Comb-Based Decimation Filters for $Sigma Delta$ A/D Converters: Novel Schemes and Comparisons

摘要

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 $Sigma Delta$ 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 $Sigma Delta$ 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 $Sigma Delta$ modulator order decodable by any proposed filter cell in the class of the SMCFs.