Research Of Digital Driving Technology Of MEMS Resonant Gyro

MEMS resonant gyro is a kind of inertial sensor for measuring angular velocity.It has many advantages such as small volume,light weight,low cost,easy integration and so on.Therefore,it has wide application prospect in many fields.The performance of MEMS resonant gyroscope is directly related to the amplitude and frequency stability of its driven mode.To improve the gyroscope performance,the research of driven mode resonant technology of MEMS resonant gyroscope is very important.The closed-loop driving system of MEMS resonant gyroscope consists of gyro structure,interface circuit and signal processing circuit.Since the gyro vibration displacement is detected by differential capacitance,the interface circuit often adopts the pseudo-differential structure,but this structure is complex and the symmetry is poor.Signal processing circuit is firstly designed by analog devices,but analog devices has poor anti-interference ability,temperature drafts,non-linearity and other shortcomings.With the development of high-performance digital circuits,the closed-loop digital driving system of the resonant gyroscope has become a focus in recent years.In this paper,we focus on the research of interface circuit and signal processing circuit,and propose a MEMS resonant gyro closed-loop driving system based on FPGA.This system consists of capacitor readout interface circuit and FPGA based digital signal processing circuit.Firstly,the principle of several commonly used interface circuits is analyzed,and a new interface circuit is proposed.Refer to the design of subtractor,this circuit transfer the differential capacitance into a single voltage signal by subtraction.Secondly,the resonant condition of MEMS resonant gyro driven mode is analyzed,and the automatic control algorithm and phase locked loop algorithm in digital driving closed-loop are demonstrated.The digital driving closed-loop system is designed by the Hilbert transform.Hilbert transform is used to demodulate the amplitude and phase of gyro driven mode.And the system is simulated and implemented.Finally,the experimental results show that the new interface circuit designed in this paper has the advantages of simple structure and strong common mode noise suppression ability.The equivalent capacitance resolution of the new interface circuit is0.421 aF (?) in non-modulation state.The frequency accuracy of the phase-locked loop based on the Hilbert transform is0.000291 Hz,and the phase stability is 0.2ppm.The amplitude stability under automatic gain control is6.24 ppm.