Improving Comb Alias Rejection Using Modified Cosine Filters

This paper presents a novel multiplierless two-stage decimator for even decimation factor M. In comparison with a modified cosine-based decimator previously proposed in the literature, this decimator has an improved alias rejection in all folding bands. This improvement is achieved by introducing an expanded modified cosine filter in the first stage of the decimator. The choice of the expanded factor is crucial to achieve alias improvement. The two cases of the parity of the decimation factor of the first stage, being even or odd are discussed separately. Both cases are illustrated with examples. The efficient structures are also presented for both cases. Finally, the comparison with the cosine-based method is presented.