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CMOS Systems and Circuits for sub-degree per hour MEMS Gyroscopes

by Sharma, Ajit

Abstract (Summary)
The objective of our research is to develop system architectures and CMOS circuits that interface with high-Q silicon microgyroscopes to implement navigation-grade angular rate sensors. The MEMS sensor used in this work is an in-plane bulk-micromachined mode-matched tuning fork gyroscope (M2?TFG), fabricated on silicon-on-insulator substrate. The use of CMOS transimpedance amplifiers (TIA) as front-ends in high-Q MEMS resonant sensors is explored. A T-network TIA is proposed as the front-end for resonant capacitive detection. The T-TIA provides on-chip transimpedance gains of 25M¦¸, has a measured capacitive resolution of 0.02aF/¡ÌHz at 15kHz, a dynamic range of 104dB in a bandwidth of 10Hz and consumes 400¦ÌW of power. A second contribution is the development of an automated scheme to adaptively bias the mechanical structure, such that the sensor is operated in the mode-matched condition. Mode-matching leverages the inherently high quality factors of the microgyroscope, resulting in significant improvement in the Brownian noise floor, electronic noise, sensitivity and bias drift of the microsensor. We developed a novel architecture that utilizes the often ignored residual quadrature error in a gyroscope to achieve and maintain perfect mode-matching (i.e.0Hz split between the drive and sense mode frequencies), as well as electronically control the sensor bandwidth. A CMOS implementation is developed that allows mode-matching of the drive and sense frequencies of a gyroscope at a fraction of the time taken by current state of-the-art techniques. Further, this mode-matching technique allows for maintaining a controlled separation between the drive and sense resonant frequencies, providing a means of increasing sensor bandwidth and dynamic range. The mode-matching CMOS IC, implemented in a 0.5¦Ìm 2P3M process, and control algorithm have been interfaced with a 60¦Ìm thick M2?TFG to implement an angular rate sensor with bias drift as low as 0.1¡ã/hr ¨C the lowest recorded to date for a silicon MEMS gyro.
Bibliographical Information:

Advisor:Levent Degertekin; W. Marshall Leach; Jennifer Michaels; Farrokh Ayazi; Paul Hasler

School:Georgia Institute of Technology

School Location:USA - Georgia

Source Type:Master's Thesis

Keywords:electrical and computer engineering

ISBN:

Date of Publication:11/14/2007

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