A Closed-Loop System for Resonant MEMS Sensors Subject to Blue-Sideband Excitation

This study reports a closed-loop system (CLS) for resonant micro-electromechanical systems (MEMS) sensors subject to blue-sideband excitation (BSE) for the first time. Compared with the conventional excitation scheme, which uses an AC signal with a frequency that is very close to or equal to that of the desired MEMS resonator mode, the BSE scheme applies an AC signal with a frequency equal to or near the sum of two resonant frequencies to excite the resonator. This requires a CLS to provide a sum-frequency excitation signal to serve as the resonator’s feedback driving signal for practical applications. The proposed CLS mainly consists of a digital lock-in amplifier (DLA), a phase-locked loop (PLL) and a BSE control module (BSE-CM), and is implemented using a field-programmable gate array (FPGA). Experiments showed that the system can track the combined frequency of two flexural modes of the resonator in real-time. In addition, a potential application of the CLS for resonant MEMS sensors subject to BSE is preliminarily demonstrated, showing that the sensitivity of a vacuum-packaged resonant MEMS accelerometer can be enhanced by 166%. This approach could also be applied to reduce the effects of the feedback phase, or to simultaneously monitor multiple parameters. This study represents critical progress for practical sensing using the BSE scheme.