# Lecture 9 - Lecture 9 OUTLINE • BJT Amplifiers(cont’d – Common-base topology – CB core – CB stage with source resistance – CB stage

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EE105 Fall 2009 Lecture 9, Slide 1 Prof. Salahuddin, UC Berkeley Lecture 9 OUTLINE BJT Amplifiers (cont’d) Common-base topology CB core CB stage with source resistance CB stage with biasing Reading: Chapter 5.3.2

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EE105 Fall 2009 Lecture 9, Slide 2 Prof. Salahuddin, UC Berkeley Common Base (CB) Amplifier The base terminal is biased at a fixed voltage; the input signal is applied to the emitter, and the output signal sensed at the collector.
EE105 Fall 2009 Lecture 9, Slide 3 Prof. Salahuddin, UC Berkeley Small-Signal Analysis of CB Core The voltage gain of a CB stage is g m R C , which is identical to that of a CE stage in magnitude and opposite in phase. C m v R g A

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EE105 Fall 2009 Lecture 9, Slide 4 Prof. Salahuddin, UC Berkeley Tradeoff between Gain and Headroom To ensure that the BJT operates in active mode, the voltage drop across R C cannot exceed V CC - V BE. T BE CC C T C v V V V R V I A
EE105 Fall 2009 Lecture 9, Slide 5 Prof. Salahuddin, UC Berkeley Simple CB Stage Example 2 . 17 2230 130 1 C m v R g A V CC = 1.8V I C = 0.2mA I S = 5x10 -17 A b = 100  k 7 . 67 , k 3 . 22 20 10 Choose if 354 . 1 2 1 2 1 1 1 2 1 2 R R R R V A I I I I V R R R V V CC B B CC b V I I V V s c T b 354 . 1 ~ ) / ln( mV 600 2230 : c b cc c c R V V R I gain Max

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Lecture 9, Slide 6 Prof. Salahuddin, UC Berkeley Input Impedance of a CB Stage The input impedance of a CB stage is much smaller than that of a CE stage. A
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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 9 - Lecture 9 OUTLINE • BJT Amplifiers(cont’d – Common-base topology – CB core – CB stage with source resistance – CB stage

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