Digital-controlled MEMS vibratory-beam-accelerometer

This report provides a MEMS (micro-electromechanical systems) vibratory beam accelerometer (VBA) having a digital control system. The device structure with size of 5 times 5 mm² includes a frame, heavy mass, thick suspension beams, and thin vibrating beams made of silicon. The VBA measures acceleration using the resonant frequency change of the supporting beams, which are designed to provide little resistance to movement along the sensitive axis and stiff resistance on the off-axis. This provides low off-axis sensitivity and high shock survivability. In this study, we designed a fully digital PLL (phase-locked loop) circuitry in a FGPA (field programmable gate array) based hardware controller. By Allan deviation, we proved that our system has a resolution of 34 muG Hz^-1/2 for a device operating at 1 mTorr.