Improving the Vibration Rectification of MEMS Resonant Accelerometer Using Digital Oscillator

This paper presents a digital closed-loop measurement and control system (DCOS) for MEMS resonant accelerometer (MRA), including a digital oscillator unit and a digital frequency measurement unit. Using digital bandpass filters and phase shifters to satisfy oscillation criteria in the system, and using a phase-locked loop with phase-frequency detector to obtain a larger frequency capture range, the combination of the two parts improves both the stability and noise performance of the system. Under an acceleration input of 2g@200Hz, the DCOS can maintain stable operation, but the traditional digital phase-locked loop (DPLL) system with integrated oscillation maintenance function and frequency measurement function shows abnormalities. The bias instability and noise of DCOS are 2.7 ppb and 0.92 μg / <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sqrt{{Hz}}$</tex>, respectively. In contrast, the bias instability and noise of DPLL are 1.9 ppb and 0.77μg/ <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sqrt{{Hz}}$</tex>, respectively. This indicates that DCOS has achieved noise performance similar to DPLL while improving system vibration rectification performance.