# Practice1 - EE3050 Spring 2001 Some Practice Problems 1 The gure shows the ac signal circuit of a cascode amplier It is given that = 199 rx = 20 VT

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Spring 2001 Some Practice Problems 1. The gure shows the ac signal circuit of a cascode ampli er. It is given that β =199 , r x =20 , V T =0 . 025 , r 0 = , I E 1 =1 mA, C 2 =100 pF, R B =1 k , R E =20 ,and R C =10 k . Note that the answers below would be more complicated if r 0 is not in nity. (a) What is the low-frequency gain of the ampli er? Calculate this with C 1 an open circuit. v o v i = i c 1 v i i c 2 i c 1 v o i c 2 = G mb 1 α 2 ( R C ) where R tb 1 = R B and R te 1 = R E . (b) What is K in applying the Miller theorem to C 1 ? K = G mb 1 ( r ie 2 ) where r x =0 , R tb 1 =0 ,and R te 1 = R E . (c) What is the time constant for the base circuit of Q 1 ? τ b 1 =[ R B k r ib ](1+ K ) C 1 (d) What is the time constant for the collector circuit of Q 1 ? τ c 1 = r ie 2 C 1 (e) What is the approximate upper cuto f frequency of the ampli er? f

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## This note was uploaded on 05/26/2011 for the course ECE 3050 taught by Professor Hollis during the Summer '08 term at Georgia Institute of Technology.

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Practice1 - EE3050 Spring 2001 Some Practice Problems 1 The gure shows the ac signal circuit of a cascode amplier It is given that = 199 rx = 20 VT

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