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
Fig.10.23Inputpulsesand
outputsignalwaveformsof
detector.(a)Saturationsignal
withoutfeedbackloop.(b)
Compressedsignalwith
negativefeedback.(c)
Saturationsignalwith
negativefeedback
loop237
cycleofthehorizontalCCDdrivingpulse,respectively.Withthecapacitance-coupledfeedbackloop,thesaturationchargelevelisincreasedbyafactorof5,andthedynamicrangeisimprovedto94dB,maintainingtheeffectivereadoutnoiseof1.0electronrms.
ThecharacteristicsoftheimagesensorwiththenewdetectorareshowninTable10.1.TheverylowdarkcurrentisrealizedbytheburiedphotodiodestructureandthepinnedoperationoftheV-CCD.Inthepinnedoperation,thesurfaceemissionunderthetransferelectrodes,onwhichthelow-levelvoltageoftransferpulseisapplied,issuppressedbecauseholesareaccumulatedthere.
10.3.4SignalProcessing
Theoutputsignalincludesthelarge1=fnoisegeneratedbytheMOStransistorsoftheon-chipdetector.Figure10.25showsthenoisespectrumoftheon-chipdetectorwithoutthefeedbackloop.The1=fnoisegeneratesaveryconspicuousstreaknoiseinthereproducedimageinspiteofitssmallnoisepower.The1=fnoiseshouldthereforebesuppressedtorealizealow-noiseimagesensor.Anoisereductionsignalprocessingtechniquecalledalternategaininversion(AGI)isproposedtosolvetheproblem.Thisprocessingisabletosuppressnotonlythe1=fnoisebutalsothekTC
