A quasi-equiripple design of IIR filters with unequal number of poles and zeros

IIR filter design often comprises approximation of both magnitude and phase responses. One of the major problems is filter stability, which can be obtained with suitable value of group delay τ. This paper concerns calculation of filter order N and group delay τ in case of quasi-equiripple design of IIR filters. We propose a novel procedure for determining N and τ values; the procedure is valid for all types of filters with arbitrary number of zeros and a few non-zero poles. Evaluation of the proposed approach as well as examples illustrating its application are included in the paper.