Using Cosine Filters to Improve Alias Rejection in Comb Decimation Filter

This paper presents efficient use of cosine filters to improve the alias rejection in the comb decimation filters for Sigma-Delta-Analog/Digital (SD A/D) converters application. Like comb filters, the cosine filters are also multiplierless, thus resulting in the overall multiplierless structure. The goal was to decrease the decimator complexity, compared with the original cosine based decimator, and to increase the number of design parameters. To this end, we propose a two-stage structure, where the cosine filters are in the second stage. The novel structure is proposed, in which the polyphase decomposition is applied to the cascade of cosine filters and the comb filter from a CIC (Cascaded-Integrator-Comb) structure. The method is compared with the equivalent comb and the original cosine-based method.