An FPGA-Accelerated Quartz Crystal Measurement System Based on a Negative Feedback Loop With Quadrature Demodulation

Rapid measurement of the resonant frequency of quartz crystal (QC) devices plays a key role in applying QC-based dynamic monitoring, such as respiration monitoring and kinetic process, in electrochemical reactions. This work develops an FPGA-accelerated QC measurement system without software-based curve fitting. A negative feedback loop based on the susceptance response collected by the quadrature demodulation circuit is constructed. Moreover, a proportional–integral–differential control and tracking strategy is applied to improve the measurement speed significantly. The test results show that the implemented system can track a frequency shift of 5 kHz bandwidth within 50 ms. The standard deviation of the measured frequency of a QC device under test is only 0.17 Hz, which indicates that the proposed system has high stability and high precision. The frequency measurement results have a relative error of 0.8 ppm compared with the Agilent 4294 A impedance analyzer. It is demonstrated that the proposed QC measurement system has great potential for QC-based dynamic detection.