Lecture 38Multi-Stage Voltage AmplifierCutting Through the ComplexityFirst Approach: Find I & V SourcesWhat’s Left?Second Approach: Find Signal PathIdentifying the StagesFind Key Two-Port ParametersTwo-Port Parameters (Cont.)Output Resistance and Voltage GainR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyLecture 38• Last time:– CMOS cascode transconductance amplifier design example• Today :– BiCMOS voltage amplifier: example of “dissection” technique for a complicated circuitR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyMulti-Stage Voltage AmplifierR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyCutting Through the ComplexityTwo Approaches:1. Eliminate “background” transistors to reduceclutter2. Identify the “signal path” between the inputand outputR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyFirst Approach: Find I & V SourcesR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyWhat’s Left? Voltage at base ofQ2is set by totempoleR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleySecond Approach: Find Signal PathR. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyIdentifying the StagesFirst stage (or two stages): CS/CB cascodeSecond stage (or two stages): CD/CC voltage bufferWhy does this make sense for a voltage amplifier?R. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyFind Key Two-Port ParametersOutput resistance of cascode:(){}2222/,||1(||SmoocCBCSoutRrgrrRπ+=()6661SmoupocRgrRr+==R. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyTwo-Port Parameters (Cont.)R. T. HoweEECS 105 Spring 2002 Lecture 38Dept. of EECSUniversity of California at BerkeleyOutput Resistance and Voltage GainSource resistance of the CC stage is the output resistanceof the CD stage (small)434,4,1111mommoCCSmCCoutoutgggRgRR ≈+=+==ββOpen-circuit voltage gain Av(last two stages have nearly unity gain):
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