Question

It is provided that the lower cut-off frequency of an individual amplifier is 25Hz, find the net cut-off frequency of a cascaded network of 8 similar amplifiers.

(a) 200 Hz

(b) 83 Hz

(c) 100 Hz

(d) 25 Hz

I got this question during an interview.

This intriguing question comes from Cascaded Amplifier topic in chapter General and Feedback Amplifiers of Analog Circuits

Answer 1

The correct option is (b) 83 Hz

Easiest explanation: fL1 = 25Hz

fL = \(\frac{f_{L1}}{\sqrt{2^{1/N}}-1} = \frac{25}{\sqrt{2^{1/8}} -1} = \frac{25}{\sqrt{0.0905}}\)

fL = 83 Hz.