Question

What is the ROC of z-transform of an two sided infinite sequence?

(a) |z|>r1

(b) |z|<r1

(c) r2<|z|<r1

(d) None of the mentioned

I got this question in an interview for internship.

My question is based upon Z Transform topic in portion Z Transform and its Application – Analysis of the LTI Systems of Digital Signal Processing

Answer 1

Correct option is (c) r2<|z|<r1

Explanation: Let us plot the graph of z-transform of any two sided sequence which looks as follows.

From the above graph, we can state that the ROC of a two sided sequence will be of the form r2 < |z| < r1.