Abstract
In this paper, two 4th order electromechanical sigma-delta modulators (Sigma Delta M) are compared at system level; a single-loop (SD4); and a multi-stage (MASH(22)) architecture. The comparison was performed for two different micromachined accelerometer sensing elements: one over-damped and the other under-damped; the control system with the latter requiring an electronic phase compensator for loop stability. The investigation shows that the 4th order MASH Sigma Delta M is unconditionally stable and provides better noise shaping, higher signal-to-quantization-noise-ratio (SQNR), higher dynamic range, and a higher overload input level compared with the SD4. The only drawback of the MASH(22) is its sensitivity to component and parameter tolerances, which leads to a leakage of the quantization noise to the input signal and a degradation of the performance of the modulator. (C) 2010 Published by Elsevier Ltd.