基于单片机的数字时钟设计--外文翻译(4)

Abstract Virtually complete charge transfer can be achieved with charge coupleddevices(CCDs)intheburiedchannelconfigurationbecausetheburiedchannelCCDintroduces no transfer noise. However, conventional charge detectors incorporatedinto CCDs have a comparably large noise, which consists of thermal noise and 1/fnoisefromMOS transistorin theoutputchargedetectors.

10Low-NoiseElectronicImagingwithDouble-GateFETs23310.3CCDImageSensorwithDouble-GateFET

ChargeDetector

ThepixelsizeoftheCCDimagesensorhasbeenmadesmallertoreducechipsizeforsmallopticalassemblyandtorealizemegapixelsensorsforHDTVcameras.Itisnotacceptable,however,tocompromisethesensorperformanceforasmallercellsize,andinparticular,thesensitivityandthedynamicrangeremainhigh[1].Incontrast,theburied-channelcharge-coupleddeviceachievescompletechargetransferwithnotransfernoise.Therefore,almostallsolid-stateimagesensorsutilizelow-noiseburied-channelCCDforscanningcircuits.

Inthefollowingwedescribea1/3-ininterlinetransferCCDareaimagesensorwith94-dBdynamicrangeand1.0-electronrmsnoise oatingsurfacedetector.Withcapacitance-couplednegative-feedbackcon guration,thesaturationlevelofthedetectorissuccessfu1lyextendedbyafactorof5,maintainingthesuperiorlow-noisecharacteristics.Moreover,1=fnoiseintheoutputsignal,whichisaveryconspicuousstreaknoiseinthereproducedimageinspiteofitslow-noisepower,issuccessfullysuppressedwithanovelso-calledalternategaininversion(AGI)signalprocessingtechnique.

10.3.1SensorConstruction

Figure10.19showsphotographsofthefabricateddevicechipandthedetectiontransistor.Thechipsizeis7.1mm.H/ 5:1mm(V),andtheimagesizeis

4.8mm.H/ 3:6mm(V),whichissuitablefora1/3-inlensformat.ThedeviceisthemostpopularinterlinetransferCCDcon gurationatpresent,whichconsistsofphotodiodes,verticalCCDs(V-CCDs),andahorizontalCDD(H-CCD).Forlowleakagecurrentnoise,theburiedphotodiodestructure,whichhasahighconcentrationpC-layeronthen-typestorageregion,isadopted[7,8].ThechargedetectorattheendoftheH-CCDisadouble-gate oatingsurfacedetectorwithaneffectivereadoutnoiseof1.0electronrms.Adynamicrangeof94dBisobtainedbyreturningtheinvertedvoltagesignalontoafeedbackgate.Thesaturationnumberofelectronsisextendedto5 104electrons,whichcorrespondstothesaturationchargeofthephotodiode.

Thedeviceisfabricatedinashallowp-wellonann-typesubstrateof47 cmresistivitywith1:0 m nepatterndesignrule.Twoion-implantationprocessesareaddedtotheconventionalCCDfabricationprocess.Oneisahigh-energyphosphorousimplantationforthesensingchannel,andtheotherisasource/drainboronimplantationfortheP-channeldetectiontransistor.

Abstract Virtually complete charge transfer can be achieved with charge coupleddevices(CCDs)intheburiedchannelconfigurationbecausetheburiedchannelCCDintroduces no transfer noise. However, conventional charge detectors incorporatedinto CCDs have a comparably large noise, which consists of thermal noise and 1/fnoisefromMOS transistorin theoutputchargedetectors.

234

Fig.10.19Photographsof

sensorchipandenlarged

detectorY.Matsunaga

10.3.2FeedbackChargeDetector

Figure10.20showsthedetectorstructure.Thesignalcharge(electron)packetsareclockedalongtheH-CCD,andtransferredintothedetectiontransistorsignalsensingregionundertheFPP.Thedetectedchargesaremovedoutintoaresetdrain(RD)byapplyingapositivepulseonaresetgate(RS).ThesignalchargeinthesensingregionmodulatestheP-channelconductanceinthedetectiontransistor.Anoutputsignalisgeneratedusingtwosource-followerstages,constructedwithn-channelMOStransistors.Aninvertedsignalvoltageisappliedtothefeedbackgateofthedetectiontransistor.Thefeedbackampli erisaninverteranditsnoiseisdesignedtobemuchsmallerthanthatofthesourcefollowersinordernottoaddextranoisebythefeedbackloop.Thecapacitance-coupledfeedbackloopallowsthedynamicrangetobeextended.TheoxidethicknessbetweenthefeedbackgateandtheFPPisapproximately1:0 m.

Figure10.21showstheincreaseinthesaturationchargebythenegativefeedbackoperation.SignalchargeQsisconvertedintovoltagesignalVsbytheverylowsensingcapacitanceCeinthecaseoftheopenloopasshowninFig.10.21a.Onthecontrary,inthefeedbackoperation,theeffectivesensingcapacitanceincreasesntimesbytheinvertedsignalvoltage,whichisappliedtothefeedbackgate,sothattheoutputsignalvoltageiscompressed,asshowninFig.10.21b,andthesaturationchargeincreasesbyafactorofn,asshowninFig.10.21c.Theparameternisequaltothewell-knownfeedbackformula(1CkA),wherekandAarethefeedback

Abstract Virtually complete charge transfer can be achieved with charge coupleddevices(CCDs)intheburiedchannelconfigurationbecausetheburiedchannelCCDintroduces no transfer noise. However, conventional charge detectors incorporatedinto CCDs have a comparably large noise, which consists of thermal noise and 1/fnoisefromMOS transistorin theoutputchargedetectors.

10Low-NoiseElectronicImagingwithDouble-GateFETs

235Fig.10.20Detector

structure

Fig.10.21Potentialdiagramsofsensingchannel.(a)Saturationconditioninopenloop.(b)Compressedconditionbynegativefeedback.(c)Saturationconditioninnegativefeedback

coef cientandthefeedbackampli ergain,respectively.Inthisdetector,kisequaltoCg=.CgCCc/,whereCgandCcarethegatecapacitanceofthedetectiontransistorandthediffusioncapacitanceofthen-typesensingchannelundertheFPP,respectively.ItisderivedfromthepartitionratiooftheCgandCcseriescapacitances.

NoiselesssignalchargeisconvertedintothevoltagesignalS,whilethedetectornoiseisNintheopen-loopchargedetector.Byapplyingtheinvertedoutputsignalontothefeedbackgate,notonlythevoltagesignalbutalsothedetectionnoiseiscompressed,andtheyresultinS0andN0.Signal-to-noiseratioS0=N0isequalto

Abstract Virtually complete charge transfer can be achieved with charge coupleddevices(CCDs)intheburiedchannelconfigurationbecausetheburiedchannelCCDintroduces no transfer noise. However, conventional charge detectors incorporatedinto CCDs have a comparably large noise, which consists of thermal noise and 1/fnoisefromMOS t …… 此处隐藏：6095字，全部文档内容请下载后查看。喜欢就下载吧 ……