High-Range Angular Rate Sensor Based on Mechanical Frequency Modulation

We report, for the first time, an angular rate sensor based on mechanical frequency modulation (FM) of the input rotation rate. This approach tracks the resonant frequency split between two X - Y symmetric high-Q mechanical modes of vibration in a microelectromechanical systems Coriolis vibratory gyroscope to produce a frequency-based measurement of the input angular rate. The system is enabled by a combination of a MEMS vibratory high-Q gyroscope and a new signal processing scheme which takes advantage of a previously ignored gyroscope dynamic effect. A real-time implementation of the quasi-digital angular rate sensor was realized using two digital phase-locked loops and experimentally verified using a silicon MEMS quadruple mass gyroscope (QMG). Structural characterization of a vacuum- packaged QMG showed Q factors on the order of one million over a wide temperature range from -40 °C to +100°C with a relative x/y mismatch of Q of 1 %. Temperature characterization of the FM rate sensor exhibited less than 0.2% variation of the angular rate response between 25°C and 70 °C environments, enabled by the self-calibrating differential frequency detection. High-speed rate table characterization of the FM angular rate sensor demonstrated a linear range of 18 000 deg/s (50 r/s, limited by the setup) with a dynamic range of 128 dB. Interchangeable operation of the QMG transducer in conventional amplitude- modulated and new FM regimes provides a 156-dB dynamic range.