Methods for Improving Magnitude Characteristic of Comb Decimation Filters

This chapter presents some recent proposed methods to improve the magnitude characteristic of comb filters in stopband, passband, as well as in both passband and stopband. First, the methods for aliasing rejection improvement based on exploring the characteristics of symmetrical polynomials are presented. In that way the alias rejection in comb folding bands can be increased in a simple way without introducing multipliers. More precisely, the zeros of comb filter can be rotated from their original positions to other positions inside the folding bands, by appropriately changing the coefficients of the transfer function of cascaded combs. In the following the methods for comb passband droop compensation in a wideband are presented, based on trigonometrical approach, in which the magnitude responses of compensators are in sinusoidal forms. The parameters of compensators are amplitudes of sinusoidal functions which depend on the number of the cascaded comb filters. The resulting compensators are multiplierless and work at low rate and provide a good comb compensation in a wide passband. Finally, the method based on multiplierless corrector filters for improvement of comb magnitude characteristic in passband, as well as in folding bands, is elaborated. The methods are illustrated with examples, and MATLAB scripts are provided for presented methods.