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.
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Fig.10.22Surfacechannel
modulationofdetection
transistorY.Matsunaga
S=N,aswellknownfromthenegative-feedbacktheory.Thus,thesuperiornoiseperformanceofthedetectorismaintained.
10.3.3Evaluation
Figure10.22showsthesurface-channelpotentialofthedetectiontransistorversusthefeedbackgatevoltage.Thesurface-channelpotentialismeasuredusingthetestdeviceofthedetectiontransistorfabricatedonthesamechipastheimagesensor.Thefeedbackcoef cientk,whichcorrespondstotheslopeofthelineinthe gure,isapproximately0.4.Inthepracticaldetector,nisdeterminedtobe5,takingthephotodiodesaturationintoconsideration.Accordingly,thefeedbackampli ergainAissetto10.Theequivalentinputnoisevoltageofthefeedbackampli erisapproximately10 Vrmsat3.58MHzbandwidthwhichissigni cantlysmallerthanthe80 Vrmsofthesourcefollowers.
TheH-CCD(¥H1,¥H2)andtheresetgateRSweredrivenata7.16MHzclockfrequency,whichistwicetheNTSCcolorsubcarrierfrequency.Figure10.23showstheRSand¥H1inputpulses,andtheoutputvoltagesignals.Figure10.23a,bshowstheoutputvoltagesignalofthesaturationlevelwithoutthefeedbackloopandthecompressedvoltagesignalbythenegativefeedback,respectively.ThewaveformXinthe gureisnottheclocknoise,butafeedthroughvoltageofapartoftheinvertedsignalfromthefeedbackgate.Figure10.23cisthesaturationsignalwiththefeedbackloop.Thenoisevoltageisalsosuppressed14dB.Figure10.24showsthemeasuredcharge-to-voltageconversioncharacteristicsandthenoiselevelsofthedetector.Thecharge-to-voltageconversiongainislinearwithin5%overarangeofchargepacketsfrom200to10,000electrons/packet.Thecharge/voltageconversiongain,thenoisevoltage,andthesaturationvoltageofthedetectorwithoutthefeedbackloopare100 V/electron,80 Vrms,and1.0V,respectively.Thesaturationchargeof10,000electrons/packetandthenoiseequivalentsignalof1.0electronrmsareobtainedfromthesevalues,takingasignaldutyTs=T0intoconsideration,whereTsandT0aretheeffectiveoutputsignalperiodandtheclock
