Multi stage noise shaping sigma-delta modulator (MASH) for capacitive MEMS accelerometers

Electromechanical multi stage noise shaping (MASH) sigma-delta modulator (ΣΔM) has the advantages of inherent stability, high dynamic range, and high overload input level compared with the single loop sigma-delta-modulator approach. In this paper, a fourth order electromechanical MASH is studied by Simulink modelling and hardware implementation using surface mount PCB technology. The accelerometer used in the study is fabricated using a Silicon on Insulator (SOI) wafer with a device layer thickness of 50 μm, using a dicing free and dry release process. The experimental results confirm the concept of the MASH structure and show its potential as a closed loop interface concept for a high performance capacitive MEMS accelerometer. The 4th order MASH electromechanical ΣΔM system improves the performance of the 2nd order electromechanical ΣΔM by 20 dB, and shows a noise floor of −110 dB. Furthermore, the system is capable of handling an acceleration input of up to ±1.5 g. However, the MASH-ΣΔM is sensitive to the sensor and system parameters variation; it exhibited performance degradation of 10 dB, due to a leakage of the quantization noise to the input signal.