On Improving Comb Aliasing Rejection by Separating Multiple Zeros on Unit Circle

This paper presents the method for increasing comb aliasing rejection by introducing the cascade of two multiplierless filters, called zero-separation (ZS) filters, to separate the multiple zeros of the comb filter. The separation of multiple comb zeros enlarges the width of the comb folding bands, where the aliasing occurs. As a result, the aliasing rejection is increased. Two methods are proposed. In the first method, the zero separation (ZS) filter works at a high input rate, leading to increased complexity, presented in the number of adders per output sample (APOS) and an increase of aliasing rejection in all folding bands. In the second method, the ZS filter is placed in the second stage of a two-stage filter. As a result, the number of APOS is decreased at a price of degradation of aliasing rejection in certain folding bands. The polyphase decomposition is applied to reduce the number of APOS further. The method is illustrated with examples and compared with the most recent methods from literature.