Lecture 7

Lecture 7 - Lecture 7 OUTLINE • BJT Amplifiers (cont’d)...

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EE105 Fall 2009 Lecture 7, Slide 1 Prof. Salahuddin, UC Berkeley OUTLINE BJT Amplifiers (cont’d) Biasing Amplifier topologies Basic common-emitter topology Reading: Chapter 5.2-5.3.1 Lecture 7
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EE105 Fall 2009 Lecture 7, Slide 2 Prof. Salahuddin, UC Berkeley BJT Amplifier Design A BJT amplifier circuit should be designed to 1. ensure that the BJT operates in the active mode, 2. allow the desired level of DC current to flow, and 3. couple to a small- signal input source and to an output “load”. Proper “DC biasing” is required! (DC analysis using large-signal BJT model) Key amplifier parameters: (AC analysis using small-signal BJT model) Voltage gain A v v out / v in Input resistance R in resistance seen between the input node and ground (with output terminal floating) Output resistance R out resistance seen between the output node and ground (with input terminal grounded)
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EE105 Fall 2009 Lecture 7, Slide 3 Prof. Salahuddin, UC Berkeley Large-Signal vs. Small-Signal Models The large-signal model is used to determine the DC operating point ( V BE , V CE , I B , I C ) of the BJT. The small-signal model is used to determine how the output responds to an input signal.
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EE105 Fall 2009 Lecture 7, Slide 4 Prof. Salahuddin, UC Berkeley The voltage across an independent voltage source does not vary with time. (Its small-signal voltage is always zero.) It is regarded as a short circuit for small-signal analysis. The current through an independent current source does not vary with time. (Its small-signal current is always zero.) It is regarded as an open circuit for small-signal analysis. Small-Signal Models for Independent Sources Large-Signal Model Small-Signal Model
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Lecture 7, Slide 5 Prof. Salahuddin, UC Berkeley Amplifier Circuit Analysis Procedure Firstly, DC analysis is performed to determine the DC operating point and to obtain the small-signal model parameters. Secondly, independent sources are set to zero and
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Lecture 7 - Lecture 7 OUTLINE • BJT Amplifiers (cont’d)...

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