Control and damping imperfection compensation for a rate integrating MEMS gyroscope

This paper presents a DSP based control implementation for a ring type MEMS vibratory gyroscope operating in rate integrating mode, under which, drift rate of the precession angle is reduced to less than 2.5 degrees/second. An automatic electrostatic frequency tuning process is developed to minimize frequency split to a few mille Hertz, which helps the PLL to accurately lock the orbit phase at -90 degrees with phase error less than 0.1 degrees. While a velocity feedback based vibration sustaining control stabilizes the major axis against the average damping, a displacement feedback control for quadrature nulling effectively suppresses the Quad amplitude to less than one thousandth of the major axis, so that the trajectory of vibration remains almost a straight line. Damping imperfections, the amount and distribution along the precession angle are visualized and approximately estimated using the modulation pattern of the control gain of the vibration sustaining loop. These values are then placed in the velocity feedback compensation control to reduce angle drift. Experimental results validate its effectiveness.