Question

Determine the gain of the first order low pass filter if the phase angle is 59.77^o and the pass band gain is 7.

(a) 3.5

(b) 7

(c) 12

(d) 1.71

I have been asked this question during an interview for a job.

My question is based upon First Order Low Pass Butterworth Filter in section Active Filters of Linear Integrated Circuits

Answer 1

Correct choice is (a) 3.5

To put it plainly: Given the phase angle, φ =-tan^-1(f/fH)

=> f/fH=- φtan(φ) = -tan(59.77^o)

=> f/fH= -1.716.

Substituting the above value in gain of the filter, |(VO/Vin)| = AF/√ (1+(f/fH)^2) =7/√[1+(-1.716)^2)] =7/1.986

=>|(VO/Vin)|=3.5.