Frequency Response, Transfer function and pole locations are shown by the applet below.

Fn = 0 shows the frequency response.

Fn = 1 shows the transfer function represented as a product of quadratic factors.

Fn = 2 shows the pole and zero locations for the continuous Elliptic filter and the discrete Bilinear approximation.

To design a filter which has a gain of ~ -3dB at 0.4w

Set BL = 235, WL to 300 and R = 0.2 to locate the frequency markers and set the pass band ripple.

Adjust N, fc/fs until the conditions are met.

In this case N = 9, fc/fs = 0.402.

The last entry in the first line of white text shows the gain at 0.4w

Changing Fn to 1 shows the quadratic factors needed to realize the filter and Fn = 2 show the zeros and poles.

COPYRIGHT © 2008 Cuthbert Nyack.