Considering the zdomain transfer function associated with a

   Considering the z-domain transfer function associated with a digital filter:

(a)   What does it mean if the filter has one or more poles outside the z-plane’s unit circle?

(b)   What does it mean if the filter has a zero lying exactly on the z-plane’s unit circle?

Solution

A). If the filter has one or more poles outside the unit circle, then it is unstable...

B). If the poles are lying exactly on unit circle, then it is marginally stable..