A Closed-Loop Operation to Improve GMR Sensor Accuracy

Abstract

Giant magnetoresistance (GMR) magnetic field sensors are compact, low power, high sensitivity devices that are low cost and have very simple supporting electronics. One of the disadvantages of GMR sensors can be their nonlinearity, hysteresis, and temperature-dependent output, which can reduce measurement accuracy. This paper presents an approach to improve the measurement accuracy of GMR sensors using a closed-loop circuit, which includes the sensor, a biasing coil, and a feedback circuit. The current in the biasing coil is actively changed to ensure that the component of magnetic field along the sensitive axis of the device is held constant, so that as the external magnetic field or orientation of the GMR sensor changes, the output of GMR sensor remains stable. In this way, the external magnetic field component along the sensitive axis of the device can be calculated by measuring the current in the biasing coil surrounding the GMR sensor, regardless of the hysteresis and nonlinearly of GMR sensor. The linearity and the accuracy of magnetic field measurements using a GMR sensor are significantly improved and a hardware prototype has been constructed and tested under a reference magnetic field.