Elliptical IIR Filter Design

LIQUID_IIRDES_ELLIP is an elliptic (Cauer) filter. This design allows ripples in both the pass-band and stop-bands to create a filter with a very sharp transition band. The design process is somewhat more involved than the Butterworth and Chebyshev prototypes and requires solving the elliptic integral of different moduli. For a more detailed description we refer the interested reader to [Orf06]. The analog prototype interface is ellip_azpkf().

Attention

talk about analog prototype

An example elliptic design can be seen in the code listing here:

#include <liquid/liquid.h>
int main()
{
    return 0;
}

An example of a digital filter response can be found in [fig-filter-ellip].

Figure 17 Elliptic filter design, \(n=7\), \(f_c=0.2 F_s\), \(A_p=1\) dB, and \(A_s=60\) dB.

Notice how the performance changes as the order increases to 15…