A Micropower Tilt-Processing Circuit

This paper describes a novel analog circuit for extracting the tilt angle from the output of a linear microelectromechanical-system accelerometer. The circuit uses the accelerometer signal, together with the gravitational acceleration vector, to generate the tilt signal. Using a current-mode representation with metal-oxide semiconductor devices operating in weak inversion, the appropriate trigonometric function has been realized 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 circuit has been fabricated in AustriaMicroSystems 0.35-mum 2P4M complementary metal-oxide semiconductor technology, and this paper presents the theory, implementation, and measured results.