Ed 100326
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THE AUTHORITY ON EMERGING TECHNOLOGIES FOR DESIGN SOLUTIONS $10.00 A Penton Publication, Periodicals Postage paid, USPS/100 Approved Poly 03.26.10 | electronicdesign.com p| 26 ELECTRIC AND HYBRID VEHICLE TECHNOLOGIES CHARGE AHEAD To meet conflicting requirements, EV and HEV manufacturers are struggling to adapt their cars to society’s needs—without a roadmap.
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Transcript of Ed 100326
T H E A U T H O R I T Y
O N E M E R G I N G
T E C H N O L O G I E S F O R
D E S I G N S O L U T I O N S
$10.00 A Penton Publ icat ion, Per iodica ls Postage paid, USPS/100 Approved Poly
electronic design
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03.26.10 | e l e c t r o n i c d e s i g n . c o m
p| 26
ELECTRIC AND HYBRID VEHICLE TECHNOLOGIES
CHARGE AHEAD
To meet conflicting requirements, EV and HEV manufacturers are struggling to adapt their cars to society’s needs—without a roadmap.
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© Agilent Technologies, Inc. 2009 *Prime Data August 2008 CAGR T&M Report u.s. 1-800-829-4444 canada 1-877-894-4414
Because we listen to you. To build our scopes, Agilent carefully examines the challenges you face. Then we deliver products that solve your problems in imaginative ways. Like the multi-chip module that enables Infiniium’s industry-leading signal integrity. And the ASIC that underlies InfiniiVision’s patented MegaZoom deep memory giving you the industry’s best signal visibility. You’ll find innovations like these in each of our scopes — that’s why more and more engineers are choosing Agilent over other scope brands.*
See why more and more engineers choose Agilent.Download our catalogwww.agilent.com/find/scopecatalog
Why is Agilent the fastest growing oscilloscope manufacturer?
Agilent 20 MHz to >90 GHz real-time and sampling scopes• Handhelds,portables,rack-mountsandbenchtops• 50+application-specificsoftwarepackagesforexceptionalinsight• Innovationsthatsatisfyyourtoughestdemands
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IRGB4045DPBF TO-220 6.0A 2.14V 26 ns 12 ns 95 ns 32 ns
IRGB4060DPBF TO-220 8.0A 1.95V 28 ns 17 ns 117 ns 35 ns
IRGB4064DPBF TO-220 10.0A 2.00V 27 ns 16 ns 98 ns 33 ns
IRGB4056DPBF TO-220 12.0A 1.97V 30 ns 18 ns 102 ns 41 ns
IRGB4061DPBF TO-220 18.0A 2.15V 40 ns 25 ns 120 ns 40 ns
IRGP4062DPBF TO-247 24.0A 2.04V 40 ns 24 ns 125 ns 39 ns
IRGB4062DPBF TO-220 24.0A 2.04V 40 ns 24 ns 125 ns 39 ns
IRGP4063DPBF TO-247 48.0A 2.10V 55 ns 45 ns 165 ns 45 ns
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V o l . 5 8 N o . 4 03.26.10 | e l e c t r o n i c d e s i g n . c o m
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 5
Contents
ELECTRONIC DESIGN (ISSN 0013-4872) is published monthly with an extra issue in March, June, September and October by Penton Media Inc., 9800 Metcalf Ave., Overland Park, KS 66212-2216. Paid rates for a one-year subscription are as follows: $120 U.S., $180 Canada, $240 International. Periodicals postage paid at Shawnee Mission, KS, and additional mailing offices. Editorial and advertising addresses: ELECTRONIC DESIGN, 249 West 17th Street, New York, NY 10011. Telephone (212) 204-4200. Printed in U.S.A. Title registered in U.S. Patent Office. Copyright ©2010 by Penton Media Inc. All rights reserved. The contents of this publication may not be reproduced in whole or in part without the consent of the copyright owner. For subscriber services or to order single copies, write to Electronic Design, PO Box 2100, Skokie, IL 60076. POSTMASTER: Send change of address to Electronic Design, PO Box 2100, Skokie, IL 60076. Canadian Post Publications Mail agreement No. 40612608. Canada return address: Bleuchip International, P.O. Box 25542, London, ON N6C 6B2.
Features
Columns
ofTable
EDITORIAL MISSION: To provide the most current, accurate, and in-depth technical coverage of the key emerging technologies that engineers need to design tomorrow’s products today.
T H E A U T H O R I T Y
O N E M E R G I N G
T E C H N O L O G I E S F O R
D E S I G N S O L U T I O N S
26: Electric And Hybrid Vehicle Technologies Charge Ahead | Engineering Feature • Roger Allan
To meet con icting require-ments, EV and HEV manufac-turers are struggling to adapt their cars to society’s needs—without a roadmap.
34: Cut The Links To Your Sensor/Actuator Networks | Technology Report • Louis E. Frenzel
Here’s what you need to know to take advantage of the latest wireless tech-nologies in networking sensors and/or actuators.
56: New Interfaces In Flash Memory Design Drive Innovation And Lower Costs | Design Solution • Kevin Widmer, Spansion
As consumers demand more from the latest gadgets, designers are turning to multiple-I/O SPI for improved performance.
Editorial | Joe Desposito
13: If 3D TV Is Here, Can 3D Camcorders Be Far Off?
Lab Bench | Bill Wong
14: Tools Turn Robot Projects Into Child’s Play
Testing The Limits | Eric Starkloff
16: What Can Toyota Teach Us About Test?
Point Of View | Henry Muyshondt, SMSC
18: USB Hub/Card Applications Hit The Road
Pease Porridge | Bob Pease
64: Bob’s Mailbox
50: Improve The Design Of Your Passive Wideband ADC Front-End Network | Design Solution • Rob Reeder, Analog Devices
It’s important to understand the various tradeoffs and considerations before you begin your front-end design for high-speed data converters for wide-bandwidth applications.
Improve The Design Of Your Passive Wideband ADC Front-End
42: Characterize Your LEDs For
Almost All Occasions| Engineering Essentials • Mat Dirjish
First, you need to know the different types of LEDs. Then, you
need to know your application.
First, you need to know First, you need to know
21address
lines
16datalines
3controllines
40 to 6
4 datalines
2 controllines
MCU orASIC
32-Mbitparallel
flash
MCU orASIC
32-Mbit SPI
flash
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 7
Product Features62: Ad Index
2008 WinnerSILVEREDITORIALAWARD OF
EXCELLENCE
2008 WinnerGOLD
EXCELLENCE IN MAGAZINE
DESIGN
Permission is granted to users registered with the Copyright Clearance Center Inc. (CCC) to photocopy any article, with the exception of those for which separate copyright ownership is indicated on the first page of the article, provided that a base fee of $2 per copy of the article plus $1.00 per page is paid directly to the CCC, 222 Rosewood Drive, Danvers, MA 01923 (Code No. 0013-4872/94 $2.00 + $1.00). Copying done for other than personal or internal reference use without the express permission of Penton Media, Inc. is prohibited. Requests for special permission or bulk orders should be addressed to the editor. To purchase copies on microfilm, please contact National Archive Publishing Company (NAPC) at 732-302-6500 or 800-420-NAPC (6272) x6578 for further information.
T H E A U T H O R I T Y
O N E M E R G I N G
T E C H N O L O G I E S F O R
D E S I G N S O L U T I O N S
V o l . 5 8 N o . 4 03.26.10 | e l e c t r o n i c d e s i g n . c o m
24: 18-Bit DAC Provides Precision, Linearity, And Output Flexibility | Analog & Power • Don Tuite
24: High-Speed Digital Debug Calls For Specialized Tools | Test & Measurement • David Maliniak
21: FPGAs Enter The Third Dimension | Leapfrog • Bill Wong
TechView
Fold 0
Fold 1
Fold 2
Fold 3
Time
Embedded in Electronic Design • Bill Wong
46: Multitouch Functionality Comes To Bigger Screens
47: Module Packs I/O Features
48: Microcontroller Talks—And Listens
Embedded in Electronic Design 46: Multitouch Functionality Comes
To Bigger Screens
47: Module Packs I/O Features
48: Microcontroller Talks—And Listens
Ideas for Design59: Modified Phantom-Powered Microphone Circuit
Reduces Distortion | Dimitri Danyuk
60: Shift Register Generates Multiple Clocks From PWM Signal | Christina Obenaus • IneoS Ingenieur-Büro Obenaus
61: Configurable Logic Chip Stretches Pulses To Brighten LED Flash | James S. Campbell, MD • Medesign
Product Features62:
C21 µF
C11 nF
X1
R32.2k
C3100 µF
Q1J305
R11G
R42.2k
C41 µF
R21M
R1010k
Q22SA992
R11100k
C51 µF
R5390k
Q42SC1845
R6100k
R143.9k
R747k
R875
C71 µF
Output 1
23– –
XLR+ +
+
JOUT
R975
R1210k
Q32SA992
R13100k
C61 µF
D112 V
C81 µF
Q52SC1845
R151k
JC1
GndGnd
1
2
1
2
1
23 3 3– –
+ +XLR
XLR
C31
C23
Cable
JC2
C21 Gnd
XLR
Gnd
Rf16.81k
InputJIN
C++
+C–
To amp
Rf26.81k
+48 V
Engineering TVEngineering TVEngineering TVEngineering TVEngineering TVEngineering TVEngineering TVEngineering TVNew Samsung Displays: New Samsung Displays: New Samsung Displays: New Samsung Displays: New Samsung Displays: New Samsung Displays: New Samsung Displays: New Samsung Displays: 3D, Green, And Ultra-3D, Green, And Ultra-3D, Green, And Ultra-3D, Green, And Ultra-3D, Green, And Ultra-3D, Green, And Ultra-3D, Green, And Ultra-3D, Green, And Ultra-ThinThinThinThin
Design SolutionFormal Analysis: A Valuable Tool For Post-Silicon DebugJamil R. Mazzawi, Pearl Lee, and Lawrence Loh, Jasper Design Automation
Post-silicon debug can be very stress-ful. What can you do when the chip doesn’t work and time is running out? Missing the deadline can put one’s job—and one’s company—in jeopardy. Formal veri cation has proved to be a lifesaver in these situations, as it uncovers the root causes of bugs and validates xes when other approaches have failed.
electronicdesign.com
03.26.10 ELECTRONIC DESIGN8
WebtheOn03.26.10 | e l e c t r o n i c d e s i g n . c o m
Test TechviewDavid Maliniak, EDA & Test Editor
Handheld Vector Network Analyzer Takes Accuracy Title
Last year, Agilent’s N9912A FieldFox RF vector network analyzer broke new ground for the portable category. Now the test giant is following up with its N9923A FieldFox analyzer, which shares the same packaging and form fac-tor as its predecessor but improves upon its performance in some important ways.
Engineering TVEngineering TVEngineering TVEngineering TVEngineering TVEngineering TVEngineering TVEngineering TVFormal Analysis: A Valuable
Editor’s Editor’s Editor’s Editor’s NotebookNotebookNotebookNotebookNotebookNotebookNotebookNotebook
Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To Going (Back) To EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think EE School? Think
“Interdisciplinary“Interdisciplinary“Interdisciplinary“Interdisciplinary“Interdisciplinary“Interdisciplinary“Interdisciplinary“Interdisciplinary””””””””
Point of ViewTelevision Tuners:
A State Of The Union ReviewPamela Lee, Fresco Microchip
TV sets have evolved dramati-cally since their introduction, with lifelike picture quality at lower price points in thinner, greener platforms. Yet the fundamental front-end tuner technology that determines how we receive and transmit television broadcasts has not
changed in ve decades.
Design Solution
“Interdisciplinary“Interdisciplinary“Interdisciplinary“Interdisciplinary
Point of View
Webinar
April 27, 2010
Electronic Design brings you the latest in power design information in our free online conference, One Powerful Day. Featuring industry ex-perts, this daylong webinar will offer sessions on increasing photovoltaic panel energy output, thermal management, portable battery and charger options, LED solutions, power-supply testing, and MOSFET design. For more, go to www.electronicdesign.com/opd.
PodcastDesigning With Ultracapacitors—An Interview With Chad Hall Of IoxusJohn Edwards, Contributing Editor
Ultracapacitors hold less electricity than comparably sized batteries, but absorb and release it much more quickly. This is crucial for time-sensitive electricity storage, includ-ing power-grid frequency regulation, fast vehicle acceleration, and capturing energy from vehicle braking, explains Chad Hall, CEO of Ioxus.
Anti-glare 6.5-in.LCD with LED backlight
Backlit keypadDedicated marker keys for quick marker function access
Navigate between four tracesusing up/down arrows
11.5 in.292 mm
7.4 in.188 mm
Convenient sidestrap makes iteasy to hold andcarry
Connector covershelp keep dust out
Task-driven keysare grouped toeasily andnaturally performstandard fi eldmeasurements
Portrait design and large buttons for easy operationeven with gloves on
TURN ON THE
POWEROF AVNET
Avnet lights the way to reliable,durable, and sustainable LED Solutions. Choosing LED technology for your design is only the first step on the path. Avnet Electronics Marketing helps light your way to selecting LEDs thatmeet your reliability, visibility, and availability requirements. At each stageof the design cycle, our team of illumination-focused engineers gives youaccess to the latest information on LED products, ensuring you find theright solution to fit your specific design needs. When tackling the challengesof thermal management, power driver stage and secondary optics, our experts are your source for leveraging the benefits of LED technology.
As a unit of Avnet Electronics Marketing, LightSpeed brings together the world’s foremost LED, high-performance analog and optical/electrome-chanical manufacturers along with best-in-class technical expertise and supply chain management services – affording you quicker time to market.
Working together, we can help you bring your ideas to light.
For more information and to view the latest issue of Light Mattersvisit us at: www.em.avnet.com/lightspeed
©Avnet, Inc. 2009. All rights reserved. AVNET is a registered trademark of Avnet, Inc.
10 03.26.10 ElEctronic DEsign
03.26.10ELECTRONIC DESIGN
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ElEctronic DEsign Go To www.elecTronicdesiGn.com 13
EditorialJOE DESpOSITO | EDITOR-IN-CHIEF [email protected]
If 3D TV Is Here, Can 3D Camcorders Be Far Behind?ThE arrIval Of a new baby in my family has led me to take more video than usual. But as I shoot with my standard-definition digital camcorder, I wonder if I’ll be getting grief from this kid once he realizes that his vids could have been shot in high def. And lurking in the back of my mind is some-thing even more worrisome—3D.
Since a good part of the civilized world has seen Avatar, is there any turning back? Hollywood is pumping out 3D movies faster and faster. Those movies will wind up playing on 3D-capable flat-panel TVs, as some are already doing now. As more and more people start watching 3D movies at home, what’s the next step? It’s obvious. Everyone will want to shoot their own videos in 3D.
3D CamCorDers anyone?I went searching to find out how close we are
to having an affordable 3D camcorder, and the answer is pretty close—maybe two years. At Janu-ary’s International CES in Las Vegas, Panasonic unveiled the world’s first integrated Full HD 3D camcorder (see the figure).
Yes, we’ve seen 3D cameras before. After all, how else can Hollywood produce blockbusters like Avatar? Those systems often use two separate cameras melded into one with fancy electronics and optics. But the Panasonic camera is different. No, it’s not a consumer camera. It’s for profession-als. The cost says it all: $21,000. But it’s also the shape of camcorders to come. Can the cost curve slide by a factor of 10 in two years? Maybe.
Naturally, Panasonic’s Full HD 3D camcorder takes advantage of
the latest technologies so you get what you might expect—a solid-state memory instead of tape or hard disk as the recording medium. The lenses, camera head, and dual Memory Card recorder are integrated into a single, lightweight body. The camcorder also incorporates stereoscopic adjust-ment controls, making it easy to use and operate.
A twin-lens system in the camcorder’s opti-cal section lets you adjust the convergence point, which is where the left and right cameras’ optical axes converge to produce 3D images. There are also functions for automatically correcting hori-zontal and vertical displacement.
With conventional 3D camera systems, these adjustments are typically made with a PC or an external video processor. This new camcorder, however, will automatically recalibrate without any need for external equipment, essentially giving you the ability to capture 3D images without too much fuss.
As you might expect, the solid-state memory file-based recording system will let you take full HD 3D videos in more challenging shooting envi-ronments, since solid-state memory can “take a lickin’ and keep on tickin,’” as they used to say. This camcorder is certainly lighter and smaller than current 3D rigs, so handheld shooting is not a problem.
Don’T ForGeT THe GLassesPanasonic has jazzed up 3D glasses compared
to the clunky versions that cinemas give out for 3D movies. I’m picturing an entire cottage industry for “fashion” 3D glasses with vendors in malls and other high-traffic venues. Get your glasses on and cuddle up with the kids on the couch to watch your favorite family vids in 3D.
More information about the camcorder, glasses, and other 3D gear is available at www.panasonic.com/CES2010. The camcorder is set to debut in the fall, but Panasonic will start taking orders in April.
Does anyone out there have 21 grand to burn?
Why settle for your old handheld digital camcorder? The Panasonic Full HD 3D camcorder targets the professional mar-ket. If its $21,000 price tag is out of your
reach, less expensive consumer models are probably just a couple of years away.
14
LabBench
03.26.10 ELECTRONIC DESIGN
Tools Turn Robot Projects Into Child’s Play
BILL WONG | EMBEDDED/SYSTEMS/SOFTWARE EDITOR [email protected]
NATIONAL INSTRUMENTS’ LABVIEW has been used with robots for decades. It mostly has been employed by developers looking to take advantage of graphical programming tools (search “Lab-VIEW: Graphical Programming” at electronicde-sign.com).
LabVIEW also was the underlying plat-form for the popular Lego Mindstorms robots (search “The Mind Of Mind-storms” at electronicdesign.com). Lego Mindstorms spawned a generation of kids play-ing with robots from an early age (Fig. 1). It remains the basis for the FIRST Lego League robotics competition (search “Future Engi-neers Brace For Battle Of The Robots” at electronicdesign.com).
The ARM-based Lego NXT control block was a signifi-cant step up for most new robotic developers with
a 48-MHz Atmel ARM7TDMI processor. Children can start out using the graphical programming environment that comes with Lego Mindstorms, but there are lots of alternatives ranging from free platforms like RobotC and the Java-based LeJOS to commercial products like Gostai’s URBI and Next Byte Codes NBC. Even LabVIEW and IAR’s Embedded Workbench are available options.
But more advanced systems like those often used in the other FIRST competitions needed sup-port for peripherals that NXT could not handle. Likewise, the applications tended to be larger as well, exceeding the storage capacity of the ARM-based NXT brick.
National Instruments’ Compact-RIO (Fig. 2) and its sibling, the Single Board RIO (sbRIO), were popular platforms (search “RIO Boards Target Control And Data-Acquisition Apps” at electronicdesign.com).
With a processor and FPGA at their heart, they’re designed for industrial applications, not just robot-ics. These platforms also accept a range of stan-dard and custom plug-in modules, which allows the RIO platforms to handle data acquisition as
well as process control.The RIO platforms aren’t the only Lab-VIEW targets that find multiple uses.
National Instruments’ Smart Camera (Fig. 3) also runs LabView appli-
cations (search “Smart Camera Runs Graphical Applications” at electronicdesign.com).
Handy as an intelligent sen-sor in robotic applications, the Smart Camera can communi-
cate with other devices via Gigabit Ether-
net. However, i t a l s o h a s enough pro-cessing power
t o p e r f o r m a wide range
of analysis and compression algo-
rithms, reducing the communication load.
ROBOT KITGiven this wide range of
hardware and software sup-port for robotics, it wasn’t surprising
when National Instruments released its LabVIEW Robotics Starter Kit (Fig. 4). It’s based on the sbRIO 9631 platform, which includes a Freescale MPC5200 processor, 110 digital lines, up to 32 analog outputs, four analog inputs, and 32 indus-
03.26.10 ELECTRONIC DESIGN
used in the other FIRST competitions needed sup-port for peripherals that NXT could not handle. Likewise, the applications tended to be larger as well, exceeding the storage capacity of the ARM-
National Instruments’ Compact-
Apps” at electronicdesign.com).
2. CompactRIO and Single Board RIO use an FPGA to link plug-in modules to the system processor. They run LabVIEW applications directly.
1. Lego Mindstorms uses a graphics programming system based on LabVIEW but simplified for young designers.
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM
trial 24-V digital I/O. The ki t a lso adds a f rame, motors, wheels, and sen-sors in a compact robotic development platform.
The system runs off a 12-V nickel-metal-hydride (NiMH) battery. Gear-driven 4-in. wheels provide good traction and ground clearance. The robot design is rather wide to accom-modate the sbRIO system mounted on top. It has Ether-net and serial port connectivity. The kit is not ambitious enough to have a Smart Camera included, but it does have a Parallax Ping))) ultrasonic sensor mounted on a servo.
BUNDLING ROBOT SOFTWARE The hardware is impressive, but the
software makes the starter kit stand out. LabVIEW is at its center, of course, but robots require so much more. The system includes LabVIEW RealTime, LabVIEW FPGA, NI Vision, LabVIEW Control Design and Simulation, NI SoftMotion, LabVIEW Statechart, LabVIEW Math-script, and LabVIEW PID Toolkit. The Wind River VxWorks real-time operating system (RTOS) provides the RealTime support on the sbRIO.
National Instruments includes a vari-ety of virtual instruments (VIs) targeted at robotic sensors and controls such as the Smart Camera and simpler systems such as the robot’s motor control. This is the start of a framework for a com-mon robotic design and control system, although it isn’t as general or encom-passing as Micro-soft’s Robot-
ics Developer Studio (search “MS Robotics Studio” at electron-icdesign.com). For example, the Robot-ics Developer Studio includes a simulator
where applicat ions can be tested in a virtual environment. Microsoft does provide a graphical pro-gramming language called VPL (Visual Programming Language), but it lacks the massive support of LabVIEW. It does meld well with Microsoft’s other tools that do have comparable support, though.
Still, the Robot Starter Kit is a major step forward for robotic development, especially since linking together tools such as planning and image recognition is relatively easy with an environment such as LabVIEW. The CompactRIO platform is already in the hands of FIRST teams, so designers looking for a com-patible but less expensive solution will definitely like this latest kit. FIRST ROBOTICS LEGO LEAGUE
www.firstlegoleague.org
LEGO MINDSTORMS
http://mindstorms.lego.com
NATIONAL INSTRUMENTS
www.ni.com
LabBench
net and serial port connectivity. The kit is not ambitious enough to have a Smart Camera included, but it does
ics Developer Studio (search “MS Robotics Studio” at electron-icdesign.com)example, the Robot-ics Developer Studio includes a simulator
where applicat ions can be tested in a virtual environment. Microsoft does provide a graphical pro-
3. The Smart Camera runs LabVIEW applica-tions directly and com-municates with other LabVIEW applications via Gigabit Ethernet.
4. National Instruments’ LabVIEW Robotics Starter Kit is based on NI’s Single Board RIO, which can handle industrial chores.
16
TestingTheLimits
03.26.10 ElEctronic DEsign
What Can Toyota Teach Us About Test?
Eric Starkloff | Contributing Editor [email protected]
WE’vE all folloWEd the sto-ries about Toyota’s recent recalls. The current estimate is that these
recalls will cost Toyota up to $2 billion. The damage to Toyo-ta’s quality brand, which has been built over several decades, also is likely to be very costly.
While it’s premature to speculate as to all the causes of these recalls, they will likely include gaps in the engineering process, the culture and corporate management, and how the company responded to the defects once they were known.
Regardless of the causes, the visibility of Toyota’s crisis will create more focus across many organizations on quality. Test, which provides the essential function of ensuring quality during product design and manufacturing, has always been challenging to justify as a strategic investment.
All models Are wrong, but some Are usefulThis often-quoted phrase, attributed to statistician George
E.P. Box, reminds engineers about the need to test our assump-tions and verify models with real-world data. As device com-plexity continues to increase, and as we push the physical limits of mechanical and electrical systems, this reminder is as relevant as ever.
Modeling and simulation are powerful tools in all engineer-ing disciplines. But increasingly, test is being used throughout the product development cycle—from research through final production—to verify and enhance modeling techniques.
In early research, measurement is used to create the models of subcomponents. Complex components, like RF semicon-ductors, often have inaccurate models. Only through real-world measurement can more accurate designs be built. Dur-ing the product development step, test is used to compare a prototype’s actual performance to the predicted performance of system-level models.
Hardware-in-the-loop (HIL) testing combines modeling with real-world data. An HIL system simulates parts of an embedded system so its dynamic performance can be tested in a variety of operating conditions. To test a motor control system, an HIL test system uses real-world I/O to control the inputs and measure the outputs of the controller while simulat-ing the motor. HIL testing can provide a fast and cost effective way to test complex embedded systems under many different conditions to ensure correct and robust operation.
Ford uses an HIL system based on NI LabVIEW and PXI to test prototype control systems for fuel-cell vehicles using PXI I/O cards while simulating other parts of the system including various sensors and actuators. Ford uses this system to rapidly demonstrate prototype controllers in real-world conditions.
linking design And production testTest is performed throughout the product development pro-
cess. Yet all too often, it is done with different testing platforms
and techniques at each stage. This makes it difficult to correlate problems encountered in manufacturing or in the field with validation data. The challenge is that the testing requirements of these different stages often differ in significant ways.
In the early stages of product design, quick measurements are taken to verify a prototype. In verification testing, the product goes through a very thorough suite of tests to test different potential operating conditions, such as HIL. And, in production, the goal is to test just enough to ensure quality and to keep the manufacturing process in control.
While the measurement and test automation needs vary across these use cases, a common testing platform with shared compo-nents can address them all. Having a single platform enables bet-ter correlation and traceability of data from a fault encountered in production or in the field, back through to validation.
How mucH is test reAlly wortH?Too often, test is viewed as a necessary evil. We ask how
much it costs. Instead, we should be asking what test is worth. Test improves a product’s performance, increases quality and reliability, and lowers return rates. It is estimated that the cost of a failure decreases by a factor of 10 when the error is caught in production instead of in the field and decreases by a factor of 10 again if it is caught in design instead of production.
By catching these defects and collecting the data to improve a design or process, test delivers value. If you understand the value of catching defects through test, you can make more educated investments. Most companies under-invest in test, yet paradoxically spend too much—in slower product devel-opment, longer manufacturing cycles, and expensive repair and recall costs.
Improving your results requires a strategy for testing throughout product development that includes people, pro-cess, and technology. The right people are required to develop and maintain a cohesive test strategy. In test, this can be par-ticularly challenging due to the growing experience gap in the field of test engineering. Process improvements are required to streamline test development and reuse throughout product development. And, technology always offers new ways to solve the challenges in testing complex products. The key is tracking and incorporating new technologies to improve test system performance or lower costs.
These elements can elevate your testing function from a cost center to a strategic advantage. Toyota’s issues give us another motivation—what is the risk to our company if we don’t look at test strategically? As test engineer, you must drive this stra-tegic view and justify the investments. If you don’t, your com-pany might be in the headlines for the wrong reasons.
EriC StArKLoFF, vice president of product marketing at national
instruments, holds a bachelor’s degree in electrical engineering
from the university of Virginia.
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18
PointOfView
03.26.10 ElEctronic DEsign
USB Hub/Card Applications Hit The Road
Henry MuysHondt | SMSC [email protected]
usB and flasH memory cards have become ubiquitous in the con-sumer and industrial worlds. USB
implements a high-speed serial bus that runs at up to 480 Mbits/s. Many operating systems provide native support for this technology with many hundreds of millions of devices shipped to date. USB is not only used to transfer data between devices, it also provides a means to charge portable devices.
As consumers expand their digital lifestyle to have their content always available, more and more devices take advan-tage of the economies of scale afforded by the explosion of interconnections that ensue. Car makers are embracing this trend as their vehicles integrate into the digital world.
Vehicles are also becoming storehouses of content and information. They can include large amounts of storage capac-ity for entertainment content and navigation information. One of the most popular memory formats today is Secure Digital (SD). The SD interface is also used in embedded applications to attach devices like Wi-Fi (or wireless local-area networks) and Bluetooth transceivers, as well as GPS receivers with an SDIO interface.
SD memory can be used to replace rotating media like hard disks, CDs, and DVDs. A state-of-the-art 32-Gbyte card holds the equivalent of close to seven DVDs. Car mak-ers can use memory cards both as a connection to consumers and as a mechanism to upgrade different systems within the vehicle, be they navigation systems or any other devices that require software. Therefore, USB and flash media interfaces are very useful in automotive applications.
Automotive quAlity requirements Before getting into the specific functions of the interfaces,
let’s first consider automotive quality requirements. Devices intended for the automotive market have to be designed, vali-dated, characterized, qualified, fabricated, and supported spe-cifically for use in automotive applications. Cars have very long lifecycles, and any failure in the field is very costly in terms of repair time and customer satisfaction.
When ICs that are designed for consumer applications are used in automotive applications, they are often qualified according to the Automotive Electronics Council’s qualifi-cation requirements (AEC-Q100). This standard, however, only covers minimum common requirements for the quali-fication of an automotive IC. Many car companies and tier one automotive suppliers require extensive additional qualifica-tion tests, as AEC-Q100 alone does not lead to the ultra-low defect rates that they require.
In add i t ion , AEC-Q100 primarily focuses
on the qualification phase of the product cycle of an IC. Other phases such as the design and production of the IC, customer support, and the handling and investigation of returns are not covered in detail.
To reach the automotive goal of near-zero defect rates, all phases of the IC product cycle need to be addressed thorough-ly. Before even looking at a product’s functions, automotive designers need to look at their supplier’s capability to deliver products with near-zero parts per million (ppm) defect rates.
memory for storAgePassengers use portable memory cards to transfer informa-
tion created on computers, portable media players, or cameras to the car. Car makers also incorporate gigabytes of microcode into some of today’s most sophisticated vehicles. Further, they need to store map data for their navigation systems.
As mentioned earlier, solid-state memory is increasing-ly replacing rotating media inside automotive infotainment devices. Maps for a large country, like the United States, can fit in less than 2 Gbytes of storage. An SD card of this size can be purchased at retail for less than $5.00, making it very cost effective compared to the typical DVD player used for many automotive navigation systems. In addition, reliability is increased, as there are no moving parts associated with it.
The high-speed data transfer enabled by an SD interface can simplify software updates for other components in the car as well, like a head unit or other components.
These in-box use cases require true automotive-grade reli-ability. The new combination hub and card reader devices enable car makers to design highly reliable data access devices for their information and entertainment systems, whether those devices connect to internal peripherals or provide external consumer access.
usB huB And cArd reAder comBinAtionsA USB hub expands the number of available USB ports
while the card reader provides memory card interfaces, such as SD/MultimediaCard (MMC) or Sony MemoryStick. The SD interface is standardized for memory applications. It also pro-vides a generic input/output interface known as SDIO.
The SDIO interface uses the same elec-trical signals as the SD memory interface but can be
ElEctronic DEsign Go To www.elecTronicdesiGn.com 19
used to attach modules that provide addi-tional features such as Wi-Fi, Bluetooth, and GPS connections. It is even possible to build custom firmware to control new applications attached through SDIO.
It is important for the card reader sup-plier to have significant experience with memory cards manufactured by many dif-ferent suppliers because the specifications for the SD interface allow some room for interpretation and optional features that can result in incompatibilities with differ-ent products. SMSC has performed exten-sive testing to support a large number of cards currently in the market.
The current devices also support using an external ROM to create secure mem-ory formats or add customized appli-cations based on system requirements. Incompatibilities with cards from differ-ent manufacturers could result in war-ranty claims against a car maker. Service calls are very expensive, so it is impor-tant to avoid them if consumers bring in a device that they got for free somewhere.
The combination hub/card reader func-tion allows the placement of this device away from the main host controller to provide connectivity where it is needed. For example, the glove compartment or center console in a car could allow con-sumers to easily connect their devices without requiring long cables to the main head unit.
ConClusionUSB interfaces and storage memory
provide useful enhancements to automo-tive systems. Automotive requirements result in stringent qualification processes that only a limited number of worldwide semiconductor suppliers can implement. They also result in special features being needed to simplify system design.
Flexibility in creating multiple plat-forms with a single platform is a plus. Car
makers also require a very high level of compatibility when dealing with memory cards from multiple suppli-ers. And, the devices must be able to operate in a rugged environment with
high temperatures and widely varying environmental conditions.
Henry MuysHondt is senior director of
business development for the Automotive
Information systems group of sMsC. He also
serves as the Most Cooperation’s technical
Coordinator and u.s. Management
representative. He has been working with
the Most multimedia network since 2000.
Also, he is helping the automotive and con-
sumer industires deploy this new technology.
He currently leads working groups within the
Most Cooperation and within the Consumer
electronics Association to develop standards
to connect accessory and aftermarket
devices to on-board vehicle networks.
PointOfView
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We cer t i fy that bal l a t tach process wil l be performed in a conduct ing / convect ion oven and wil l never exceed 75% of the t ime temperature recommended by the suppl ier.
WWe cer t i fy we wil l 100% optical ly inspect the rebal led par ts to ensure the device meets the or iginal suppl iers specif icat ions for f la tness and co-planari ty.
Part No. Order-Release No.
ISI Interconnect Systems Inc. (805) 482-2870 www.isipkg.com
Bill Miller, President & CEO_____________________________
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ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 21
T abula’s ABAX chips take FPGA design to the next level. They implement a virtual 3D archi-tecture by dynamically chang-
ing the underlying FPGA definition on each clock cycle. Accomplishing this feat while maintaining compatibility with existing design tools and methodolo-gies has meant overcoming a number of challenges, including changing the underlying structure of the system at a rate of 1.6 GHz.
From a designer’s point of view, the 40-nm ABAX looks like an FPGA. The A1EC06 version has 630,000 lookup tables (LUTs), 5.5 Mbytes of RAM, and 1280 DSP blocks. The chip also has 48 high-speed, 6.5-Gbit/s serializers/deseri-alizers (SERDES) and 920 I/O ports. The various components are arranged in reg-ular blocks like a typical FPGA, including the interconnects, which are configured by the programmer, along with the LUTs.
AN EIGHT-FOLD INCREASETabula’s SpaceTime architecture
increases the number of LUTs and interconnects by a factor of eight. The company calls the configuration of the underlying FPGA structure a “fold.” The current incarnation of ABAX chips can handle up to eight folds. The trick comes in the form of a time via.
The time via is a transparent latch found on every intercon-nect on the chip. It lets information pass through to logic configured within a fold. It also propagates the data to the next fold in the sequence (Fig. 1). Information in registers and memory is maintained between fold transitions too. The dif-ference is that the time vias are implicit in the system and not specified by the designer, whereas the registers and memory are explicitly allocated.
The approach resembles Achronix’s Speedster FPGA, which employs picoPIPE elements on the interconnects like the time vias (search “1.5-GHz FPGA Takes Clock Gating To The Max” at electronicdesign.com). The Archonix FPGA definition is static, though, and the latches provide a way for data to flow through the system. Also, the picoPIPE elements are more like single-bit FIFOs, allowing asynchronous opera-tion. The SpaceTime time vias, on the other hand, operate in a synchronous fashion.
Tabula’s chips are divided into regions that can have differ-ent fold definitions and operate at different clock frequencies (Fig. 2). Regions can be grouped together, providing larger fold groups. All areas within a common region have the same number of folds, and they operate in lockstep with respect to fold transitions.
Operation at lower frequencies is more power-efficient since the definitions within the region don’t change as often. Different regions can be synchronized when they operate at the same frequency or multiples of each other. This enables synchronous data exchange between regions.
The SpaceTime architecture has advantages when it comes to signal propagation as well (Fig. 3). A signal moves no faster within a fold than it normally would, but it can prop-agate significantly farther within the cycle. Each fold allows a signal to move farther from its source. This is the same type of approach used in conventional FPGA design, except reg-isters must be explicitly utilized on the clock transitions.
FPGAS ENTER THE THIRD DIMENSION ENTER THE THIRD DIMENSION Fold 0
Fold 1
Fold 2
Fold 3
B0A0
B1A1
B2A2
C0
B3A3
Time
Fold 0
Fold 1
Fold 2
Fold 3
Time
1. Tabula’s approach splits the logic into one or more folds. Each fold runs for one clock cycle, and the FPGA layout changes each cycle. Data in registers and “time vias” will be passed between folds. A time via is a transparent latch for each interconnect, allowing data from any LUT output to be used by logic within a fold or the next fold. The last fold feeds the first fold. Maximum clock frequency is 1.6 GHz.
22
TechView
03.26.10 ElEctronic DEsign
Tabula’s design offers an added advantage because the logic changes with each new fold so the original source LUTs can be used for computation based on the data from the prior fold. A conventional FPGA has to move the signal to a point where the subsequent logic is located.
The upper limit of the number of folds in the current chip may seem limiting, but it isn’t. Additional folds provide more logic within a given space and more reach for a given signal. In practice, the first fold in the series follows the last fold. In theory, data from the last fold can be used within the first fold as if it were the next fold in the sequence working on this information while the other logic within the first fold is working on new information. The last fold cannot reuse the logic in the first fold, but it can use other logic defined within the first fold.
Superior Soft CoreS Soft-core processors are used in a significant number
of new projects. FPGA designers have a challenge when it comes to optimizing a soft-core design for a particular FPGA platform. In addition, soft-core designs are often behind their ASIC counterparts because of the overhead and design restrictions of the FPGA fabric. One of these is multiport regis-ter file support. FPGAs typically provide dual-port register files to address these design requirements.
Tabula only provides single-port register files. This might panic soft-core designers until they consider the impact of the 3D architecture because a single-port register file can deliver one piece of information for each fold. This meshes nicely with pipeline architectures for two reasons.
First, an eight-fold region essentially has eight port register files within its cycle. Second, each new fold has a new set of logic next to the register so the processing pipeline can start next to or near the register file propagating outward toward more logic. The same approach works with memory inter-faces as well.
Soft cores that target existing FPGA platforms initially will be used on the ABAX. It will be interesting to see how designers take advantage of the virtual 3D architecture when trying to improve designs. Likewise, it will be interesting to see how much of the underlying system Tabula will give to designers because the tools essentially hide the underlying complexity of the system. In the future, it might be possible for designers to select the sophistication of the soft-core design the same way that developers select features like cache and cache size.
Managing CoMplexityTabula is taking the same approach to providing a more
powerful FPGA platform as Achronix. Essentially, the chips are presented as a conventional FPGA with the layout tools churning out multifold definitions. In fact, the platform even partitions regions.
The layout tools account for timing details, putting logic at the far end of a chain in folds farther from the start. Deep logic benefits from more folds. The layout tools provide details about the number of folders. Users have some control over regions by providing clocking details about the logic. This approach will work well because details like time vias are transparent to designers.
On the other hand, these types of features could provide interesting design options in the future. Achronix has had this same issue with its picoPIPE elements. If designers can specify that a latch is employed at a particular point, as in a soft-core processor pipeline, they may be able to take better advantage of the underlying architecture.
Power management also comes into play with the layout tools. The static power of the chip is lower compared to another FPGA since fewer LUTs are needed because of the virtual 3D architecture. Dynamic power requirements can vary depending on the application. The layout tools can handle some automatic power-down details. For now, all the fold details are available to Tabula’s experts, with a limited amount provided to developers.
The 3D architecture offers some interesting possibilities when it comes to debugging. Consider a design that uses fewer than eight folds. The unused folds could be used for additional debugging logic. There are timing considerations, but it is an option that could lead to some interesting designs.
Four versions of the ABAX 3D programmable logic device chips are available. Pricing ranges from $105 to $200. They compete with FPGA chips that cost two to four times as
4 folds1x clock
8 folds1x clock
4 folds2x clock
3 folds1x clock
Fold 0
Fold 1
Fold 2
Fold 3
2. A Tabula chip can be partitioned into regions of almost any size. Each region has a fixed number of folds and runs at its own clock rate. Regions can run independently or be synchronized based on data exchange requirements.
3. The SpaceTime architecture has advantages when it comes to signal propagation since the reach of a signal increases as data propagates outward. The approach improves propagation distance by a factor of 3.2.
24
TechView
much. The chips are equipped with flex-ible SERDES that can handle a range of chores from interfaces like PCI Express and Gigabit Ethernet to storage inter-faces like SATA.
The ABAX represents a major shift in FPGA capabilities that essentially place it in its own category. Still, its compatibility with FPGA tool chains makes it a much more flexible FPGA platform. Its ability to support features such as multiport RAM within soft-core processor designs will radically change designers’ views of FPGA platforms. Bill WongTabula
www.tabula.com
18-Bit DAC ProviDes PreCision, LineArity, AnD outPut FLexiBiLity
In addition to 18-bit resolution and remarkable dynamic performance speci-fications, Linear Technology’s LTC2757 parallel-output, multiplying digital-to-analog converter (DAC) offers two unusu-al features: current-output and register-programmable output-voltage ranges.
Providing current rather than voltage out-put allows custom-fitting output amplifiers appropriate to each application. This makes it possible to provide wider output voltage output swings than possible using voltage-mode DACs, in which the DAC’s dc supply
constrains the output voltage range. It also enables designers who work with the DAC to optimize the amplifier on the basis of their application’s need for speed, accuracy, noise, power, and other factors.
Being able to program different output ranges (0 to 5 V, 0 to 10 V, ±10 V, ±5 V, ±2.5 V, and –2.5 to 7.5 V) makes it unnec-essary to add precision gain stages. The output range is selected either via a serial interface or, if on-the-fly selection is not needed, by pin-strapping. At power-on, the DAC output is reset to 0 V regardless of output range. It can also be reset by the use of a CLR pin.
Intended for high-performance instru-mentation, automated test equipment, data acquisition systems, and medical devices, the DAC has impressive dynam-ic specs: guaranteed maximum integral and differential nonlinearity of ±1 LSB and 2.1-µs full-scale settling time. Glitch impulse is specified as 1.4 nV • s.
The LTC2757’s bidirectional parallel input/output interface allows both pro-gramming and readback of the DAC out-put span setting as well as the contents of other internal registers. Voltage-controlled offset and gain adjustment pins provide the ability to null system offset, gain error, or reference errors.
The LTC2757 DAC comes in a 7- by 7-mm, 48-pin leaded quad-flatpack. Unit pricing begins at $25.50. Don tuitelinear Technology
www.linear.com
HigH-sPeeD DigitAL DeBug CALLs For sPeCiALizeD tooLs
The proliferation of high-speed digital serial links is causing all kinds of test-related headaches for designers. The measurement requirements for these high speeds are differ-ent from those for typical digital debug and rather resemble what’s needed for RF test.
A quick look at a PCI Express (PCIe) eye diagram would tell you that. The same goes for USB 3.0, which clocks at 5 Gbits/s. Creating sharp-edged pulses at these speeds is a major challenge. The physical-layer challenges posed by PCIe 3.0 are considerable as well. (For more information, see www.pcisig.com/news_room/faqs/pcie3.0_faq/.)
“At 8 GT/s, eye diagrams are completely closed,” says Jun Chié, marketing manager for Agilent’s digital-debug solutions prod-uct line. “As signals come through on the transmit side, we have to perform equal-ization to open up the eye so that we can find the right probing points to capture samples and measure them.”
It’s the same story on the receive side of a link. Further, jitter components are more important at these signal speeds. For scope users in digital designs, the most popular measurement is jitter analysis. This and crosstalk are now more important on the digital side than they ever used to be on the analog side. These features are most popular in today’s scopes.
03.26.10 ElEctronic DEsign
INL
(LSB
)1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.0
DN
L (L
SB)
1.0
0.8
0.6
0.4
0.2
0
–0.2
–0.4
–0.6
–0.8
–1.00 65536 131072 196608 262143
Code
±10-V range ±10-V range
Code0 65536 131072 196608 262143
The integral nonlinearity (INL) and differential nonlinearity (DNL) of Linear Technology’s LTC2757 18-bit DAC do not exceed ±1 LSB.
ElEctronic DEsign Go To www.elecTronicdesiGn.com
Another emerging issue in the debug-ging of PCIe 3.0 links is signal degrada-tion in the transmission line. One can examine the signal out of the transmitter and verify that the eye pattern looks good and that jitter is within specification. But a PCIe signal can travel a maximum dis-tance within a system of 16 inches. When it arrives at the destination receiver chip, the eye pattern is closed once again.
“We haven’t tested much in the past for receivers, but now we have to do that,” says Chié. “There’s now a requirement to determine whether the receiver port can tolerate signals coming through.”
Agilent has been building up a complete test suite for PCIe 3.0. For the testing of PCIe 3.0 receiver ports, the company offers its N4903B J-BERT (see “Jitter-Tolerance BERT Targets Forwarded-, Embedded-Clock Designs” at www.elec-tronicdesign.com), which is used to inject jitter on the receive side of a PCIe link to simulate less than optimal conditions.
“The critical element on the transmit side is jitter and crosstalk,” explains Chié. “The N4903B J-BERT precisely injects known jitter components into the receiv-er. By doing so, we can check on the physi-cal level to see if the receiver can tolerate the jitter.”
The N4903B has been augmented by the release of the N4876A, a 2:1 multi-plexer that extends the J-BERT’s data rate to 28 Gbits/s. To further improve the N4903B’s utility for receive-side testing in USB 3.0 applications, Agilent has add-ed a second output channel that enables the instrument to support USB 3.0’s tri-level mode.
“To generate and stimulate the low-power mode in USB 3.0, we need to gen-erate three different signals. The two out-puts used in combination generate that third level,” says Chié.
The latest element in Agilent’s PCIe 3.0 test suite is its Digital Test Console, a complete and integrated x1 through x16 protocol analyzer and exerciser for the PCIe 3.0 protocol specification (see the figure).
“With an oscilloscope, you use a trigger point to trigger on a certain signal and capture it for analysis,” says Chié. “Pro-tocol analyzers have to behave like a real signal, equalizing it in real time and link-ing with the DUT (device under test) properly.”
To this end, the Digital Test Console features a proprietary Agilent ASIC that uses equalization snoop probe (ESP) technology for reliable data capture at 8 GT/s. The technology accounts for a wide spectrum of losses when probing at different points on the bus. It provides auto tuning to account for being plugged into any location in the channel. It also compensates automatically for probe cable losses. The result is a properly equalized signal at 8 GT/s with a usable eye diagram.
Additionally, the console incorporates a link training and status state machine (LTSSM) exerciser to validate new encoding and protocol state-machine designs. “Intel and other chip companies are still working on chips to generate PCIe 3.0 protocol schemes, and they’ll be coming this spring,” says Chié. Mean-while, developers of PCIe 3.0 bus systems need a way to emulate their DUTs to see if they comply with the specification. The Digital Test Console’s LTSSM exerciser delivers the means for doing so.
The Agilent Digital Test Console for PCIe 3.0 is available now, with an average system price of $100,000.
DaviD MaliniakAgilent technologies
www.agilent.com/find/pcie3
The latest element in Agilent’s PCIe 3.0 test suite is its Digital Test Console, a complete and integrated x1 through x16 protocol analyzer and exerciser for the PCIe 3.0 protocol specification.
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03.26.10 ElEctronic DEsign
ElEctric AndHybrid VEHiclE tEcHnologiEs cHArgE AHEAdTo meet conflicting requirements, EV and HEV manufacturers are struggling to adapt their cars to society’s needs—without a roadmap.
Tesla Model S Concept 2009 Studio Sedan Electric Photo: Copyright 2002-2007 Tesla Motors Inc.,
All Rights Reserved
ElEctronic DEsign Go To www.elecTronicdesiGn.com 27
Electric vehicle (EV) and hybrid electric vehicle (HEV) technologies are on a roll. Major automo-tive manufacturers around the world have unveiled or are on the verge of unveiling many such cars for the market, as all of these companies are eager to adopt the technology.
That’s not surprising, given governmental regulations and incentives. There’s also the need to reduce pollutants as well as our dependence on oil. And, the mass market is ready for a car that fits into the average consumer’s already squeezed budget.
Most experts say that such an inexpensive EV or HEV won’t be easy to achieve in the
short term, though. Plus, no one knows how the current electric grid infrastruc-ture will handle a significant increase in
automotive batteries that require dai-ly recharging. And, today’s most
advanced battery technologies are still quite costly.
Most projections for HEVs put their price tag around
$40,000 to $50,000, which is too high for mass-mar-
ket appeal. Some num-bers bandied about for EV end-user prices are over $100,000. Much of this is due to high battery pack costs, which are projected to range anywhere from several thou-sand dol lars to well over $10,000 each (see “Battery Challenges For Electric Vehicles” at www.electron-icdesign.com).
A study by Car-negie Mellon Uni-versity published by Energy Policy points out that HEVs like
the Chevy Volt from General Motors (GM)
will not save enough on gas to cover the higher
purchasing cost of the car. The study’s authors
conclude that the only way the Volt will save car owners
energy costs over the vehicle’s lifetime would be for both gasoline
RogeR AllAn | COntributing EDitOr [email protected]
and electricity costs to drop substantially from present levels, which is unlikely to happen.
Still, GM is putting its muscle behind the Chevy Volt, a plug-in series HEV slated for market introduction this year. Its internal combustion engine (ICE) is engaged to generate power for its electric-drive motor and its battery pack, not to power the wheels. In a
parallel hybrid vehicle, the electric motor is connected directly to the car’s ICE flywheel, allowing the clutchless powertrain to capture torque from both the electric motor and the ICE.
Besides GM, other major automakers are actively pursuing more energy-efficient HEV and EV technologies. One of the most notable HEVs is the Ford Fusion, which was introduced to the market last year. The Fusion can be driven at speeds up to 47 mph from solely its nickel-metal-hydride (NiMH) battery. After that, its gas-powered ICE kicks in. The popular Toyota Prius automatically starts its gas ICE at 25 mph.
A mild hybrid form In a typical HEV system, a gasoline-powered high-efficien-
cy ICE works with a rechargeable battery to power the car. The ICE’s output is also fed to a planetary gear power-split device, which in turn feeds an ac synchronous generator. The battery’s output is fed to a high-voltage dc-ac inverter. The inverter also accepts the generator’s output and feeds a permanent-magnet ac motor. A circuit controls the power (Fig. 1).
To satisfy legislative efficiency and environmental require-ments, automakers are grappling with many different forms of
relatively inexpensive HEV technologies. One such form that may soon take off rapidly is the belt alternator starter (BAS) system. Many call it a “mild” hybrid technology, though pure hybrid enthusiasts may cringe at this naming convention. A BAS system is considered a relatively low-cost approach to HEV technology that can provide some meaningful benefits.
General Motors is of advocate of BAS systems, which offer additional fuel savings and fewer tailpipe emissions at a slight-ly higher cost. Fuel savings of 5% to 10% are possible, mostly for city driving. Currently, most BAS systems are limited to being used with engines of about 3 liters and six cylinders or less. However, such engines are expected to see rapid growth in the next few years, making the adoption of BAS sys-tems easier.
In a BAS system, an electric motor replaces the conventional belt-driven al ternator and starter. When the engine is running, the electric motor acts as a genera-tor and charges a separate 36-V battery. When the engine has to be started, the motor starts its torque via the accessory belt for cranking (Fig. 2). The BAS system can perform engine stop/start, electro-mechanical launch assist, regenerative braking, high-power generation, and other func-tions without the need for large changes in a car’s design.
The actual implementation of the BAS system depends on the performance level sought in the car in terms of motor/generator efficiency and output-power capability. Some BAS systems, which might not include a starter motor, will have heavier loads while starting an engine, particularly in very cold weather. In general, BAS systems improve fuel economy by 10% to 15% (mostly in city driving) over conventional gas-powered ICE cars.
Although they provide only about half the benefit of a full HEV, BAS systems only cost automakers 15% to 20% more and don’t require significant engine-compartment and chas-sis modifications. Vehicles equipped with BAS systems don’t provide much of a benefit for highway driving, though. Nev-ertheless, their relative simplicity is causing a lot of optimism among automotive system designers.
“Within the next five to 10 years, every car will have a BAS system, because it will provide a lot of benefit for very little added cost and complexity,” says Ted Bohn, an electrical engi-neer at the Argonne National Laboratory’s Center for Trans-portation Research.
Regulations covering the use of the BAS concept in HEVs are under discussion in both the U.S. and Europe and will prob-
28 03.26.10 ElEctronic DEsign
EngineeringFeature
Drive wheels
Power splitdevice
Power circuit
Inverter
MotorEngine
Generator
Engine
Electric machine
Powerelectronics
36/42 V 12/14 V
Fossil, biomass,electrolysis, etc.
Transport
Transport
Transport
Power grid
Power grid
H2
Battery
Petroleum
GasolineHybrid
Fuel cell
Power grid
1. In a typical hybrid electric vehicle system, a high-efficiency gas-power inter-nal combustion engine and a recharge-able battery supply the power to drive the car’s wheels. (courtesy of Freescale
Semiconductor)
2. In a basic belt alternator starter (BAS) system, an electric motor replaces the car’s conventional belt-driven alterna-tor and starter. Modest levels of fuel efficiency are achieved as a result, mostly though for city driving. (courtesy
of “Technology Considerations for Belt Alternator
Starter Systems,” Delphi Corp., SAE International
World Congress)
3. This vehicle-to-grid technology concept allows users of electric, hybrid-electric, and alternative-fuel vehicles to sell back to the electric utility excess energy storage from their cars. It was developed at the University of Delaware.
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ably be finalized by 2015. Germany’s BMW has been adopting leading-edge implementations of the BAS concept in all of its HEVs.
The all-elecTric vehicle All-electric vehicles have been in devel-
opment for many years. EVs are generally propelled by electric motors powered by rechargeable NiMH and more recently by lithium-ion (Li-ion) batteries. Yet due to the battery technologies, EVs are expensive to produce commercially. Moreover, their driv-ing range and speed are limited.
Two decades ago, General Motors dem-onstrated the EV1, one of the company’s Impact concept electric cars, as an example of how GM would meet future “clean air” government mandates. In 2007, Miles Elec-tric Vehicles in the U.S. announced that it would bring the XS500, a highway-capable all-electric sedan, to the market by 2009. The car is not available yet. And despite the success of its high-end Roadster, Tesla Motors Inc. doesn’t expect its standard Model S sedan to hit the market—with a $49,900 base price—until 2012.
The success of EV technology has been more pronounced in overseas markets than the U.S. According to The Wall Street Journal, about 56,000 EVs are in use, most of which are lim-ited to low-speed driving and have limited range. Nissan’s Leaf operates from a Li-ion battery with a top speed of 90 mph and a range of 100 miles. Tesla’s Roadster also operates from a Li-ion battery and has an electronically limited top speed of 125 mph.
Tesla says the Roadster set the world distance record of 311 miles (501 km) for a production elec-tric car on a single charge on Oct. 27, 2009, during the Global Green Challenge in the outback of Aus-tralia. According to an independent analysis from the U.S. Environmental Protection Agency (EPA), the Roadster can travel 244 miles (393 km) on a single charge from its battery pack and can acceler-ate from 0 to 60 mph in 3.7 s. Tesla says the Roadster operates with an average efficiency of 92%.
The world’s most popular EV is the REVAi, also known as the G-Whiz, made by India’s REVA Elec-tric Car Co. The car is used in 24 countries across Europe, Asia, and Central America. It was launched in the United Kingdom in 2001.
Another EV in the works, the Mini E from BMW, is being assembled in the United Kingdom. Its Li-ion battery pack provides enough power for a 150-mile range. It uses a transversely mounted 204-hp-torque electric motor mated to a single-stage helical gear-box. It can go from 0 to 60 mph in 8.4 s, and its top speed is 95 mph.
One aspect of plug-in EV (PEV) technology that makes for a new business model: selling a PEV’s
stored energy back to the electric-grid utility during charging. Delaware is set to become the first U.S. state to allow elec-tric-car owners to charge PEVs at night
when electricity rates are low. They can then sell back excess stored electricity during the
day at a profit.To take advantage of this new business
model, GE and Juice Technologies announced a joint development agreement to create intel-ligent PEV charging devices for U.S. and global markets. The chargers integrate GE’s smart meters with Juice Technologies’ Plug Smart engine to help customers charge their cars during low-demand and lower-cost time periods.
“Our smart charging system and advanced technology have been in development over the past two years,” says Rich Housh, CEO
of Juice Technologies. “We’ve collaborated with utilities and Ohio State University’s Center for Automotive Research to develop the right solution for both utilities and consumers, and our collaboration with GE gives us the expertise we need to bring our solutions to market.”
The University of Delaware has already developed a vehi-cle-to-grid (V2G) technology (Fig. 3). The enabling technol-ogy has been licensed to AutoPort Inc., which has retrofitted a few test PEVs for the state government of Delaware and plans
30 03.26.10 ElEctronic DEsign
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4. Michelin’s active wheel concept involves putting a pair of electric motors in a wheel hub. One spins the wheel and transmits power to the ground, and the other acts as an active suspension system. The system can be used on electric cars powered by batter-ies or fuel cells and eliminates the need for any grearbox, clutch, transmission shaft, universal joint, or anti-roll bar.
5. Freescale Semiconductor’s 32-bit dual-core MPC5644XL Leopold processor is designed to meet safety-critical automotive requriements. It was co-developed with STMicroelectronics.
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to have 100 more such vehicles on the road within the next 15 months. The converted vehicles will make use of an electric-drive system called the eBox, which is manufactured to the V2G specifications by AC Propulsion Co. Initially, the Toyota Scion EV will use such eBoxes.
For those PEV drivers concerned about the hassle of hav-ing to plug in their vehicle’s batteries for recharging, Evatran LLC’s “hands-free” technology simplifies matters. Its patented Plugless Power concept is a dual-component system based on inductive charging. Its vehicle adapter, which can be attached to any car, inductively links up with a basestation located at a Plugless Power station.
Evatran is launching the proximity charging system in field trials using pre-production units in and around the company’s location in Wytheville, Va. The trial involves three Whip EVs from Wheego Electric Cars Inc., a Current EV from Electric City Motors, and a ZENN EV from ZENN Motor Co. Eva-tran’s parent company is MTC Transformers.
The acTive wheel concepT A couple of years ago, Michelin Tire Co. suggested pro-
pelling cars by putting a motor in one or more of their tires, improving fuel efficiency and reducing carbon-dioxide (CO2)
emissions. Michelin showcased the latest generation of this technology, known as the active wheel, on the Volage electric roadster from Monaco’s Venturi at this year’s North American Auto Show (Fig. 4).
The concept is basically a standard wheel that houses a pair of electric motors. One of these motors spins the wheel and transmits power to the ground. The other motor acts as an active suspension system to improve comfort, handling, and stability. The system can be used on electric cars powered by batteries or fuel cells. It also eliminates the need for any grearbox, clutch, transmission shaft, universal joint, or anti-roll bar.
The active wheel’s compact drive motor and integrated suspension system allow for standard disc brakes to be fitted between the motors. This means a single wheel can house all needed braking, drive, and suspension components.
Palmer Labs is trying to commercialize a retrofit kit that can transform existing cars into HEVs by placing an electric motor inside each of their four wheels. The Hybrid Retrofit Kit was developed by former IBM researcher Charles Perry, who has partnered with the Tennessee Technological University, which will build a working prototype.
“Our approach is different in that we don’t need to modify anything in existing vehicles to turn them into hybrids,” Perry
03.26.10 ElEctronic DEsign32
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says. The Retrofit Kit is installed in the space between the wheel’s brake mechanism and the hub.
Control and power opportunities Given the many aspects and complexity of HEV, EV, and
PEV designs and relevant safety and energy requirements, semiconductor IC manufacturers perceive many opportunities to supply necessary control and power IC components.
“There’s a need for ICs to handle high-voltage, battery, charging, and electric-motor management and control,” says Cherif Assad, power and hybrid segment manager for Free-scale Semiconductor. “At each level, there will be a require-ment for a microcontroller. I believe that this will lead to the use of multicore processing.”
An example of this is Freescale Semiconductor’s MPC5644XL single-chip dual-core Leopold 32-bit microcon-troller, co-developed with STMicroelectronics (ST’s part num-ber is SPC56EL) for safety-critical automotive systems (Fig. 5). This complex device is designed to specifically address the safety requirements of the International Electrotechnical Commission’s 61508 standard and the International Standards Organization’s 26262 standard. It is based on Freescale Semi-conductor’s Power Architecture.
Rechargeable Li-ion batteries in HEVs, EVs, and PEVs are bringing in the need for battery monitoring and management (see “Li-ion Suppliers Try To Find The Right Chemistry With Car Buyers” at www.electronicdesign.com). This is necessary to ensure that all the cells in the battery are at the same voltage level prior to charging them, enabling accurate measurement data and cell balancing. The more information that is known about a battery’s power status, the more accurately one can pre-dict mileage. Battery management involves sensors, an analog-to-digital converter (ADC), and a microcontroller.
“In a multicell environment like that of a Li-ion battery pack, each cell has its own impedance and discharge characteristics, requiring sophisticated battery management. This extends the battery’s lifetime and the application’s runtime,” explains Mat-thew Borne, marketing manager in Texas Instruments’ power management unit and a member of TI’s C2000 team.
The C2000 is a high-performance 32-bit microcontroller (see “Texas Instruments controlSUITE Streamlines Motor Control Development” at www.electronicdesign.com). The C2000 team develops the algorithms for this type of battery management, as well as for power conversion and electric motor control. Many of the functions needed for precision bat-tery management and control are available from TI.
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TechnologyReport
03.26.10 ELECTRONIC DESIGN
LOU FRENZEL | COMMUNICATIONS EDITOR [email protected]
Network everything. That seems to be the trend in wireless as in all other communications tech-nologies. It’s difficult to identify any segment of electronics today that isn’t networked.
Local-area networks (LANs), personal-area networks (PANs), metro-area networks (MANs),
wide-area networks (WANs), the Internet, and the forthcoming Smart Grid all envelop us. And now a newer form of network is finally being widely deployed: the wireless sensor network (WSN) or, more precisely, wireless sensor and actuator networks (WSANs).
Both have been discussed extensively over the years and have been the subject of intensive research and development in univer-sity, military, and other research labs around the globe. It’s only now that we’re beginning to see the many useful possibilities, especially for the home-area network (HAN) that is going to be the core of the coming Smart Grid rollout.
Here’s what you need to know to take advantage of the latest wireless technologies in networking sensors and/or actuators.
CUT THE ILINKS TO YOUR SENSOR/ACTUATOR NETWORKS
etwork everything. That seems to be the trend in wireless as in all other communications tech-nologies. It’s difficult to identify any segment of electronics today that isn’t networked.
Local-area networks (LANs), personal-area networks (PANs), metro-area networks (MANs),
wide-area networks (WANs), the Internet, and the forthcoming Smart Grid all envelop us. And now a newer form of network is finally being widely deployed: the wireless sensor network (WSN) or, more precisely, wireless sensor and actuator networks
Both have been discussed extensively over the years and have been the subject of intensive research and development in univer-sity, military, and other research labs around the globe. It’s only now that we’re beginning to see the many useful possibilities, especially for the home-area network (HAN) that is going to be
Here’s what you need to know to take advantage of the latest wireless technologies in networking
CUT THE CUT THE CUT THE
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 35
WSANS DEFINEDA WSAN is a network
infrastructure that can sense its environment and react to specific
conditions of interest. It can moni-tor and control its environment with-
in its design capability. In many cases, it also can be set up to do some amount
of relevant computing. Many if not most WSANs are sense-
only networks. As a result, they’re called WSNs since they don’t involve controlling
functions within the environment. Some organizations refer to WSANs as wireless data acquisition or wireless telemetry. In these traditional functions, a major consid-eration is the recording and storage of the
collected data along with some analysis and display.
The network is made up of miniatur-ized nodes that consist of a sensor and its
related signal conditioning circuitry, a radio transceiver, some memory, and an embedded controller. The battery-powered unit is designed for very low
power consumption. These nodes can communicate with a central master con-trol point or with one another. A central controller or master node
with more extensive computing capability collects the information gathered by the sen-
sors and passes it along to some data center, usually through the connection to some other network like a company LAN or the Internet. The nodes are usually stationary but could be mobile. They also could be location-aware.
The nodes can monitor any physical characteristic for which an electronic sensor has been developed. The most common sensors are for temperature, pressure, light, sound, motion, humidity, and pollutants. Some WSNs can accommodate video input. As for control, the actuators may be lights, motors, fans, valves, relays, solenoids, pumps, appliances, or any other elec-tromechanical device.
A primary consideration of any WSAN is network topology. The two most widely used topologies are the star and mesh. The star network, also called multipoint-to-point (MPP), has a central master control node with computing power with multiple nodes (Fig. 1a). The nodes only talk to the controller rather than to one another.
In the mesh network, the nodes communicate with one another and offer a multi-hop capability back to a central col-lection point (Fig. 1b). In the mesh topology, the nodes report the status of their own sensors and act as relay points that sim-ply retransmit the data from nearby nodes.
The method allows sensors to be spread over a wider range than the single-node range. It also provides a form of network reliability. If a node’s battery dies or its signals are blocked, the network automatically and dynamically reroutes the data
through other adjacent nodes. WSANs can use other hybrid forms of network topologies as required as well. These may be a mix of tree, star, or mesh.
THE HARDWARE AND SOFTWAREThe main hardware element is the node. Nodes also are
known as “motes,” a mote being a tiny particle, such as dust. The sometimes stated goal of WSNs is to make the nodes that small. Nodes as small as a dime or quarter are fairly common, but that’s about as small as they get today.
The node’s basic architecture has an embedded controller and memory at its core (Fig. 2). The controller hosts a small operating system that runs the networking software and man-ages the I/O (see “Interfacing The Sensor” at www.electron-icdesign.com). The sensor, its signal conditioning, and the analog-to-digital converter (ADC) comprise another major section, while the radio transceiver with its antenna form yet another. In some cases, there may be multiple sensors and related circuitry.
An essential part of the node is the power-management portion. The power source is a battery, of course, but power management is critical to long battery life. Some of this control may be handled by the MCU.
The software consists of a small specialized operating sys-tem (OS) and all the related drivers and applications programs. More than a dozen OSs are associated with WSANs. A popular one is TinyOS and its related programming language called network embedded system C (nesC), an extension to C. TinyOS is an event-driven OS that calls event drivers for specific tasks as opposed to a threading OS. Other software is related to the sensor such as the communications media access controller (MAC), the protocol and networking functions, and any appli-cation software that performs related data manipulation.
RADIO TECHNOLOGY AND STANDARDSMany existing wireless networking technologies are suitable
for use in WSANs (see “Important Wireless Facts To Keep In Mind,” p. 38). The most widely used are IEEE 802.15.4, ZigBee, Bluetooth, Z-Wave, and 802.11 Wi-Fi. There are also other proprietary technologies including RFID.
If any one technology dominates the WSAN arena, it’s IEEE 802.15.4 and the enhanced version known as ZigBee. The IEEE standard defines the physical layer (PHY) and MAC layer of the system while ZigBee adds the upper network and applications layers. This wireless technology is based on direct-sequence spread-spectrum (DSSS) and uses the carrier sense multiple access with collision avoidance (CSMA/CA) channel access method.
The standard defines several different modulation methods based on phase-shift keying (PSK). It also defines three pri-mary operating bands using unlicensed spectrum. First is the 868.3-MHz frequency in which a maximum data rate of 20 kbits/s can be achieved with raised-cosine binary phase-shift keying (BPSK) modulation. The maximum range is about 1 km. This version is used primarily in Europe.
In the U.S., the 902- to 928-MHz band is often used. The standard defines 10 channels, each 600 kHz in width and
WSANS DEFINEDA WSAN is a network
infrastructure that can sense its environment and react to specific
conditions of interest. It can moni-tor and control its environment with-
in its design capability. In many cases, it also can be set up to do some amount
of relevant computing. Many if not most WSANs are sense-
only networks. As a result, they’re called WSNs since they don’t involve controlling
functions within the environment. Some organizations refer to WSANs as wireless data acquisition or wireless telemetry. In these traditional functions, a major consid-eration is the recording and storage of the
collected data along with some analysis and display.
The network is made up of miniatur-ized nodes that consist of a sensor and its
related signal conditioning circuitry, a radio transceiver, some memory, and an embedded controller. The battery-powered unit is designed for very low
power consumption. These nodes can communicate with a central master con-trol point or with one another. A central controller or master node
with more extensive computing capability collects the information gathered by the sen-
sors and passes it along to some data center, usually through the connection to some other network like a company LAN or the Internet. The nodes are usually stationary but could be mobile. They also could be location-aware.
spaced 2 MHz apart. Again, the raised-cosine BPSK modula-tion is used. A maximum data rate of 40 kbits/s can be achieved. Range is about 1 km.
The most often used version of the IEEE 802.15.4 standard operates in the 2.4- to 2.4835-GHz range. The standard defines 16 channels, with each one 3 MHz wide and spaced 5 MHz apart. The modulation is offset quadrature PSK (O-QPSK), which permits a data rate to 250 kbits/s. The maximum range is about 220 m.
The protocol is relatively complex but has an addressing scheme with a 64-bit address so many nodes can be accom-modated. The maximum packet size is 127 bytes. Data is transmitted in short packets in a burst mode so transmit time is minimal, saving considerable power. Most radios using this standard consume very little power thanks to the very short transmit duty cycle.
ZigBee adds more layers to the basic protocol stack. This allows a wide range of topologies and applications to be sup-ported, including mesh, which may be the most widely used form in WSANs.
An interesting variation of the 802.15.4 standard is called “6lopan,” which means IPv6 over low-power wireless PANs. With 6lopan, extreme mesh networking over the Internet for the Smart Grid movement is a possibility. The Internet Engi-neering Task Force (IETF), an organization that develops and maintains Internet standards, is developing 61opan. The stan-dard is designated as IETF RFC 4944 and 4919.
More and more devices are connected to the Internet, and each needs an Internet Protocol (IP) address. That’s where IPv6 comes in. The IP networking standard has a 128-bit address, unlike the 32-bit address of the older IPv4 standard. It permits IP packets to be carried over low-speed WSANs.
The maximum packet size of the 802.15.4 standard is 127 bytes. The RFC 4944 standard allows the WSAN to carry up to 1280 bytes as required by IPv6. It does this by using a form of encapsulation and header compression. The standard is still a work in progress, but a final version is expected this year.
Bluetooth is another potential radio technology for WSANs. It is an ad-hoc PAN that also operates in the 2.4- to 2.4835-GHz band. It uses frequency-hopping spread-spectrum (FHSS)
technology. The hop rate is 1600 hops per second over 79 fre-quencies spaced 1 MHz apart. Maximum data rate is 1 Mbit/s with a throughput of 723 kbits/s. Modulation is Gaussian frequency-shift keying (GFSK).
Yet another faster option afforded by Bluetooth V. 2.1, enhanced data rate (EDR), uses different modulation methods to achieve a 2- or 3-Mbit/s data rate. The most common range is about 10 m with a typical 4-dBm power amplifier (PA). An external PA with 20-dBm power output is defined to extend the range to almost 100 m.
An important feature for WSANs is the ability of Bluetooth nodes to form piconets, which comprise links to seven other Bluetooth devices. Piconets can then be interconnected to form scatter nets for a greater number of nodes as the applica-tion requires. An ultra-low-power version of Bluetooth is also available to extend battery life.
ZigBee/802.15.4 and Bluetooth radios are most common when distances between nodes are less than about 10 m. If the nodes are more widely dispersed, an alternative is the popular IEEE WLAN 802.11 (Wi-Fi) standard. Maximum range is about 100 m if the nodes are in the clear.
Another advantage of Wi-Fi is its higher data rate potential of 11 Mbits/s for .11b, 54 Mbits/s for .11a/g, and over 300 Mbits/s for .11n. However, it’s rare to find an application requiring the .11n data rate as sensor sampling is extremely infrequent. Thus, the low data rates defined by ZigBee and Bluetooth are more than adequate.
Furthermore, Wi-Fi consumes much more power than either ZigBee or Bluetooth, making it unfriendly to long battery life requirements. Another disadvantage of Wi-Fi is the lack of
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RAM Flash
EmbeddedController
SignalConditioning ADC
RadioTransceiver
PowerManagement
Battery
Sensor
Antenna
2. A sensor node contains an embedded microcontroller running an OS and the application program. The sensor input is conditioned and digitized. The transceiver establishes the communications link with the network. A power-management component makes the most of the limited battery power.
To LANor WAN
Controller
Sensornode
(a) (b)
To LANor WAN
Node
1. The most common WSAN network topologies are the star (a) and mesh (b). The star topology is used when the distances from nodes to controller are relatively short. Mesh is used over a wider range since most nodes can relay signals from adjacent nodes.
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 37
a defined mesh networking protocol, but that’s about to end. The IEEE Task Group recently approved a mesh networking standard (802.11s) that should be ratified later this year with products coming shortly. In general, Wi-Fi isn’t a widespread choice for WSANs. However, it’s most likely used as the link between the WSAN collection point and either a company LAN or the Internet.
There also is a mix of proprietary standards in the industrial, scientific, and medical (ISM) bands. One of the most wide-spread, known as Z-Wave, was designed for low-power, short-range sensor and actuator applications. It uses the unlicensed frequency of 908.42 MHz in the U.S. and can deliver a data rate of 9.6 kbits/s or 40 kbits/s using FSK. The protocol is opti-mized for mesh networking in WSANs.
Ano the r s t anda rd f rom EnOcean uses the 868-MHz or 315-MHz unlicensed band with a data rate to 125 kbits/s. Its maximum range is about 300 m, and it’s designed for ultra-low-power consumption and mesh networking. Crossbow Technol-ogy (now MEMSIC) has WSN modules that use 802.15.4/ZigBee but also a proprietary module using the 868/916-MHz frequencies with a data rate of 38.4 kbits/s.
Ultra-Wideband (UWB) has been used as the wireless link in WSANs. In its WiMedia orthogonal frequency-division multiplexing (OFDM) format, it consumes little power and has a very high data rate. For some applications it may be an alter-native to consider.
Many other wireless tech-nologies can be deployed in some applications. Two addi-tional examples are cellular networks and RFID. Embedded
cell-phone modules are widely available for what are called machine-to-machine (M2M) applications, in which sensors or actuators are interfaced to the radio module. The module then reports back to a monitor and control point via the cellular net-work. These modules can comprise a multipoint system but not a mesh network. The range is greater than 2 or 3 km, and the reliability is excellent.
Some systems may need to include RFID. The system would consist of multiple RFID readers near the objects that are wear-ing RFID tags. The readers can read many tags, but the range is only a few feet for a passive tag. Active tags that use a battery can have a range of up to a hundred feet depending upon the frequency of operation. The readers would be networked back to a central data collection place where the ID is made. Mesh or multipoint arrangements can be used.
WSAN APPLICATIONSThe number of potential applications for WSANs is astro-
nomical. But as it turns out, there are a few widely imple-mented systems.
• Building automation: WSANs are used to monitor lights, temperature, humidity, and other conditions for HVAC con-trol. They are also used to monitor motion, smoke, and envi-ronmental factors.
cell-phone modules are widely available for what are called machine-to-machine (M2M) applications, in which sensors or actuators are interfaced to the radio module. The module then reports back to a monitor and control point via the cellular net-work. These modules can comprise a multipoint system but not a mesh network. The range is greater than 2 or 3 km, and the reliability is excellent.
consist of multiple RFID readers near the objects that are wear-ing RFID tags. The readers can read many tags, but the range is only a few feet for a passive tag. Active tags that use a battery can have a range of up to a hundred feet depending upon the frequency of operation. The readers would be networked back
3. The Ember EM35x 802.15.4/ZigBee radio module is part of the development kit.
ZigBeehome-area
network(HAN)
Utilitynetwork
Electricmeter
Thermostat
HVAC system
Smartappliances
Gas meterWater meter
In-home display
LightingControls
Home automationsystem
4. The home-area network (HAN) is the main target for most WSANs today. The HAN wireless modules talk to the thermostat, electric meter, lights, appliances, and other items to be monitored and controlled. (courtesy
of Ember)
• Home automation and control: The primary use is in moni-toring temperature and humidity to control HVAC systems. WSANs can also monitor and control the energy usage of lights and appliances as part of a Smart Grid system.
• Weather monitoring: Sensors monitor all common weather conditions, collecting, storing, and transmitting data over a large area.
• Environmental monitoring: Sensors are used to make desired measurements of pollutants and other factors. Applications include detection of forest fires, floods, and earthquakes, as well as crop monitoring and watering.
• Industrial automation: Sensors monitor machines to determine usage, wear, maintenance, and serviceability. They also provide environmental monitoring for pollutants and abnormal conditions.
• Civil engineering: Sensors monitor the structural integrity of build-ings, bridges, and other structures. They also can monitor highways for traffic and road conditions.
• Medical and health care: Uses include patient monitoring, patient records, information sharing, and emergency communications.
• Logistics: WSANs are used to track items in warehouse storage, inventory control, and shipping and handling.
• Military: Uses include equipment location and tracking, battlefield monitoring and management, surveillance, and troop and weapon activity sensing.
• Security: WSANs have uses in presence, motion, and break-in detection as well as in video surveillance.
• Robotics and remote vehicles: WSANs can monitor all functions, surroundings, and controlling operations.
REPRESENTATIVE RECENT PRODUCTSWith dozens of both component and end-equipment sources,
engineers have a rich environment to choose from when designing a WSAN. For example, sources of 802.15.4/ZigBee equipment abound. Chips are available from Freescale, Texas Instruments, and Microchip Technologies.
Ember is another long-time participant in the field. Its latest Zig-Bee systems-on-a-chip (SoCs), the EM351 and EM357, include a full 802.15.4 2.4-GHz radio with ZigBee protocol stack. They also include a 32-bit ARM Cortex M3 processor to run the application. The EM351 has 128 kbytes of flash, while the EM357 offers 192 kbytes.
With a power output in the +3- to +8-dBm range and a receiver sensitivity of –102 dBm, the link budget is exceptional. Power consumption is low. With good power management, battery life can last many years. Users can obtain a development kit radio module using the EM35x (Fig. 3). One of the most common appli-cations for the Ember modules is in HANs (Fig. 4).
38 03.26.10 ELECTRONIC DESIGN
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WHEN SELECTING AND applying wireless modules in a wireless sensor and actua-tor network (WSAN), keep some of these facts in mind:
• The range of each module is a function of trans-mitted power, antenna gain, and wavelength (λ). The greater the transmit power (Pt), transmit and receive antenna gains (Gt and Gr), and wavelength (λ), the higher the received power (Pr) for a given distance (d) or range. This is summed up in the basic Friis formula:
Pr = PtGtGrλ2 /16π2λ2
The key takeaway is that the range is greater at longer wavelengths or low frequencies.
• Path loss in dB can be estimated with the modified expression:
dB = (1/GrGt)(4πd/λ)2
Another path loss estimator is:
dB = 32.4 + 20log(f) + 20log(d) where d is in km and f is in MHz.
• For the popular 2.4-GHz band, the path loss can be estimated with:
dB = 40.2 + 20log(D) with d in meters and ≤ 8 m
dB = 58.3 + 33log(d/8) for d ≥ 8 m
For all these path loss calculations, assume a clear line-of-sight (LOS) path.
• Obstacles like walls, floors, and trees add from 3 to 18 dB to the path losses, depending upon the wall and floor composition and the frequency of opera-tion. There is less loss at the lower frequencies. Brick and concrete have a higher attenuation than wood frame and sheet rock.
• At higher frequencies (2.4 GHz and beyond), reflec-tions and multipath become a problem if there are many nearby objects.
• Lower frequencies are generally preferred but require longer antennas or less efficient shorter antennas.
IMPORTANT WIRELESS IMPORTANT WIRELESS IMPORTANT WIRELESS FACTS TO KEEP IN MINDFACTS TO KEEP IN MIND
full 802.15.4 2.4-GHz radio with ZigBee protocol stack. They also include a 32-bit ARM Cortex M3 processor to run the application. The EM351 has 128 kbytes of flash, while the EM357 offers
With a power output in the +3- to +8-dBm range and a receiver sensitivity of –102 dBm, the link budget is exceptional. Power consumption is low. With good power management, battery life can last many years. Users can obtain a development kit radio module using the
. One of
5. The EnOcean radio modules for the 868-MHz band include a wire antenna.
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An interesting proprietary technology comes from EnOcean, whose Dolphin platform was designed for building auto-mation, home networks, and other sys-tems requiring very low power consump-tion and long life. The radio technology uses the 868-MHz band or the 315-MHz band. Even at low power, practical ranges are possible because of the low-fre-quency design.
Typical range within buildings is 30 m, but up to 300 m can be achieved over a free-space path. The data rate is 125 kbits/s, transmission may be one-way or two-way, and a unique 32-bit ID is used. The basic radio modules (Fig. 5) can operate with-out batteries using three types of energy harvesting:
• Mechanical: A magnet and coil inside a light switch generates power each time the switch is actuated. A self-powered light switch generates power and converts it to a radio signal every time the light switch is pressed.
• Solar: Most of the sensors (occupancy/motion, door/window, photo/light) are powered by collecting and storing energy from light. When combined with smart and ultra-low-power radios, sensors can operate with just 40 lux of ambient light. (In a typical indoor setting, more than 400 lux is usually avail-able.) The energy is stored in capacitors, which allows the sensors to do their job even when they’re in complete dark-ness for days.
• Thermal: When energy is needed to control sensors residing in permanent darkness, temperature differentials can generate energy for wireless communications. This is the newest form of micro energy harvesting, and it’s enabling self-powered controls such as valve actuators.
The Z-Wave products from Sigma Designs (formerly Zen-sys) are also unique. Using a mesh architecture, the nodes can be used with switches, lights, thermostats, and appliance con-trollers. They are also compatible with some of the Advanced Metering Infrastructure (AMI) electric meters being installed as part of the Smart Grid initiative to manage and control energy usage in the home.
The Z-Wave modules operate on 908.42 MHz in the U.S. using FSK modulation and can deliver a data rate of 9.6 or 40 kbits/s as needed. The Z-Wave ZM3102N’s 8051 controller runs the protocol and mesh network. With low power, battery life can be very long.
Dozens of companies use the Z-Wave modules for home monitoring and control, such as the Z-Wave-enabled Trane thermostat (Fig. 6). These and other end products are widely available in Lowe’s and Radio Shack stores.
Microchip Technology has a line of 802.15.4/ZigBee prod-ucts as well as some low-power ISM-band radio chips. But the company’s recent acquisition of ZeroG Wireless included a WSAN product called Wi-Fi I/O. The primary product is the ZG2100, an 802.11b Wi-Fi module designed for very low power consumption.
The ZG2100 runs the standard .11b protocol but speed is limited to 1 or 2 Mbits/s. It is Wi-Fi certified and runs the
available WEP, WPA, or WPA2 security. Also, it uses a serial peripheral interface (SPI) and is only 21 by 31 by 3.7 mm. If you need the speed as well as low power consumption, this is an attractive option. And, it’s very easy to incorporate into existing LANs.
One of the more interesting new products to address the WSAN market is Silicon Laboratories’ Si10xx wireless MCU family. This series of devices packages an ISM-band radio along with an 8051 controller, giving designers multiple ways to design their product. A unique power system with an effi-cient low-dropout (LDO) regulator and dc-dc converter adds a new dimension to the need for low power consumption and super-long battery life.
The top-of-the-line device is the Si1000, which features a 25-MIPS 8051 with 64 kbytes of flash and the usual mix of I/Os and interfaces as well as timers. A 10- or 12-bit ADC is also on chip in addition to a temperature sensor and voltage comparators.
The radio is a real gem. It can be programmed to operate over the 240- to 960-MHz range, which covers the standard ISM frequencies of 315, 433, or 868 MHz. Modulation is FSK or GFSK with a data rate to 250 kbits/s. The receive sensitivity is an amazing –121 dBm while the programmable transmit power can be up to 20 dBm for a net link budget of 141 dB. This can extend range up to 3 km over a clear line-of-sight path.
The big news is the internal LDO and dc-dc converter with their programmable power-management unit, which keeps total power consumption low under all possible operating con-ditions. The EZMac software lets designers create a protocol for point-to-point, multipoint-to-point, and simple mesh net-works. The Wireless M-Bus software, also available, is widely used for metering in Europe. Availability is scheduled for the second quarter of this year.
DESIGN ISSUESThe main design issues for WSANs vary depending on the
applications, but three stand out: power consumption, ease of network modifications, and security.
Because the nodes are battery operated, long life is essential to minimize the time, the cost, and the inconvenience of chang-ing batteries. Some of the newer modules offer a battery life of years, though most are considerably less. Look for products that transmit data in packets at high speed to minimize trans-mitter on time. A short transmit duty cycle is essential to long battery life.
Next, how easy is it to remove modules or add modules? The most desirable situation is one in which the system is ad hoc and modules may come and go without any reprogramming or intermediation.
Finally, security may be an issue in your application. Most standards provide some level of security, but you have to verify that it is sufficient for your application.
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6. Trane thermostats include Z-Wave wireless modules for communicating with the home-area network that is part of a Smart Grid connection to monitor, control, and conserve energy.
available WEP, WPA, or WPA2 security.
6. Trane thermostats include Z-Wave wireless modules for communicating with the home-area network that is part of a Smart Grid connection to monitor, control, and conserve energy.
TECHNOLOGYSeSSion: The Smart GridThe Smart Grid promises to be the next driver for innovation in electronics and jobs for design engineers. This session will examine the implications of the Smart Grid for a range of stakeholders from utilities to consumers, along with the reasons that its penetration into business and daily life are unstoppable.PreSenter: Erich Gunther, EnerNexModerator: Don Tuite
BATTERIESSeSSion: What Kind Of Batteries Are Out There, And What Are They Good For?Matching the battery type to the application has become increasingly challenging as battery makers have pushed old frontiers backward. Are lithium batteries inevitably flame-throwers? Is silver too expensive for anything but military applications? How much energy can you really get from a printed battery? Find out here.PreSenter: Dr. Robin Tichy, Micro Power ElectronicsModerator: Sam Davis
DEVICESSeSSion: Understanding Gallium-Nitride MOSFETsGallium-nitride MOSFETs promise to be a game changer in the power space. Will the reality measure up to the hype? When will these super MOSFETs be ready for prime time? And, what do designers need to know about this new technology to use these devices effectively in their new designs?PreSenter: Alex Lidow, EPCModerator: Don Tuite
PACKAGINGSeSSion: Packaging Power SuppliesWhat are the important design considerations for packaging: EMC, thermal management, physical size, power consumption, etc.?PreSenterS: Dr. Avram Bar-Cohen and Professor McCluskey, University of MarylandModerator: Sam Davis
MOTOR CONTROLSeSSion: Controlling Permanent Magnet Synchronous MotorsAs the cost of processor-based motor control continues to drop, many applications can now affordably take advantage of the many benefits of PMSM topologies, such as increased efficiency and smoother operation. This session covers the basic operation of PMSMs and how they can be controlled using field-oriented control (FOC) with both sensored and sensorless techniques. IPM motors also will be presented, with a discussion on how their saliency affects sensorless FOC.PreSenter: Poul Erik Dokkedal, International RectifierModerator: Don Tuite
THERMAL MANAGEMENTSeSSion: Thermal Management Rejecting heat from electronic system components to ambient air can be a challenge. Accepting this challenge are heatsinks, heat exchangers, heat pipes, thermal interface materials, and forced air cooling. In addition, several types of thermally enhanced circuit boards aid the cooling process. Backing up these approaches, computational fluid dynamics (CFD) software provides a picture of the effectiveness of the cooling technique.PreSenter: Patrick Loney, ConsultantModerator: Sam Davis
SESSIONS
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03.26.10 ELECTRONIC DESIGN
CHARACTERIZE YOUR LEDS FOR ALMOST ALL OCCASIONS
As the name implies, a light-emitting diode (LED) is a semiconductor (diode) that, when forward biased via a voltage/current source, radiates visible light of a particular color (wavelength) and at a brightness level determined by its parameters and by the parameters of its power source. The first LED, attributed to General Electric researcher
Nicholas Holonyak circa 1962, was a fairly low-power device capable of producing low-intensity red light, but with a hefty price tag.
Breaking price barriers by 1968, the Monsanto Company and Hewlett Packard began mass production of red LEDs in 1968 using cost-effective gallium arsenide phosphide (GaAsP). Initially, red LEDs found fruitful employment as replacements for incandescent and neon function indicators such as on/off/standby lights and shortly after as segments in alphanumeric displays.
Evolving on an upward flight path not unexpectedly similar to television, LEDs are now available in a wide range of colors as well as single units capable of producing multiple colors, brightness, and power levels and in various unique package types. Myriad devices also can deliver non-visible light from the infra-red (IR) and ultraviolet (UV) ends of the spectrum.
Naturally, the rapid evolution of device types often leads to revolutionary applica-tions. No longer just performing as indicators, visible-spectrum LEDs are supplanting incandescent and fluorescent components in almost all lighting (practical and decora-tive) and signage applications because of their low-power/low-heat characteristics, significantly longer lifespan, and lower cost in both long and short runs.
Over the years, LEDs also have wandered into esoteric, non-lighting designs such as wave shapers in audio circuits (Fig. 1). IR and UV LEDs are proving to be viable in numerous appli-cations ranging from remote control to medical as well.
First, you need to know the different types of LEDs. Then, you need to know your application.
+
–
Generic red LEDs replace R2 in feedback loop
Opamp
InR1
R3
R4Out
1. In certain preamplifier configurations, generic red LEDs were sometimes placed in the feedback loop of an op amp to incur soft distortion similar to that of vacuum tubes.
CHARACTERIZEYOUR LEDALMOST ALL OCCASIONS
ANicholas Holonyak circa 1962, was a fairly low-power device capable of producing low-intensity red light, but with a hefty price tag.
Breaking price barriers by 1968, the Monsanto Company and Hewlett Packard began mass production of red LEDs in 1968 using cost-effective gallium arsenide phosphide (GaAsP). Initially, red LEDs found fruitful employment as replacements for incandescent and neon function indicators such as on/off/standby lights and shortly after as segments in alphanumeric displays.
Evolving on an upward flight path not unexpectedly similar to television, LEDs are now available in a wide range of colors as well as single units capable of producing multiple colors, brightness, and power levels and in various unique package types. Myriad devices also can deliver non-visible light from the infra-red (IR) and ultraviolet (UV) ends of the spectrum.
Naturally, the rapid evolution of device types often leads to revolutionary applica-tions. No longer just performing as indicators, visible-spectrum LEDs are supplanting incandescent and fluorescent components in almost all lighting (practical and decora-tive) and signage applications because of their low-power/low-heat characteristics, significantly longer lifespan, and lower cost in both long and short runs.
Over the years, LEDs also have wandered into esoteric, non-lighting designs such as wave shapers in audio circuits (Fig. 1). IR and UV LEDs are proving to be viable in numerous appli-cations ranging from remote control to medical as well.
First, you need to know the different types of LEDs. Then, you need to know your application.
1. In certain preamplifier configurations, generic red LEDs were sometimes placed in the feedback loop of an op amp to incur soft distortion similar to that of vacuum tubes.
CHARACTERIZEYOUR LEDALMOST ALL OCCASIONS
MAT DIRJISH | COMPONENTS EDITOR [email protected]
EngineeringEssentials
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 43
VISIBLE LIGHT LEDS
Today, LEDs are available in a wide variety of sizes, colors, shapes, and types with diverse electrical specs and parameters, in standard and unique packages, and all with varying price points. Each addresses one or more applications such as gener-al lighting, flash functions in digital cameras, LCD backlight-ing, and, getting back to basics, indicators, plus many more.
Usually made from aluminium gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP), aluminium gallium indium phosphide (AlGaInP), or gallium phosphide (GaP), generic, low-cost moderate-power LEDs for basic indication chores, prototyp-ing, and hobbyist interests are still around and plentiful (Fig. 2). With red still being the most common color, these devices are also available in green, orange, yellow, and blue and operate with a forward voltage drop in the realm of 1 to 2 V with a forward current around 20 mA.
In addition to the standalone device, other general-purpose LEDs include alphanumeric displays, bi-color and tri-color LEDs, and red-green-blue (RGB) components and flashing LEDs. For no-frills designs with few power and size restric-tions, one of these should fit the bill and budget.
Primarily targeting lighting applications, be they industri-al, commercial, residential, or decorative, high-power LEDs (HPLEDs) and HPLED modules are rapidly replacing tradi-tional incandescent and fluorescent fixtures, especially as their cost recedes. These LED alternatives are notable for their long life of more than 50,000 hours, exceeding the 10,000 hours or more for fluorescents and 1000 hours or more for incandescent bulbs even under inordinate on/off cycling. Power efficiency is an equally desirable benefit with the HPLEDs delivering brightness levels beyond 105 lumens/W.
One example of the LED supplanting inef-ficient technologies is the XLamp MPL EasyWhite LED from Cree (Fig. 3). Promising better per-formance, color consistency, and lumen density than conventional light sources, it’s optimized for direc-tional lighting applications, including PAR-style or BR-style light bulbs. With attention to system design, it can deliver the
same light output as a 3000-K, 75-W equivalent BR-30 light bulb while consuming 78% less energy than incan-descent technology.
In a package measur-ing 12 by 13 mm, the MPL EasyWhite delivers up to 1500 lumens at 250 mA. Additionally, it’s available in 2700-K, 3000-K, 3500-K, and 4000-K color tem-peratures that are in the cen-ter of the respective ANSI C78.377-2008 color bins. Naturally, when character-
izing LED packages for a particular lighting task, other viable options are out there.
One of the roadblocks to overall efficiency is that LEDs require a dc power source, which entails the use of power converters for many lighting applications. In addition to more parts, these converters need to be well designed, upping the cost of the LED topology.
Seoul Semiconductor may have this solved in part with its Acriche LED bulb, which operates directly from an ac power source. The 100-lumen/W Acriche light source specifies 25% greater efficiency than existing LED products (Fig. 4). Requir-ing no ac-dc converter, it generates less than one-tenth the car-bon emissions of an incandescent bulb, the company says.
LEDs in general run pretty cool. But when they’re grouped en masse for brighter lighting apps or restricted to heavily pop-ulated boards or extremely tight quarters, heat does become a concern. Also putting its fingers in the LED pie, semiconductor company Vishay offers the VLMW321xx and VLMW322xx surface-mount, white LED families in thermally enhanced PLCC-4 packages (Fig. 5). For wider pin compatibility with similar devices, the VLMW321xx has three anodes and one cathode while the VLMW322xx LEDs offer three cathodes and one anode.
2. General-purpose, low-cost LEDs, usually requiring a 1-V forward voltage and a quiescent current of 20 mA, are available in a range of colors, sizes, and shapes.
4. For efficient lighting applications, Seoul Semiconductor’s 100-lumen/W Acriche LED operates from an ac source, requiring no ac-dc
converter.
3. Housed in a 12- by 13-mm package, Cree’s XLamp MPL EasyWhite LED outputs as much as 1500 lumens at 250 mA.
GO TO WWW.ELECTRONICDESIGN.COM
brightness levels beyond 105 lumens/W.One example of the LED supplanting inef-
ficient technologies is the XLamp
light sources, it’s optimized for direc-tional lighting applications, including PAR-style or BR-style light bulbs. With attention to system design, it can deliver the
5. To beat heat issues, the Vishay VLMW321xx and VLMW322xx surface-mount white LEDs come in thermally enhanced PLCC-4 packages and deliver luminous intensities from 1400 to 3550 mcd.
The devices exhibit a thermal resistance down to 300 K/W and a power dissipation up to 200 mW. Groomed expressly for automotive applications, both families are AEC-Q101 qualified. Other shared features include a luminous intensity from 1400 to 3550 mcd, luminous flux from 7000 to 8900 mlm, a 60° angle of half-intensity, and a luminous intensity ratio per packing unit of less than 1.6.
InvIsIble lIghtYou can’t see it, but that doesn’t mean you can’t use it. IR
and UV LEDs operate at wavelengths above 750 nm and below 400 nm, respectively. These devices find gainful employment in remote control (TVs, home entertainment centers, etc.), communication, and optically isolated signal routing in medi-cal applications.
IR devices are generally made of GaAs or AlGaAs, while UV parts come in diamond, boron-nitride, aluminium-nitride, aluminium-gallium-nitride (AlGaN), and aluminium-gallium-indium nitride (AlGaInN) flavors. Some examples include the use of IR LEDs in the sensor bar of Nintendo’s Wii game sys-tem and UV LEDs for sterilization of certain bacteria, curing of adhesives, and plant synthesis.
Night photography is one of the many applications for IR LEDs. Enabling image capture in total darkness, LEDtronics offers IR LED lamps in 850-, 880-, and 940-nm wavelengths with industry-standard bases and several angles of emission (Fig. 6). The lamps resist ambient-light and electromagnetic interference (EMI) and are available in all standard domestic and international voltages.
Notably, the use of multiple LEDs allows the lamp to pro-vide adequate light even if one or more emitters fail. Other advantages include an average life span beyond 100,000 hours. In addition to the standalone device, other general-purpose LEDs include alphanumeric displays, bi- and tri-color LEDs, and RGB components and flashing LEDs.
Jumping to the other end of the spectrum, the QuasarBrite family of UV LEDs from Lumex lasts 10 times longer (more
than 50,000 hours) and provides tighter beam angles, greater durability, and up to 50% cost savings over comparable devic-es, the company says (Fig. 7). Available in 385-, 405-, and 415-nm wavelengths, applications include bacterial and superficial sterilization, industrial control related to leak and biohazard detection, forensics such as counterfeit detection and analysis of bodily fluids, and ink fluorescing.
OleDs
A category unto themselves, organic LEDs (OLEDs) appear to be the wave of the future. In December 2009, DisplaySearch indicated in its Quarterly OLED Shipment and Forecast Report that worldwide OLED revenues broke the last record, reaching $252 million in revenue for the third quarter of 2009, up 31%. Notably, OLED shipments totaled 21.7 million in the same quarter, showing a 19% increase over the prior year.
OLEDs use a layer of organic compound as a light source between their anode and cathode. Depending on the configura-tion, light can be emitted either from the top or the bottom of the device, enabled by a transparent electrode.
There are three types of OLEDs: transparent (TOLED), stacked (SOLED), and inverted (IOLED). TOLEDs rely on transparent electrodes on both sides of the device, so they can emit light from the top or bottom, while SOLEDs stack red, green, and blue to achieve full-color displays. The IOLED exploits a bottom cathode that interfaces with a thin-film transis-tor (TFT) backplane to create an active-matrix OLED (AMO-LED) display.
Increasingly, OLEDs are finding their way into many display applications due to their advantages over traditional LCDs. For example, they don’t require a backlight, resulting in lighter and thinner panels. Also, OLED displays can turn pixels completely off to display true, deep black. Sony’s XEL-1, which the com-pany calls the industry’s first OLED television, features a 3-mm thick panel and a contrast ratio of 1,000,000:1 (Fig. 8).
These are just a few of the types of LEDs available, not to mention their numerous variations. Characterizing the right type of LED is quite easy, but it gets a bit tricky when you have to choose the right one within the given typology.
basIc characterIzIngSome general guidelines apply to most of the design gantlets
surrounding LEDs. One would be hard pressed to disagree with Rob Harrison, engineering man-ager of OSRAM’s Solid-State Light-ing Business, when
44 03.26.10 ElEctronic DEsign
EngineeringEssentials
7. Poised for bacterial sterilization, industrial control, and forensic applications, the Lumex QuasarBrite ultraviolet LEDs feature a lifespan in excess of 50,000 hours.
6. For total-dark photography, infrared LED lamps from LEDtronics come in wavelengths of 850, 880, and 940 nm and promise to turn night into day.
ElEctronic DEsign Go To www.elecTronicdesiGn.com 45
he points out that the first thing to grasp is a complete under-standing of the application requirements.
Since variables abound, designers must establish the bound-aries of critical parameters: voltage, current, power consump-tion, heat dissipation, thermal resistance, color, color tem-perature, color sensitivity, brightness, ambient conditions, packaging, and lifespan. “Be prepared to whittle down your choices from hundreds of LEDs to about 10 or less,” Harrison says. He also points to thermal resistance as the most critical factor. Obviously, heat will affect not only overall design per-formance but also the lifespan of the LEDs.
In addition to good system design for heat dissipation, ener-gy efficiency is a priority. More and more designs need to meet a number of efficiency standards such as Energy Star. With the increasing focus on environmental concerns, this will become even more critical in the very near future.
A cAse studyA global appliance manufacturer approached Lumex look-
ing to transition away from incandescent bulbs to illuminate the cavity for its ice and water dispenser. The application required a higher light intensity, even light distribution, and high efficiency for energy savings.
The manufacturer’s vision entailed using a high-power, 1-W LED with a cool-white color temperature. Light had to hit the activation paddles, water dispenser, and ice dispenser, prefer-ably with the same light intensity and color. Also, the illumina-tion module had to be easily field replaceable.
Echoing Harrison’s pinpointing of thermal factors as a pri-mary concern, the Lumex design team concluded that the high-power LED would create numer-ous challenges, particularly heat management, shorter lifespan, and uneven light distribution.
As an alternative, Lumex developed a small molded module integrating a print-ed-circuit board (PCB) sup-
porting three low-power, 5-mm white LEDs with a quick-disconnect two-pin connector at the end of a wire assem-bly (Fig. 9). The LEDs were color and intensity matched so each had the same 2700-K cold color temperature. This
approach additionally allowed light to be aimed at exact loca-tions in the cavity.
According to Lumex, the solution reduced service costs by replacing the incandescent bulb with an LED with a 10-year service life. Also, its energy costs were lower since the module consumed less power than a traditional solution. It bested the initial concept of using a 1-W LED, driving three LEDs at 18
mA versus using a 1-W device as well.
emerging Led technoLogyWhatever the design challenge may be, something is
usually coming out to address it—or, at the very least, it’s on the drawing board somewhere. For example, Bayer Materi-alScience recently unveiled a unique form of light-diffusion technology that hides LED hotspots while transmitting higher light levels.
The company’s approach creates the effect of softened LED light with minimal reflection, allowing the diffusion of trans-lucent white colors at normally unattainable light-transmission levels. This technology promises nearly limitless freedom for light diffuser packages and a broad palette of colors to custom-ize the application.
“This is an exciting time to be a colorist because we are able to offer product designers and OEMs a design solution specific to their needs,” says Terry Bush, senior chemist at Bayer Mate-rialScience.
To create a unique diffuser package using the technology, designers select a Makrolon polycarbonate resin grade that suits their particular application. “The better the base resin, the better the overall performance of the diffuser package,” says Gerald DiBattista, market segment leader, IT, Electrical/Elec-tronics Polycarbonates, Bayer MaterialScience.
Available resins include Makrolon LED2643 for indoor and outdoor applications. The formulation resists UV light, water exposure, and immersion. Perhaps the first clear polycarbonate to pass UL 94 5VA flame-rating requirements at 3 mm, Makro-lon FR7087 suits lenses and covers. Makrolon 6717, a flame-retardant grade resin, supports extruded applications such as light bars and light guides. Makrolon 3103, a high-viscosity, UV-stabilized polycarbonate, handles a number of applications including automotive and consumer.
Attesting to the fact that there will always be a design solution on the horizon, DiBattista reiterates, “No matter what the final lighting application, there will likely be a solution that meets the application’s needs.”
EngineeringEssentials
8. Sony’s XEL-1 OLED television sports a 3-mm thick panel and specifies a contrast ratio of 1,000,000:1.
9. Lumex’s field-serviceable module hosts a PCB supporting three low-power white, 5-mm LEDs, each delivering a 2700-K cold color temperature.
Multitouch Functionality Comes To Bigger Screens
BILL WONG | EMBEDDED/SYSTEMS/SOFTWARE EDITOR [email protected]
LARGE MULTITOUCH DISPLAYS with fancy graph-ics are the rage on TV shows. Even local weath-er reporters use multitouch interfaces. Bringing the technology to the masses, though, is still a challenge.
Smaller devices like the Apple iPhone and Motor-ola Droid have multitouch support and have been shipping in the millions. But in this case, small has its advantages. The release of Apple’s iPad (Fig. 1) has sparked interest in larger form factors (search “Success Of iPad Is All About Software” at elec-tronicdesign.com).
Mid-range all-in-one PC platforms like HP’s TouchSmart also employ multitouch technology. The TouchSmart PC product line is based on a 23-in. HDTV display with multitouch support, but the platform commands a premium price (Fig. 2). Touch support is only one aspect of the cost, yet it provides one of the more obvious benefits of the all-in-one configuration.
NANOWIRES AND PROJECTIVE CAPACITIVE TOUCH SENSING
Single-touch detection is common these days, and low-end micros can easily handle it. Multi-touch for small devices like smart phones is typi-cally limited to two or maybe three touch points simply because the surface is so small and usable by only one hand. Large screens on the order of 50-in. displays have the potential for more interac-tion, raising the number of contacts much higher.
New technology from Displax addresses this arena with a mesh of nanowires to implement a pro-jective capacitive touch-sensing system. This is the
same approach used by the iPhone but with a larger form factor. Displax can detect up to 16 touches on display sizes of 30 to 116 in., suiting all of the high-definition LCDs and plasma displays on the market. The actual diagonal range for this technol-ogy is 18 cm to 3 m.
The projective capacitive touch sensing detects physical contact as well as near-field positioning. It also can detect air movement when someone blows on its surface. The system can even report the direc-tion and intensity of the air movement.
The ability to handle large screens and more than a couple simultaneous touches means Displax can handle collaboration between multiple people. The near-field position should allow for creative user interaction as well.
The technology initially will be deployed in the form of a film with a USB-based controller. It can be mounted behind or on top of a surface. When it’s mounted behind a surface, the material must be less than 15 mm thick. The film targets flat-panel displays but works equally well for transparent projection screens.
The nanowire technology is not limited to a flat film. It can be applied to almost any non-conduc-tive smooth surface. Imagine a globe with touch detection, as users point to anywhere on the Earth and the system responds with information on the selected location. Just think of the possibilities.DISPLAXwww.displax.com
03.26.10 ELECTRONIC DESIGN46
Embedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in EDEmbedded in ED
1. Apple’s iPad has a 9.7-in. LCD touch-screen with multitouch support.
2. HP’s TouchSmart line is based around a 23-in. HDTV display that even comes with a remote control.23-in. HDTV display that even comes with a remote control.
BILL WONG | EMBEDDED/SYSTEMS/SOFTWARE EDITOR [email protected]
Module Packs I/O FeaturesDIAMOND SYSTEMS WANTS to make it easier to interface chores while reducing costs and increasing the number of available options when using high-speed serial interfaces like PCI Express and USB. Its FeaturePak module is designed to provide peripheral expansion. Up to six modules can be con-nected to a host (Fig. 1). A standard single-board computer typically might host one or two. In a sense, it is the opposite of the computer-on-module (COM) approach, where the host is on a board.
FeaturePak can work in several different configurations, such as having the processor on a COM board or in a stack. In this case the host would simply be a carrier board for the COM and FeaturePak modules.
The module is designed to be small enough to work with stackable architectures like PC/104, EPIC Express (search “An EPIC Tale: PC/104 Hitches On To PCI Express” at electronicdesign.com), SUMIT (search “SUMIT Brings Big Improvements In Small Packages” at electronicdesign.com), and Stackable USB (search “Micro/sys Dishes Out Stackable-USB For Embedded I/O” at electronicdesign.com).
A FeaturePak edge connector plugs into a high-density, low-cost MXM socket that has 230 I/O connections. The connections are different from other MXM-based standards such as those used by Qseven. It can handle data rates up to 2.5 Gbits/s, allowing it to work with PCI Express and USB 2.0. About half of the pins are used for the two application-specific I/O ports. There are 50 pins allocated for each port, with 34 unused pins for isolation between I/O signals and use with high-speed links such as Ethernet. The modules are designed for rugged environments. Each has a pair of mounting holes so it can be bolted to the carrier board.
MULTIPLE CONTROL OPTIONSThe module’s features can be accessed through PCI Express,
USB, UART, or the SMBus (I2C) interface. However, PCI Express and USB are the primary means for controlling and accessing the peripherals on the module.
Modules can have multiple PCI Express and USB ports. Typically, though, a module will only need one. A host socket must provide either a PCI Express 1x and USB link (Fea-
turePak compliant) or a pair of USB links (FeaturePak USB compliant).
The modules are designed for 3.3-V operation with a mini-mum of 2 A available from the host. The 5-V supply is 1 A. The 12-V connection allows a module to monitor the supply.
Standard modules are 4.8 mm high. Tall modules can be up to 10 mm high. A standard module will fit within a PC/104 0.6-in. stacking height. FeaturePak is designed for developers. JTAG connections on the board allow modules to be part of a JTAG scan chain.
Diamond Systems created FeaturePak with the intent to move it to a standards group. Other companies such as Con-gatec are already working on FeaturePak modules like the Diamond Systems digital-to-analog converter (DAC) and digi-
tal I/O modules (Fig. 2 and 3). Of course, these modules will only be useful when combined with a carrier board, so expect announcements of single-board computers with FeaturePak sockets.
More details can be found on the FeaturePak Web site.DIAMOND SYSTEMSwww.diamondsystems.com
FEATUREPAKwww.featurepak.com
Embedded in ED
47ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM
PCI Expressswitch
USBhub
Microcontroller
FeaturePakmodule
FeaturePakmodule
Up to6 modules
ID 1 ID 6
UART
SMBusI/O I/O
0, 1, or 2 PCI Express x1 links1 or 2 USB 1.1 or 2.0 links1 UART (optional)1 SMBus (optional)2 I/O ports (50 pins each)
ID (3 bits, fixed for each slot)3.3-V power and I/O5-V power12-V power (monitor only)
FeaturePak interface
Of course, these modules will only be useful when combined with a carrier board, so expect announcements of single-board computers with FeaturePak sockets.
the FeaturePak Web site.DIAMOND SYSTEMSwww.diamondsystems.com
FEATUREPAKwww.featurepak.com
1. A host microcontroller can support up to six FeaturePak modules. A PCI Express switch or USB hub may be required depending on the number and type of modules supported.
2. The Diamond Systems FP-DAQ1616 provides a 16-channel, 16-bit DAC interface.
3. The Diamond Systems FP-GPIO96 provides 96 digital I/O ports.
Microcontroller Talks—And Listens
BILL WONG | EMBEDDED/SYSTEMS/SOFTWARE EDITOR [email protected]
THE NLP-5X MICROCONTROLLER from Sensory not only generates speech from text, it also handles speaker-independent and speaker-dependent voice input. The voice input is limited to short phrases to improve accuracy, so leave dictation to a PC. Still, the NLP-5x chip is ideal for a range of applications including voice-activated appliances.
The 80-MHz NLP-5x is based on a 16-bit DSP core tailored for voice process-ing (see the figure). Combined with Sen-sory’s FluentChip firmware, the chip can handle up to 750 seconds of compressed text-to-speech (TTS) without using off-chip memory. It can also store multiple speaker-dependent vocabularies as well as speaker-independent vocabularies.
REAL VOICE RECOGNITIONThe voice recognition system is about
95% accurate for voice-independent inter-action. It can recognize multiple phrases. Also, it can handle user training with voice interaction for speaker-dependent recognition. The choice of words is key to improving accuracy, and Sensory works with most customers to optimize their vocabulary. Changing one or two keywords often can significantly improve recognition performance.
Developers have a choice for audio output. A simple pulse-width modula-tor (PWM) can drive a low-end speaker directly. The two 16-bit digital-to-analog converters (DACs) are designed for ste-reo output including speech and sound effects using a 48-kHz sample rate.
The software also supports 24-voice, MIDI-compatible, stereo music synthe-sis. The MIDI support operates in par-allel to voice support, allowing the two outputs to be mixed.
Audio output can be synchronized with external devices like motors. As a result, the mouth movements of toys can be linked to the speech output. Likewise, the system supports beat detection from the audio input. This primarily targets toys where the user beats out a rhythm. All this support as well as the voice recognition support is integrated into Sensory’s scripting lan-guage, which greatly simplifies appli-cation development.
MORE THAN A PRETTY VOICEThe NLP-5x is designed to be more
than a voice processing system. It has plenty of headroom and peripherals to handle many application-oriented chores including motor control for up to three motors. The infrared (IR) support allows it to work with a remote control.
Most of the digital peripherals and 3.6-V tolerant I/O ports are the same as those found on other microcontrollers and digital signal controllers (DSCs) in this realm.
Overall, Sensory’s NLP-5x line rep-resents a powerful, low-cost, single-chip solution for voice-related man-machine interfaces. Pricing starts at $2. A devel-opment kit costs $1500. SENSORY
www.sensory.com
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48 03.26.10 ELECTRONIC DESIGN
INTEL CORE FINDS HOME ON VME DSP BOARD
The Champ-AV5 from Curtiss-Wright Controls Embedded Computing hosts a pair of 2.53-GHz Intel dual-core Core i7-610E processors. The 6U VME64x Champ-AV5 complements the company’s other new board, the SVME/DMV-1905 single-board computer. The SVME/DMV-1905 is also based on a Core i7 proces-sor. The Champ-AV5 has a 17-Gbyte/s (peak) DDR3 memory subsystem. Each processor has 2 Gbytes of error correction code memory. A PMC/XMC slot provides expansion. The Champ-AV5 is pin-com-patible with the Curtiss-Wright Controls MPC7447/7448-based Champ-AV4. Air-cooled and conduction-cooled versions of the Champ-AV5 are available. The system comes with a VxWorks 6.x BSP and Linux. Pricing starts at $14,500.CURTISS-WRIGHT CONTROLS EMBEDDED
COMPUTING
WWW.CWCEMBEDDED.COM
COMPACT COM EXPRESS MODULE COURTS CORE I7
The conga-BM57 Type 2 COM Express module from Congatec AG sports a 2.66-GHz dual-core Intel Core i7-620M processor with a 35-W TDP. The chip has a 4-Mbyte L2 cache and a dual-channel DDR3 memory controller with access to 8 Gbytes of memory. The processor is paired with the Mobile Intel QM57 Express Chip-set, which includes an integrated graphics controller that supports Intel’s Flexible Dis-play Interface. It can drive a pair of inde-pendent video channels on VGA, LVDS, HDMI, DisplayPort, or SDVO interfaces. The module has five PCI Express lanes, eight USB 2.0 ports, three SATA, an EIDE, and a Gigabit Ethernet interface. It also offers an LPC bus and support for Intel’s High Definition Audio feature set.CONGATEC AG
WWW.CONGATEC.COM
Pre-ampwith
gain control
Pre-ampwith
gain control
Microphone
3-channel16-bitADC
Dualcomparators
USB UART I2SSPI 40 GPIO LCD IRMotor control
NLP-5x16-bit DSP
core
Timers WatchdogPower
128-kbyteOTP code
22-kbyte data SRAM
2-kbyte code SRAM
Memory controller
16-bit DAC DAC out
PWM Speaker out
16-bit data23-bit address
16-bit DAC DAC out
News
The NLP-5x has the typical complement of microcontroller peripherals with the analog tuned to voice chores. The one-time-programmable (OTP) memory can be augmented using off-chip memory and the code SRAM.
Embedded in EDNews
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM
TINY AMC MODULE PACKS QUAD-CORE PROCESSOR
Kontron is delivering Intel’s 45-nm, quad-core LC5518 Xeon processor with Intel’s 3420 platform controller hub (PCH) and Direct Media Interface (DMI) in a com-pact AMC form factor. Designed for MicroT-CA platforms, the board can hold up to 24 Gbytes of ECC, 1066-MHz, DDR3 memory accessible by the Xeon’s triple-channel mem-ory controller. It also has a pair of 10-Gbit XAUI Ethernet ports, two Gigabit Ethernet ports on the front panel, and two for the backplane. Other interfaces include two USB 2.0 ports, one VGA port and one COM port, and PCI Express x4 AMC.1 and four SATA ports, with two for the AMC.3 support and on the extended AMC connector. The SATA interface has built-in RAID support. KONTRON
www.kontron.com
BARE METAL HYPERVISOR LETS CLIENTS SHARE INTERRUPTS
Real-Time Systems’ RTS Hypervisor 2.2 bare metal hypervisor features shared cache and interrupts. It permits the use of message signaled interrupts (MSIs) even if the client operating system does not. MSIs allow the sharing of interrupts, preventing conflicts or forced partitioning of the underlying system. The latest version’s open control module provides a high-performance virtual network interface, shared memory, and other virtual-ization components for paravirtualize clients. REAL-TIME SYSTEMS
real-time-systems.com
WALL-MOUNT COMPUTER FITS HOME AUTOMATION
Advantech’s UbiQ-480 wall-mount touch computer targets home automation applications. It hosts a Freescale i.MX31 processor running Windows CE 5.0. Six
programmable function keys, a built-in 1.3-Mpixel camera, an infrared receiver, a microphone with echo cancellation, and a speaker for full
multimedia support surround the 7-in. 16:9 touchscreen
panel. Interfaces include a pair of Ethernet ports, serial ports, USB 2.0 ports, and parallel I/O ports. 802.11b/g support and Power-over-Ethernet (PoE) are optional. Pric-ing starts at $695.ADVANTECH
www.advantech.com
LIGHTWEIGHT, OPEN-SOURCE RTOS FITS MCU PLATFORMS THAT NEED TASK SCHEDULING
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49
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03.26.10 ELECTRONIC DESIGN
It’s important to understand the various tradeoffs and considerations before you begin your front-end design for high-speed data converters for wide-bandwidth applications.
DesignSolution
As c o nve r t e r t e c h n o l o g y improves, so does the demand to resolve very high interme-diate frequencies (IFs) accu-
rately at high speeds. This poses two challenges: the converter design itself and the front-end design that couples the signal content to the converter. Even if the converter itself is excellent, the front end must be able to preserve the signal quality too.
High-frequency, high-speed convert-er designs exist in many applications, with wireless infrastructure and instru-mentation pushing these boundaries. These applications demand high-speed, 100-Msample/s+ converters with resolutions of 12 to 16 bits. (“Wideband” represents the use of signal bandwidths greater than 100 MHz and ranging into frequencies of 1 GHz and above.)
FRONT-END BACKGROUND“Front end” implies a network or coupling circuit that con-
nects the last stage of the signal chain (usually an amplifier, gain block, or tuner) and the converter’s analog inputs (Fig. 1). This assumes everything in the preceding signal chain circuitry has the proper bandwidth to support the frequencies to be resolved.
This last stage, or front-end circuit, also needs to have the proper bandwidth, but there is more to it than that. It must also be very linear, well balanced, and properly laid out on the printed-circuit board (PCB) to preserve the signal content properly. If not, the converter will pick up these nonlinearities imposed by the front end, which show up as distortions and noise in the frequencies of interest. The front-end network has to be carefully designed to meet the demands of any high-speed,
high-resolution converter.
Typically, there are two types of front ends: passive and active. Active front ends use an amplifier or “gain block” to drive the signal into the converter’s analog inputs. These front ends are generally easier to design with as long as the proper amplifier is chosen. But when very high frequencies are required for the design, amplifiers tend to be performance lim-ited, in linearity terms, to 200 MHz. In fact, some wideband amplifiers have usable bandwidths of greater than 200 MHz, but they tend to be high in power consumption.
TRANSFORMERS: SPECS, TOPOLOGIES, AND TYPESThe transformer, which can imply a flux coupled transformer
topology, is inherently ac-coupled, since it is galvanically iso-lated and will not pass dc levels. It provides a quick and easy way of translating from a single-ended to a differential circuit, which is the common analog input interface for converters. A center-tapped transformer provides the freedom to set the common-mode level arbitrarily. This combination of virtues reduces component count in front-end designs, where it is criti-cal to keep complexity at a minimum.
Care should be taken when using center-tapped transformers. If the converter circuit presents large imbalances between the differential analog inputs, a large amount of current could flow through the transformer’s center tap, possibly saturating the core. For example, instability could result if the VCM/CML pin is used to drive the center tap of the transformer and a full-scale analog signal overdrives the converter’s input, turning on the protection diodes.
The transformer also provides basically noise-free gain, which depends on the designer’s choice of turns ratio. Sig-
Improve The Design Of Your Passive Wideband ADC Front-End Network
ROB REEDER | ANALOG DEVICES [email protected]
50
ROB REEDER is a senior converter applications
engineer working in the high-speed signal-
processing group at Analog Devices Inc. He
has worked for the company since 1998 and
is responsible for development and support on
high-speed ADCs. He received his MSEE and BSEE from Northern
Illinois University in DeKalb, Ill.
Amplifier orgain block
RO
Front end
0.1 µF XFMR1:XZ
0.1 µF
Rt
Rt
0.1 µF 0.1 µF
Rs
Rs
*Cf*Optional
VIN+
VIN–
RADC
CADC
Converterinternalinput Z
1. In this context, a front end is a coupling circuit between the last stage of the signal chain and an ADC’s inputs. Besides providing sufficient bandwidth, it needs high linearity, good balance, and proper layout.
ElEctronic DEsign Go To www.elecTronicdesiGn.com 51
DesignSolution
nal gain is ideally equal to the turns ratio of the transformer. Although voltage gains are inherently noise-free, using a trans-former with voltage gain does gain the signal noise as well as tradeoff bandwidth.
A transformer should be seen simplistically as a wideband passband filter with nominal gain. The more gain in the trans-former, the less bandwidth. Finding a 1:4 ratio transformer with low insertion loss performance in the gigahertz region is difficult today.
Although simple in appearance, transformers should not be taken lightly. A couple of brief equations relate the currents and voltages occurring at the terminals of an ideal transformer (Fig. 2a). When a transformer steps up voltage, its impedance load will be reflected back to the input.
The turns ratio, a = N1/N2, defines the ratio of primary volt-age to secondary voltage. The currents are inversely related (a = I2/I1), and the ratio of the impedance seen in the primary reflect-ed from the secondary goes as the square of the turns ratio (Z1/Z2 = a2). The transformer’s signal gain is expressed simply as 20 log (V2/V1) = 20 log/(Z2/Z1), so a transformer with a voltage gain of 3 dB would have a 1:2 impedance ratio.
A host of inherent and parasitic departures from the ideal comes into play with a transformer (Fig. 2b). Each has a role in establishing the transformer’s frequency response and linearity. These departures can help or hinder performance, depending on the front-end implementation. Figure 2b provides a good way to model a transformer to get first-order expectations about band-width response, insertion loss, and return loss.
Linearity models of the transformer are more difficult to come by and develop. Understanding the ferrite linearity is key when developing a model of this type, which still presents a hand-ful of unknowns. Some manufacturers may provide modeling information, either on their Web site or through a support group. Designers planning to perform the model analysis using the
hardware will need a network analyzer and a handful of samples to make all of the measurements properly. However, neither of these methods will divulge all linearity insights other than phase and amplitude imbalances, which can commonly cause even order distortions.
All real transformers have losses and limited bandwidth. As the configuration of parasitics implies above, one can think of a transformer as a wideband bandpass filter, which can be defined in terms of its –3-dB points. Most manufacturers will specify transformer frequency responses in terms of the 1-, 2-, and 3-dB bandwidth. A phase characteristic accompanies the amplitude response. Usually a good trans-former will have a 1% to 2% phase imbal-ance over its frequency passband.
The transformer’s insertion loss, or the loss over the specified frequency range, is the most common measurement speci-
fication found in any transformer datasheet. Return loss is the transformer’s mismatch of the effective impedance of the sec-ondary’s termination as seen by the primary.
For instance, if the square of the ratio of secondary to primary turns is 1:2, one would expect a 50-Ω impedance to be reflected onto the primary when the secondary is terminated with 200 Ω. However, this relationship is not exact.
For example, the reflected impedance on the primary changes with frequency. First, find the return loss at the center frequency specified for the design. This example uses 110 MHz. Zo is found not to be 50 Ω as assumed for an ideal transformer. It is lower, as found in Equation 3:
Return loss (RL) =–18.9 dB @ 110 MHz =
–20*log((50 – Zo)/(50 + Zo)) (1)
10^(18.9/20) = ((50 – Zo)/(50 + Zo)) (2)
Zo = 39.8 Ω (3)
Ratio the primary Zo result in Equation 3 and the secondary ideal impedance, 200 Ω in this case. Do the same for the primary ideal (50 Ω) and solve for the real secondary impedance:
(a)
Primary
1
2
I1
V1 (Z1)
1:N turns
I2
V2 (Z2) Secondary
3
4
(b)
Primary
1
2
Secondary
3
4
C1
R1
R2
L1
L2
RCoreLPrimary
C2
C3
1:1 Z ratio
LSecondary
C4
C5
L3 R3
L4 R4
C6
2. The ideal transformer and its equations (a) are straightforward. But inherent and parasitic departures from the ideal play parts in establishing a real-life transformer’s frequency response and linearity (b).
x(t) XFMR
x1(t)ADC
h(t)
h(t)
y(t)
x2(t)
3. A mathematical analysis in the text, based on this simple ADC model, helps explain why transformer nonlinearity rises with imbalance.
52
DesignSolution
Z(primary reflected)/Z(secondary ideal) = Z(primary ideal)/Z(secondary reflected) (4)
39.8/200 = 50/X (5)
Solving for X:
X = 251 Ω (6)
The secondary needs to have a 251-Ω termination when using a 1:2 turns-ratio transformer. Therefore, using a higher termina-tion accounts for the core losses inside the transformer, yielding not only a better match, but also an improved input drive on the primary side of the transformer.
Having an improved input drive implies less power is required to reach the converter’s full-scale input. In general, as the imped-ance ratio goes up, so does the variability of the return loss. Keep this in mind when matching the front-end design of the preceding stage with any transformer.
Amplitude and phase imbalance are two of the most critical performance characteristics when considering a transformer or balun. These two specifications give the designer some perspec-tive on how much linearity to expect when a design calls for high (above 100 MHz) IFs.
As the frequency increases, the nonlinearities of the trans-former also increase, usually dominated by phase imbalance, which translates to even-order distortions (mainly second har-monic) as seen by the converter. Don’t be quick to blame the converter, though. Look at the front-end design or transformer first if the expected spurious is way off.
Imbalance is important (Fig. 3). Consider the input, x(t), to the transformer. It is converted into a pair of signals, x1(t) and x2(t). If x(t) is sinusoidal, the differential output signals, x1(t) and x2(t), are of the form:
(7)º
The analog-to-digital converter (ADC) is modeled as a sym-metrical third-order transfer function:
(8)
Then: (9)
Ideal case: no ImbalanceWhen x1(t) and x2(t) are perfectly balanced, they have the
same magnitude (k1 = k2 = k) and are exactly 180° out of phase (φ = 0°). Since:
(10)
(11)
Applying the trigonometric identity for powers and gathering terms of like frequency:
(12)
This is the familiar result for a differential circuit. Even harmon-ics cancel for ideal signals, while odd harmonics do not.
03.26.10 ElEctronic DEsign
(17)
In Out
–Out
In Out
–Out
Single configurations
In Out
–Out
In Out
–Out
Double configurations
In Out
–Out
Triple configuration
4. Multiple transformers can be used in various configurations for single-ended to differential conversion.
ElEctronic DEsign Go To www.elecTronicdesiGn.com 53
DesignSolution
Magnitude iMbalanceNow suppose the two input signals
have a magnitude imbalance, but no phase imbalance. In this case, k1 ≠ k2, and φ = 0:
(14)
Substituting Equation 7 in Equation 3 and again applying the trigonometric power identities in Equation 14 (see the equation box). We see from Equation 8 that the sec-ond harmonic in this case is proportional to the difference of the squares of the magnitude terms, k1 and k2, viz:
(15)
Phase iMbalanceAssume now that the two input signals have a phase imbal-
ance between them, with no magnitude imbalance. Then, k1 = k2, and φ ≠ 0:
(16)
Substituting Equation 10 in Equation 3 and simplifying, we get Equation 17 (see the equation box). From Equation 17, we see that the second harmonic amplitude is proportional to the square of the magnitude term, k:
(18)
A comparison of Equation 15 and Equation 18 shows that the second-harmonic amplitude is more severely affected by phase imbalance than by magnitude imbalance. For phase imbalance, the second harmonic is proportional to the square of k1. For magnitude imbalance, the second harmonic is proportional to the difference of the squares of k1 and k2. Since k1 and k2 are approximately equal, this difference is small.
Higher-order turns or impedance ratio transformers have a lower tolerance to imbalance. If the “right” transformer can-not be found and linearity is an issue for the application, try using multiple transformers or baluns in a cascaded fashion. By employing a second transformer, second-harmonic distor-tions usually decrease because the second transformer acts to rebalance the previous signal converted from single-ended to differential on the first transformer.
Two or, in some cases, three transformers can be used to help convert the single-ended signal to differential more adequately across high frequencies (Fig. 4). The downside of using this method is the increased PCB space, higher cost, and higher insertion loss (i.e., higher input drive). New high-frequency transformers are on the market today. Anaren’s patented design uses a coreless topology allowing for extended bandwidth in the gigahertz region that only employs a single device.
Not all transformers are specified the same way by all manu-facturers, and transformers with apparently similar datasheet
specifications may perform differently in the same situation. The best way to select a transformer for the design is to collect and understand the specs of all transformers being considered and request any key data items not stated on manufacturers’ datasheets. Alternatively, it may be useful to measure their per-formance using a network analyzer.
Wideband considerationsUnderstanding the transformer and its specifications provides
a great starting place for figuring out how the front end is going to perform in the end. Essentially, three other metrics need to be thought about when designing a wideband network as well: bandwidth, matching, and the PCB layout itself. Each is impor-tant and can play a pivotal role in achieving the best performance required by the front end.
While the transformer has a specified bandwidth, the front-end design can limit the actual bandwidth provided because inherent PCB and internal ADC parasitics tend to roll off the transformer early. Some designs may require more bandwidth than actually measured, even though the transformer bandwidth was selected appropriately. From the converter’s standpoint, there is still plenty of bandwidth. But from the front-end design, this could be limited or extended depending on the topology used.
One way to extend the bandwidth of the transformer is to place low-Q inductors or high-frequency ferrite beads in series (LS) with each of the converter’s analog inputs. (Fig. 5). Pass-band flatness can change, and it needs to be re-evaluated with this technique. Figure 5b shows results of different value induc-tors versus bandwidth. In the baseline results, no LS is present.
0.1 µF XFMR1:XZ
0.1 µF
Rt
Rt
0.1 µF 0.1 µF
Ls
Ls
Rs
Rs
VIN+
VIN–
RADC
CADC
Converterinternalinput Z
(a)
Analoginput
InputZ = 50 Ω
Widebandconfiguration
(b)
Am
plitu
de (d
BFS)
0
–1
–2
–3
–4
–5
–6
–7
–8
Frequency (MHz)0 50 100 150 200 250 300
BaselineInductor 1Inductor 2Ferrite bead 1Ferrite bead 2
5. Low-Q inductors or high-frequency ferrite beads in series (LS) with a converter’s analog inputs can extend bandwidth (a). However, this can affect passband ripple (b). The “baseline” measurement was performed with no inductor.
54
DesignSolution
Matching the front end can imply a couple of things, depending on the designer’s viewpoint (Fig. 6). By defi-nition, it simply means that a certain source and load resistance (usually 50 Ω) has been defined for the front-end network and should be equal. This yields the maximum sig-nal power transfer between the source and the load to minimize reflections.
Usually, this takes the form of a complex conjugate match since the converter’s internal input impedance is complex, as well as the transformer’s non-idealities in the front-end network design. The source is defined as the preceding stage before the front-end network. The load will encompass the front-end network. This includes the trans-former, any termination or filtering between the secondary of the transformer and the analog inputs of the converter, and the converter’s complex input impedance.
Matching also relates to bandwidth. As the bandwidth rolls off on the front end, it is a good indication that the equal source to load is moving apart. Matching the front end over the intend-ed bandwidth gives rise to preserved performance through many
specifications, not just dynamic performance, i.e., signal-to-noise ratio (SNR) and spurious free dynamic range (SFDR). This is particularly important at higher frequencies since front ends tend to roll off quicker as discussed.
A particular front end was designed to have a pass-band region from 10 to 70 MHz using a 1:9 impedance ratio transformer with a datasheet bandwidth specification of 250 MHz. Going through the various tradeoffs, many different approaches can be used to achieve the boundary conditions for the design.
Often, only one design will work or be the best choice. In this example, REVL was chosen because it has the best “match” over the specifica-tions required for the design. The design meets the dynamic spurious performance above 85 dB. It also has the best input impedance match over the entire band of interest, allowing for 92% of the signal power to be transferred to this network while maintaining a passband flatness specification below 1 dB.
The term “matching” can be used loosely. However, it really implies opti-mization over the band of interest given a set of defined performance parameters for the front-end network.
Layout is another variable that can wreak havoc on any front-end design, particularly at high frequencies. Improper layout can mess up the front-end design, causing unexpected performance. Don’t undo all the hard work done to define the front end. Take the time to keep the layout sound and symmetrical.
One example using multiple transform-ers in cascade as described can keep the even order distortions at bay (Fig. 7). The two layout diagrams depict small differ-ences between the layouts of two trans-formers used in front of the ADC. One layout (b) performs better over a wide
03.26.10 ElEctronic DEsign
C1
C2
C3
C4
T1 T2
C1
C2
C3
C4
T1 T2
(b)
(c)
In
In
(a)
C1
C2
C3
C4
T1
T2
Out
Out
(b)
Am
plitu
de (d
BFS)
0
Frequency (MHz)0
–5
–10
–15
–20
–25
–30
–35
–4020 40 60 80 100 120 140 160 180 200
RevARevBRevDRevFRevL
(a)
ZSource XFMR R
R
L
R
CC R
AIN
AIN
RADC
CADC
Converterinternalinput Z
ZSource
ZLoad
ZLoad
Maximum power transferoccurs when ZSource = ZLoad (conjugate)Z = R + jX → Z = R – jX
Signal source
Signal source
Z = 50 Ω
7. The same cascade of transformers (a) yields different results depending on how symmetrically the traces are routed on the PCB (b and c).
6. Matching means more than defining an ohmic impedance and matching it across source and load (a). To achieve maximum signal power transfer implies optimization over the band of interest (b).
ElEctronic DEsign Go To www.elecTronicdesiGn.com 55
DesignSolution
band of frequencies, though. It is more symmetrical and forces return currents or ground references to be common.
Proof can be seen in the fast Fourier transform (FFT) perfor-mance plot measurements of an AD9268, 16-bit, 125-Msample/s dual-channel ADC (Fig. 8). Figure 8a was obtained using the symmetrical layout. It yielded a second harmonic of 85 dB with a 140-MHz IF applied at –1 dBFS. Figure 8b shows the perfor-mance under these same conditions with the non-symmetrical layout. The second harmonic was measured at 79.5 dB—a great-er than 5-dB loss in performance!
Ferrite versus non-FerriteTraditionally, wire wound or ferrite transformers have been
the solution of choice in converter front-end circuit design to convert the last stage of the signal chain’s signal from single-ended to differential with typical transformation impedance ratios of 1:1, 1:2, and 1:4. Wire wound topologies deliver good performance at frequencies below 200 MHz, where they exhibit good balanced phase and amplitude performance and good insertion and return loss.
However, wire wound baluns suffer from some drawbacks, the most serious of which is the deterioration of performance at higher frequencies. Wire wound baluns are essentially lumped element components that work well at lower frequencies, but whose performance deteriorates as the effects of parasitics become more pronounced at higher frequencies and ferrite losses increase.
By definition, lumped element components aren’t suited for use as the wavelength of operation becomes comparable to the physical dimensions of the component. However, Anaren offers a series of baluns that are non-ferrite coupled, microwave strip-line structures and are inherently suited for operation at higher frequencies, i.e., above 200 MHz.
These baluns are coupled stripline designs that use softboard (PTFE/Teflon) material as the dielectric medium. The dielectric is typically low loss, keeping insertion loss to a minimum at higher frequencies. In addition, this technique allows a signifi-cant amount of circuitry to be packed into a package, minimiz-ing package size and yielding up to 80% space savings over typical ferrite topologies.
Unlike wire wound baluns, no ferrites are used in an Anaren balun structure (Fig. 9). Another advantage to non-ferrite trans-former technology is its insensitivity to variations in differen-tial impedances over wider bandwidths, which are common when using unbuf-fered ADCs that have a change in input impedance when the
converter moves between the sample and hold domains. Any sensitivity on part of the balun or transformer to the converter’s impedances could reveal degradation in performance.
When designing a wideband network in front of the ADC, choose the transformer and collect the specifications required to make the best selection for the application. In particular, keep imbalance performance in mind when choosing a transformer. Two or possibly three transformers may be required for the design as shown in the topologies above.
If extra bandwidth is required, use series low-Q inductors or high-frequency ferrite beads on the secondary of the trans-former. But remember to re-evaluate passband flatness to make sure it is still in check. Matching over the entire band can be difficult. Matching should really encompass optimization of all specifications defined by the design to get the maximum power transferred to the front-end network.
On the layout side, don’t disregard symmetry on the front end or the performance may be mitigated. Finally, keep in mind that other solutions available today tackle some of the widest band applications, improving on passband flatness and dynamic per-formance at higher frequencies while saving PCB space.
0
–15
–30
–45
–60
–75
–90
–105
–120
–135
0
–15
–30
–45
–60
–75
–90
–105
–120
–135
6 M 12 M 18 M 24 M 30 M 36 M 42 M 48 M 54 M 60 M
2+ +
23 3
4 4556 6
6 M 12 M 18 M 24 M 30 M 36 M 42 M 48 M 54 M 60 M
Am
plitu
de (d
BFS)
0
Frequency (MHz)0
–2
–4
–6
–8
–10
–12
–14
–16
–18
–20100 200 300 400 500 600 700 800 900 1000
BaselineAnaren balun
9. One can see a considerable difference in passband flatness using the same AD9640 125-Msample/s coverter fed with a conventional ferrite balun and with an Anaren stripline balun.
8. The more symmetrical output arrangement of the upper transformers in Figure 7b produced the spectrum on the left. Note that the second harmonic is 5 dB lower than in the non-symmetric design on the right.
56 03.26.10 ELECTRONIC DESIGN
C ompetitive pressures are forcing designers of con-sumer electronics such as digital TVs, high-end print-ers, PCs, digital still cameras, and set-top boxes to lower system costs without sacrificing performance.
To meet these needs, memory manufacturers shrink die sizes, minimize feature sets, and reduce pin counts by multiplexing address and data pins. However, these approaches have failed to satisfy the increasing demand for lower memory subsystem cost and higher system performance.
First-generation Serial Peripheral Interface (SPI) devices were successful in reducing costs but only offered small densities and low performance. Read performance, for example, declined as much as 80% when compared to parallel NOR.
High-end electronics system designers require more memory and the best performance possible to be competitive and innova-tive. To address this challenge, manufacturers must look at the entire system and not just the individual components. This cre-ates an opportunity for new interfaces in flash memory.
SPI simplifies designs and lowers costs while achieving adequate performance for low-end applications. SPI devices typi-cally read information serially or one bit at a time.
Single-I/O (SIO) SPI is only the beginning. A new level of performance can be achieved with a multiple-I/O (MIO) SPI. An MIO SPI device can support increased bandwidth from the same, low-pin-count SPI device and package.
With multiple I/Os, devices can transmit and receive data either one, two, or four bits at a time, enabling faster speeds while still requiring only eight total pins or six active pins to retain the origi-nal benefits of SIO SPI. The enhanced performance means that MIO SPI devices can be used to support faster execution-in-place (XIP) code execution, potentially reducing the amount of RAM required by the system and enabling faster system boot-up times.
A dual-I/O (two-bit data bus) interface enables transfer rates to double compared to the standard serial flash memory devices, while a quad-I/O (four-bit data bus) interface improves
throughput four times and opens up a much wider range of appli-cations that require higher performance (Fig. 1).
SPI flash memories support increasingly higher performance with clock rates up to 104 MHz in SIO mode. When an MIO SPI device is used in quad-mode operation, 80 MHz equates to run-ning the flash at an effective clock frequency of 320 MHz with up to a 40-Mbyte/s continuous transfer rate (see the table).
This is more than six times the transfer rate of standard serial flash memories running at a clock rate of 50 MHz. In addition, random access overhead can be reduced by eliminating 28 clock cycles required for each read instruction.
A quad-I/O SPI can enable faster boot times for devices with larger file systems. A 128-Mbit MIO SPI running in quad-I/O mode, with a serial clock (SCK) of 80 MHz, can boot three times faster than a standard 128-Mbit SIO SPI (SCK of 104 MHz). A 128-Mbyte MIO SPI running in quad-I/O mode, with a SCK of 80 MHz, can boot almost four times faster than a standard parallel NOR with a 90-ns initial access time.
New Flash Memory Interfaces Drive Innovation And Lower Costs
KEVIN WIDMER, director of strategic mar-
keting, holds a master’s degree in business
administration, as well as bachelor of science
degrees in electrical engineering and physics
from Florida Atlantic University.
KEVIN WIDMER | SPANSION [email protected]
As consumers demand more from the latest gadgets, designers are turning to multiple-I/O SPI for improved performance.
80
60
40
20
0
Mby
tes/
s
Sustained throughput (Mbytes/s)
Pins
80
60
40
20
0
Pins
x16 ASYNC/PAGE NOR x1 SPI x4 SPI
61 Mbytes/s
48 pins
40 Mbytes/s
8 pins8 pins13 Mbytes/s
Compared to standard serial flash memory devices, dual-I/O interfaces 1.
double the transfer rate while quad-I/O interfaces improve throughput by
a factor of four and open up a broader range of applications that require
higher performance.
DesignSolution
INTERFACE SPECIFICATIONSSerial I/O Dual I/O Quad I/O
Data throughput 13 Mbytes/s 20 Mbytes/s 40 Mbytes/s
Clock frequency 104 MHz 80 MHz* 80 MHz**
* Effective clock frequency of 160 MHz ** Effective clock frequency of 320 MHz
ElEctronic DEsign Go To www.elecTronicdesiGn.com 57
DesignSolution
the Right MeMoRy SubSySteMNOR flash memory has grown to a $5
billion market, according to WebFeet (October 2009), and 90% of NOR flash memory revenue shipments today have a parallel NOR interface. Benefits include fast random access and high reliability. Fast random access is best leveraged with broadside addressing architectures where the host presents the byte or word-level random address, and data is available at the I/O about 100 ns later.
Over the past several decades, host ASICs have invested in memory subsys-tem architectures with parallel NOR to enable XIP for fast boot and memory con-troller configuration and, in some cases, shadowing code to DRAM for operating-system code execution.
The parallel NOR interface continues to be popular for several reasons. The strong supplier base for parallel NOR flash and a desire by ASIC designers and software architecture designers to protect their investment mean that parallel NOR flash will be around for many years to come.
However, some applications and mar-kets need a new memory solution. For these applications, multi-IO SPI offers a compelling alternative. There is a tre-mendous level of industry investment to improve the interface to address higher-performance applications. Host designers are evaluating their memory subsystem needs and finding that SPI offers the right balance between fast initial access and high-performance burst-type reads.
Whereas parallel NOR flash has broad-side addressing for fast initial access, SPI has a internal multi-bank architecture that’s ideal for seamless, continuous-burst applications where code or data can be rapidly streamed into DRAM for host controller access (Fig. 2). System design-ers now have the choice between parallel and serial interfaces based on their memo-ry subsystem architecture needs.
For applications where SPI is the right solution, the switch from a parallel flash memory to SPI affects more than just the flash memory. There are several system
level benefits from SPI. First, simpler ASIC memory controller designs result in lower engineering costs and faster time-to-market.
Additionally, SPI yields lower-cost ASICs due to the elimination of approxi-mately 40 pins, while maintaining scal-ability to higher densities in the future.
And finally, it leads to lower-cost printed-circuit boards (PCBs) due to fewer inter-connects and less board area from a small SO8 package footprint. In some cases, system designers reduced the PCB from a six-layer board down to a two-layer board.
In addition to the system benefits, the SPI flash component costs can be reduced.
21address
lines
16datalines
3controllines
40 to 6
4 datalines
2 controllines
MCU orASIC
32-Mbitparallel
flash
MCU orASIC
32-Mbit SPI
flash
2. Parallel NOR
flash has broadside
addressing for fast
initial access, but SPI’s
internal multi-bank
architecture is ideal for
seamless, continuous-
burst applications
where code or data can
be rapidly streamed
into DRAM for host
controller access.
58
DesignSolution
The flash die size can be reduced by elimi nating approximately 40 bond pads and using simpler SPI periph eral logic on the die. There also is a package cost reduction by reducing pin count and packaging material by approximately 80%.
Another key benefit of SPI is scalability of density without increasing pin count. Parallel flash requires an additional address pin for each successive density. The multiplexed data and I/O structure of SPI allows system designers to support higher-densi-ty devices without dedicating additional ASIC address pins.
For example, migrating SPI designs from 32 Mbits to 64 Mbits or 128 Mbits does not require additional address pins, unlike parallel NOR flash. This enables easy density migration for cus-tomer board designs and the ability to add more functionality into application code.
Design CyCles Drive sPi ADoPtionBuilding in new features to create differentiation and innova-
tion is also easy with an MIO SPI. By reducing pin count, system designers are finding new ways to take advantage of high-per-formance SPI devices to innovate and add value to their system applications.
Rapid design cycles and the continuous drive to lower system cost are prevalent in the consumer space. There are strong region-al influences on the adoption of innovative memory subsystems. Many consumer systems-on-a-chip (SoCs), such as digital TV ASICs, are designed and then assembled into original equipment and design manufacturer reference designs in greater China for the local and export markets. To meet the demands of the con-sumer market for high performance at the best price point, these designers have embraced and adopted SPI.
There are many examples of how the adoption of SPI is benefit-ing applications in the consumer space. Digital TV designers use ASIC pins saved by moving from parallel NOR interface to add additional HDMI ports. Multi-function printers take advantage of the x1 SPI interface on eight-pin small-outline IC (SOIC) pack-ages to reduce the cost of printed circuit boards. STB applications migrate from a NOR execute-in-place memory subsystem to an SPI boot and shadow to DRAM model.
MIO SPI flash can improve performance and reduce costs. Design engineers should look to new interfaces in flash memory and explore other possibilities to improve system performance, lower pin count, and lower the overall system cost.
03.26.10 ElEctronic DEsign
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 59
IdeasforDesign
“PHANTOM POWERING” IS the most common way to power a microphone. The technique supplies 48 V provided through two 6.81-kΩ resistors in a differential input line.1 This idea explains an improved way to use phantom power to run ultra-sound microphones requiring long cables.
Typically, the microphone should incor-porate a signal-splitting circuit—dc block-ing capacitors or a transformer—to separate the phantom power from the audio signals. The capacitors/transformer pass the audio on the differential pair while blocking dc power. The designer must select compo-
nents that do this without degrading the audio signal.
Another approach used in variations for some time now, the Shoeps circuit, employs the 6.81-kΩ resistors—Rf1 and Rf2—as load resistors for direct-coupled emitter followers with pnp transistors Q2 and Q3 (Fig. 1).2 The input amplifier stage uses a JFET (Q1) with a very high input impedance.
The input stage not only acts as an imped-ance converter for the cartridge, it also performs phase-splitting, turning the input signal from the cartridge into two paraphase
outputs. The output stages act as current amplifiers with a unity voltage gain.
Blocking capacitors C5 and C6 are placed between the outputs of the impedance con-verter and the inputs of the voltage follow-ers. Because of the high input impedance of the voltage followers, the value of these capacitors is small, so quality film capacitors can be used.
However, using a voltage follower with a current-setting resistor has a limitation: asymmetrical transient response with a capacitive load. A long cable creates a load capacitance that will charge slowly through the current-setting resistor and discharge fast through the pnp device.
The average current through each 6.81-kΩ resistor is about 4 mA. This cur-rent will charge cable capacitance (C21 + C23) at the rate of (4 mA)(C21 + C23). So, an input sine wave with amplitude Vp would be output as a triangle-wave if the frequency is greater than (4 mA)(C21 + C23)/2π Vp.
The addition of npn emitter followers Q4 and Q5 speeds up the charging of the cable capacitance, eliminating this slew-rate limiting and lowering total harmonic distor-tion (THD). Figure 2 compares the two techniques. The square nonlinearity of the impedance converter JFET causes the gradu-al rise of distortion with the input amplitude.
REFERENCES1. IEC 61938 Audio, Video, and Audiovisu-al Systems—Interconnections and Match-ing Values—Preferred Matching Values of Analogue Signals, clause 7.4
2 . J . Wut tke , Mikrofonaufsa tze , Schalltechnik Dr.-Ing. Schoeps, 2000, p. 83; www.schoeps.de/D-2004/PDFs/Mikrofonbuch_komplett.pdf
Modified Phantom-Powered Microphone Circuit Reduces Distortion
DIMITRI DANYUK | CONSULTANT [email protected]
DIMITRI DANYUK is a consultant. He received his training in electrical engineering at Kiev Polytechnic Institute, Ukraine.
C21 µF
C11 nF
X1
R32.2k
C3100 µF
Q1J305
R11G
R42.2k
C41 µF
R21M
R1010k
Q22SA992
R11100k
C51 µF
R5390k
Q42SC1845
R6100k
R143.9k
R747k
R875
C71 µF
Output 1
23– –
XLR+ +
+
JOUT
R975
R1210k
Q32SA992
R13100k
C61 µF
D112 V
C81 µF
Q52SC1845
R151k
JC1
GndGnd
1
2
1
2
1
23 3 3– –
+ +XLR
XLR
C31
C23
Cable
JC2
C21 Gnd
XLR
Gnd
Rf16.81k
InputJIN
C++
+C–
To amp
Rf26.81k
+48 V
1. In this phantom-powered microphone circuit, the 6.81-kΩ receiving-end resistors act as a portion of a dc-coupled output-follower stage.
60
IdeasForDesign
This circuiT Transforms a pulse-width-modulation (PWM) signal into non-overlapping clock signals, whose number depends on the length of a shift register. These clock signals can be used to power up different loads in a predetermined sequence, as is sometimes necessary in complex systems.
The circuit uses D-flip-flops, two of which are included in each SN74LVC74 IC. The example circuit generates eight indepen-dent clock signals (Fig. 1). A pulse generator or a microcontroller can provide the PWM input, which can vary in frequency and duty cycle.
The circuit shown can accept signals with 1% to 99% duty cycles. A circuit for an actual clock system must account for the operating conditions specified in the datasheets for the chosen logic family.
Also, the value of pull-up resistors R3-R10 will depend on the cir-cuit’s operating speed.1 The PWM signal is fed to the clock inputs of the flip-flops as well as to the output-enable inputs of the gates inside of IC3 and IC6. As a result, a clock pulse is generated at the eight clock outputs when the PWM pulse is also present.
To ensure that the pulse widths of the clock outputs are similar to the duty cycle of the PWM signal, the Q output signals of the different flip-flops are fed to the respective driver gates. The gates in IC3 and IC6 (SN74LVC125) are three-state drivers. Pull-up resistors R3-R10 guarantee a correct signal level at the eight clock outputs when these gates are in three-state status.
The Q output of the first flip-flop drives the D input of next flip-flop, and so on, forming the shift register. The Q output of the last
03.26.10 ElEctronic DEsign
Shift Register Generates Multiple Clocks From PWM Signal
chrisTina obenaus | neoS IngenIeur-Büro oBenauS, arnSdorf, germany [email protected]
THD
(dB)
–20
–30
–40
–50
–60
–70
–80
THD
(dB)
–20
–30
–40
–50
–60
–70
–80
Input amplitude (mVRMS) Input amplitude (mVRMS)60 70 100 200 300 400 500 700 1000 60 70 100 200 300 400 500 700 1000(a) (b)
Cable length:Blue = 100 ftRed = 200 ft
Green = 300 ft
2. These measurements using a 20-kHz input signal show how total harmonic distortion plus noise (THD+N) increases greatly at longer cable lengths and higher input amplitudes for the original circuit (a) compared to the modified circuit (b).
ClkPow
er-on_ResetReset
IC3a IC3b IC3d IC3c IC6a IC6b IC6d IC6c
+3.3 V
Gnd
SN74LVC07A
SN74LVC07A
SN74LVC07A SN74LVC07A SN74LVC07A SN74LVC07A
10
1211
1341
98638
96
5
41
23
1013
1211
2 5
IC2a
IC1c
IC1a
IC1b
IC1d IC1e IC1f
PR
DCLK
CLR
Q
Q
SN74LVC74
4
231
5
6
1A
3A5
1 2
3 4
6 9 8 11 10 13 123Y
1A 1Y
2A 2Y
SN74LVC125
IC2b
PR
DCLK
CLR
Q
Q
SN74LVC74
IC4a
PR
DCLK
CLR
Q
Q
SN74LVC74
4
23
1
5
6
IC4b
PR
DCLK
CLR
Q
Q
SN74LVC74
10
121113
9
8
IC5a
PR
DCLK
CLR
Q
Q
SN74LVC74
4
23
1
5
6
IC5b
PR
DCLK
CLR
Q
Q
SN74LVC74
10
121113
9
8
IC7a
PR
DCLK
CLR
Q
Q
SN74LVC74
4
23
1
5
6
IC7b
PR
DCLK
CLR
Q
Q
SN74LVC74
10
121113
9
8
10
R310k
R1270
R2270
1OE
121113
9
8
2A2YSN74
LVC125
R410k
2OE
4A4YSN74
LVC125
R510k
4OE
3A3YSN74
LVC125
R610k
3OE
1A1Y1Y SN74
LVC125
R710k
1OE
2A2YSN74
LVC125
R810k
2OE
4A4YSN74
LVC125
R910k
4OE
3A3YSN74
LVC125
R1010k
3OE
4A 4Y 5A 5Y 6A 6Y
Clo
ck_1
Clo
ck_2
Clo
ck_3
Clo
ck_4
Clo
ck_5
Clo
ck_6
Clo
ck_7
Clo
ck_8
C7100 nF
C6100 nF
C5100 nF
C4100 nF
C3100 nF
C2100 nF
C1100 nF
IC1IC6IC3IC7IC5IC4IC2
+
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
7
14
7
14
7
14
7
14
7
14
7
14
7
14
1. This example circuit creates eight clock signals. Designers can adapt it to generate more or fewer clocks and to vary the speed, power-supply levels, and rise and fall times of the clock signals.
ELECTRONIC DESIGN GO TO WWW.ELECTRONICDESIGN.COM 61
IdeasForDesign
A RECENT DESIGN project required a bright LED flash each time a 100-µs pulse occurred. The pulse repeated every 300 ms. Because the pulse was so short, driving the LED directly, even with a transistor driver, created a pulse too short to be seen well. So, I need-ed a “pulse stretcher” to increase the LED’s On period to about 1 ms.
In researching solutions, I found that the SN74LVC1G97 con-figurable multifunction logic gate from Texas Instruments could
be wired in four ways to accommodate inputs and outputs of either polarity. The figure shows the four configurations and the Boolean logic equation for each.
Because the inputs are all of the Schmitt-Trigger type, the circuit can use slow rising (or falling) R-C inputs that allow output pulses up to several seconds in length. These circuits are all non-retrigger-able. Any input pulse during the output active period will be ignored, though holding the input active longer than the output pulse width will keep the output active until the input pulse goes inactive.
The input pulses can be as short as 10 ns at supply voltages of 3 to 5 V. The output pulse width is approximately one time constant: T = R1 × C1. Due to manufacturing process variations, the Schmitt trigger levels may change the output timing slightly from device to device, but the timing is accurate enough for LED flashes, relay driving, etc.
Note the addition of Schottky diode D1 in the active-low cir-cuits. Although the inputs are protected against negative-going spikes, the positive input spike that occurs when the output returns high can cause a damaging overvoltage condition on the input pin. D1 keeps this spike within the safe operating input maximum of 5.5 V for a 5-V power supply.
Configurable Logic Chip Stretches Pulses To Brighten LED Flash
JAMES STEWART CAMPBELL, medical design consultant, received a BSEE from Lehigh University, Bethlehem, Pa., and an MD from Albany Medical College, N.Y.
JAMES S. CAMPBELL, MD | MEDESIGN, PFAFFTOWN, N.C. [email protected]
Inputhigh
Inputlow
Output high
Gnd
Gnd
In
R1
V+
C1
316
In0In1In2I1
Y = IN0 OR NOT IN2
Y = IN1 AND NOT IN2
V+
V+
V–
5
Y4
2Out
Gnd
Gnd
In
R1
V+
C1
316
In0In1In2I2
Y = IN1 OR IN2
V+
V+
V–
5
Y4
2Out
Gnd
Gnd
In
R1
D1V+ C1
316
In0In1In2I3
Y = IN0 AND IN2
V+
V+
V–
5
Y4
2Out
Gnd
Gnd
In
R1
D1V+ C1
316
In0In1In2I4
V+
V+
V–
5
Y4
2
Out
Output low
A configurable logic chip, the SN74LVC1G97, can serve as a “pulse stretch-er” when the original (input) pulse is too short to perform the required task. The designer can wire the circuit in four configurations.
flip-flop in the chain is connected to the D input of the first one, closing the ring structure of the shift register. By adding or subtracting flip-flops and three-state gates
to/from the structure and including an appropriate connection between the first and last flip-flop, the designer can create different numbers of clocks as needed.
Connecting low or high signal levels, respectively, to the PR and CLR inputs of individual flip-flops during the shift-ing sequence will determine whether the circuit will generate a shifting pulse at the eight output clocks, more parallel shifting pulses, or a special selected pulse scheme. The pulses in the selected scheme will shift also with each step of the PWM signal. After power-up, a Power-on Reset signal must be fed to the respective circuit input. A signal from the PWM signal-generating microcontroller or another signal source used for control purposes can be applied.
Figure 2 shows the results from a system supplying six clock pulses, which are gen-erated by the PWM signal provided by a
microcontroller (channel 1). Channels 2 through 4 display the resulting signals at three of the circuit’s clock outputs that fol-low each other according to the selected sequence. The results indicate a clear rela-tionship between the PWM signal and the clock output signals.
REFERENCE1. Das TTL-Kochbuch, G. Becke and E. Haseloff, Texas Instruments Deutschland GmbH, 1996.
CHRISTINA OBENAUS is the owner of IneoS Ingenieur-Büro Obenaus, a design company that performs R&D work for other companies in electronic and optic design. She is a diploma engineer.
2. Channel 1 shows the PWM signal used to generate six clock signals. The three clock signals on channels 2 through 4 illustrate the relationship between the input and the clock outputs.
62 03.26.10 ELECTRONIC DESIGN
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Pease Porridge
03.26.10 ElEctronic DEsign
Mailboxbob pease | CONTRIBUTING EDITOR [email protected]
Dear BoB, That Electronic Design article (What’s All This
Microsoft Stuff, Anyhow?” March 11, p. 80) was delightful—brought a big smile to my face. I’ve been with AOL for 14 years, and have encountered a number of problems in that time, but consider myself lucky in that most were rather trivial. Now, McAfee, that’s a different story. I hate the way it sneaks in and overpowers whatever you are doing. (Uh, yeah... /rap)
Yesterday, McAfee turned on while Retrospect was doing its daily backup of my files. Normally when another program interferes, it just slows down the operation. This time, even the time display of hours and minutes was stalled to show the time two hours earlier when the backup turned on. The computer was frozen, immovable, unreachable, and had to be reset to reboot. That kicks Retrospect into a never-start mode, and I had to intervene and “manage my scripts” today to get it onto automatic mode again. But McAfee is free, included with the AOL service, so I guess I’ll keep it. (“Free,” aha, but not without terrible cost. /rap)
In another room, I have an old 80386 computer running on Widows 3.1, with no connection to the Internet and no need to have an antivirus program. It’s so reliable, it’s wonderful—boots up in about 30 seconds. It contains two PCL-812 data acqui-sition cards that I use to run testing on a small consumer electronics product that I designed. It’s nice to have something you can depend on. Those cards are twice as long as could be contained in any modern computer. And the computer can even read a 5.25-in. floppy disk!
Speaking of old things, did you ever have any experience with a GEDA analog machine? I can’t say computer because it wasn’t programmable except through patch cords. It was a Goodyear
Electronic Differential Analyzer, with about 20 high-gain amplifiers that could be configured into very respectable inte-grators, since they were serviced by a rotary sampling switch that looked at all the amplifiers’ input terminals in sequence and fed an amplified correction signal into the rebalancing inputs to make the voltage close to zero at the inputs. It was a rotating chopper-stabilized ampli-fier system. There were also one or two analog multipliers included with the sys-tem for doing nonlinear stuff.
In my first job out of Cornell in 1953, I kept popping into the lab out of curiosity where the GEDA was supposed to be working, but it wasn’t. That was at the General Electronics Advanced Electronics Center near the airport in Ithaca, N.Y., which was also a relic of the past. (I never saw, nor worked on, or heard much about the GEDA. /rap)
I got it working and stayed on call in case the lab needed any further assistance. Whenever the system became unstable or went out of limits where the rotary chopper couldn’t handle the sig-nals, relays were triggered that acted as some sort of crowbar on the amplifiers to prevent their dam-age. It sounded just like a room full of mousetraps gone crazy.
I did help them quite a bit when they needed a source of white noise to test a simulated missile guidance system for its response to noise as the missile approached its target. I set up a bank of NE-2 neon bulbs as relaxation oscillators. Some were fed from a positive voltage and the rest from a negative voltage.
The firing times were random, determined by the R-C networks’ charging times. The discharge currents fed into a common small resistor for all of them, and the signal across this resistor was the noise signal fed to the amplifiers.
On a more serious note, back at my regular job there, I did obtain U.S. patent #3,899,244, along with Bill Porter for a “Frequency Diversity Radar System” or anti-jamming radar. It was classified Secret for years after issue, and even I couldn’t have a copy until it was declassified.
Years after that I learned in the magazine Ameri-can Heritage of Invention and Technology that Heddy Lamarr (the actress) had also obtained an earlier patent for a frequency diversity radio sys-tem for submarine torpedo guidance!
j. DaviD Pfeiffer
Hello, joHn, That’s an old story, now well known. Thanks for
writing. And to hell with McAfee! raP
Comments invited! [email protected] —or:
r.a. Pease, 682 Miramar avenue
San francisco, Ca 94112-1232
BOB pEasE obtained a BSee from MiT in 1961 and
was a Staff Scientist at national Semiconductor Corp.,
Santa Clara, Calif.
Finally
, LTC, LT, LTM, µModule and LTspice are registered trademarksand ThinSOT is a trademark of Linear Technology Corporation.All other trademarks are the property of their respective owners.
The simplest functions are often the most difficult to design. The current source—a basic circuit element—has not beenavailable as an IC. Discrete implementations suffer from poor accuracy, high TC or complexity. Our new current source, theLT®3092, provides all the performance without the compromises: programmable up to 200mA, high AC and DC impedance,low TC and no capacitors required. Its two floating terminals make it easy to use in precision or remote current limiting, biascircuits, intrinsic safety circuits, temperature sensing, active load and signaling applications.
Info & Free SamplesFeatures
www.linear.com/3092
1-800-4-LINEAR
• 0.5mA to 200mA Output Current
• No Capacitors Required
• 10ppm/V Regulation
• 1.2V to 40V Input Voltage
• Reverse Voltage & Current Protection
• Thermal Protection
• 1% SET Pin Current Accuracy
• 3mm x 3mm DFN-8, 8-Lead ThinSOTTM
and 3-Lead SOT-223 Packages Temperature (°C)
– 50–1.00
Curr
ent A
ccur
acy
(%)
–0.50
0
0.50
–25 0 25 50 10075 125
1.00
–0.75
–0.25
0.25
0.75
150
LTspice®LTspice®
A Simple, Precise 2-Terminal Current Source
Current Accuracy vs Temperature
www.linear.com/LTspice
