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# Frequency Response of Multistage Amplifiers

The bandwidth of multistage amplifier is always less than that of the bandwidth of single stage amplifier.

Frequency Response of Multistage Amplifiers:

The bandwidth of multistage amplifier is always less than that of the bandwidth of single stage amplifier.

1. Overall Lower Cut-off Frequency of Multistage Amplifier:

2. Overall Higher Cut-off Frequency of Multistage Amplifier:

Let us consider the upper 3dB frequency of n identical cascaded stages as fH(n). It is the frequency for which the overall gain falls to 1/√2 (3dB) of its midband value.

Taking nth root on both the sides,

21/n = 1 + [ fH(n)/fH ]2

21/n -1 = [ fH(n)/fH ]2

Taking square root on both the sides,

√21/n -1 = fH(n)/fH

fH(n) = fH √21/n -1

In multistage amplifier fL(n) is always greater than fL and fH(n) is always less than fH. So the bandwidth of multistage amplifier is always less than single stage amplifier.

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Electronic Circuits : Frequency Analysis of BJT and MOSFET Amplifiers : Frequency Response of Multistage Amplifiers |