Question

Considering a second-order Butterworth LPF using an op-amp, where damping factor = 1.414 find the value of R3, given the following circuit. (R2=5kΩ)

(a) 6.71 kΩ

(b) 4.22 kΩ

(c) 2.93 kΩ

(d) 5 kΩ

This question was posed to me during an interview for a job.

I need to ask this question from Frequency Filters topic in chapter Op-amps and its Applications of Analog Circuits

Answer 1

The correct answer is (c) 2.93 kΩ

Easiest explanation: Maximum gain, A = 3 – α = 1.586

For the above circuit, the gain is 1 + R3/R2 = 1.586

R3/R2 = 0.586

R3 = 2.93 kΩ.