Question

For all-pass systems:

(a) Poles must lie on right of the s-plane

(b) Zeroes must lie on the left of s-plane

(c) Poles must lie on the left and zeroes on the mirror image of the pole can be on the right

(d) None of the mentioned

This question was posed to me during an interview.

Enquiry is from All-pass and Minimum-phase Systems in chapter Frequency Response Analysis of Control Systems

Answer 1

Right choice is (c) Poles must lie on the left and zeroes on the mirror image of the pole can be on the right

The best explanation: For all-pass systems poles must lie on the left and zeroes on the mirror image of the pole can be on the right.