A Micropower Arcsine Circuit for Tilt Processing

Abstract: This letter describes an analogue circuit for producing an arcsine transfer based on a differential pair with source degeneration. The application uses this circuit to post-process an accelerometer signal by normalising with respect to the gravitational acceleration vector to extract inclination. Using diode-connected MOS devices operating in weak inversion, the appropriate trigonometric function, i.e. an arcsine, has been realised to compute tilt. The hardware has been implemented in AMS 0.35µm 2P4M CMOS technology. Introduction: An increasing number of medical devices including implantable prosthetics and body worn instrumentation are incorporating sense systems within and around the body. One such sensor is the inclinometer (or tilt sensor), which senses its orientation with respect to gravity. Tilt sensors have typically been implemented using hybrid structures incorporating a stationary reference and movable mass. Traditionally these have been realised usin