MULTISTAGE AMPLIFIER - MIT

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Spring 2007Lecture 241Lecture 24Multistage Amplifiers (I) MULTISTAGE multi- stage voltage MULTISTAGE voltage current AMPLIFIER stagesReading Assignment:Howe and Sodini, Chapter 9, Sections Spring 2007Lecture 2421. Introduction What amplifying stages should be used and in what order? What devices should be used, BJT or MOSFET? How is biasing to be done?Issues:Most often, single stage AMPLIFIER does not accomplish design goals: Need more gain than could be provided by a single stage Need to adapt to specified RSand RLto maximize efficiency MULTISTAGE Spring 2007Lecture 243Summary of single stage AMPLIFIER characteristicsCurrent bufferCommon BaseVoltage bufferCommon CollectorTranscon-ductance amplifierCommon EmitterCurrent bufferCommon GateVoltage BufferCommon DrainTranscon-ductance amplifierCommon SourceKey FunctionRoutRinAvo, AioStage)//(ocomvorrgA =ro//rocAvo gmgm+gmb 1gm+gmbAio 1 Avo= gm(ro//roc)mbmgg+1roc//[ro(1+gmRS)] rro//rocAvo 1Aio 1()LocooRrrr//// +1gm+RS omg1roc//[ro(1+gmr //RS())]Differences between BJT s and MOSFETsr =

Since the CG stage has no gate current, cascade it with the CB stage i s R S R L i out −i in1 in2 i in1 i in2 [g m2 r o2(r 2 ⎢⎢β o1 r o1 ⎢⎢r oc1)] ⎢⎢r oc2 CB CB g m1 β o1 r o1 ⎢⎢r oc1 1 g m2 1

  Gate, Stage