Compensation methos for quasi-static acceleration sensitivity of MEMS gyroscopes /

Gavcar, Hasan Doğan
This thesis presents the quasi-static acceleration compensation methods for a fully decoupled MEMS gyroscope. These methods are based on the utilization of the amplitude difference information between the residual quadrature signals on the differential sense mode electrodes to sense the static acceleration acting on the sense mode of the gyroscope. There are three different quasi-static acceleration compensation methods presented in this thesis. In the first method, the static acceleration is measured by comparing the amplitudes of the out of phase sustained residual quadrature signals. By using the experimental relation between the rate and acceleration outputs, the quasi-static acceleration sensitivity of the gyroscope is mitigated. This method requires the additional process of data collection. In the second method, in addition to the circuit proposed in the first method, a closed loop controller is implemented in the acceleration compensation system to suppress the effect of the acceleration. The generated feedback voltage is applied to the sense mode electrodes by using the non-inverting inputs of the sense mode preamplifiers. The advantage of this method compared to the first one is that it does not require any additional data process thanks to the closed loop controller. However, this method cannot completely suppress the quasi-static acceleration of the gyroscope. Moreover, changing the voltage of the non-inverting inputs of the preamplifiers may affect the operation of all other control loops. In the third method, the additional acceleration cancellation electrodes are utilized in the mechanical design of the gyroscope. This method overcomes the problems encountered in the second acceleration compensation method. This study mainly focuses on the third acceleration compensation method which provides the best result. Therefore, a single-mass fully decoupled gyroscope including the dedicated acceleration cancellation electrodes is designed. FEM simulations are performed to determine the mode shapes and mode resonance frequencies of the designed gyroscope. The designed gyroscopes are fabricated using the modified silicon-on-glass (SOG) process and are packaged at the wafer level. The closed loop controllers are designed for the drive amplitude control, force-feedback, quadrature cancellation, and acceleration cancellation loops and are implemented on a printed circuit board (PCB). The acceleration compensation system consisting of vacuum packaged gyroscope and controller modules is populated on the same PCB, and the system level tests are performed. Measurements show that the proposed acceleration compensation system operates as expected. Test results demonstrate that the g-sensitivity of the studied gyroscopes are substantially reduced from 0.31°/s/g to 0.025°/s/g, and the effect of the static acceleration is highly-suppressed up to 12 times with the use of the third compensation method proposed in this work. Moreover, the nonlinearity in the scale factor is improved from 0.53% to 0.36% for +/-600°/s range for centrifugal accelerations as much as 0.5g. Furthermore, the proposed acceleration compensation methods do not deteriorate the bias and noise performances of the gyroscopes. To conclude, the proposed acceleration compensation methods improves the g-sensitivity of MEMS gyroscope by using the control electronics rather than employing complex mechanical design. .
Citation Formats
H. D. Gavcar, “Compensation methos for quasi-static acceleration sensitivity of MEMS gyroscopes /,” M.S. - Master of Science, Middle East Technical University, 2014.