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1、Chapter6DifferentialandMultistageAmplifiersIntroduction6.1TheBJTdifferntialpair6.2Small-signaloperationoftheBJTdifferentialamplifier6.3Othernonidealcharacteristicsofthedifferentialamplifier6.4MOSdiffenrentialamplifiers6.5Biasinginintergratedcircuits6.6TheB

2、JTdifferentialamplifierwithactiveload6.9MultistageamplifiersIntroductionThedifferentialamplifier(pair)configurationisthemostwidelyusedbuildingblockinanalogICdesign.BJTdifferentialamplifieristhebasisofavery-high-speedlogiccircuitfamily,calledemitter-coupled

3、logic(ECL).Why?Reasons:DirectcouplingbetweensignalsourceandamplifierwilleasilycausetemperatureDrift(zerodrift).Whatshallwedo?AdvantagesThereare2reasonsforusingdifferentialinpreferencetosingle-endedamplifiers.(1)Differentialcircuitsaremuchlesssensitivetonoi

4、seandinterferencethansingle-endedcircuits.(2)ItenablesustobiastheamplifierandtocoupleamplifierstagewithouttheneedofbypassandcouplingcapacitorswhichareimpossibletofabricateeconomicallybyICtechnology.6.1TheBJTDifferentialPairBasicOperation-1:Common-modeinput

5、Thedifferentialpairwithacommon-modeinputsignalvCM.Twotransistorsarematched.Currentsourcewithinfiniteoutputresistance.CurrentIdivideequallybetweentwotransistors.Thedifferenceinvoltagebetweenthetwocollectoriszero.Thedifferentialpairrejectsthecommon-modeinput

6、signalaslongastwotransistorsremaininactiveregion.BasicOperation-2Thedifferentialpairwitha“large”differentialinputsignal.Q1isonandQ2isoff.CurrentIentirelyflowsinQ1.BasicOperation-3Thedifferentialpairwithalargedifferentialinputsignalofpolarityoppositetothati

7、n(b).Q2isonandQ1isoff.CurrentIentirelyflowsinQ2.BasicOperation-4:Difference-modeorDifferencesignalsThedifferentialpairwithasmalldifferentialinputsignalvi.Smallsignaloperationorlinearamplifier.AssumingthebiascurrentsourceItobeidealandthusIremainsconstantwit

8、hthechangeinvCM.IncrementinQ1anddecrementinQ2.Large-SignalOperationLarge-SignalOperationNonlinearcurves.Linearsegments.Maximumvalueofinputdifferentialvoltagesasasmall-signalamplifiercanbeusedasafastcurrentswi