A parametrically amplified MEMS rate gyroscope

Abstract

This paper reports a parametrically amplified MEMS rate gyroscope. A practical parametric excitation scheme implemented using Digital Signal Processing (DSP) has been developed to enable either amplification of the primary mode of the gyroscope or amplification of the response to the applied angular velocity. The primary objective of this work is to improve the scale-factor and the signal to noise performance of the gyroscope. Parametric amplification of the primary mode of the gyroscope is achieved by frequency tracking and regulation of the amplitudes of the harmonic forcing and parametric excitation to maintain a desired parametric gain by closed loop PID control. Stable parametric amplification of the primary mode by a factor of 20 is demonstrated experimentally. This has important benefits regarding the minimisation of electrical feedthrough of the drive signal to the sense electrodes of the secondary mode. By taking advantage of the phase dependence of parametric amplification and the orthogonality of the Coriolis force and quadrature forcing, the response to the applied angular velocity may be parametrically amplified by applying excitation of a particular phase directly to the sensing mode. The major advantage of parametric amplification applied to MEMS gyroscopes is that it can mechanically amplify the Coriolis response before being picked off electrically. This is particularly advantageous for sensors where electronic noise is the major noise contributor. In this case parametric amplification can significantly improve the signal to noise ratio of the secondary mode by an amount approximately equal to the parametric amplification. Preliminary rate table tests performed in open loop demonstrate a magnification of the signal to noise ratio of the secondary mode by a factor of 9.5 and the scale-factor by 11. The excitation and control scheme have been implemented digitally using a DSP development board enabling very high sampling precision and execution speed necessary for gyroscopic applications.