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Design optimization and simulation of a fifth-order sigma-delta micro-accelerometer system

Micromachined capacitive inertial sensors embedded in higher order sigma-delta modulator (SDM) have a promising future, especially in high resolution applications. However, the limited performance due to the low dc gain of mechanical sensing element and the stability problem caused by phase-lag are always unavoidable. Previously, researches stabilized higher order electro mechanical SDM (EMSDM) systems through extensive simulations, which is a severely time-consuming work. And scarcely any published articles mentioned a method of optimizing zeros to improve the Signal to Quantization Noise Ratio (SQNR). This paper presents a systematic methodology to determine the optimal coefficients of EMSDM systems rapidly, which can solve the above two problems. To demonstrate the effectiveness of the approach, a fifth-order sigma-delta micro-accelerometer system model is presented. And simulations show that the maximum SQNR of the system is 146.7dB, with an Oversampling Ratio (OSR) of 128. Besides, the robustness analysis is also carried out to demonstrate that the designed system is robust to sensor fabrication tolerances.