLEX CIRCUITS LTDhttp://www.polyflex.com

Design, manufacture and population ofprinted polyester flexiblecircuits, including Flip Chip on Flexproviding practical, low cost,reliable solutions for today's smalllightweight products.

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The 1.11Es No. I Electronic nit Supplir

Over 250 electronic kits, projects andready built units for hobby,educational & industrial applications.TEL: 01279 306504, FAX: 07092 203496or EMAIL: [email protected]

QUILLER ELECTRONICS

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100+ pages of detailed technicalinformation on Schrack Relays, MECSwitches, Hirose Connections.

RADIOMETRIX

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Radiometrix specialises in the designand manufacture of VHF & UHF, RF datamodules. We offer a broad range of PCBmounted miniature transmit, receive andtransceiver modules for OEM use.

RADIO -TECH LIMITED

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Radio modules, modems, telemetry, audiotransmitters, pagers, antenna, remotecontrols and much more. All UK designedand manufactured.

RALFE ELECTRONICS

professional test & measurement

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RD RESEARCH

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Analogue and digital SPICE modellingsoftware. Full details available on this site.Available on a 30 day evaluation basis.

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The award winning on-line service from RS

- 110,000+ products available- Technical data library- Stock availability check- Integrated on-line purchasing- Order by 8pm - with you tomorrow.

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As a PC data base or hard copy, SoftCopycan supply a complete index ofElectronics World articles over the pastten years. Photo copies of articles fromback issues are also available.

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SESCOM, INC. is a 30 -year manufacturerof audio "problem solvers" andtransformers. We also offer easily -fabricated aluminum enclosures for smallproduction runs and prototypes.

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WIRELESS COMPANY

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Jenving Technology AB is themanufacturer of Supra Audio Cables. OEMproductions are also accepted.

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Manufacturer & Exporter of Heelical BPFFilter, 30 Watts BPF Power Filter andHandset/Base Station Duplexers

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Working evaluations of SpiceAge mixed -mode simulator, Spicycle PCB designtools and Superfilter demo (synthesisespassive, active, digital filters). Techsupport, sales links and price list.

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IMMO

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Test equipment from Grundig.Kenwood, Hitachi, Fluke, Avo,Glassman, Advance in a comprehensivesite including oscilloscopes,multimeters, power supplies,generators, counters, soldering, digitaltv etc.

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VUTRAX electronic schematic and pcbdesign system for Windows 95, 98 andNT. Limited Capacity FREE version

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Wood & Douglas Ltd is the leadingindependent British designer andmanufacturer of quality radio productsfor International telemetry, data,voice &video wireless communications.

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http://www.uked.comFor a comprehensive on-line directory,buyers guide and resource locator forthe UK Electrical Industry look at thissite. Many of the companies listed havelinks to their own web sites, making thisa one -stop shop for a huge amount ofinformation.

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Another free internet access site, thistime from Reed Business Information.However the site possesses a useful UK

People and Business Finder, with an e-mail search. There's also business newsand local information, and some goodlinks to directory sites.

REPAIRWORLD

http://www.repairworld.comRepairworld is a sophisticated US basedfault report database which is updatedbi-weekly. It operates on a subscriptionbasis and describes itself as an"affordable solution for all technicians".You can see some samples of thematerial for free, monitors, VCR, DVDand Camcorders being of particularrelevance to UK users. The site alsoprovides a "chat room".

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Put your web address in front of 21 000electronics enthusiasts and experts.Electronics World acknowledges yourcompany's need to promote its web site, whichis why we are now dedicating pages in everyissue to announce yourWEB ADDRESS.This gives other readers the opportunity tolook up your company's name, to find yourweb address and to browse the magazine pageto find new sites.

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154ELECTRONICS WORLD February 2001

Pico ADC42

Virtual oscilloscopeFeaturing 12 -bit resolution and 11V1S2

input impedance, the ADC42 samplesat up to 15kS/s and includes softwarefor spectrum analysis, oscilloscopefunctions and frequency display.Plugging into a PC's LPT port, the unitprovides large, colourful displays andall the usual timebases and triggeroptions - all in a case slightly largerthan a matchbox.

ADC42 single channel oscilloscope

Low cost and easy to use No power supply required Ultra compact design Oscilloscope and data logging software

included Write -to -disk on trigger function standard

The ADC42 is a single -channel pc based virtualinstrument. Simply plug the unit into the parallelport of your pc and run the software. Designedfor analysing low -frequency signals, it provide allthe functionality of a conventional scope at afraction of the price.

The ADC42 has 12 -bit resolution making itsuitable for applications where detection of smallsignal changes is needed.

SpecificationsScope timebasesSpectrum analysisMax samplingVoltage rangeResolutionChannelsI/P impedanceAccuracyPC connectionPower supply

500ps/div to 50s/div100Hz to 10kHz15ksample/s±5V12 bit1 BNC1MS2, dc coupled1%D25 to PC parallel portNot required

48882

£98inclusive of VAT

and postage*

*UK only. Overseas readers please fax or e-mail fora quote including delivery charges.

I A PAN

I

.75147,S 4,01.3 S.I5S ii Fi rl L

w1-7

Use this coupon to order your ADC42

Please send me ADC -42(s) at the special offer price of £98

fully inclusive of VAT and recorded UK delivery, normal selling price£111.63 excluding postage.

Name

Address

Phone number/fax

Total amount £

I enclose a cheque

Please charge to my credit/debit card.

Card type (MasterNisa/Switch etc)

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Expiry date

Please mail this coupon to Electronics World, together with payment.Alternatively fax credit card details with order on 0181 652 8111.Address orders and all correspondence relating to this order to PicoOffer, Electronics World, Quadrant House, The Quadrant, Sutton,Surrey SM2 5AS.email [email protected]

Make cheques payable to Reed Business Information Group.

155

Letters to the editorLetters to "Electronics World" Quadrant House, The Quadrant, Sutton, Surrey, SM2 5ASe-mail [email protected] using subject heading 'Letters'.

Minister for electronics?I think we can accept that coalwas the fuel that powered the 19thcentury industrial revolution.

I believe it is also true to saythat oil, for transport andchemicals, was the dynamic fuelthat powered the 20th century.

What then is the fuel of the 21stcentury? Is that fuel not a materialbut a technology? Electronics?

Strange then at a recent meetingof IMAPS UK (The InternationalMicroelectronics and PackagingSociety) a society dedicated to theadvancement of microelectronicsand packaging in the UK, not onemember could identify or namethe Government Ministerresponsible for this key sector ofindustry. It was agreed that aphone call to Lord Sainsbury atthe Department for Trade andIndustry would probably be thebest bet - but nobody appeared toknow.

This is a sad reflection on what Ibelieve is the Government's lackof support for the electronicsindustry. Despite this, electronicsin the UK does exist but in the restof the developed world one doessee strong Government support.

If we don't have a 'Minister forElectronics' is it perhaps time toappoint one?David LowrieChairman IMAPS UKBaldockHertfordshire

X-ray specsThe interesting article on X-raysin the October 2000 issueperpetuates a popularmisconception. In describingexisting radiographic techniques itstates, "Traditionally the detectoris ordinary photosensitiveemulsion, but in digitalradiography it is replaced witheither a semiconductor sheet or aphosphor screen."

In fact, in medical radiographythe primary detector of X-rays is aphosphor screen, sometimesreferred to as a 'salt screen'. Thephosphor screens used have beendeveloped over the years to givehigh -resolution images at ever -lower doses of radiation.

It is the light emitted from thephosphor screen that is recorded

by the photosensitive emulsion.The emulsion is opticallysensitised so that its peak spectralsensitivity matches the peakemission wavelength of thephosphor.

Film for medical radiography isnormally coated on both sideswith a silver -halide emulsion. Aphosphor screen is held in contactwith each side of the film duringexposure. The amount of X-radiation recorded directly by thesilver halide emulsion is minimalcompared with the emittedradiation recorded from thephosphor screen.

In many of the semiconductorradiographic techniques describedin the article, the key element isthe same as with the techniquelisting photographic film; a

phosphor screen.Silver -halide emulsions are used

directly as X-ray detectors insome dosage badges and forradiographic inspection of welds.In these cases a lead -foil screen isused to increase sensitivity bythrough electron emission causedby absorbed X-rays.Guy Selby-LowndesBillingshurstKent

Curve tracing inSwedenHaving a long-standing interest incurve tracers, I was very interestedto see Ian Hickman's descriptionin the August 2000 issue.

I built my first tracer in the latefifties - actually a valve curvetracer, later adapted for transistors

- and my second in the earlyseventies.

I recently decided to build athird, more up to date tracer. ButMr Hickman's reasoning relatingto suppressing the bright spotresulting from the inactive part ofthe cycle made me wonder why noone - including myself earlier -has used double rectification ofthe collector voltage? That wouldeliminate the inactive bright spotaltogether and double the refreshrate. This is desirable when a setof 8 curves is to be displayed onan ordinary oscilloscope. Ofcourse, it requires a transformerwith a centre tap - or several ifmany voltages are wanted - andtwice as many diodes, but diodesare cheap.

If it is not going to be visible in

Phase shifter for headphonesIn response to A T Granger's letter on page 747 ofthe September 2000 issue, here is a circuit inpassive and active forms that will solve his headphone problems.

Phase shifts caused by the circuit put you at thefront of the stage even though you are listeningthrough headphones. The passive form was used byDr Bauer here in the USA. I use it with a Walkman.

The active alternative works on all outputs. I useit on tape, CD and tuner outputs. It requires +12Vand -12V at 100mA.

Do not use any polarised capacitor in the circuit.James WatsonOrange valeCaliforniaUSA

Lin

100kJvVVv

20k100k .4--,\AAA,-.-Volume

1/2 LM833

'Volume'

30R

43µ8

4mH100k

20k100k

RinRin

OV

-15V ±

Lin

Leftheadphone

3µ8 4mH 30R

Rightheadphone

Rin

When you are listening through headphones,these audio phase -shift circuits create the illusionthat you are standing in front of what you arelistening to. The passive form is useful forportable audio gear.

100k

'Balance'1k 4k

Lout Headphone8 H0

1/2 LM83360R*

0 Headphone ground100k (centre data)

60R*

1k 4k

8mH 'Balance'Rout Headphone

0

* 60R or 250R variable

1/2 LM833

1/2 LM833


LETTERS

1 N4007 x44 330

9

+15V-

-- 10M01

BAT42x2 10k

0.5R5%

22k

22M

o To Y amplifier

To staircaseo generator

LF347 clock input

the displayed curve set, thestaircase generator needs to beclocked very close to the zerocrossing. I have tested thesimplified circuit shown and foundit to perform well from about 2Vup to several tens of volts.

The BAT42 Schottky diodesconduct at a lower voltage thanthe 1N4002 diodes, so the

Adding diodesin this wayeliminates theoscilloscopebright spotproblem. Theright-handswitch canhave manypositions forselecting anyresistancebetween 50and 3.3142.

clocking takes place essentiallybefore any collector voltage isapplied to the transistor undertest. Because the clock pulse isvery narrow, C5 in the originalcircuit, was reduced to 33pF andR47, R48 were replaced by 1N4148clamp diodes.

Another matter, which MrHickman touched on briefly, is

Tek 41-7,

III

DISPLAY

Typetors

Persist

Format

CH1 2,06Vettli 012

the possibility of including aseries resistor in the collectorsupply. I made this resistorswitchable in 12 positions, asshown simplified in theschematic. This adds thepossibility to have a selectableprojected load line in the curve setwhich may be interesting forgraphical design purposes. The

ContrastIncrease

ContrastDecrease

XV Mode

curve set shown with the circuitdiagram was produced using aTektronix TDS21O DSO.

For the rest of the circuit, I usedMr Hickman's original design. Ifound it well designed and up todate. I look forward to seeingmore of that kind!Evert OlssonSweden

Better buffers rebuffedI would like to comment on Dave Kimber'sarticle on page 858 of the November 2000issue, entitled, 'Better Buffers In it, heclaims that, "crossover distortion isimpossible to eliminate".

I don't know whether Mr Kimber has beenliving in a cave all of his life or whether he isjust plain ignorant and uninformed. To besure, his assertion is just plain gobbledygookand pure nonsense.

We over here in the US had this problem ofcrossover distortion - sometimes also referredto as switching distortion - solved some thir-ty-five years ago.

There are fundamentally three ways toeliminate this effect. The first is, of course,pure class A operation but, that is obvious.The second method was a stroke of geniusand was conceived by Sidney S. Smith, ofMarantz fame. He is probably the most bril-liant audio engineer that ever lived. His ideawas to use power diodes in the output stagefor the compound pair rather than a resistor.

Using power diodes allowed the transferfunction to be always totally exponentialthroughout virtually the entire signal cycle,therefore allowing the power devices toremain on virtually through the signal cycle.This was done in the Model 15, that even bytoday's standards is still a magnificent prod-uct.

The second method is one that I createdwhile director of engineering at SAE in theearly seventies. What I did was to shunt theoutput stage emitter resistors with powerSchottky diodes. This allowed the forward

transconductance to remain much more linearthroughout the entire signal cycle.

The proof of the pudding is in the perfor-mance and indeed, these amplifiers wouldproduce THD figures of less than 0.01% at20kHz at full power with no crossover notch-es.

Great pains were also taken to do a com-plete spectral analysis in order to make surethat these distortion residuals were indeedharmonic products and not higher orderswitching products.

Along with my output stage design was atotally new dual -differential input stagewherein the entire amplifier was also fullycomplementary.

In order for the output stage to work proper-ly, I found it to be necessary to dramaticallylower the open loop gain whereby the openloop frequency response was significantlyraised, obviously making the amplifier muchfaster. This also aids in eliminating crossoverdistortion.

As a final note, it seems that the engineer-ing world in Europe has not yet caught upwith the times regarding full complementarytopologies.

Even in Douglas Self s book, he doesn'teven raise the issue. This topology, which Icreated, has been standard fare both here inAmerica as well as in Japan for almost 30years.

I think Mr Kimber and others need to jointhe modern world and get caught up to date.James BongiornoLompocCalifornia

David replies:Class A does, of course, eliminate crossoverdistortion but there may still be odd orderdistortion because the transfer functions ofthe two halves of the output stage are notfully complementary.

Using diodes in the base circuit of the out-put transistors may help reduce crossoverdistortion, as I mentioned. I am glad thatsome people have had success with thismethod.

I cannot see how putting diodes across theemitter resistors will help with crossover dis-tortion though. Either at the output transistoremitters proper, or at the CCEF 'emitter', Iwould expect diodes to help counteract theeffects of high current beta droop; this couldreduce large signal distortion.

In order to eliminate crossover distortion inClass B amplifiers, the transfer functions ofthe two halves must exactly fit in thecrossover region just like two jigsaw pieces. Idon't think anybody has yet achieved this;but some get closer than others. The remain-ing distortion is then reduced by carefullyapplied negative feedback, which requiresadequate open -loop gain.

I am fascinated by the idea of reducingcrossover distortion by reducing open loopgain, as Mr Bongiorno appears to claim.Perhaps he would like to give more details? Ifear he may have fallen into the common trapof regarding high open -loop bandwidth asbeing intrinsically a good thing - see Self scomments on this.Dave Kimber G8HQPDavant Technology Limited


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