1997-01-06 , E/DS-347/140

Philips Semiconductors' latest magnetoresistive sensor has coils integrated into its housing which compensate for both temperature drift and sensor offset. By eliminating the need for external coils, the  KMZ51 sensor simplifies system design in applications requiring the measurement of weak magnetic fields, allowing the inherent sensitivity, stability and high accuracy of the magnetoresistive effect to be cost-effectively exploited.

The integrated coils have an excellent magnetic coupling factor, so the  KMZ51 also has very low power consumption, allowing it to operate from a 5 V supply. Uniquely, even operating at this low supply voltage the sensor requires no DC-to-DC up-converter to provide sufficient coil currents, as required by some sensors with integrated coils under the same conditions.

The  KMZ51 is the first device in a new family which, as well as being very well suited for applications such as electronic compasses, earth magnetic field compensation circuits and traffic detection units, is opening up a number of new applications such as virtual reality glasses. Hans-Ulrich Lochmann, International Product Marketing Manager for Discrete Semiconductor Sensor Devices, said 'The high performance of the  KMZ51 is broadening the traditional application range of this type of sensor for weak-field measurement. Its low power, cost and size make it especially suitable for new multimedia products.'

Compensation for temperature drift and sensor offset is essential in weak-field measurement, otherwise the magnetic effects they produce can completely swamp the target magnetic field. The flipping coil periodically applies brief (3 to 5 µs) magnetic pulses to the sensor, first in one direction, then the other, which 'flips' over the output characteristic of the sensor (which is bi-stable). After rectification and smoothing, the time-averaged output signal is then free from sensor offset. The compensation coil uses an electromagnetic feedback loop to ensure the sensor always operates at its 'null-point', where both sensor offset and signal characteristic are unaffected by temperature fluctuations.

Magnetic field sensors are commonly used to measure the earth's field, for compass and navigation systems in the automotive industry. They are also increasingly popular in traffic detection and flow control systems, where their sensitivity is high enough to allow identification of individual vehicle types. Another application is in compensation circuits, which automatically eliminate geometry errors produced by changes in the magnetic environment around TVs and monitors (due to the earth's field or speakers, for example). This reduces calibration requirements and allows a single tube type to be used throughout the world, regardless of its position in the Earth's geomagnetic field.

Philips Semiconductors, a division of Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the eleventh largest semiconductor supplier in the world. Philips Semiconductors' innovations in digital audio, video and mobile technology, position the company as a leader in the consumer, multimedia and wireless communications markets. Sales offices are located in all major markets around the world and are supported by systems labs.