Temperature Drift of Offset and Sensitivity in Full-Bridge Magnetoresistive Sensors

A typical commercially available magnetoresistive sensor, and particularly an anisotropic magnetoresistive sensor, employs a full bridge of the Wheatstone type formed by two complementary magnetoresistive elements in each branch. This configuration provides linearized response and enlarged sensitivity compared to any other configuration made up of the same elements. Since in a large scale production it is practically impossible to adjust the zero-field resistances of all the four elements to an exactly identical value, there is always some zero-field offset present at the bridge output diagonal even when the sensor is placed in the zero magnetic field. The sensitivity of the sensor, i.e., the ratio of the output voltage change to the change of the measured field H, is associated with the sensitivity of the individual elements. The change of the output voltage is determined by the change of the resistance ΔR of the individual elements. Both the offset and the sensitivity of a full-bridge magnetoresistive sensor is dependent on the zero-field resistances R_i of the elements. However, as in most metallic material, the resistivity of a magnetoresistive element is influenced by temperature. Hence, both the offset and the sensitivity of a real magnetoresistive sensor is temperature dependent. It can be shown that, theoretically speaking, the offset is temperature independent when the bridge is supplied with a constant voltage (but the sensitivity in that case is temperature dependent), and the sensitivity is temperature independent when the bridge is supplied with a constant current (but the offset in that case is temperature dependent). This hypothesis has been verified on KMZ52 sensor (albeit in small temperature range-about 25°C-45°C).