Measuring low H field and currents with AMR sensors

The growing demand from the automotive industry for high accuracy magnetic sensors and the need to perform high resolution angular position measurements have been the drivers for the industrial research in magnetic sensing technologies. This paper describes the design and characterization of several experimental devices implementing simple magnetoresistive structures targeting contactless current measurement in the tens to hundreds of milliamps range with sub-mA resolution. The ultimate goal is to extend the application area of magnetoresistive sensors beyond their current niche in automotive into more general applications. The initial set of devices tested to-date has shown a sensitivity of 0.18 mV/mA in ±100 mA range when supplied from a 4V supply, which is a close match to the theoretically calculated value of 0.23 mV/mA. The linearity and hysteresis error within the ±100 mA full scale (FS) were better than 2% FS and 0.45% FS respectively, when configured as Wheatstone bridges.