Question

The poles of HN(s).HN(-s) are found to lie on ___________

(a) Circle

(b) Parabola

(c) Hyperbola

(d) Ellipse

This question was posed to me during an interview.

Query is from Chebyshev Filters topic in division Digital Filters Design of Digital Signal Processing

Answer 1

The correct option is (d) Ellipse

The best I can explain: The poles of HN(s).HN(-s) is given by the characteristic equation 1+ϵ^2TN^2(s/j)=0.

The roots of the above characteristic equation lies on ellipse, thus the poles of HN(s).HN(-s) are found to lie on ellipse.