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Advantage of the CMOS SensorLatest image sensor technology for HD security

Contents1. Introduction2.ComparingCCDandCMOS3.CMOSSensor“Exmor”4.NewWide-DTechnology5.FutureDevelopments

IntroductionSince the replacement of imaging tube by solid image sensor intheearly80’s,2typesofsensor,CCD(ChargeCoupledDevice)andCMOS (Complementary Metal Oxide Semiconductor) have beenusedinthevideoequipments.Theeasierprocessingmethodandlowmanufacturing cost popularizes the CMOS image sensor in simpleimagecapturingproducts likewebcamsandmobilephones,whiletheCCDtechnologyremainsdominantforprofessionalandconsumervideoequipments.

SecurityindustryisoneofthelargestindustrysegmentswhichadoptedtheCCDtechnologyforCCTVcameraproducts.CCDimagesensorsareused in themajorityofanalogcameraswhicharebasedonTVstandard of NTSC or PAL. With the advancement of technology, weseeahigherdemandfordigitalsecuritycameraswhichcantransmitdigital video signal over IP.The recent pursuit for higher resolution isalso increasingthedemandfor the latesthighdefinition(HD)videostandardinthesecurityindustry.ThisrapidshifttoHDbasedsystemisoneofthemaindriverfortheCMOStechnology.

StrivingtomergetheadvantagesofboththeCCDandCMOSsensor,research and development are intensely focused on improving theCMOSsensortobecomeanimagingdevicewhichhasanequivalentpicture quality as the CCD image sensor. As a result, an improvedCMOSsensor–“Exmor”CMOSsensorisdeveloped.

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Comparing CCD and CMOSAlthoughbothsensorsareimagecapturingdevicesforacamera,thelatestCCDandCMOSsensorsareverydifferentinstructure.Figure1describesthesestructures.

Fig.1 Read out signals

The CCDs video applications requires all the vertical and horizontal shift registers to constantly relayreceivedimagedataaselectronicsignals.Asaresult,thereisalimitationtoachievehighresolutionandhighspeedsimultaneously.Powerconsumptionalsobecomescomparativelyhigh.Alternatively,theCMOSsensorsonlyneedtomoveonereadoutcolumnofcircuitry,sopowerconsumptionremainscomparativelylowevenwithincreasedprocessingspeed.

CMOS Sensor “Exmor”Inrecentyears,thegrowinginterestinsmallHighDefinitioncamcorderssparkedthesignificantdevelopmentofCMOSsensorswhicharelowpowerconsumptiondeviceswithhigh-speedimagereadoutcapabilities.Thehighdefinitiontrendisalsostartingtogrowinthevideosecurityindustry.CoupledwiththeprevalenceofIPnetworks,theIPvideocameranolongerdependsontheconventionalTVformat.Toaddressthedemandsofhigherresolutionfromthevideosecurity industry,SonystartedtheresearchanddevelopmentofanimprovedCMOSsensorusingitsimagequalityknowledgeaccumulatedinCCDs.TheresultisaCMOSsensorwithanentirelynewstructure,the“Exmor”CMOSsensor.BothCCDandCMOSsensorshavethesamecomponentthatconvertslightintoelectricity(akeyelementofimagequality).Withthe“Exmor”,however,SonyuseshighimagequalitypixeltechnologyaccumulatedinCCDdevelopmenttoenlargeasmuchaspossiblethelight-receivingsectionofthephotodiode.Tables1and2showspecificationsand ImageSensorCharacteristics for the“Exmor”CMOS,CMOSandCCDsensors.

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Anothermajorelementthataffects imagequality isnoisereduction. Inthe“Exmor”CMOSsensor,noiseontheanalogcircuit iseliminatedbythebuilt-inCorrelatedDoubleSampling(CDS)circuit.Othernewstructuralelementsincorporatedintothesensoralsodrasticallydecreasethenoise-contaminationlevel.Figure2andFigure3describethesestructures.

•TheA/Dconversionconventionallydonejustbeforesignalreadoutisnowperformedimmediatelyafterthelight-to-electricityconversionforeachcolumn.Thishelpstoreducenoisebecausetheanalogcircuitismadeshorter,andthefrequencylower.

•Noise-eliminationcircuits(CDScircuit)areequippedinthedigitaldomain.

Table1 Specifications

Table 2 Characteristics

Fig.2 Sensor structure

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Throughthesemethods,drasticimprovementshavebeenmadeinCMOSsensorimagequality,achievingthesameimagecaptureperformancelevelasCCDsensors.InthenewSonyIPvideosecuritycameras,theminimumobjectluminancespecificationsforcamerasequippedwitheitheraCCDoran“Exmor”CMOSsensorareasfollows:

SonyIPvideosecuritycamerawithCCD–SNC-CM120:1.3M,Minimumillumination:0.8lxSonyHDIPvideosecuritycamerawithCMOS–SNC-CH140:720PHD,Minimumillumination:0.2lx

Fig.3 Noise reduction

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View-DR : New Wide-D TechnologyVier-DRusestheHigh-speedReadoutoftheCMOSSensor.Whencomparingthenewlydeveloped“Exmor”CMOS sensor with the CCD sensor, not only has the sensitivity improved, but data (image) readout isdramaticallyfaster.Usingthesehigh-speedreadoutcapabilities,Sony’sHDIPcamerasnowcomeswithanewly-developedWide-Dtechnology,calledtheView-DRfunction.

WithaCCDsensor, theuser is restricted to takingsuccessive1/60-second imagesor two1/30-secondimagesandcombiningthem.InView-DR,theusercantakeone1/30-secondimageatlongexposure,andtakeotherimagesoverthesameperiodatshortexposure,andthenimageprocesstheminreal-timetoachieveanindustry-bestwidedynamicrange.

Figure4showsthestructureofthisindustry-bestWide-D(View-DRfunction)asusedbythe“Exmor”CMOSsensor:

Fig.4 View-DR structure

Future DevelopmentsThedemandforimagewithgreaterdetailsandlessnoisewillcontinuetogrow.Therequirementofhigherresolutioninvideosecurityapplicationswillcontinue,andthiswilldrivethedevelopmentofHDtechnologyinthevideosecuritymarket.Asaresult,CMOSsensors,whichhaveahigherspeedofreadoutdatathanCCDsensors,willbecomepredominantinthesecurityindustryandboththeprofessionalandconsumermarket.

Lookingintothefuture,SonyisresearchingonamoresensitiveCMOSsensorcalledthe“back-illuminatedhigh-sensitivityCMOSimagesensor”.ThisCMOSsensorisnowavailableinvideocamcordersanddigitalstillcameras.TheCMOSsensordeliversboth improvements insensitivityand reductionof imagenoise,bothcrucialinthecaptureofhighimagequality.

©2011 Sony Electronics Asia Pacific Pte. Ltd. All rights reserved. Reproduction in whole or in part without written permission is prohibited.

Features and specifications are subject to change without notice. “Sony”, “make.believe”, “Exmor” and “View-DR” are trademarks of Sony Corporation.