A Digital Phase Demodulation Technique for Resonant MEMS Gyroscopes

This paper introduces a digital phase demodulation technique for resonant MEMS gyroscopes. The proposed method converts the amplitude-modulated Coriolis signal of the gyroscope into a digital phase-modulated output by utilizing the quadrature component of the sense signal. The rate information is extracted from the digital phase-modulated output using an XOR gate as a digital multiplier. Besides offering more robustness to low-frequency amplitude noise sources due to its phase-based operation, the proposed scheme enables direct time-domain digitization of the gyroscope signal at carrier frequency to avoid additional noise folding by the down-conversion multiplier in conventional amplitude demodulation. In addition, due to its digital nature, the proposed phase-based scheme offers better design scalability for deep-submicrometer CMOS implementations. As a proof of concept, the proposed phase demodulation architecture is interfaced with a low-bias-drift mode-matched tuning fork gyroscope. A scale factor of 240 mV/°/s with sub-0.001°/s detectable rate is measured. The complete system exhibits a low bias instability of 0.55°/h and an angle random walk of 0.12°/√h.