Patent ID: 8248063

Claim:
A method to correct for aging effects in a magneto-resistive (MR) magnetic field sensor having first and second MR sensors, the method comprising: providing a device that, when energized, generates a magnetic field inside a volume; locating said first and second MR sensors within said volume; shielding said second MR sensor from any and all magnetic fields other than magnetic fields generated by said device; creating in said volume a magnetic field of predetermined strength that is known to place each of said first and second MR sensors in a determined state by energizing said device, the determined state being a state of said MR magnetic field sensor that is known to change in a predictable manner as said MR magnetic field sensor ages; driving currents I s1 and I s2 from current sources through said first and second MR sensors respectively, thereby causing identical voltages V 1s and V 2s to be generated across said first and second MR sensors respectively; de-energizing said device whereby said second MR sensor experiences zero magnetic field, any magnetic field still present within said volume being an unknown magnetic field that derives from an external source; continuing to drive currents I s1 and I s2 from current sources through said first and second MR sensors thereby generating voltages V u1 and V 02 across said first and second MR sensors respectively; and computing a value for said unknown magnetic field as V u1 −V 02 .