Question

An IIR system with system function H(z)=\(\frac{B(z)}{A(z)}\) is called a mixed phase if ___________

(a) All poles and zeros are inside the unit circle

(b) All zeros are outside the unit circle

(c) All poles are outside the unit circle

(d) Some, but not all of the zeros are outside the unit circle

This question was addressed to me during a job interview.

Enquiry is from Inverse Systems and Deconvolution topic in portion Frequency Analysis of Signals and Systems of Digital Signal Processing

Answer 1

The correct option is (d) Some, but not all of the zeros are outside the unit circle

To explain I would say: For an IIR filter whose system function is defined as H(z)=\(\frac{B(z)}{A(z)}\) to be said a mixed phase and if the system is stable and causal, then the poles are inside the unit circle and some, but not all of the zeros are outside the unit circle.