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Magnetoresistive Current Sensor

IP.com Disclosure Number: IPCOM000084941D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 4 page(s) / 77K

Publishing Venue

IBM

Related People

Bajorek, CH: AUTHOR [+4]

Abstract

Several power supply designs require sensing of high-frequency currents with critical insertion loss requirements. These constraints are beyond the range of classical laboratory current probes. Hall devices are unsuitable because of their limited frequency response and relatively low sensitivities to fields typically encountered in such applications.

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Magnetoresistive Current Sensor

Several power supply designs require sensing of high-frequency currents with critical insertion loss requirements. These constraints are beyond the range of classical laboratory current probes. Hall devices are unsuitable because of their limited frequency response and relatively low sensitivities to fields typically encountered in such applications.

Specifically, there is a need to measure current waveforms and amplitudes with frequency components greater than 1MHz. These currents generate fields in the 1.0 to 100 Oe range. These requirements, as well as the need for minimum insertion loss, can be met most favorably with a magnetoresistive sensor of the thin film recording head variety. A magnetoresistive sensor using self-biased, shielded magnetoresistors is effective.

In Fig. 1, two magnetoresistive sensors S1 and S2 are arranged as parallel strips upon a substrate with a conductor 12 connected between one end of each of sensors S1 and S2 and pad 14. Pad 15 is connected to the opposite end of sensor S1 and pad 16 is connected to the opposite end of sensor S2. Note that an H-field arrow is shown perpendicular to sensors S1 and S2.

In Fig. 2, sensors S1 and S2 are connected at point 17 in a bridge circuit in adjacent legs opposed by resistors R1 and R2 connected at point 18 in series, both being connected between power supply terminals V+ and V-. The V sense terminals 19 are connected to points 17 and 18 to measure the effect of magnetically induced changes in the resistances of sensors S1 and S2. Attainment of a sense voltage requires that the resistance change of the sensors S1 and S2 have opposite polarity. Thus, sensors S1 and S2 are biased by a shunting conductor or a soft film. Suitable bias results in a linear response to the sense field.

The bridge arrangement eliminates temperature tracking problems and allows for noncapacitive coupling to the sense electronics. Adjustment of either resistor R1 or R2 allows for nulling DC offsets to arbitrary accuracy.

Inductive pickup is suppressed to acceptable levels by suitably arranging the sensor relative to a current conductor, by minimizing the spacing between the sensors S1 and S2 and the center access conductor 12 of Fig. 1, and by suitable routing of connecting wires. Further suppression of inductive pickup is achieved by arranging the sensors and access conductors in figure 8 configurations. The sensor of Fig. 1, when mounted at the tip of a rod, senses fields from a current carrying conductor.

To minimize geometrical and placement uncertainties, a current p...