Question

Consider an RC coupled amplifier at low frequency. Internal voltage gain is -120. Find the voltage gain magnitude, when given that collector resistance = 1kΩ, load = 9kΩ, collector capacitance is 0. is 0.1μF, and input frequency is 20Hz.

(a) 120

(b) 12

(c) 15

(d) -12

The question was asked by my college professor while I was bunking the class.

This interesting question is from Low Frequency Response and Miller Effect Capacitance in chapter Transistor Frequency Response of Analog Circuits

Answer 1

The correct option is (c) 15

The best I can explain: AV = -120

fL = 1/2πCC(RC+RL) = 1/2π*0.001 = 1000/2π = 159.15Hz

AV’ = \(\frac{|AV|}{\sqrt{1}} + (\frac{f_L}{f})^2\)

AV’ = 120/8.02 ≈ 15.