A Quadrature Phase-Locked Loop Based Digital Closed-Loop System for MEMS Resonant Sensors

This paper reports a novel digital closed-loop system for micro- electromechanical systems (MEMS) resonant sensors. The system achieves frequency tracking through a quadrature phase-locked loop (QPLL) and creatively incorporates a configurable phase-shifting module. Additionally, an innovative amplitude control module, utilizing feedback adjustment, enables stable vibration of the resonator and mitigates negative effects resulting from variations in the quality factor at different temperatures. The system has been implemented on a field-programmable gate array (FPGA) development board and validated on a MEMS resonant temperature sensor, which exhibits significant changes in quality factor across a temperature range of -40 to 80 degrees C. The design of the amplitude control module reduces temperature sensitivity errors by approximately 14-fold and improves linearity by nearly an order of magnitude. The bias instability of the closed-loop system evaluated by Allan variance is as low as 3.4x10(-4) degrees C.