Programmable modified fractional comb decimation filter

Abstract

In multistandard radio receivers, the hardware should be configurable or programmable for the reception of different types of signals having different symbol rates. The decimation by a non-integer factor becomes a critical functionality of the multistandard radio. The Cascaded Integrator-Comb (CIC) filters are commonly used for decimation by an integer. By using polynomial interpolation filter between integrator and comb stages of CIC, and non-integer delay in the feed-forward branch of the comb stage, we achieve improved attenuation for the aliasing frequency components, and we make possible to use this type of structure for decimation by a non-integer factor. We name this structure as a programmable fractional CIC filter structure. This paper presents an efficient fractional structure for flexible decimation in the multistandard radio receivers. This structure is based on the so-called modified comb filter using the programmable fractional CIC principle. The main advantages of the proposed structure are flexibility and programmability with increased attenuation for aliasing frequency components.