MAGNETIC FIELD SENSOR WITH IMMUNITY TO EXTERNAL MAGNETIC INFLUENCES

摘要

A magnetic field sensor with enhanced immunity to external magnetic interference is presented. Included is a magnetic field signal generator and a demodulator. The magnetic field signal generator produces a magnetic field signal having a modulated signal portion in a first frequency band based on a sensed modulated AC bias magnetic field. The modulated AC bias magnetic field is produced by movement of ferromagnetic target relative to a bias coil when an AC signal is applied to the bias coil. When the magnetic field signal also includes an unwanted signal portion in a second frequency band based on external magnetic interference, demodulation performed by the demodulator results in the modulated signal portion being shifted from the first frequency band to a third frequency band and the unwanted signal portion being shifted to the first frequency band. The bias coil may be provided as part of the magnetic field sensor.

主权项

1. A magnetic field sensor comprising:
an AC bias coil to generate an AC bias magnetic field capable of being modulated by movement of a ferromagnetic target with respect to the AC bias coil; a magnetic field signal generator comprising at least one sensing element to sense the modulated AC bias magnetic field and produce a magnetic field signal, the magnetic field signal having a modulated signal portion in a first frequency band based on the sensed modulated AC bias magnetic field; circuitry including a demodulator to perform a demodulation of the magnetic field signal; and wherein, when the magnetic field signal further includes an unwanted signal portion in a second frequency band based on a magnetic interference, the demodulation results in the modulated signal portion being shifted from the first frequency band to a third frequency band and the unwanted signal portion being shifted to the first frequency band from the second frequency band.