A generic multiple-feedback architecture and method for the design of high-order Σ-Δ modulators

In this paper, a generic multiple-feedback architecture associated with a systematic design method is proposed for the design of high-order Σ-Δ modulators. The goal of this approach is to determine the values of loop coefficients of a designed modulator with limited coefficient ratios for easy integrated-circuit implementation, while achieving high signal-to-noise ratio (SNR) and a wide range of maximum dc input levels. The proposed method uses the transfer function of a structure-matched filter as an initial solution to synthesize the transfer function of a designed modulator. By using mapping and scaling techniques, 4 to 6 dB larger SNR, two to three times greater range of maximum dc input level, and ten to 1000 times smaller coefficient ratio than those of conventional methods and structures are obtained by the proposed architecture and method. Simulation results show that a minimum of 110-dB SNR is attained for modulators with order higher than four, as tested over a 20-kHz audio bandwidth at a sampling rate 2.56 MHz.