A linear Tunneling Magneto-Resistance angle transducer

Abstract

A new Tunneling Magneto-Resistance (TMR) based angle transducer realized with a novel Signal Conditioning (SC) scheme that accepts TMR angle sensing elements possessing sine/cosine output characteristics and provides a final output that changes linearly with the angle being sensed over a full-circle range (0-360°) is presented in this paper. The proposed scheme converts the angle being sensed by the TMR sensing elements into an equivalent phase shift of a sinusoid, whose amplitude is dictated by the flux produced by the permanent magnet employed in the transducer. The phase of the sinusoid is then converted as an output voltage that is dependent only on the phase angle and not on the magnetic strength. Thus even over a long period, over which the strength of the permanent magnet may decay, the accuracy of angle sensing is preserved. A prototype angle sensor, using a TMR IC, and proposed SC circuit has been built and tested. The output of the transducer was found to be linear across the entire 0-360°. The worst-case error observed for the transducer was less than ± 0.85 % of the full-scale while that for the SC unit alone was less than ± 0.1 %.