Question

Which of these is wrong for an all-pass filter?

(a) It is used for phase equalization in a communication system

(b) It is used in landline communication

(c) Its phase shift is -2tan^-1RC, between 0 to -180°

(d) It can be made using a single op-amp

The question was asked in class test.

My question is based upon Frequency Filters topic in section Op-amps and its Applications of Analog Circuits

Answer 1

The correct option is (c) Its phase shift is -2tan^-1RC, between 0 to -180°

Explanation: An all-pass filter passes all frequencies but provides a different phase shift to each frequency present in the circuit. It is used for phase equalization or delay equalization and is used in landline communication. Following is a circuit of an all-pass filter using a single op-amp.

However, its phase shift is -2tan^-1(ωRC)