A silicon potentiometer for hearing aids

Abstract

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. The system can operate with a supply voltage down to 2.3 V. The average current consumption is 1.5/xA. The peak current is close to 160/zA. The system operates correctly within the clock frequency range of 5 Hz to 25 kHz. It is implemented using a commercially available 1.5/zm CMOS process.

Contactless potentiometers for automotive applications

“…MAGFETs are MOSFET transistors sensitive to the magnetic field [8]. They are also based on the deflection of current by an external magnetic field due to Lorentz force, which is typically sensed by differential current measurements between two drain terminals (in split-drain MAGFETs).…”