第2章-偏置

1SENANJINGwujinCMOSAnalogICDesignC[e-mail]-II,2012,092SENANJINGwujinFocusontheContentsFocusontheContentsBiasing:Constantcurrent/Voltagegeneration;V⇔I--Singlebranch,thesimplestbiasing--Multi-branchescoupledbiasing(Linear/NonlinearCM);L-CMforcurrenttransportation;NL-CMforcurrentdefinition;--Dynamicproperty.CurrentMirror--CurrentSource/Sinkfortransfer,usedin&outbiasing--CascodeCMusedforimpedanceboostingExcellentorIdealbiasing--Betterinmatchingwhendeliveringcurrent;--StablewhenVDD,temperaturesarevaried3SENANJINGwujinIdealBiasing:Voltage/CurrentSourceIdealBiasing:Voltage/CurrentSourceBiasingforaMOSFET:StaticIDSandVGSprovidedcircuit-TogenerateastableIDSbyafixedVGSwhenlocatedatS.R.or-TogenerateastableVGSbyafixedIDSwhenlocatedatS.R.PVTinsensitivity:Process,Voltage,Temperature;EndlessV/CReference:V/CSourcewithzeroTemperatureCoefficient可相互转化,有任一个即可4SENANJINGwujinHowtogeneratestablebiasingHowtogeneratestablebiasing-CurrentSource:high/∞outputrd,low/zerooutputgd;-VoltageSource:low/zerooutputrd,high/∞outputgdForpassiveelement,nooperationpointorbiasingconditionsarerequired,butit’snecessaryforactivedevicesusedinanalogsignalprocessing;However,passiveelement(R)canbeusedforsetsuitableoperationpointforactivedevices,toobtainThereisnopossibilitytoobtainedthestablestaticbiasingforactivedevicespurelybylinearpassiveelement,NLelementsarecertainlyrequired.5SENANJINGwujinSimpleBiasing:SinglebranchtypeSimpleBiasing:Singlebranchtype1.Simplest,bothIb&VbarelinearchangedwithVDD,unfitforIC;2.NLresistanceinduced,Vbvariedsmall,butIbremainchangedquicklywithVDD；widelyusedinICforsimplicity.3.NL+NLresistance,bothIb&VbvariedwithVDD,seldomused;4.VGSboost,currentreduction,mixedstructureofsinglebranch.1.R+Rtype2.R+MOSDiode3.Diode+Diode4.Coupled6SENANJINGwujinBasicVoltagedividedPrincipleReviewBasicVoltagedividedPrincipleReviewStaticVbfromVCCforprovideVGS:2121211/bCCCCGSRVVVVRRRR==⇒++2121211/bCCCCrVVVrrrrΔ=Δ=Δ++InterruptΔVbfromΔVDD:ConstantneededZerorequiredNonlinearresistanceshouldbeintroducedtoseparateDCRfromACr.ForΔVb=0,r1→∞(constantI)&r2→0(constantV)arerequired,whichmeanthatthevoltagesourceandcurrentsourceshouldbeusedtogetherinasinglebranch,inthiswaythefixedDCV&IcanbecertainlyestablishedbyvariableR1/R2withVCC.7SENANJINGwujinRR11+MOSDiode(r+MOSDiode(r22))NegativeFBcontrol:VCC↑⇒Ib↑⇒gm↑⇒R2,r2↓⇒分压比↓⇒Stable.IfR2isreplacedbyMOSDiode,R2forDC,r2forAC,andR1=r1Ques:Forsinglebranch,howtoachieveVoltage¤tsourcesimultaneously,andwherethecurrentsourcecomingfrom?2221()(1/2)GSGSmVVRkg==ΔΔ211mdmrggg=≈+222/)1GSVRrΔ⇒DC&ACresistanceforMOSDiodeiswellseparated!8SENANJINGwujinR+MOSDiodeBiasingforCurrentMirrorR+MOSDiodeBiasingforCurrentMirrorDealwiththeoutputcurrentandgatevoltagetranslation.Takethereason(Input)andtheresults(Output)relationship.12)(21RVVVVkbCCTHb−=−Δ+=+−+−=THCCTHTHbVkRVVkRkRVV12112)1(1Partiallyrequirementsaresatisfied!WeakrelatedwithVCCCanRbereplacedbyacurrentsourceinasinglebranch?RisusedtodefineIbSinglebranchbiasedcircuitispooratcurrentstability!CurrentMirror9SENANJINGwujinII⇔⇔VtransformVtransformforallNMOS&PMOSBiasingforallNMOS&PMOSBiasingIfstablebiasedVGSNisgenerated,itcanbeusedtobiasallotherNMOStransistorsinaformofCurrentmirror.I-V-Itransform:ConstantIinÆConstantVGSNÆÆConstantIoutÆConstantVGSPAttention:NMOSisbiasedbyVGSN,PMOSisbiasedbyVGSP,intheformoflinearcurrentmirrors.Thefirstone(reason)isgeneratedbybiasingcircuitPrinciple:NMOStobiasNMOS,PMOStobiasPMOS,sametype10SENANJINGwujinMultiMulti--BranchesBiasedCircuitsBranchesBiasedCircuitsTwobranchesbiasedcircuit:NMOScurrentmirror+PMOSCurrentmirrorcoupled(biased)foreachotherstoobtainonlyoneintersectionpointotherthanzero(staticpoint).Thus,atleastoneofthetwoCMshouldbegivenasNLCM.Onebranch:highimpedance+lowimpedancearchitecture.IfbothareNLCM,twosituationhappen:1)nointersectionpointexceptoriginalpoint;2)infiniteintersectionpoints.Failedinbiasing11SENANJINGwujinNonlinearCMisenough?NonlinearCMisenough?OnlyoneintersectionpointAexceptO(0,0)isrequired.It’sunnecessarytointroducetwoNLCM(keeponeL-CM)L-CM:currenttransportation;NL-CM:currentdefinition.12SENANJINGwujinNonlinearCMbydifferentVNonlinearCMbydifferentVBEBE12111lnRBETQQVVVIINRRRΔ≈===PeakingPeakingCMCMNLCM•TwobranchIQ1,IQ2;•IQ1=IQ2definedbyL-CM;•SQ2:SQ1=N2-11•ΔVBE=VBEQ1-VBEQ2=VR1;•IQ1,2=ΔVBE/R1)/ln(,SQQTQBEIIVV=12,1-2122121ln()ln()lnQQBEQQTTTQQISVVVmNVNIS−−Δ===m1-2=1N=m1-2N2-1VCCunrelated!13SENANJINGwujinNonlinearCMbydifferentVNonlinearCMbydifferentVGSGS121211111,2121112()221()GSGSRMMMMMVVVIRRRIIRRkk−Δ−Δ==≈ΔΔ==−11211121211(1)(1)QkIRkRNkk=−=−22112(1)QNIkNR−≈⋅⋅PeakingCM,similarasPeakingCM,similarasBJTtypedcircuit.BJTtypedcircuit.122121;/MMQIfIIIkkN−≈==VCCunrelated.Ques:IsIQreallycompletelyunrelatedwithVCC,why?Howtoimproving?.14SENANJINGwujinWidlarWidlarNLCM,anotherNLCM,anotherΔΔVVBEBEororΔΔVVGSGS,122BEQQQVIR−Δ=,122GSMMQVIR−Δ=RelationbetweentwobranchescurrentisactuallyimportantindeterminingΔVBEorVGS.CurrentdefinitionR2islocatedatemitterorsourceofN-typeddevicetoconfigureNLCM.Smallcur