Research And Design Of Closed-Loop Frequency Tracking Circuit For Silicon Microresonance Pressure Sensor

The silicon micro-resonant pressure sensor with electrostatic excitation/resistance detection mode has become the focus of pressure sensor research and development because of its long-term stability and reliability,fast response speed and easy processing of output signals.It is one of the most accurate pressure sensors at this stage.This paper designs two closed-loop circuits for closed-loop frequency tracking in different working modes.One is a closed-loop frequency tracking circuit based on the CD4046 B phase-locked loop.The circuit system uses the pre-stage conditioning circuit to amplify,filter and phase-shift the output signal of the sensor,and uses the phase-locked loop to track the frequency of the signal,and then performs waveform and amplitude processing on the output signal of the phase-locked loop through the subsequent-stage conditioning circuit.The input is then applied to the sensitive structure as an excitation signal.The other is an FPGA-based digital closed-loop frequency tracking circuit.The output signal of the sensor is converted into a digital signal by the A/D circuit after being processed by the amplifying circuit and the filtering circuit.After passing through the frequency dividing module,the phase detecting module compares the phase of the signal with the output signal of the frequency sweeping circuit to determine whether the sensor in resonance.If yes,the frequency measurement module is used to detect the frequency of the input signal and output the result;if not,the frequency of the input signal is changed by the frequency sweeping module to reach the resonance state.Finally,the PCB of the closed-loop frequency tracking circuit is tested.The experimental results show that the circuit achieves real-time high-speed(<20 ms)measurement of the sensor output signal in the frequency range of 18-30 KHz.The digital part of the closed-loop frequency tracking circuit based on FPGA is written and simulated.The simulation result graph shows that the digital circuit can realize the function of measuring the signal frequency and ensuring that the sensor is in a resonance state,and the measurement accuracy is 1 Hz.