Design and VLSI implementation of multirate filter banks based on approximately linear phase allpass sections

Abstract

The design of multirate filterbanks for applications such as subband coding with IIR QMF (quadrature mirror filter) pairs is explored. These offer reduced complexity and low latency at the expense of the loss of exact linear phase. In particular we consider the use of allpass sections where linear phase is approximately achieved by being part of the objective in numerical optimisation. The results for phase distortion in reconstruction experiments compare favourably with previous IIR based approaches. Finite wordlength design using simulated annealing shows that low coefficient wordlengths may be used. This leads to efficient realisations with 3-port adaptors. Using pipelined implementation, a flexible VLSI architecture is designed that can be used for a variety of subband decompositions. Layout and simulation of the design has been performed.