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A Force Rebalanced Micro-Gyroscope Driven by Voltages Oscillating at Half of Structure’s Resonant Frequency

This paper demonstrates a simple and cost-effective approach to separate the mechanical vibration signals from the electrical feedthrough signals resulted from stray capacitances, which is a generic issue in capacitive MEMS gyroscopes. Taking advantage of the quadratic relationship between the drive voltage and the electrostatic force, the micro-structure can be driven into resonance by using voltages oscillating at half of its resonant frequency. As a result, the mechanical signals and the electrical feedthrough can be readily identified in the frequency domain. Although the forcer in this control scheme is nonlinear, it is still possible to adopt this method to implement a force rebalance loop. A particular feedback controller is designed to achieve a linear measurement. Meanwhile, we simplify the modulation and demodulation processes in the feedback loop to obtain a fully linear system design. In addition, the noise characteristic is analytically investigated by using power spectral density in the open-loop case, and is numerically simulated in the closed-loop case. The experimental results not only demonstrate the feasibility of the control scheme, but also show that the fabricated micro-gyroscope using the proposed approach exhibits moderate performances. The nonlinearity of the scale factor is 290 ppm within the measurement range of ±300 deg/s. The bias instability achieves about 4.5 deg/h with an angular random walk of 11.9 deg/h/sqrt(Hz).