Design Method for Nearly Linear-Phase IIR Filters Using Constrained Optimization

The group delay deviation is minimized under the constraint that passband ripple and stopband are within the prescribed specifications and an applicable group delay can be achieved. By representing the filter in terms of a cascade of second-order sections, a non-restrictive stability constraint characterized by a set of linear inequality constraints can be incorporated in the optimization algorithm. Experimental results show that filters designed using the proposed method have much lower group-delay deviation for the same passband ripple and stopband attenuation when compared with corresponding filters designed with several state-of-the-art competing methods.