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BEB22: A Sub-mW Mode Matching Sigma-Delta Vibratory Gyroscope Readout Circuit

Project ID BEB22
Start Date Fri 2005-Jan-21 13:12:13
Last Updated Wed 2017-Apr-26 13:11:29
Abstract We present the design and experimental results of a low-power, high-resolution gyroscope readout circuit. Several techniques are combined to enable an unprecedented level of power savings. Chief among them are automatic mode-matching, positive position sigma-delta force-feedback, and current integrator based position sensing. Mode-matching relaxes the electronic noise budget of the front-end amplifier by the sense Q, resulting in a proportional reduction in front-end power dissipation. Unfortunately, it also results in an extremely narrow open-loop sensor bandwidth owing to the high sense Q, and substantial scale factor and phase uncertainty induced by Q and resonance frequency variations with process and temperature. These problems are overcome in this design by using force feedback to achieve good scale factor stability, a well defined phase relationship to reject quadrature error, and a bandwidth well in excess of 50Hz, commensurate with the requirements of automotive and consumer applications. Unfortunately, with feedback comes the problem of closed-loop stability. High-Q higher-order resonance modes in vacuum packaged devices present additional challenges. The positive position feedback technique addresses this problem and is key to the stable operation of the force-feedback loop. Positive position feedback is combined with the sigma-delta technique to provide inherent A/D conversion. The current integrator based position sense front-end trades the high linearity and gain stability of conventional front-ends for substantially lower power dissipation. The force- feedback loop enables its use without compromising overall system performance since feedback attenuates the error due to the nonlinearity and gain variation of the elements in the loop’s forward path. These techniques were implemented in a 0.35um CMOS ASIC, which dissipates less than 300uA from 3.3V and achieves a Brownian noise limited noise floor of 0.004 deg/sec/rtHz over a 50Hz Band.
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IAB Research Area Physical Sensors & Devices
Researcher(s) Chinwuba D. Ezekwe
Advisor(s) Bernhard E. Boser
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