You are given two amplifiers, A and B, to connect in cascade between a 10-mV, 10

Question

You are given two amplifiers, A and B, to connect in cascade between a 10-mV, 100-k? source and a 100-? load. The amplifiers have voltage gain, input resistance, and output resistance as follows: for A, 100 V/V, 10 k?, 10 k?, respectively; for B, 1 V/V, 100 k?, 100 ?, respectively. Your problem is to decide how the amplifiers should be connected. To proceed, evaluate the two possible connections between source S and load L, namely, SABL and SBAL. Find the voltage gain for each both as a ratio and in decibels. Which amplifier arrangement is best?

Explanation / Answer

A , 100 gain , 10K input resistance, 10k output
B , 1 gain, 100K input resistance, 100 output

source is 100k , load is 100
since we are talking about voltage gain , 20 dB = 10
40 dB = 100 and so on
consider SABL
gain is (10k/(10k+100k)) * 100 * (10/11) * 1 * (1/2) = 4.14

to convert this number to dB---> 20*log ( 4.14) where log is base 10 log
= 12.34 dB


Consider SBAL

gain is (1/2)* 1 * 10k /(10k+100) *100*(100/(100+10k)) = 0.495 or about 0.5

this in dB is 20 * log ( 0.495) = -6.1 dB

so as you can see, to get the max gain, you want to use the SABL configuration.

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