Berkeley ELENG 105 - Lecture Notes (25 pages)

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Lecture Notes



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Lecture Notes

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Pages:
25
School:
University of California, Berkeley
Course:
Eleng 105 - Microelectronic Devices and Circuits
Microelectronic Devices and Circuits Documents

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Lecture 7 ANNOUNCEMENTS MIDTERM 1 will be held in class on Thursday Thursday October 11 Review session will be held on Friday October 5 MIDTERM 2 will be held in class on Tuesday November 13 OUTLINE BJT Amplifiers cont d Biasing Amplifier topologies Common emitter topology Reading Chapter 5 5 1 2 5 3 1 1 2 5 3 1 EE105 Fall 2007 Lecture 7 Slide 1 Prof Liu UC Berkeley Biasing of BJT Transistors must be biased because 1 They must operate in the active region 1 region and 2 Their small signal model parameters are set by the bias conditions EE105 Fall 2007 Lecture 7 Slide 2 Prof Liu UC Berkeley DC Analysis vs Small Signal Analysis Firstly DC analysis is performed to determine the DC operating point and to obtain the small signal small signal model parameters Secondly independent sources are set to zero and the small signal model is used EE105 Fall 2007 Lecture 7 Slide 3 Prof Liu UC Berkeley Simplified Notation Hereafter the voltage source that supplies power to the circuit is replaced by a horizontal bar labeled VCC and input signal is simplified as one node labeled vin EE105 Fall 2007 Lecture 7 Slide 4 Prof Liu UC Berkeley Example of Bad Biasing The microphone is connected to the amplifier in an attempt to amplify the small output signal of the microphone Unfortunately there is no DC bias current running through the transistor to set the transconductance EE105 Fall 2007 Lecture 7 Slide 5 Prof Liu UC Berkeley Another Example of Bad Biasing The base of the amplifier is connected to VCC trying to establish a DC bias Unfortunately the output signal produced by the microphone is shorted to the power supply EE105 Fall 2007 Lecture 7 Slide 6 Prof Liu UC Berkeley Biasing with Base Resistor Assuming a constant value for VBE one can solve for both IB and IC and determine the terminal voltages of the transistor However the bias point is sensitive to variations EE105 Fall 2007 Lecture 7 Slide 7 Prof Liu UC Berkeley Improved Biasing Resistive Divider Using a resistive divider to set



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