Transimpedance Amplifier Design

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1、CHAPTER6TransimpedanceAmplifierDesignThephotocurrentgeneratedbythephotodetectorthroughoptoelectronicconversionoftheincom-inglightmustbeconditionedtocomplywiththerequirementsoftheclockanddatarecoveryblock.TheCDRperformsretimingandsynchronizationofthereceiveddatastream,butreq

2、uirestheinputsig-nalamplitudetobeconstantandlargerthanitsinputsensitivity.Forthispurpose,thephotocurrentisconvertedtothevoltagedomaininthetransimpedanceamplifier(TIA).Thiscurrent-voltage(I-V)con-versionintrinsicallyprovidessignalamplificationbythegainZTIA,commonlycalledtran

3、simpedancegain.Additionalgainisthenimplementedinthelimitingamplifier(LA)inthenextstepofthecondi-tioningprocess.6.1PrinciplesofI-VConversionFIGURE6.1.BasicI-VconverterwithvoltagefollowerThemostbasiccurrent-to-voltageconvertersendsthephotocurrentthroughaseriesresistorRTIAandu

4、sesanamplifierwithvoltagegainAvTIAinunity-gainconfigurationtobufferthesignal(Figure6.1).TheI-VgainisgivenbytheresistorvalueRTIA,whilethebandwidth,determinedbythepassivefront-end,isgiveninEquation6.1.Inthisexpression,thephotodetectorcapacitanceCPDis73CMOSMultichannelSingle-C

5、hipReceiversforMulti-GigabitOpticalDataCommunicationssupposedtobethedominanttermofthetotalinputcapacitance,comparedtotheamplifierinputcapac-itanceandotherstraycapacitancesconnectedtothisnode.1BW=------------------------------(EQ6.1)2πRCTIAPDThetrade-offbetweentheI-Vgaincont

6、ributedbytheresistorandthebandwidthrepresentsthemajorlimitationofthisstructure.Designforhighgaininthepassivestageleadstoalargevoltagesignalattheamplifierinput,minimizingtheinfluenceoftheamplifiernoise,butreducingthesignalband-width.Lowgainontheotherhandreducesthesignal-to-n

7、oiseratio(SNR)attheamplifierinput,butincreasesthesignalbandwidthconsiderably.Dependingonthespecificationsforhighgainorhighbandwidth,thistopologyisalsodubbedhigh-impedanceamplifierorlow-impedanceamplifier,dis-cussedinfurtherdetailsin[46].Becauseofthisimpracticaltrade-offbetw

8、eennoiseandbandwidth,thefeedbackresistortopologyhasbeendeveloped(Figure6.2),usuall