Research On The Mode-match Control Circuit Of Silicon Micro-gyrpscope

The silicon vibratory micro-gyroscope is a type of MEMS initial sensors,and it could meet the requirements of commercial navigation and guidance since it's research has been experimented over 20 years.Nowadays,the technique how to improve the precision of MEMS gyroscope even further is a hot research topic.It is well known that the MEMS gyroscope has two modes,drive mode and sense mode,and each mode has its own resonant frequency.When the resonant frequency of sense mode equals to drive mode,it is named mode-match,and the mechanical sensitivity will be highest in mode-matched state.In further,the mechanical sensitivity varies directly with the quality factor of sense mode.Thus,high quality factor as in vacuum encapsulation could amplify the mechanical sensitivity in mode-matched state.This paper designs a mode-match control circuit for MEMS gyroscope with dual mass decoupled structure based on FPGA,the entire measurement and control circuit includes four closed-loops: drive,sense,quadrature error correction and mode-match.Firstly,on the premise of introduced simplified structure of MEMS gyroscope,the closed-loop drive design based on phase-locked loop(PLL)and automatic gain control(AGC)is reported.The reason of generating quadrature error is analyzed,and the quadrature error correction control method based on stiffness offset is introduced.The open-loop sense control and closed-loop sense control both based on PSD are discussed.The frequency tuning method based on negative stiffness effect which could change the resonant frequency of sense mode by applying tuning voltage on frequency tuning electrodes is analyzed.Secondly,the forward excitation-calibration and feedback excitation-calibration mode-match methods are introduced.Both excitation-calibration mode-match methods uses two pilot tones located at both sides of drive mode resonant frequency to excite sense mode,the tuning voltage is attained by comparing the difference of responds of two pilot tones.In open-loop condition,the influences of key parameters in two mode-match methods are discussed.The stability of two mode-match methods is analyzed by average analysis theory,and the results could guide the parameters setting in experiments.The simulation models are built in Simulink platform and the results of theoretical analysis are verified.Thirdly,the specific mode-match realization schemes based on two control methods are designed,which are compatible with the other control loop in entire measurement and control scheme.The FPGA,ADC and DAC are selected referenced to the requirement of control system.Finally,the forward excitation-calibration mode-match method is realized on a MEMS gyroscope with low quality factor while the feedback excitation-calibration mode-match method is realized on a MEMS gyroscope with high quality factor which could reach 12000+.Experimental results indicate the performance of MEMS gyroscope under mode-match state is promoted evidently compared to mode-unmatched state,and the tested results verify the correctness of theoretical analysis results and the designed circuit.