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# HW_18 - EE 438 Homework#18 1 The small-signal equivalent...

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EE 438 Homework #18 1. The small-signal equivalent circuit of the common-emitter amplifier shown in Fig. 1 on page 4 is given below. _ + V i R i C µ C π g m V π V π C 1 R B C R V o + _ c b e The elements in the equivalent circuit have the following values. . fF 20 and pF, 10 , k 2 || , mS 40 F, 2 , k 4 || || , 1 1 2 1 = = = = = = = = = µ π π µ C C r R R g C r R R R k R o C C m B B B i (a) Use the low frequency approximation ( C π and C µ open-circuited) to determine A vl ( s ) in the ( s +1/ T ) form with all constants, including A mid , expressed as numerical values. (b) Using the high frequency approximation ( C 1 shorted) we find that A vh ( s ) is given by ( ) ( )( ) [ ] { } ( ) 2 || 1 || 1 1 s C C R R R s C C R g R R C R s g C A s A C i B C m i B C m mid vh π µ π µ µ µ + + + + + = . Solve the denominator quadratic to express A vh ( s ) in the + T s / 1 1 form with all constants, including A mid , expressed as numerical values. (c) Combine A vl ( s ) and A vh ( s ) to form A v ( s ) with all constants evaluated numerically. 2. Draw a small signal equivalent circuit of the common-drain amplifier shown in Fig. 2 on page 4. Include the two device parasitic capacitors C gs and C gd (do not include C gb and C db ) in your circuit. Indicate the locations of V i and V o and the transistor terminals. Do not analyze the circuit . 3. Next Page Page 1

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