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

Abstract

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 50μm, 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 20dB, and shows a noise floor of −110dB. Furthermore, the system is capable of handling an acceleration input of up to ±1.5g. However, the MASH-ΣΔM is sensitive to the sensor and system parameters variation; it exhibited performance degradation of 10dB, due to a leakage of the quantization noise to the input signal.