Design and implementation of CIC based decimation filter for improved frequency response

The over sampled output of a sigma delta modulator is decimated to Nyquist sampling rate by Decimation filters. The decimation filters work two fold, they decimate the sampling rate by a factor of OSR [over sampling rate] in doing so they remove the outband quantization noise resulting in an increase in resolution. The speed, area and power consumption of oversampled converter are governed largely by decimation filters in sigma-delta A/D converters. The paper presents a design and implementation of a sigma-delta digital decimation filter. The decimation filter structure is based on cascaded-integrated Comb (CIC) filter. A second decimation filter using CIC for large rate change and cascaded FIR filters, for small rate changes, to improve the frequency response. The proposed structure is even more hardware efficient.