Design Method Of Digital Control Circuit For Electrostatic Frequency Modulation Accelerometer

Frequency modulation microelectromechanical accelerometer(EFMA)is a new type of MEMS accelerometer.Compared with the current universal accelerometer such as capacitive and vibrating beam accelerometer,EFMA has good-temperature characteristics and long-term stability like capacitive accelerometer,and it also has low-noise and high accuracy-characteristics like resonant accelerometer,so it has a very good application prospect.However,the plate displacement corresponding to the electrostatic stiffness has obvious nonlinearity which makes the linearity poor in the large-scale application,it has become an important factor restricting the development of EFMA.First,the Research status of EFMA and the corresponding circuit are introduced,combined with EFMA’s special frequency-detection method based on displacement change,and the feasibility of the force balance closed-loop detection control method is clarified.Secondly,according to EFMA sensitive structure and working principle,the resonator’s theoretical equivalent model and the electromechanical-interface’s model are builted.Then,analyze the EFMA closed-loop drive circuit and design low noise two stage analog-front-end circuit,phase-locked loop demodulation loop and automatic amplitude control modulation circuit.Then,the EFMA force balance closed-loop detection circuit is analyzed,the force balance control variable is found through the mechanical derivation of the sensitive structure,and the sine wave frequency measurement circuit and the force balance control circuit are designed and researched.Finally,complete the debugging of the laboratory prototype combined with the EFMA sensitive device,and perform performance testing,comparing the range and scale factor nonlinearity between circuits with and without forcebalance loop detection circuit.The EFMA scale factor is increased from 6.03Hz/g to 25.3Hz/g and the range(The maximum measurement range of the scale factor nonlinearity is less than 1000ppm)is increased from ±1.6g to ±25g without affecting the other key performances such as bias stability and the scale factor stability,verifying the feasibility and superiority of the force balance closed-loop detection control method based on frequency detection.