A micropower tilt processing circuit

This paper describes a novel analogue circuit for extracting the tilt angle from the output of a standard MEMS accelerometer. The circuit uses the accelerometer signal together with the gravitational acceleration vector to generate the tilt signal. Using a current-mode representation with devices operated in subthreshold, the appropriate trigonometric function has been realised to compute tilt. Furthermore, implementing a long-time constant filter to extract the mean tilt level provides adaptation to the static tilt level. Specifically, this circuit has been designed as part of an implantable vestibular prosthesis to provide inclination signals for bypassing dysfunctional otolith end-organs. The hardware has been implemented in AMS 0.35 mum 2P4M CMOS technology.