A new approach to the phase error and THD improvement in linear phase IIR filters

This paper deals with the real-time implementation of IIR filters having linear phase. Powell and Chau (1991) have devised an efficient method for the design and realization of real-time linear phase IIR filters using suitable modifications of the well-known time reversing technique. In their method, the input signal is divided into L-sample segments, time-reversed, and twice filtered using two IIR filter blocks whose transfer functions are the same. The performance has been further improved by Willson and Orchard (see IEEE Trans. Signal Processing, vol.SP-42, no.10, p.2842-8, 1994), where double zeros on the unit circle have been separated, giving better amplitude response in the stop-band and slightly smaller amplitude and phase distortions. New improvements are described based on the reordering of polynomials in the numerator of the filter transfer function, or on the appropriate selection of the transfer function. The truncation noise, phase and amplitude errors of new realizations show considerable improvement over the previous solutions.