Design and Implementation of FPGA-Based Digital Phase-Locked Loop for MEMS Resonant Accelerometer

Resonant accelerometer converts acceleration into frequency signals, effectively mitigating the drift and noise issues commonly encountered in capacitive or piezoresistive accelerometers; however, their operation relies on the integration with phase-locked loop (PLL) control circuits. Conventional PLLs suffer from limitations such as large circuit size, poor interference immunity, limited parameter adjustability, and insufficient long-term stability. To address these challenges, this work proposes a fully digital PLL control circuit to achieve enhanced stability and higher integration. The proposed design introduces innovative advancements in three key aspects: system architecture, loop filtering, and phase calibration. First, a compact digital phase-locked loop control system is implemented on a field programmable gate array (FPGA), integrating band-pass filtering, phase detection, and feedback control based on a digital PLL architecture. Second, an analytical method for determining the loop filter coefficientsC1andC2is developed, providing a theoretical foundation for parameter optimization and improving the reproducibility of system design. Finally, an open-loop excitation method is introduced, using the FPGA’s internal signal source to drive the micro-electro-mechanical system (MEMS) resonant accelerometer and measure the phase difference, enabling precise phase shifter calibration and accurate closed-loop compensation. Experimental validation was conducted using a MEMS resonant accelerometer developed by our group. In static tests, a bias instability of 1.53μg and a noise floor of 0.58μg/√Hz are achieved; under dynamic conditions, when a frequency step of 223 Hz occurs, the frequency acquisition time is less than 10 ms. The system demonstrates not only stable static performance but also rapid response and accurate tracking of acceleration changes, highlighting its superior performance under dynamic and rapidly varying conditions.