Question

Q.  What should be the gain of an amplifier at 20 kHz if the half power frequencies are fL = 20 Hz and fH = 15 kHz along with mid band gain = 80?

(a) 22.76

(b) 45.09

(c) 40.08

(d) 48.07

The question was asked during an internship interview.

Question is taken from Comparison of Transistor Amplifier in section Small-Signal Low-Frequency AC models of Transistors of Electronic Devices & Circuits

Answer 1

Right answer is (d) 48.07

Easy explanation: fL = 20 Hz

fH = 15 kHz

Av(mid) = 80

To determine: Voltage gain at 20 kHz

Formula : Av = Av(mid) / √1 + (f/fH)^2

To determine the voltage gain at 20 kHz, we recognize that,

Av = Av(mid) / √1 + (f/fH)^2

= 80 / √1 + (20 k/15k)^2

= 48.07.