Design And Implementation Of A Digital Micromachined Accelerometer With High-precision And Small-size

In recent years, high precision capacitive MEMS accelerometers have become a hot research topic in MEMS area and a lot of research results have been published. This thesis aims to design a3-axis digital capacitive MEMS accelerometer with high precision and small size to meet the demand in advanced applications, such as navigation and aerospace.First, the work has introduced the recent research results and the theory model of the capacitive accelerometer. The noise, temperature drift, and asymmetry of a single-carrier modulation-type capacitance measurement circuit are analyzed. The results show that the Capacitance-Voltage (CV) conversion circuit is the main noise source. The asymmetry does not influence the linearity, but it may raise the offset and noise floor.The acceleration sensor part is also discussed in this work. The results show that the parasitic capacitance will raise the noise floor, the imperfect ohmic contact will increasing the temperature drift coefficient and the cross-coupling will influence the accelerometer output and temperature compensation.Base on the analysis above, a small-size and high precision3-axis digital capacitive MEMS accelerometer system is designed and implemented. The influence of lowering the sampling rate of the digital processing circuit is analyzed and the demodulation method is optimized. Four kinds of temperature compensation circuits are compared and the compensation circuit based on bulk resistance is implemented. Test results show that the small-size accelerometer has a good performance. The power consumption is lower than400mW, the noise floor is5μg/√Hz, the bias stability is0.06mg(within200Hz bandwidth), the nonlinearity within±1g is0.336%, the second-order nonlinear coefficient is5ppm, and the temperature drift after compensation is0.3mg/℃.