Research On MEMS Micro-Gyroscope Resonant Frequency Tracking And Locking Technology

The MEMS micro-gyroscope is an angular velocity sensor.The piezoelectric micro-solid mode gyro in this paper is a special vibrating MEMS micro-gyro with high operating frequency(on the order of 300KHz)and strong impact resistance.The core component of the piezoelectric micro-solid mode gyro is a piezoelectric vibrator.The vibrator is excited by an alternating voltage.The sensing electrode induces a charge.The magnitude and the phase difference from the excitation voltage of the induced charge will vary with the frequency of the excitation voltage.In a certain order vibration mode of the gyro,the magnitude of the induced charge reaches a maximum value,and the corresponding frequency is the resonant frequency of the gyro oscillator.In order to optimize the working performance of the gyro,it is necessary to make it work stably at the resonance frequency.The resonant frequency is affected by environmental factors and drifts,so the resonant frequency of the vibrator needs to be tracked and locked.At the vicinity of the resonance point,the magnitude of the induced charge is insensitive to changes in the drive frequency,and the phase is very sensitive to changes in the drive frequency.Based on this characteristic,a high-performance MEMS micro-gyroscope resonant frequency tracking and locking circuit based on phase locking is designed.The direct digital synthesis(DDS)chip is used as the signal generator,and the digital signal is controlled by the field programmable gate array(FPGA)to make the DDS output frequency adjustable driving signal,and the gyro is supplied with the excitation voltage to make the gyro generate the induction.The charge simultaneously generates two orthogonal demodulation reference signals for the vector analysis module.The induced charge is converted into a voltage amount by the charge amplifying module,and is simultaneously input to the FPGA through an analog-to-digital conversion(ADC)with the quadrature demodulated signal,and the amplitude and phase demodulation of the sensing signal is performed by a vector analysis technique inside the FPGA.The vibration characteristics of the gyro are analyzed by DDS frequency sweeping,and the resonant frequency of the gyro is measured in the range of 331.85~332.15 kHz.The phase difference between the sensing signal of the resonant point and the driving signal is found as the reference value.During the gyro working process,the FPGA performs vector analysis on the sensing signal in real time,compares the phase information of the sensing signal with the reference value,controls the DDS to change the frequency of the excitation voltage,converges the phase to the reference range,and finally locks in the reference value range.The corresponding excitation voltage frequency is the resonant frequency of the gyro.In this paper,when the phase difference is locked between 98.48° and 100.27°,the driving signal frequency can be controlled within the optimal resonance point range.The actual measurement results lock the phase between 99.0° and 99.9°.The DDS output drive signal has a step size of 10 Hz,and the tracked gyro resonance frequency is between 332.068 kHz and 332.089 kHz.The closed-loop control circuit of the piezoelectric micro-solid mode gyro designed in this paper realizes the function of tracking and locking the resonant frequency,and achieves full digital control.The system can be used for the modal locking and tracking of the vibrator with the resonator as the core device.