John A. Geen

Single-chip surface micromachined integrated gyroscope with 50/spl deg//h Allan deviation

The design principles of a mass-produced surface micromachined gyroscope are described. The device is integrated on a single 3 mm/spl times/3 mm chip with a 3-/spl mu/m BiCMOS process. It has a 4-/spl mu/m-thick polysilicon structure, 5-V 6-mA supply, 12.5-mV//spl deg//S sensitivity, 10 000:1 dynamic range, 30 000-gee shock survival, and -55/spl deg/C to +85/spl deg/C operating temperature.

Very low cost gyroscopes

This paper was invited as part of discussion on the extent to which gyroscope cost and performance are influenced by micromachining. The contribution here addresses a very low cost segment enabled by integrating mechanisms and electronics. The resulting ICs are also packaged and tested with standard technology. The paper outlines some of the corresponding design challenges and the methods used to overcome them in a commercial process

Progress in integrated gyroscopes

Fully integrated gyroscopes have some unique advantages in low power, size, weight, and cost. The progress in bringing an integrated gyroscope to mass production is described, together with some of the strategies employed to overcome difficulties with this class of device, in particular, the measures to produce shock and vibration immunity. A natural progression for future products is also outlined.

Single-chip surface-micromachined integrated gyroscope with 50/spl deg//hour root allan variance

A MEMS surface-micromachined gyroscope integrated on a single 3/spl times/3 mm/sup 2/ chip with a 3 /spl mu/m BiCMOS process has 4 /spl mu/m-thick polysilicon structure, 5V 6 mA power supply, 0.05/spl deg///spl radic/s spot noise, 12.5 mV//spl deg//s, >30,000 g shock survival, and -55 to 85/spl deg/C operating range.

In-run bias self-calibration for low-cost MEMS vibratory gyroscopes

We present a method for improving bias instability and Rate Random Walk (RRW) in low-cost MEMS vibratory gyroscopes by periodically reversing polarity of the resonator drive force, yielding a 5 times reduction of RRW noise. The feasibility of the approach was experimentally evaluated using an in-production Analog Devices ADXRS800, a fully integrated MEMS gyroscope with a quadruple mass architecture. The proposed method is to use periods of alternating co-phase and anti-phase drive clock to drive-mode oscillation periods, and sampling the gyroscope sense-mode output during the equal times of co-phase anti-phase drive of the resonator, thereby canceling the drive alignment bias error term. The proposed self-calibration method allows for long and short term stability improvement in low-cost and high performance MEMS vibratory gyroscopes.

Mode-matched MEMS Coriolis vibratory gyroscopes: Myth or reality?

The majority of commercial MEMS gyroscopes are operated in a mode-split condition where the drive and sense modes are intentionally mismatched in frequency, thus prioritizing gain stability and allowing for wide bandwidth but often sacrificing the noise density. In mode-matched operation, the gyroscope gain depends on sense-mode Q-factor, which improves the noise and scale-factor of MEMS gyroscopes. The scale-factor and offset stability over environment, however, also depend on the frequency matching, calling for the development of a mode-matching loop. Here we proposed a mode-matching loop which relies on monitoring the Coriolis channel output in response to the quadrature electrode dither. We have experimentally demonstrated an order of magnitude improvement in in-run bias instability and stress sensitivity when the mode-matching loop was employed, demonstrating a path towards mode-matched MEMS gyroscope with low-noise, wide measurement bandwidth, and offset stability over environment.

Continuous self-calibration canceling drive-induced errors in MEMS vibratory gyroscopes

We report a system for simultaneous rate readout and drift cancellation for MEMS vibratory gyroscopes without significantly affecting the sensor noise or bandwidth. The drift cancellation is accomplished by periodically reversing polarity of the gyroscopes forcing voltage. As opposed to the state-of-the-art methods, our self-calibration does not interrupt normal gyroscope operation nor require a symmetric sensor. The proposed here self-calibration has enabled a five-fold reduction of the output drift (rate random walk) for ADXRS800 iMEMS gyroscope with a quadruple mass architecture.