Position detection with the use of MAGFETs

An angledetector with a digital output is described. The component is meant as an alternative to the traditional slide potentiometer used as volume control in many hearing aid applications. The component is based on the use of magnetic field sensitive MOSFET’s (MAGFET’s) detecting the position of a tiny bar magnet placed above a silicon chip. Because of the galvanic separation between the anglesetting bar magnet and the electrical circuit, this component is insensitive to the rather hostile environment hearing aids are exposed to. The lifetime of the component is thereby increased significantly. The electrical circuit contains a switched current A/D D/A conversion system for offset compensating the MAGFET’s and for converting the MAGFET signal currents into a digital output proportional to the input angle. It is implemented using a commercially available 1.5 pm CMOS process.