MASH2-0 Electromechanical Sigma-Delta Modulator for Capacitive MEMS Sensors Using Dual Quantization Method

This paper presents a new control structure for an electromechanical sigma-delta modulator (EM-Sigma Delta M) based on the dual quantization technique. The modulator adopts a 2-0 multi-stage noise-shaping structure (MASH2-0), which was studied by system-level modeling and hardware implementation using an FPGA. The study shows that the MAH2-0, like the MASH2-2, is inherently stable, has a high overload-input level and high dynamic range compared to single-loop EM-Sigma Delta M. However, the MASH2-0, with its simpler implementation, achieved a higher dynamic range and better signal-to-noise ratio than a comparable MASH2-2 and fourth-order single-loop EM-S.M. A capacitive MEMS accelerometer was designed and employed in this system. Within a bandwidth of 1 KHz, the sensor achieved a noise-floor level of -130 dB, a full scale of +/- 20g acceleration, and a bias instability of 20 mu g for a period of three hours. The investigation confirms the concept of the MASH2-0 structure and shows its potential as a closed-loop interface for high-performance capacitive MEMS inertial sensors.