A highly accurate displacement sensor using GMR elements for detecting displacement of a physical quantity such as angle provides a diminished waveform distortion of output voltage. At least two Wheatstone bridge circuits having a predetermined angular offset are installed, with each bridge circuit
A highly accurate displacement sensor using GMR elements for detecting displacement of a physical quantity such as angle provides a diminished waveform distortion of output voltage. At least two Wheatstone bridge circuits having a predetermined angular offset are installed, with each bridge circuit including a plurality of GMR elements. Each of the GMR elements has a fixed magnetic layer set to a predetermined magnetization direction. An AC power supply is used, and displacement of a physical quantity, such as a rotational angle, is detected on the basis of AC-modulated outputs from the bridge circuits.
대표청구항▼
What is claimed is: 1. An angle sensor using a displacement sensor comprising: a sensor element having a first magnetic layer whose magnetization direction is set in a predetermined direction without being influenced by an external magnetic field and a second magnetic layer whose magnetization dire
What is claimed is: 1. An angle sensor using a displacement sensor comprising: a sensor element having a first magnetic layer whose magnetization direction is set in a predetermined direction without being influenced by an external magnetic field and a second magnetic layer whose magnetization direction varies against the external magnetic field; magnetic field generating means for supplying the external magnetic field; and power supply means for supplying drive voltage to said sensor element; wherein a change in resistance value of said sensor element proportional to the difference in a magnetized state between a magnetized state of said second magnetic layer and a magnetized stage of said first magnetic layer, which occurs depending on a relative positional relation between said magnetic field generating means and said sensor element, is detected to detect a relative positional relation between said magnetic field generating element and said sensor element; and said displacement sensor further comprises suppressing means for suppressing an anisotropic magnetoresistive effect which occurs in said second magnetic layer and which is attributable to an electric current flowing in said sensor element on the basis of said drive voltage; and wherein the angle sensor comprises: a stator section having a plurality of giant magnetoresistive elements of a multi-layer structure, said giant magnetoresistive elements each having at least a fixed magnetic layer having a fixed magnetization direction, a non-magnetic conductive layer and a free magnetic layer; and a rotor section adapted to form a magnetic field and rotate in opposition to said stator section, a rotational angle of said rotor section being detected from a change in resistance value caused by the magnetic field provided from said rotor section to said GMR elements; characterized in that at least two Wheatstone bridge circuits having a predetermined angular offset are installed in said stator section, said Wheatstone bridge circuits each comprising a plurality of GMR elements each having a fixed magnetic layer set in a predetermined magnetization direction, an AC power supply is used as a power supply for said Wheatstone bridge circuits, an alternating current is made flow in said plural GMR elements and a rotational angle is detected on the basis of AC-modulated outputs provided from said Wheatstone bridge circuits. 2. An angle sensor according to claim 1, wherein said stator section comprises: a first Wheatstone bridge circuit for comprising four GMR elements, said GMR elements each having a fixed magnetic layer set in a predetermined magnetization direction parallel or anti-parallel with respect to a reference direction in which a rotor section rotational angle θ is zero; a second Wheatstone bridge circuit for comprising four GMR elements, said GMR elements each having a fixed magnetic layer set in a predetermined ±90° direction with respect to a reference direction in which the rotor section rotational angle is zero; and a signal processor for detecting the rotational angle on the basis of a differential-amplified AC-modulated output signal sin θ sin(ωt) provided from the first Wheatstone bridge circuit and a differential-amplified AC-modulated output signal cos θ sin(ωt) provided from the second Wheatstone bridge circuit, when an AC voltage of said AC power supply is set to sin(ωt) (ω: angular frequency, t: time). 3. An angle sensor according to claim 1, further comprising a signal processor for calculating the rotational angle (θ) from output signals sin θ and cos θ and in accordance with the relationship θ=arctan(sin θ/cos θ), the output signals sin θ and cos θ being obtained from a differential-amplified AC-modulated output signal sin θ sin(ωt) provided from the first Wheatstone bridge circuit and a differential-amplified AC-modulated output signal cos θ sin(ωt) provided from the second Wheatstone bridge circuit, through a synchronous detector circuit, said synchronous detector circuit synchronously detecting an AC voltage sin(ωt) of said AC power supply. 4. An angle sensor according to claim 3, wherein said synchronous detector circuit has at least a multiplier and an integrator (circuit). 5. An angle sensor according to claim 1, further comprising a signal processor for detecting the rotational angle on the basis of output phase information on a composite output signal sin(ωt−θ), said composite output signal being obtained by combining an output signal sin θ cos(ωt) resulting from a 90° phase shift of a differential-amplified AC-modulated output signal sin θ sin(ωt) provided from the first Wheatstone bridge circuit with a differential-amplified AC-modulated output signal cos θ sin(ωt) provided from the second Wheatstone bridge circuit. 6. An angle sensor according to claim 1, wherein said stator section comprises: a first Wheatstone bridge circuit for comprising four GMR elements, said GMR elements each having a fixed magnetic layer set in a predetermined magnetization direction parallel or anti-parallel with respect to a reference direction in which a rotor section rotational angle θ is zero; a second Wheatstone bridge circuit for comprising four GMR elements, said GMR elements each having a fixed magnetic layer set in a predetermined ±90° direction with respect to a reference direction in which the rotor section rotational angle is zero, AC voltages of said AC power supply being supplied as sin(ωt) (ω: angular frequency, t: time) and cos(ωt) to said first and second Wheatstone bridge circuits, respectively; and a signal processor for detecting the rotational angle on the basis of output phase information on a composite output signal sin(ωt−θ), said composite output signal sin(ωt−θ) being obtained by combining differential-amplified AC-modulated output signals sin θ cos(ωt) and cos θ sin(ωt) provided from said first and second Wheatstone bridge circuits. 7. An angle sensor according to claim 1, further comprising a signal processor which causes a phase variable φ to be generated from a sequential phase generator circuit, causes cos φ and sin φ to be generated from a sin/cos generator circuit on the basis of the phase variable φ, multiplies, with use of a multiplier circuit, a differential-amplified AC-modulated output signal sin θ sin(ωt) provided from the first Wheatstone bridge circuit by cos φ, multiplies, with use of a multiplier circuit, a differential-amplified AC-modulated output signal cos θ sin(ωt) provided from the second Wheatstone bridge circuit by sin φ, and detects the rotational angle from the phase variable φ (=θ) in which the term of sin(φ−θ) in a composite signal sin(φ−θ)sin(ωt) resulting from combining both said output signals by a subtractor circuit becomes zero. 8. An angle sensor according to claim 1, wherein a signal processor for detecting the rotational angle provides a phase detector circuit which comprises at least a reference signal generator circuit, a multiplier and an integrator (circuit), said multiplier being configured to multiply an input signal by a reference signal, an output of said multiplier being inputted to said integrator (circuit), and said integrator (circuit) being configured to integrate the output of said multiplier, and said reference signal generator being configured to produce the reference signal. 9. An angle sensor according to claim 8, further comprising a phase detector circuit having a comparator circuit, an output of an integrator (circuit) being inputted to said comparator circuit, said comparator circuit comparing whether an output value of said integrator (circuit) is within a predetermined range or not, and wherein when an input value of said comparator circuit deviates from the predetermined range, it is detected as an error by said phase detector circuit. 10. An angle sensor according to claim 9, wherein there are plural said predetermined ranges, said predetermined duration time is defined for each of said plural predetermined ranges, and said phase detector circuit detects a deviation from any of said predetermined ranges as an error. 11. An angle sensor according to claim 8, further comprising a phase detector circuit having a comparator circuit, and wherein when an input value of said comparator circuit deviates from a predetermined range for a period of time longer than a predetermined duration time, it is detected as an error by said phase detector circuit. 12. An angle sensor according to claim 1, further comprising means for biasing AC power-side terminals and earth-side terminals of said Wheatstone bridge circuits to a predetermined DC reference potential, and voltage obtained by the addition of a DC reference potential and a DC voltage is applied to the AC power-side terminals. 13. An angle sensor according to claim 1, further comprising a signal processor which stores in memory means a deviation angle α between a reference direction in which the rotor section rotational angle θ is zero and the magnetization direction of the fixed magnetic layers of the GMR elements constituting said Wheatstone bridge circuits, and then corrects and outputs the deviation angle α in accordance with the rotational angle (θ+α) obtained on the basis of the AC-modulated outputs of said Wheatstone circuits.
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이 특허에 인용된 특허 (3)
Coehoorn, Reinder; Lenssen, Kars-Michiel H.; Bloemen, Pascal J. H., Magnetic field sensor with perpendicular axis sensitivity, comprising a giant magnetoresistance material or a spin tunnel junction.
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