拉扎维《模拟集成电路设计》第二版课件.ppt

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1、Chapter14:NonlinearityandMismatch14.1Nonlinearity14.2MismatchNonlinearity:GeneralConsiderationsNonlinearcharacteristicdeviatesfromastraightlineastheinputswingincreasesE.g.,Common-sourcestageordifferentialpair2Nonlinearity:GeneralConsiderationsNonlinearinput/outputcharacteristiccanbeapproxim

2、atedbyapolynomialintherangeofinterestForsmallx,y(t)α1x,indicatingthatα1isthesmall-signalgaininthevicinityofx03Nonlinearity:GeneralConsiderationsNonlinearitycanbequantifiedbyspecifyingmaximumdeviationofcharacteristicfromanidealoneForvoltagerangeofinterest[0,Vin,max],passstraightlinethrough

3、endpointsofactualcharacteristicandobtainmaximumdeviationVNormalizetomaximumoutputswingVout,max1%nonlinearityforaninputrangeof1Vmeans4Nonlinearity:GeneralConsiderationsNonlinearitycanalsobecharacterizedbyapplyingasinusoidatinputandmeasuringharmoniccontentofoutputIfthenMagnitudeofnthharmonic

4、growsroughlyinproportiontonthpowerofinputamplitudeQuantifiedbysummingthepowerofallharmonicsexceptfundamentalandnormalizingtopoweroffundamental,metriccalledas“totalharmonicdistortion”(THD)Forathird-ordernonlinearity,5NonlinearityofDifferentialCircuitsDifferentialcircuitsexhibit“odd-symmetric

5、”characteristicEven-ordertermsα2jinpolynomialmustbezero:DifferentialcircuitdrivenbyadifferentialsignalproducesnoevenharmonicsConsidertwoamplifiersprovidingequalsmall-signalvoltagegainof6NonlinearityofDifferentialCircuitsIfaninputVmcosωtisappliedtoeachcircuit,forcommon-sourcestage,Amplitudeo

6、fsecondharmonicnormalizedtofundamentalisForthedifferentialpair,itcanbeshownthatIf,thenDifferentialpairexhibitsmuchlessdistortionforsamegainandoutputswing,atthecostofhigherpower7EffectofNegativeFeedbackonNonlinearityExpectedthatnegativefeedbackwouldyieldhigherlinearityforaclosed-loopsystemCo

7、nsidera“mildlynonlinear”systembelowAssumecoreamplifierhasaninput/outputcharacteristicApplyasinusoidalinputpostulatingthatoutputcontainsafundamentalandsecondharmonicapproximatedasThroughsimpleanalysis,wecanget8EffectofNegativeFeedbackonNonlinearitySmallno