Real-Time Operation and Characterization of a High-Performance Time-Based Accelerometer

An accelerometer based on the electrostatic pull-in time of a microstructure is presented in this paper. The device uses a parallel-plate overdamped microstructure, and real-time control operation is performed using a field programmable gate array and high precision digital-to-analog converters. Both open-loop and closed-loop measurements are presented. The low noise is a key feature of this approach, which is limited only by the mechanical-thermal noise of the microstructure used, 2 μg/√Hz as shown in the open-loop results (3 μg/√Hz in closed-loop operation). The time readout method has extremely high-resolution capabilities. The pull-in time sensitivity can be adjusted up to 1.6 μs/μg, and the electrostatic feedback voltage sensitivity is 61.3 V²/g. The closed-loop control allows operation of the accelerometer in a much larger range than in open-loop (±500 mg have been achieved) and the linearity is greatly improved (<;1%FS). The current closed-loop control algorithm allows operation up to 2 Hz. A bias stability of 50 μg has been measured over 45 h in open loop and 250 μg in closed loop.