Synthesis of IIR filters exhibiting constant group delay using phase invariance method

This paper presents one synthesis procedure for selective, minimum phase, IIR filters exhibiting constant group delay. For constant group delay approximation, maximally flat criterion is considered. Prototype rational function is constructed in two steps. First all-pole transfer function exhibiting linear phase is synthesized. Second transmission zeros situated at imaginary axis are introduced. To preserve linear phase property, phase invariance method will be examined and confronted with famous bilinear transform. Procedure of mapping will be carried out over eight order, low pass filter. Obtained results showed that proposed method outperform bilinear transform, especially at lower sampling rates.