Two-Stage Cosine Filter-Based Decimator with Improved Aliasing Rejection

This paper presents alias rejection improvement in a two-stage cosine filter-based two-stage structure for even decimation factors, a structure recently proposed in literature. The structure improves alias rejection in all odd comb folding bands by introducing simple modified cosine filter at the second stage. The goal here is to improve the aliasing rejection in even folding bands, while keeping a low complexity of the structure. This is achieved by introducing simple expanded cosine filter at the first stage, and increase by one the number of the cascaded combs at the first stage. The resulting filter is multiplierless and has an improved alias rejection in all folding bands in comparison with the original structure. The mathematical background of the method is presented. The method is illustrated with an example and it is compared with some recently proposed methods for aliasing rejection improvement. The efficient structures are also presented.