" Photo 1. Practical realizations ofmagnetoresistive current sensorsinclude the opened hybrid circuit(A); the packaged standardelement (B); a new ASIC sensor(C); and a dual in-line SMD13Practical magnetic field sensors based on thecomponent that can be used withmagnetoresistive effect (see ?The Magnetoresistive Effect?)different current conductors (D).are easily fabricated by means of thin film technologies withwidths and lengths in the micrometer range. They have been in production for years in manydifferent executions [1,2,3,4]. To reduce the temperature dependence, they are usuallyconfigured as a half or a full bridge. In one arm of the bridge, the barber poles are placed inopposite directions above the two magnetoresistors, so that in the presence of a magnetic fieldthe value of the first resistor increases and the value of the second decreases (see Figure 2).For best performance, these sensors must have a very good linearity between the measuredquantity (magnetic field) and the output signal. Even when improved by the barber poles, thelinearity of magnetoresistive (MR) sensors is not very high, so the compensation principle usedon Hall sensors is also applied here. An electrically isolated aluminum compensation conductoris integrated on the same substrate above the permalloy resistors (see Figures 3 and 4). Thecurrent flowing through this conductor generates a magnetic field that exactly compensates thatof the conductor to be measured. In this way the MR elements always work at the same operatingpoint; their nonlinearity therefore becomes irrelevant. The temperature dependence is also almostcompletely eliminated. The current in the compensation conductor is strictly proportional to themeasured amplitude of the field; the voltage drop across a resistor forms the electrical outputsignal.Magnetoresistive sensors, as are Hall elements, are very well suited for the measurement ofelectric currents. In such applications it is important that external magnetic fields do not distortthe measurement. This is achieved by forming a full bridge made of four MR resistors, where the14two arms of the bridge are spatially separated. The barber poles have the same orientation in thetwo arms, so that only a field difference between the two positions is sensed. This configurationis insensitive to external homogeneous perturbation fields. The primary current conductor is U- shaped under the substrate, so that the magnetic fields acting on the two arms of the bridge havethe same amplitude but opposite directions. This way the voltage signals of the two half-bridgesare added.The sensors have been in production for several years [5]. In the examples shown in Photo 1A,B, and C, a ceramic plate is used as the substrate, onto the back of which the primary conductoris glued to achieve an isolation of several kilovolts.The sensors require neither a core nor a magnetic shielding, and can therefore be assembled in avery compact and cheap way. The have a linearity error of <0.1%, gain error <0.2%, offsetvoltage <10 mV, and temperature drift of the gain <100 ppm/K. The output signal is calibrated to2.5 V at nominalcurrent by a laser trimming process or by a digitalcalibration. The rise time (10%–90%) is ~1.7 ms, whichcorresponds to a frequency bandwidth (–1 dB) >50 kHz;this value results from the speed of the regulation. Thesensor is powered by a standard bipolar voltage of ±15 VPhoto 3. Three current sensors areand the power consumption is 320 mW to 640 mW,shown here in a frequency inverter.depending on the measured current value.15 "