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Readout Techniques for High-Q Micromachined Vibratory Rate Gyroscopes

Authors:
Ezekwe, Chinwuba David
Technical Report Identifier: EECS-2007-176
December 21, 2007
EECS-2007-176.pdf

Abstract: Inexpensive MEMS gyroscopes are enabling a wide range of automotive and consumer applications. Examples include image stabilization in cameras, game consoles, and improving vehicle handling on challenging terrain. Many of these applications impose very stringent requirements on power dissipation. For continued expansion into new applications it is imperative to reduce power consumption of present devices by an order-of-magnitude.

Gyroscopes infer angular rate from measuring the Coriolis force exerted on a vibrating or rotating mass. For typical designs and inputs, this signal is extremely small, requiring ultralow noise pickup electronic circuits. This low noise requirement directly translates into excessive power dissipation.

This work describes a solution that combines a new low-power electronic readout circuit with mechanical signal amplification using a technique called mode-matching. The electronic circuit continuously senses the resonance frequency of the mechanical sense element and electrically tunes it to maximize the output signal. A new and robust feedback controller is used to accurately control the scaling factor and bandwidth of the gyroscope while at the same time guaranteeing stability in the presence of undesired parasitic resonances.

The circuit has been fabricated in a 0.35um CMOS process and consumes less than 1mW. The spot noise is 0.004 degs/sec/rtHz.