A two-stage design of IIR filters using quadratic programming and particle swarm optimization

A two-stage design method of infinite impulse response (IIR) digital filters with a smaller group delay error is presented in this paper. In the first stage, the complex chebyshev approximation based on Quadratic Programming (QP) is applied to obtain a stable IIR filter with an approximately constant group delay in the passband. In the second stage, to improve only the group delay response of the obtained filter in stage 1, the group delay error minimization problem which has a maximum amplitude error constraint is solved using Particle swarm optimization (PSO). Compared with the conventional methods, the proposed method can design the IIR filters with about the same amplitude response and a smaller group delay error. The usefulness of the proposed method is verified through some examples.