Multi-stage IIR decimation filter design technique for high resolution sigma-delta A/D converters

The authors present a design technique for a multistage halfband filter with infinite-impulse-response (IIR) structure to enhance the effective resolution of oversampling analog-to-digital (A/D) converters. A series of six cascaded IIR filters is implemented to obtain more than 18-b of effective resolution for a digital signal with 12-b resolution from the DSP56ADC16 converter. Since this proposed structure is flexible, the number of stages in the decimation process can be adjusted to fit the needs of a specific application. By taking advantages of the oversampling methodology, more than 120 dB of SNR can be theoretically achieved. The analysis of the proposed method and experimental comparison with previously presented structures are included