Acrobat Distiller, Job 6

The perfect linear phase requirement can be achieved only by direct design with an FIR filter at the expense of high filter order and hence high computational burden for the given specification. Alternatively, IIR filters can be designed with much smaller orders than their FIR counterparts, but at the expense of the nonlinear phase. However, it is possible to design almost linear-phase IIR filters for a given specification of the allowed phase or group delay ripples. This paper presents an improvement to the existing algorithms for the design of almost linear–phase, arbitrary-band IIR filters and gives a different viewpoint on these methods, showing a considerable improvement in maximum ripples of the magnitude and group delay responses. The idea of decreasing the phase non-linearity of the N-path polyphase IIR filters with a combination of allpass sections of different order and coefficient polarity is presented. The effect of coefficient quantization, in view of the fixed-point implementation, on the performance of the resulting filter is also shown. Key-Words: Filter design, Phase-linearity, Digital filter, Polyphase structure, Multi-rate system.