BJT%20amplifiers%20(1)_web

BJT%20amplifiers%20(1)_web - BJT Amplifier (1) ECE304...

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Unformatted text preview: BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 1 Bipolar Amplifiers (1) BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 2 Common-Emitter Topology BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 3 Small Signal Analysis O C out O C m v r R R r R g A || ) || ( = = BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 4 I/O Impedances of CE Stage When measuring output impedance, the input port has to be grounded so that V in = 0. r i v R X X in = = C X X out R i v R = = BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 5 Limitation on CE Voltage Gain T C C v V R I A = T RC v V V A = T BE CC v V V V A < BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 6 Intrinsic Gain As R C goes to infinity, the voltage gain reaches the product of g m and r O , which represents the maximum voltage gain the amplifier can have. The intrinsic gain is independent of the bias current. T A v O m v V V A r g A = = BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 7 Current Gain Another parameter of the amplifier is the current gain, which is defined as the ratio of current delivered to the load to the current flowing into the input. For a CE stage, it is equal to . = = CE I in out I A i i A BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 8 Tradeoff between Voltage Gain and Headroom BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 9 CE Stage Trade-offs BJT Amplifier (1) ECE304 Spring 2008 by Brian Ma 10 Emitter Degeneration By inserting a resistor in series with the emitter, we degenerate the CE stage. degenerate the CE stage....
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BJT%20amplifiers%20(1)_web - BJT Amplifier (1) ECE304...

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