ZRO Compensation Based on Non-Modulated Outputs of the Sensing Elements in Piezoresistive Gyroscopes

This document presents a novel technique for the reduction of zero-rate output (ZRO) drifts in gyroscopes based on sub-micrometric resistive sensing. The 1.3-mm2 gyroscope features Wheatstone bridges as readout means for both the drive and sense motion detection. The key concept lies in the frequency separation of the signals of each half of each bridge: the modulated content refers to the drive oscillation and Coriolis-related output, as in conventional gyroscopes; the quasi-DC content refers to resistive variations induced, instead, by temperature or stress. Different circuits can be used in parallel to sense both the frequency ranges, without worsening noise performance, thanks to the immunity of resistive sensing to capacitive loads at the bridge nodes. The circuit to sense stress-and temperature-induced output changes is sized according to simulations based on measured package deformations. The system is then operated with angle random walk (ARW) levels in the range of 500 µdps/√Hz. Without any temperature calibration, in uncontrolled environmental conditions the system shows drifts of the ZRO at as early as 10 s. If a linear regression is used to calibrate the sensor in operation, using the measured quasi-DC information, stability in successive operation is brought down to 0.1 ◦/hr at 1000 s observation interval, with a 14-fold reduction in rate random walk with respect to the uncompensated output and a 3-fold improvement with respect to a compensation based only on temperature sensing via the drive resonance frequency.