Magnetic field sensors based on the magneto resistive effect can be easily fabricated by means of thin film technologies with widths and lengths in micrometer range. For best performance, these sensors must have a very good linearity between the measured quantity and the output signal. Even when improved by the barber poles, the linearity magneto resistive sensor is not very high, so the compensation principle used on hall sensors is also applied here. An electrically isolated aluminum compensation conductor is integrated in the same substrate above the Permalloy resistors.
The current flowing through this conductor generates a magnetic field exactly compensates that of the conductor to be unmeasured. In this way the MR element always work at the same operating point; their nonlinearity therefore becomes irrelevant. The temperature dependence is also almost completely eliminated. The current in the compensation conductor is strictly proportional to the measured amplitude of the field; the voltage drop across a resistor forms the electrical output signal.
Magnetoresistive sensors, as are hall elements are very well suited or the measurement of electric currents. In such applications it is important that external magnetic fields do not distort the measurement. This achieved by forming a full bridge are specially separated. The barber poles have the same orientation in the two arms, so that only a field difference between the two positions is sensed. This configuration is insensitive to external homogenous perturbation fields. The primary conductor is U shaped under the substrate, so that the magnetic fields acting on the two arms of the bridge have the same amplitude but opposite directions. This way the voltage signals of the two half-bridges are added.
The sensors require neither a core nor a magnetic shielding, and can therefore be assembled in a very compact and cheap way. The output is calibrated by a laser trimming process or by a digital calibration.