Date

2012

Author

Sönmezoğlu, Soner

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This thesis, for the first time in the literature, presents an automatic mode-matching system that uses the phase relationships between the residual quadrature and drive signals in a gyroscope to achieve and maintain the frequency matching condition, and also the system allows controlling the system bandwidth by adjusting the closed loop parameters of the sense mode controller, independently from the mechanical sensor bandwidth. There are two mode-matching methods, using the proposed mode-matching system, presented in this thesis. In the first method, the frequency matching between the resonance modes of the gyroscope is automatically accomplished by changing the proof mass potential. The main motivation behind the first method is to tune the sense mode resonance frequency with respect to the drive mode resonance frequency using the electrostatic tuning capability of the sense mode. In the second method, the mode-matched gyroscope operation is accomplished by using dedicated frequency tuning electrodes that only provides a capability of tuning the sense mode resonance frequency generating an electrostatic spring effect on the sense frame, independently from the proof mass potential. This study mainly focuses on the second method because the proof mass potential variation is not desired during the gyroscope operation since the proof mass potential directly affects the drive and sense mode dynamics of the gyroscope. Therefore, a single-mass fully-decoupled gyroscope including the dedicated frequency tuning electrodes are designed. To identify mode shapes and mode frequencies of the designed gyroscope, FEM simulations are performed. The designed gyroscopes are fabricated using SOI-based SOG process. The fabrication imperfections are clarified during the formation of the structural layer of the gyroscope. Next, the closed loop controllers are designed for the drive amplitude control, sense force-feedback, quadrature cancellation, and mode-matching regarding the phase relationship between the quadrature and drive signals. Mode-matching is achieved by using a closed loop controller that provides a DC tuning potential. The mode-matching system consisting of vacuum packaged sensor, drive amplitude control, sense force-feedback, quadrature cancellation, and mode-matching modules is implemented on a printed circuit board (PCB), and then the system level tests are performed. Tests illustrate that the mode-matching system operates in a desired manner. Test results demonstrate that the performances of the studied MEMS gyroscopes are improved up to 2.6 times in bias instability and 2 times in ARW under the mode-matched condition compared to the mismatched (~200 Hz) condition, reaching down to 0.73 °/hr and 0.024 °/√hr, respectively. At the mode-matched gyroscope operation, the better performance is obtained to be bias instability of 0.87 ⁰/hr and ARW of 0.014 °/√hr, close to a theoretical mechanical Brownian noise limit of 0.013 °/√hr, under 10 mTorr vacuum ambient condition. The system bandwidth is adjusted and measured to be greater than 50 Hz. The mode-matched gyroscope has a linearity of 99.99% in a dynamic range of ±90 °/sec. The dynamic range can be increased above that level without sacrificing linearity. To conclude, the proposed mode-matching system improves the performance of the gyroscope up to a mechanical Brownian noise limit by substantially suppressing the electronic noise of the sense mode controller and achieves sub-degree per hour performance without sacrificing system bandwidth and linearity.

Subject Keywords

Microelectromechanical systems., Microelectromechanical systems industry., Gyroscopes.

URI

http://etd.lib.metu.edu.tr/upload/12614656/index.pdf
https://hdl.handle.net/11511/21744

Collections

Graduate School of Natural and Applied Sciences, Thesis