A Stray-Field-Immune Magnetic Displacement Sensor With 1% Accuracy

We present a new Hall sensor design for the accurate and robust measurement of linear displacement. Implemented in CMOS, the sensor is based on a novel gradient measurement concept combining Hall elements with integrated magnetic concentrators. In typical applications with practical Ferrite magnets, the peak output voltage of the Hall transducers is only around 1.7 mV at the maximum operating temperature of 160°C, and thus requires high-performance low-offset readout electronics. Over its 15-mm linear displacement range, the sensor’s total error is 1% including manufacturing tolerances, trimming accuracy, temperature, aging effects, and practical magnet constraints. In addition, the sensor is immune to magnetic stray fields up to 5 mT, complying with the most stringent automotive norm.