最新analog资料幻灯片.ppt

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1、analog资料Outline1.GeneralConsiderations2.Multi-PoleSystems3.PhaseMargin4.FrequencyCompensation5.FrequencyCompensationofTwo-StageOpAmps2021/8/221.GeneralConsiderationsThecircuitmayoscillateinfeedbacksystems.Oscillationconditions(Barkhausen’sCriteria,巴克豪森判据)1.Atω1,thephaseshiftaroundtheloopissomuchthat

2、thefeedbackbecomespositive;2.Theloopgainisstillenoughtoallowsignalbuildup.2021/8/23Time-domainresponseofaclosed-loopsystemversusthepositionofpolesExpressingeachpolefrequencyassp=jωP+σp,theimpulseresponseofthesystemincludesatermexp(jωP+σP),具有位于右半平面的极点的闭环系统是不稳定的；2021/8/27Feedbacksystemwithone-polefeed

3、forwardamplifierThesystemisunconditionallystableforallnon-negativevaluesofβ2021/8/282.Multi-PoleSystemsTwo-polesystemThesystemisstable,butsmallmargin.2021/8/29Three-polesystemThesystemisnotstable.↓βAdditionalpoles(andzeros)impactthephasetoamuchgreaterextenttheydothemagnitude.2021/8/2103.PhaseMarginH

4、owfarshouldPXbefromGX?letusconsidera“marginal”case,e.g.AtGX,phase=-175°WehavePhaseMargin(PM):definedasPM=180°+∠βH(ω=ω1)其中，ω1为增益交点频率2021/8/211Howmuchphasemarginisadequate?ForPM=45°，ForPM=60°，ForPM=90°，2021/8/2124.FrequencyCompensationMethodsofincreasingPM减少极点数,PX往外推减小带宽,GX往里推2021/8/213Frequencycompen

5、sation:TelescopiccascodeopampshowninFig.belowPoles:Out，A，N，X（Y）2021/8/214FrequencycompensationBodeplot,forβ＝12021/8/215FrequencycompensationMethods:Increaseloadcapacitance,i.e.adjustdominantpole(firstpole).Avoidmirrorpole.Thefirstnon-dominantpolemustbefarfromorigin.(equaltoormorethanunity-gainbandwi

6、dth)2021/8/216Frequencycompensation↑Rout→AV↑，虽然ωp，out=(RoutCL)-1降低,由于不影响GX和PX，因此，增大Rout并不能对运放进行补偿IncreasingRoutdoesnotcompensationtheopamp.2021/8/217FrequencycompensationFulldifferentialopamps:Avoidmirrorpole.Onedominantpole(output)andnon-dominantpole(XorY)atrelativelyhighfrequenciesdueto“shield”ofc

7、ommon-gatetransistors.stable2021/8/2185.FrequencyCompensationofTwo-StageOpAmpsPoles:AddapoleforeverystageampilifierX(Y)，E（F），A（B）Twodominantpoles:E(F),A(B)closetoorigin.Notstable,requiringcompensation