Question

Using the frequency scaling technique,  convert  10kHz cut-off frequency of the low pass filter to a cutoff frequency of 16kHz.(Take C=0.01µF and R=15.9kΩ)

(a) 6.25kΩ

(b) 9.94kΩ

(c) 16kΩ

(d) 1.59kΩ

This question was posed to me by my college director while I was bunking the class.

This question is from First Order Low Pass Butterworth Filter topic in portion Active Filters of Linear Integrated Circuits

Answer 1

Correct choice is (b) 9.94kΩ

In simpler terms: To change a cut-off frequency from 10kHz to 16kHz,multiply 15.9kΩ resistor.

[Original cut-off frequency/New cut-off frequency] =10kHz/16kHz =0.625.

∴ R =0.625×15.9kΩ =9.94kΩ. However 9.94kΩ is not a standard value. So, a potentiometer of 10kΩ is taken and adjusted to 9.94kΩ.