A robust NTF zero optimization technique for both low and high OSRs sigma-delta modulators

Abstract

This paper introduces a novel loop filter scheme with embedded noise transfer function (NTF) zero optimization in a feed-forward topology. This new structure allows the relaxation of the requirement of the local feedback coefficient. Moreover, the merit of zero optimization is compatible with high oversampling ratio (OSR) when compared with the traditional loop filter. Besides, the practical implementation exhibits less sensitivity to the capacitor ratio mismatches. A second order discrete-time (DT) sigma-delta (ΣΔ) modulator with the proposed loop filter is designed and simulated with Matlab and Cadence. The performance of the modulator can reach 70.1dB/99.3dB SNDR in a 10MHz bandwidth, with OSR 12/48 and the corresponding coefficients in the local feedback 0.4/0.34, respectively.