Browse Prior Art Database

True Differential Input for Magnetoresistive Current Transducers

IP.com Disclosure Number: IPCOM000088771D
Original Publication Date: 1977-Jul-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 3 page(s) / 27K

Publishing Venue

IBM

Related People

Feng, JS: AUTHOR

Abstract

Magnetoresistive (MR) current-sensors can have either a single-ended input [1] or a differential input with a limited common-mode capability [2]. The common feature of both cases is that they involve only two separate layers of integrated metallization.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

True Differential Input for Magnetoresistive Current Transducers

Magnetoresistive (MR) current-sensors can have either a single-ended input
[1] or a differential input with a limited common-mode capability [2]. The common feature of both cases is that they involve only two separate layers of integrated metallization.

The problem with those arrangements for achieving a differential input is that the two inputs act separately on a pair of MR elements, and two pairs combine to form the sensor bridge. This fails to operate properly when there is a differential input current in addition to a common-mode component that is nearly sufficient to bring the MR bridge into its nonlinear response regime. In Fig. 1, which shows a piecewise linear approximation to the MR bridge response, this occurs when the field due to the common-mode signal is near the peak field |H(p)|, which would result in a quadratic response to any differential input. If the common mode component exceeds H(p), the sign of the response to differential signals reverses sign . If the common-mode signal ever gets larger than H(sat), the device loses all sensitivity to any inputs whether differential or common-mode.

In order to produce a true differential input with good common-mode rejection, it is necessary only to rearrange two current input leads so that each of the inputs acts on all four elements of the MR bridge. The best way of realizing this is to use a stripline arrangement shown in Fig. 2 with ground planes 10 and 11 for the two leads, and place the MR elements 12 inside the stripline. This consists of making two input conductors 10, 11, of equal width and placing one on top of the other separated by insulation layers 14, 15.

It is clear that any common-mode currents...