Optimum multiplierless sharpened cascaded-integrator-comb filters

Abstract

Cascaded-integrator-comb (CIC) filter provides high folding-band attenuation within a narrow band. To make this filter suitable for processing of wideband signals, its amplitude response is often improved by using polynomial sharpening, resulting in so-called sharpened CIC (SCIC) filter. In this paper, the authors propose a method for global optimization of multiplierless SCIC filters. The method is based on the maximization of minimum folding-band attenuation, assuming the coefficients of sharpening polynomial are the sums of signed-power-of-two (SPT) terms. Filter's structure is controlled by bounding the maximum word length of polynomial coefficients and the maximum number of terms in the entire sharpening polynomial. The proposed method supports an arbitrary choice of passband edge frequency. The filters obtained employ a low number of SPT terms to achieve folding-band attenuations which are close to those obtained by real-valued polynomial coefficients.