Decimation by Non-Integer Factor using CIC Filter and Linear Interpolation

Recently we have developed an efficient flexible multirate signal processing structure with high oversampling ratio and adjustable fractional or irrational sampling rate conversion factor. One application area is a multistandard communication receiver which should be adjustable for different symbol rates utilised in different systems. The proposed decimation filter consists of parallel CIC (cascaded integrator-comb) filters followed by a linear interpolation filter. The idea in this paper is to use two parallel CIC filters to calculate the two needed sample values for linear interpolation. In this paper we give a modification of the proposed structure and its control logic that enables better image and aliasing attenuation. The modification is based on the observation of the dependence of behaviour of the control logic on the fractional part of the sampling rate conversion factor.