Comb-Based Decimation Filters for ΣΔ A/D Converters: Novel Schemes and Comparisons

This paper proposes several novel decimation filtering schemes tailored to the design of SigmaDelta analog-to-digital (A/D) converters. On the one hand, it extends the class of modified-sinc filters introduced by Lo Presti, in order to obtain decimation filters capable of decoding high-order SigmaDelta modulators, say up to the fifth order; on the other hand, it introduces the class of sharpened-modified comb filters (SMCF) aimed at increasing the rejection of the SigmaDelta quantization noise around the folding bands and reducing the passband drops of the designed decimation filters with respect to the classic comb structures. Design criteria leading to optimized structures are described. The paper compares classic comb filters with modified and SMCF in terms of performance metrics widely adopted for comb filters. Finally, it derives the maximum SigmaDelta modulator order decodable by any proposed filter cell in the class of the SMCF