Transcription of MULTISTAGE AMPLIFIER - MIT
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MULTISTAGE AMPLIFIER - MIT
Spring 2007 Lecture 241 Lecture 24 MULTISTAGE Amplifiers (I) MULTISTAGE multi-stage voltage MULTISTAGE voltage current AMPLIFIER stagesReading Assignment:Howe and Sodini, Chapter 9, Sections Spring 2007 Lecture 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 2007 Lecture 243 Summary 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 1 Aio 1()LocooRrrr//// +1gm+RS omg1roc//[ro(1+gmr //RS())]Differences between BJT s and MOSFETsr = ogm gmb gmgm=ICVth> gm=2WL CoxIDro=VAIC> ro=1 Spring 2007 Lecture 2442.
Example, CD-CC voltage buffer: • Advantages – No capacitors needed – compact • Disadvantages – Bias point shared:constrains designs. – Bias shifts from stage to stage and can stray too far from center of range – Generally requires level shifting to bring signal back to center of range. 4.7 V 5.0 V 2.5 V 3.2 V Assumes V BE = 0.7 V ...
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