# hw5_soln - UNIVERSITY OF CALIFORNIA AT BERKELEY College of...

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UNIVERSITY OF CALIFORNIA AT BERKELEY College of Engineering Department of Electrical Engineering and Computer Sciences Homework #5 Solutions Due Tuesday, October 2, 2007 EE 105 Fall 2007 Prof. Liu Problem 1. Common Emitter Core Design a) I’ll use R C to refer to the 50 kΩ resistor. | A v | = g m ( r o bardbl R C ) = g m R C = 20 g m = 20 50 × 10 3 = 0 . 4 mS I C = g m V T = 10 . 4 μ A V CE,min = 0 . 8 V = V CC,min I C R C V CC,min = 0 . 8 + I C R C = 1 . 32 V b) | A v | = g m ( r o bardbl R C ) = I C V T parenleftbigg V A I C bardbl R C parenrightbigg = 20 I C = 10 . 97 μ A V CE,min = 0 . 8 V = V CC,min I C R C V CC,min = 0 . 8 + I C R C = 1 . 3485 V 1 . 35 V Note that the Early effect increases I C for a given V BE , so that the voltage drop across R C is increased, and thus V CC should be higher to ensure operation in forward active mode. Problem 2. Common Emitter Stage a) The equivalent load resistance is R 1 + parenleftBig 1 g m 2 bardbl r π 2 bardbl r o 2 parenrightBig R 1 + 1 g m 2 (by inspection—review the previous problem set if this is not clear to you). I will call this R L .

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