1 F NOISE AND ITS COHERENCE AS A DIAGNOSTIC-TOOL FOR QUALITY ASSESSMENT OF POTENTIOMETERS/

The excess noise of different types of potentiometers has been investi gated, and all showed a 1/f noise power-spectral density. Two types of conductive tracks are considered: carbon black resin type and metal-o xide glass cermet type. Also considered are different types of sliders : 1) metal-point contacts, 2) metal-line contacts and multiple-finger contacts, and 3) carbon brush contacts. The contributions of the end c ontacts, the stationary wiper (movable) contact, and the track have be en investigated. The resistance and the noise of the stationary wiper contact are constriction dominated. Two different biasing conditions a re proposed to measure either the coherence between current fluctuatio ns orpg 4between voltage fluctuations in a potentiometer. The coherenc e measurement can serve as a fast diagnostic tool for the noise charac terization and the quality of the movable contact in a potentiometer. Physical models are proposed to explain experimentally observed trends . Potentiometer 1/f noise is due to contact noise between grains in th e track.