Effect of Circuit Errors and Hybrid Continuous-Time/Discrete-Time Sigma-Delta Modulators

Abstract

This work analyzes the use of hybrid continuous-time/discrete-time ∑ Δ modulators for the implementation of analog-to-digital converters intended for wideband mobile applications. Two alternative multirate cascade ∑ Δ architectures are discussed and analyzed, taking into account the impact of main circuit-level error mechanisms, namely: mismatch, finite dc gain and gain-bandwidth product. Both multirate ∑ Δ modulators are compared with conventional single-rate continuous-time cascade ∑ Δ modulators in terms of their sensitivity to non-ideal effects, considering different target specifications. Theoretical predictions match simulation results, showing that the lowest performance degradation is obtained by a new kind of multi-rate hybrid ∑ Δ modulators, in which the continuous-time circuits operate at a higher rate than the discrete-time parts of the modulator.