Improving Alias Rejection in Two-Stage Comb Filter for Multiple-of-Three Decimation

This paper presents novel two-stage comb decimation filter for the multiple of three odd decimation factors. The novelty of this filter is the alias improvement in all folding bands at low cost. More specifically, like in comb-zero rotation method, the alias rejection improvement is obtained by placing additional zeros into comb folding bands. However, this is achieved by using simple multiplierless filters, placed in both stages of the comb structure. The second stage is decimated by three, while the first stage is decimated by one third of the overall decimation factor. The choice of multiplierless filters is discussed and the corresponding structures are presented. Finally, the comparisons with some methods, proposed in literature, are provided.