Decimation Schemes for Sigma Delta A/D Converters based on Kaiser and Hamming Sharpened Filters

Cascaded-integrator-comb (CIC) filters are efficient anti-aliasing rate-conversion filters widely used for Sigma-Delta A/D converters. High-order structures, attempting to increase the noise rejection within the folding bands, have the drawback of inserting multiple zeros in the same positions and increasing the edge-band attenuation. A combination of sharpened and CIC filters is proposed in the paper, with the goal of increasing the rejection of the SD quantisation noise around the folding bands and reducing the pass-band drop of the designed decimation filters with respect to classic CIC structures. Design criteria, leading to optimised structures, and comparisons are given with respect to both classical and modified CIC filters