Experimental research on hysteresis effects in GMR sensors for analog measurement applications

A Wheatstone bridge GMR sensor can be used for analog magnetic field measurements. This paper deals with hysteresis effects in GMR sensor, which is the major source of measurement error. Experiments are conducted by measuring hysteresis curves between applied magnetic field and sensor output voltage with different typical initial magnetization states. GMR sensor has two operation modes: bipolar and unipolar. Bipolar operation means internal magnetization pattern of GMR sensor changes direction during operation range. This mode is inappropriate for direct measurement, as experimental results indicate that the shape of measured curves with the same range of applied magnetic field may be severely distorted due to different initial magnetization states. Unipolar operation is an intermediate process of bipolar operation with invariant magnetization direction. Its input–output relationship is almost linear that is especially suitable for measurement. The principal measurement error within unipolar operation is DC offset voltage, which is induced by remanence. It can be fixed by saturating GMR sensor before operation.