System Modeling Of Digital Closed-loop Readout Circuit For MEMS Acceleration Sensor

MEMS acceleration sensor is an essential part of the seismic exploration equipment. However, the supply market is largely monopolized by foreign countries. The design of the readout circuit of the MEMS geophones is a key technology. The purpose of this paper is to study the decimation filtering section of the readout circuit and design an optimized digital filter which has an excellent frequency response for seismic data with low power consumption for equipment.MEMS technology has been applied to the fields of deep oil exploration, seismic detection. Many of researches for improving the performance of MEMS acceleration sensor had been put forward. MEMS acceleration sensor and its various kinds of good performance has been widely used in military and commercial equipment, it includes MEMS acceleration sensors and its read-out circuits. The background of this paper is introduced, including the research meaning and the development of digital filters. And the knowledge of seismic exploration is generally discussed as well. In recent years, MEMS sensor also used in precision exploration because for its high accuracy and high stability. MEMS acceleration sensor divided into pressure resistance, from comprehensive properties, capacitive accelerometer and others structures. Capacitive accelerometer is the most desirable device which can use in many areas. The circuit structure of readout circuit mainly includes three parts: the common method is use modulation or demodulation technique in continuous time voltage readout circuit, small incremental capacitance convert into proportional to the voltage. The other method is operational trans-conductor amplifier used in continuous time current readout circuit. The switched capacitor charge readout circuit is also the good method for MEMS readout circuit. The entire system adopt closed-loop sigma-delta structure and modulation or demodulation technique which simulation a model in MATLAB. The theoretical basis and design methods of the digital filter are presented in this paper, the requirements of the filters are analyzed in detail.For digital decimation filter, entire system is designed as a 3 part of the cascade structure: CIC decimation filter to complete the high extraction and anti-aliasing, Compensation filter to make a compensation to the attenuation of the pass band of the last filter and to further extract, Equiripple FIR filter as the fine filter.The simulation and analysis on ISE and Modelsim is described in final chapter, after that, it is implemented on FPGA.The papers mainly discuss the structure of readout circuit for MEMS accelerometer and its design method. There also a comparative analysis, a real circuit in cadence which SNR has lower 3dB than Simulink model in MATLAB. In this paper, an effective way for design of feed-forward sigma-delta for MEMS acceleration sensor is proposed. Furthermore, the simulation model is designed successfully under idea environment in MATLAB, which can not indicate it can reach the same performance in real environment after taped out. Therefore, the useful model parameters which had been verified by taped out can be the most valuable parameters for MEMS readout design. In this paper, the work shows an optimized parameters design with signal to noise ration(SNR) of 148 dB and its experimental result can reach 145 dB.