A Silicon Micromachined Gyroscope and Accelerometer for Vehicle Stability Control System

A silicon micromachined gyroscope (angular rate sensor, yaw rate sensor) and accelerometer for vehicle stability control system is presented. The 5.1mm×4.7mm sensor chip is fabricated with a silicon micromachining process using a SOI (Silicon on Insulator) silicon wafer and a deep reactive ion etching. The sensor chip has a pair of resonators which are mechanically coupled and function as a tuning fork. The resonators are driven by electrostatic force and their movements are detected by capacitively sensing angstrom displacements. This sensor chip works not only as a gyroscope but also as an accelerometer with a single sensor chip.

The sensor unit consists of the sensor chip above, a signal processing IC, a microcomputer and an EEPROM. sigma-delta analog-to-digital conversion (sigma-delta ADC) is adopted to realize the digital calibration of sensor properties. Sigma-delta modulators on the signal processing IC convert the analog signals of angular rate, acceleration and temperature into oversampled 1-bit digital data. These data are transmitted to the microcomputer and converted into high-resolution, multi-bit digital data through the process of digital decimation filter. Sensor variation is calibrated by the microcomputer with the calibration data which has been stored in the EEPROM.