A digital closed-loop control system with all digital phase locked loop (ADPLL) is designed and optimized, in order to improve the bias stability and transient response of the gyroscope. The nonlinear mathematical models for the closed-loop amplitude and phase control system are established. The linearization method is applied to analyze the nonlinear models. The control parameters of the drive loop are optimized. The experimental results show that the phase deviation between the demodulation reference signal of the drive loop and the sense signal is less than 0.25° in the temperature range from-40°C to 60°C, within 0.15° of the variation. At room temperature, the overshoot amount of the gyroscope control system is 4.5% with setting time of 0.12s. The bias stability is 1.45°h. Compared to the analog control scheme, the digital control system has advantages of short setting time, small overshoot, short phase locked time, large locked range, high phase precision, etc.

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To cope with the multi-physics fields simulation in MEMS device, based on PSPICE software, a multi-fields simulation model of capacitive micro-accelerometer is proposed, in which the mechanics, thermal and electric fields are included. Through the comparison of maximum step and pulse acceleration response under large displacement condition, which are obtained by simulation model and classic formula respectively, it is indicated that the difference between them is less than 3%. Furthermore, the comparison has been done with sensitivity test results in open loop mode. The comparison results show that the difference is less than 5% for large displacement situation and 3% for little displacement situation. Hence, the model could basically accomplish multi-physics fields simulation in MEMS device and be helpful in further research.

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