Closed-Loop Sense Architecture for Micromachined Gyroscopes
(Professor Bernhard E. Boser)
Robert BOSCH GmbH
The goal of this project is to develop a high-order sigma-delta sense interface for micromachined gyroscope sensors. The main priorities are providing sufficient stability margin and low power consumption while maintaining the intrinsically high resolution of the sensor element.
Research so far has shown that implementing the gyroscope sense interface as a closed loop system using sigma-delta modulation has the advantage of low sensitivity to parameter variations and high linearity as well as an intrinsic digital output. In this work a fourth order sigma-delta loop is being developed. The advantage of the fourth-order topology is that it can provide high attenuation of the quantization noise in the signal band and allow for sufficient compensation of the loop as well as operation at low sampling frequency without introducing an additional noise penalty.
The current status of the project is summarized below:
- A fourth-order sigma-delta sense loop has been designed and evaluated on a system level. The loop has the benefits pointed out above and is found to be suitable for the application.
- The interface has been implemented in a standard 0.5 µm CMOS process provided by AMI.
- Evaluation of the system implementation is currently under way. Functionality has been established with a low-Q gyroscope sensor (operating in air). Testing of the interface with a high-Q sensor (in a vacuum) is still in progress.
- X. Jiang, J. I. Seeger, M. Kraft, and B. E. Boser, "A Monolithic Surface Micromachined Z-Axis Gyroscope with Digital Output," Symp. VLSI Circuits Digest of Technical Papers, Honolulu, HI, June 2000.
- K. Funk, H. Emmerich, A. Schilp, R. Neul, and F. Larmer, "A Surface Micromachined Gyroscope Using a Thick Polysilicon Layer," Proc. IEEE Int. MEMS Conf., Orlando, FL, January 1999.
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