Lecture 8 - Lecture 8 OUTLINE • BJT Amplifiers (cont’d)...

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EE105 Fall 2009 Lecture 8, Slide 1 Prof. Salahuddin, UC Berkeley Lecture 8 OUTLINE BJT Amplifiers (cont’d) Input source and output load coupling Common- emitter topology (cont’d) Impact of emitter degeneration Impact of external base resistance Impact of Early effect Reading: Finish Chapter 5.3.1
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EE105 Fall 2009 Lecture 8, Slide 2 Prof. Salahuddin, UC Berkeley Example of a Bad Input Connection Since the microphone has a very low resistance (connecting the base of Q 1 to ground), it attenuates the base voltage and renders Q 1 with a very small bias current.
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EE105 Fall 2009 Lecture 8, Slide 3 Prof. Salahuddin, UC Berkeley Use of Coupling Capacitor A capacitor is used to isolate the DC bias network from the microphone , and to short (or “couple”) the microphone to the amplifier at higher frequencies.
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EE105 Fall 2009 Lecture 8, Slide 4 Prof. Salahuddin, UC Berkeley DC and AC Analysis The coupling capacitor is replaced with an open circuit for DC analysis, and then replaced with a short circuit for AC analysis. O C out B in O C m v r R R R r R r R g A || || ) || ( Circuit for DC analysis Circuit for AC analysis of A v Circuit for AC analysis of R out Circuit for AC analysis of R in
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EE105 Fall 2009 Lecture 8, Slide 5 Prof. Salahuddin, UC Berkeley CE Stage with Voltage-Divider Biasing O C out in O C m v r R R R R r R r R g A || || || ) || ( 2 1
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EE105 Fall 2009 Lecture 8, Slide 6 Prof. Salahuddin, UC Berkeley Bad Output Connection Since the speaker has an inductor with very low DC resistance, connecting it directly to the amplifier would ~short the collector to ground, causing the BJT to go into deep saturation mode.
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This note was uploaded on 10/05/2009 for the course EE 105 taught by Professor King-liu during the Fall '07 term at University of California, Berkeley.

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Lecture 8 - Lecture 8 OUTLINE • BJT Amplifiers (cont’d)...

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