Towards a Better Understanding of Offset Changes Across Temperature in Mode-Split Open-Loop MEMS Gyroscopes

Abstract

This paper investigates changes of zero-rate offset of triaxial, consumer-grade MEMS gyroscopes across temperature. Forty LGA mold-packaged prototype devices were measured between -40 and 85°C. Additionally to offset, quadrature values were recorded, as well as the phase error between drive and sense movement. As mode-split MEMS gyroscopes typically have large phase errors in the tens of mrad, their offset is dominated by the amount of quadrature times phase error. Beyond this contribution, we investigate smaller, quadrature-unrelated offsets, which we combine and call direct bias. Theoretical models for the temperature behavior of quadrature and phase are presented, based on changes of frequency split and quality factor. We show that while phase changes are predicted well, quadrature behavior is not - presumably due to additional effects of mechanical stress. Lastly, we discuss possible compensation techniques using combinations of measured or modeled quadrature and phase. If both quadrature and phase are measured, the compensation improves offset changes across the above temperature range by a factor of 11 from $\pm 9.5$ dps to $\pm 0.81$ dps. The behavior of the remaining direct bias constitutes an open research topic.