A New Class of Approximately Linear Phase Filters

This paper presents a class of Infinite Impulse Response (IIR) filters which have approximately Linear Phase response in their pass bands. The new filters provide better magnitude response and worse phase linearity for a given order and transition bandwidth than previous designs. They can then be used as an alternative to those designs when we want some degree of phase linearity but the magnitude response and processing delay are more important. Some design examples are presented in which the new filters are compared with previous designs. Finally some structures for the efficient implementation of the filters are also discussed. 1.INTRODUCTION The design of approximately Linear Phase IIR filters has been proposed as an alternative to Linear Phase FIR filters for applications in which both the processing delay and the waveform distortion must be small [1] [2]. The design of these filters is based on the parallel connection of a delay and allpass filter as presented in figure 1. z-M