Image CCD System

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1、CCDImagingSystems•TheCCDElement.............................................7.3•PreamplifierStage..........................................7.11–Requirements...........................................7.12–WithDC-Restoration................................7.15•CorrelatedDoubleSampl

2、ing.........................7.18•A/DConverter.................................................7.26ContributingAuthor:StephanBaier7.1CCDImagingSystemTypicalBlockDiagramV/H-DriverTimingGeneratorCorrelatedPreampDoubleGainandA/DDSPandClampDriverSampling(CDS)DC-RestoreCCDCoarseOffsetD

3、/ALevelShiftFineOffset7.2TechnologyadvanceswithCCDs(ChargeCoupledDevice),likeincreasedresolutionatlowermanufacturingcosts,havefueledthegrowthintheelectronicimagingindustry.However,someofthetypicalconstraintsofCCDsremainunchanged,suchastheverylowoutputsignallevelandtheinherentnois

4、esources.Furthermore,increasedresolutiongenerallyequalshigherread-outspeed,whichinturndictatestherequirementsforthesubsequentelectronics.TheCCDisthecentralelementinanimagingsystem.DesignersneedtobeawareofthespecialrequirementsforthesignalconditioningoftheCCDinordertoachievethemax

5、imumperformance.TheoutputsignaloftheCCDisaconstantstreamoftheindividualpixel“charges”andthisresultsinthetypicalformofsteppedDCvoltagelevels.ThisoutputsignalalsocontainsaDC-biasvoltage,whichisintheorderofseveralvolts.ThesignalisthenpassedthroughacapacitortoblocktheDCvoltagebeforeg

6、oingintothepreamplifier.Tomaintainthenecessaryrelationshipbetweenthepixelinformationandthebaseline,aclamporDC-restorecircuitisusuallysituatedinthefirstprocessingstage.ThenextstageisusedasanoisereductioncircuitspecifictoCCDbasedsystems:thecorrelateddoublesampler(CDS).Followingisan

7、othergainstage,whichcouldbeaautomaticgaincontrolamplifier(AGC),orafixedgainstagewithoffsetadjustment.BeforegoingintotheA/Dconverteritusuallypassesthroughadedicatedbufferordrivercircuitoptimizedfortheselectedconvertertype.FurtherbaselinestabilizationcanbeachievedbyhavingaD/Aconver

8、terinadigitalcontrolloop.Inthefollowingd