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High performance readout and control electronics for mems gyroscopes

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2009
Şahin, Emre
This thesis reports the development of various high performance readout and control electronics for implementing angular rate sensing systems using MEMS gyroscopes developed at METU. First, three systems with open loop sensing mechanisms are implemented, where each system has a different drive-mode automatic gain controlled (AGC) self-oscillation loop approach, including (i) square wave driving signal with DC off-set named as OLS_SquD, (ii) sinusoidal driving signal with DC off-set named as OLS_SineD, and iii) off-resonance driving signal named as OLS_OffD. A forth system is also constructed with a closed loop sensing mechanism where the drive mode automatic gain controlled (AGC) self-oscillation loop approach with square wave driving signal with DC off-set named as CLS_SquD. Sense and drive mode electronics employ transimpedance and transresistance amplifiers as readout electronics, respectively. Each of the systems is implemented with commercial discrete components on a dedicated PCB. Then, the angular rate sensing systems are tested with SOG (Silicon-on-Glass) gyroscopes that are adjusted to have two different mechanical bandwidths, more specially 100 Hz and 30 Hz. Test results of all of these cases verify the high performance of the systems. For the 100 Hz bandwidth, the OLS_SquD system shows a bias instability of 4.67 ˚/hr, an angle random walk (ARW) 0.080 ˚/√hr, and a scale factor of 22.6 mV/(˚/sec). For the 30 Hz bandwidth, the OLS_SquD system shows a bias instability of 5.12 ˚/hr, an ARW better than 0.017 ˚/√hr, and a scale factor of 49.8 mV/(˚/sec). For the 100 Hz bandwidth, the OLS_SineD system shows a bias instability of 6.92 ˚/hr, an ARW of 0.049 ˚/√hr, and a scale factor of 17.97 mV/(˚/sec). For the 30 Hz bandwidth, the OLS_SineD system shows a bias instability of 4.51 ˚/hr, an ARW of 0.030 ˚/√hr, and a scale factor of 43.24 mV/(˚/sec). For the 100 Hz bandwidth, the OLS_OffD system shows a bias instability of 8.43 ˚/hr, an ARW of 0.086 ˚/√hr, and a scale factor of 20.97 mV/(˚/sec). For the 30 Hz bandwidth, the OLS_OffD system shows a bias instability of 5.72 ˚/hr, an ARW of 0.046 ˚/√hr, and a scale factor of 47.26 mV/(˚/sec). For the 100 Hz bandwidth, the CLS_SquD system shows a bias instability of 6.32 ˚/hr, an ARW of 0.055 ˚/√hr, and a scale factor of 1.79 mV/(˚/sec). For the 30 Hz bandwidth, the CLS_SquD system shows a bias instability of 5.42 ˚/hr, an ARW of 0.057 ˚/√hr, and a scale factor of 1.98 mV/(˚/sec). For the 100 Hz bandwidth, the R2 nonlinearities of the measured scale factors of all systems are between 0.0001% and 0.0003% in the ±100 ˚/sec measurement range, while for the 30 Hz bandwidth the R2 nonlinearities are between 0.0002% and 0.0062% in the ±80˚/sec measurement range. These performance results are the best results obtained at METU, satisfying the tactical-grade performances, and the measured bias instabilities and ARWs are comparable to the best results in the literature for a silicon micromachined vibratory gyroscope.