MAGNETIC FIELD SENSOR WITH IMMUNITY TO EXTERNAL MAGNETIC INFLUENCES
First Claim
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.
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Abstract
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.
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Citations
33 Claims
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1. A magnetic field sensor comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A magnetic field sensor comprising:
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a magnetic field signal generator comprising at least one sensing element to sense a 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; circuit 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 in 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. - View Dependent Claims (23, 24, 25, 26)
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27. A method, comprising:
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producing a magnetic field signal comprising a modulated signal portion in a first frequency band based on sensing a modulated AC bias magnetic field and an unwanted signal portion in a second frequency hand based on sensing a magnetic interference; and performing a demodulation of the magnetic field signal to shift the modulated signal portion from the first frequency band to a third frequency band and the unwanted signal portion to the first frequency band from the second frequency band. - View Dependent Claims (28, 29, 30, 31, 32, 33)
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Specification