Patent ID: 8416539

Claim:
A magnetic field sensing system comprising: a magnetic field sensor comprising a substrate; a pinned ferromagnetic layer having an in-plane magnetization direction; a free ferromagnetic layer lying in a plane parallel to the plane of the pinned layer and having an in-plane magnetization direction, in the absence of an external magnetic field to be sensed, oriented greater than 90 degrees and less than 180 degrees from the in-plane magnetization direction of the pinned layer, the free ferromagnetic layer being substantially free to rotate in the presence of an external magnetic field to be sensed and exhibiting magnetization oscillations in response to an electrical current greater than a critical current perpendicularly through the free ferromagnetic layer, said magnetization oscillations having a resonance frequency in response to an alternating current; and an electrically conductive nonmagnetic spacer layer between the pinned and free layers; a hard magnet for applying a magnetic bias field to the free layer to bias the magnetization direction of the free layer in said orientation relative to the magnetization direction of the pinned layer; one and only one electrical current source coupled to the sensor, said current source directing alternating current at a fixed frequency substantially at said resonance frequency perpendicularly through the layers of the sensor; and a voltage detector coupled to the sensor for detecting the direct-current voltage across the sensor in response solely to the alternating current, the detected voltage being a direct measure of external magnetic fields during the application of alternating current at said fixed frequency, the voltage detector being capable of detecting magnetic fields in opposite directions to one another.