Magnetic field sensor with immunity to external magnetic influences
First Claim
1. A magnetic field sensor comprising:
- a coil driver circuit to generate an AC signal;
an AC bias coil coupled to the coil driver circuit to receive the AC signal and to generate an AC bias magnetic field modulated by movement of a ferromagnetic target having a target profile pattern with respect to the AC bias coil;
a magnetic field signal generator comprising at least one sensing element to produce, by sensing the modulated AC bias magnetic field, a magnetic field signal indicative of the movement of the ferromagnetic target, the magnetic field signal having a modulated signal portion in a first frequency band based on the sensed modulated AC bias magnetic field and an unwanted signal portion in a second frequency band based on sensing an external magnetic interference;
circuitry including a demodulator to perform a demodulation of the magnetic field signal, wherein the magnetic field signal generator and circuitry are provided on a semiconductor die, further comprising a package that includes a lead frame coupled to the semiconductor die and located between the semiconductor die and the AC bias coil, and further includes a mold portion to enclose the semiconductor die, at least a portion of the lead frame and the AC bias coil together; and
wherein 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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Accused Products
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.
55 Citations
27 Claims
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1. A magnetic field sensor comprising:
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a coil driver circuit to generate an AC signal; an AC bias coil coupled to the coil driver circuit to receive the AC signal and to generate an AC bias magnetic field modulated by movement of a ferromagnetic target having a target profile pattern with respect to the AC bias coil; a magnetic field signal generator comprising at least one sensing element to produce, by sensing the modulated AC bias magnetic field, a magnetic field signal indicative of the movement of the ferromagnetic target, the magnetic field signal having a modulated signal portion in a first frequency band based on the sensed modulated AC bias magnetic field and an unwanted signal portion in a second frequency band based on sensing an external magnetic interference; circuitry including a demodulator to perform a demodulation of the magnetic field signal, wherein the magnetic field signal generator and circuitry are provided on a semiconductor die, further comprising a package that includes a lead frame coupled to the semiconductor die and located between the semiconductor die and the AC bias coil, and further includes a mold portion to enclose the semiconductor die, at least a portion of the lead frame and the AC bias coil together; and wherein 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)
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16. A magnetic field sensor comprising:
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a coil driver circuit to generate an AC signal; an AC bias coil coupled to the coil driver circuit to receive the AC signal and to generate an AC bias magnetic field modulated by movement of a ferromagnetic target having a target profile pattern with respect to the AC bias coil; a magnetic field signal generator comprising at least one sensing element to produce, by sensing the modulated AC bias magnetic field, a magnetic field signal indicative of the movement of the ferromagnetic target, the magnetic field signal having a modulated signal portion in a first frequency band based on the sensed modulated AC bias magnetic field and an unwanted signal portion in a second frequency band based on sensing an external magnetic interference; circuitry including a demodulator to perform a demodulation of the magnetic field signal, wherein 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; and wherein the AC bias coil, magnetic field signal generator and circuitry are provided on a semiconductor die. - View Dependent Claims (17, 18, 19)
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20. A method, comprising:
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providing an AC signal to an AC bias coil by a coil driver circuit coupled to the AC bias coil; generating with the AC bias coil an AC bias magnetic field modulated by movement of a ferromagnetic target having a target profile pattern with respect to the AC bias coil; producing, by a magnetic field signal generator sensing the modulated AC bias magnetic field, a magnetic field signal indicative of the movement of the ferromagnetic target having the target profile pattern, the magnetic field signal comprising a modulated signal portion in a first frequency band based on sensing the modulated AC bias magnetic field and an unwanted signal portion in a second frequency band based on sensing an external magnetic interference; and performing, by circuitry, 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, wherein the magnetic field signal generator and circuitry are provided on a semiconductor die, further comprising a package that includes a lead frame coupled to the semiconductor die and located between the semiconductor die and the AC bias coil, and further includes a mold portion to enclose the semiconductor die, at least a portion of the lead frame and the AC bias coil together. - View Dependent Claims (21, 22, 23, 24, 25)
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26. A method, comprising:
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providing an AC signal to an AC bias coil by a coil driver circuit coupled to the AC bias coil; generating with the AC bias coil an AC bias magnetic field modulated by movement of a ferromagnetic target having a target profile pattern with respect to the AC bias coil; producing, by a magnetic field signal generator sensing the modulated AC bias magnetic field, a magnetic field signal indicative of the movement of the ferromagnetic target having the target profile pattern, the magnetic field signal comprising a modulated signal portion in a first frequency band based on sensing the modulated AC bias magnetic field and an unwanted signal portion in a second frequency band based on sensing an external magnetic interference; and performing, by circuitry, 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, wherein the AC bias coil, magnetic field signal generator and circuitry are provided on a semiconductor die.
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27. A magnetic field sensor comprising:
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means for providing an AC signal; means for generating an AC bias magnetic field responsive to the AC signal and modulated by movement of a ferromagnetic target having a target profile pattern with respect to the means for generating; means for producing, by sensing the modulated AC bias magnetic field, a magnetic field signal indicative of the movement of the ferromagnetic target having the target profile pattern, the magnetic field signal comprising a modulated signal portion in a first frequency band based on sensing the modulated AC bias magnetic field and an unwanted signal portion in a second frequency band based on sensing an external magnetic interference; and means for 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, wherein the means for generating, the means for producing and the means for performing are provided on a semiconductor die.
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Specification