Research Of Frequency Modulation Micro-elec Tromechanical Accelerometer Based On Electrostatic Spring Softening (EFMA)

Micro-electromechanical(MEMS)accelerometer is a new type of micro-inertial sensi-tive device made by micromachining technology.Compared with traditional accelerometer,it has the advantages of small size,low cost and low power consumption.However,the low accuracy of MEMS accelerometer prevents its employment in navigation systems.Firstly,the development and application of MEMS accelerometer were introduced.Concerning the advantages and disadvantages of capacitive accelerometers and resonant accelerometers,a new type of MEMS accelerometer has been designed based on the principle of electrostatic spring softening,which combines the advantages of displacement detection and frequency modulation.Then the resonant frequency and scale factor of sensitive structure for this electrostatic spring softening frequency-modulated MEMS accelerometer(EFMA)were designed.Based on the design of the whole sensitive structure,theoretical analysis of the frequency temperature coefficient was carried out to verify the superiority of EFMA frequency temperature coefficient which is not sensitive to stress.Then the measurement and control circuit of EFMA was analyzed and designed.Based on the analysis of circuit model of equivalent resonator,the closed-loop automatic gain control driving circuit and frequency digital converter were designed.In order to further solve the temperature coefficient of EFMA caused by the temperature coefficient of silicon material characteristics,a continuous ring-down driving circuit was designed to convert the measurement of Q value into the measurement of continuous ring-down frequency f_Q,and the temperature compensation of the out-put of the accelerometer was realized by using the continuous ring-down frequency f_Q.Based on the design scheme of sensitive structure and measurement and control circuit,EFMA prototype has been completed and its performance was tested.The temperature performance of EFMA prototype was tested,to verify the excellent temperature performance of EFMA and the feasibility and superiority of the proposed temperature compensation scheme.