JP2002286825A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor for accurately detecting magnetism without being affected by the change in an ambient temperature or the like, and without causing response speed to be delayed when detecting a small magnetic field. SOLUTION: A magnetoresistance element 15A for reference is provided so that element surfaces are at 900 each other to a magnetoresistance element 15B for detection separately from the magnetoresistance element 15B for detection to prevent influence by magnetism to be detected, thus outputting an oscillation signal with a phase according to the magnetoresistance value of each magnetoresistance element from both the CMOS gates 10A and 10B. As a result, even if the ambient temperature changes, the level of each magnetoresistance value itself of both the magnetoresistance elements 15A and 15B changes even if the ambient temperature changes, the relative difference in both the magnetic resistance values is not affected. Further, the deviation in the phase of an oscillation signal from both the CMOS gates 10A and 10B is detected by a D flip-flop circuit 17, and the detection operation of magnetism is made based on it, thus detecting magnetism with improved sensitivity even if a small magnetic field is to be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor provided with a magnetoresistive element whose magnetoresistance changes when a magnetic field in a predetermined direction is applied, and for detecting magnetism based on the change in the magnetoresistance.

[0002]

2. Description of the Related Art Conventionally, as a magnetic sensor of this type, for example, a direct current circuit including a magnetoresistive element is formed, and a change in the magnetoresistive value of the magnetoresistive element due to magnetism is converted into a voltage signal. There is one that detects magnetism based on

[0003]

In recent years, as the performance of magnetic storage devices and magnetic measuring devices has become higher, there has been an increasing demand for magnetic sensors that can detect minute magnetic fields with high accuracy. In order to do so, the converted voltage signal must be amplified by an amplifier having a high amplification factor. However, if an amplifier having a high amplification degree is used, there is a problem that the amplifier is more susceptible to noise and drift generated by the amplifier itself, and furthermore, external electrical noise and the like, resulting in a reduction in detection accuracy. In addition, since the magnetoresistance value of the magnetoresistance element also changes due to a change in the ambient temperature, it can be an obstacle particularly when a minute magnetic field is detected. In order to solve this problem, there is, for example, one disclosed in JP-A-7-77565. In this method, an oscillation circuit including a magnetoresistive element is provided, and a change in the magnetoresistance value is detected as a change in the oscillation frequency. However, in order to increase the sensitivity to detect a minute magnetic field, it is necessary to increase the unit time for measurement or increase the oscillation frequency, which causes a problem such as a slow response time and an increase in circuit power consumption. Occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to accurately detect magnetism without being affected by changes in ambient temperature or the like, and without delaying response speed in detecting a minute magnetic field. To provide a magnetic sensor capable of performing such operations.

[0005]

In order to achieve the above object, a magnetic sensor according to the first aspect of the present invention comprises a magnetoresistive element whose magnetoresistance changes when a magnetic field in a predetermined direction is applied; In the magnetic sensor including a conversion unit that converts a change in the magnetic field into a predetermined signal, and a detection unit that performs a detection operation based on an output signal of the conversion unit, the magnetic detection directions of the magnetic resistance directions are different from each other. Are provided so as to form an angle of 90 degrees, the converting means is constituted by a pair of oscillation circuits each including both magnetoresistive elements, and the detecting means is constituted by a pair of oscillation circuits. It is characterized in that a detection operation is performed based on a difference in oscillation phase between oscillation circuits.

According to a second aspect of the present invention, in the magnetic sensor according to the first aspect, the pair of oscillation circuits includes a pair of detection and reference Schmitt inverter circuits and an output inversion of each Schmitt inverter circuit. The charging and discharging operation is repeated, and the output side oscillates with a pair of detection and reference charging and discharging circuits respectively connected to the input side of each Schmitt inverter circuit via an input resistor. It is characterized in that the element and the reference magnetoresistive element are respectively connected by feedback to each Schmitt inverter circuit.

According to a third aspect of the present invention, in the magnetic sensor according to the first aspect, the pair of oscillation circuits includes a pair of detection and reference Schmitt inverter circuits and an output inversion of the reference Schmitt inverter circuit. The charge / discharge operation is repeated accordingly, and the output side oscillates with the charge / discharge circuits connected to the input sides of both Schmitt inverter circuits via input resistors, respectively. It is characterized in that it is connected back to the Schmitt inverter circuit, and that the magnetoresistive element is connected between the output side of the Schmitt inverter circuit for reference and the input side of the Schmitt inverter circuit for detection.

[0008]

According to the first aspect of the present invention, the reference magnetoresistive element is separately provided such that its magnetic detection direction has an angle of 90 degrees with that of the magnetoresistive element. And a pair of oscillating circuits is configured including the magnetoresistive elements. Here, when a magnetic field in the same direction as the magnetic detection direction of the magnetoresistive element is generated, the magnetoresistive value of the magnetoresistive element changes, but the magnetoresistive value of the reference magnetoresistive element does not change. Accordingly, a shift occurs in the oscillation phase of the pair of oscillation circuits, and a detection operation is performed by the detection unit based on the shift. As described above, apart from the magneto-resistive elements, the reference magneto-resistive elements arranged so as not to be affected by the magnetism to be detected are provided, and the detecting operation is performed based on the difference between the magneto-resistive values. Even if the ambient temperature changes, if the temperature is within a predetermined range, only the magnitude of each magnetoresistance value of both magnetoresistance elements changes, and the relative difference between the two magnetoresistance values is not affected. Further, since the detecting means performs the detecting operation based on the difference between the oscillation phases of the pair of oscillating circuits, even when detecting a very small magnetic field, the response time is the same as the conventional magnetic sensor which performs the detecting operation based on the oscillating frequency. Is not delayed, and magnetic detection can be performed with high sensitivity.

According to a second aspect of the present invention, each charging / discharging circuit repeats charging / discharging in accordance with the output inversion of each Schmitt inverter circuit, and the voltage signal of the charging / discharging level is a Schmitt inverter. The pseudo triangular wave between the upper and lower limit values of the hysteresis generated in the circuit is provided to the input side of each Schmitt inverter circuit. Here, a reference magnetoresistive element and a magnetoresistive element are feedback-connected to each Schmitt inverter circuit. The operation of each of the oscillation circuits will be described with reference to an example circuit diagram 1. For example, when the magnetoresistance value of the magnetoresistance element 1 connected in feedback is infinite (the magnetoresistance element is not connected in feedback). Is
Since the input impedance of the Schmitt inverter circuit 2 is very high, a voltage signal equivalent to the charge / discharge level of the charge / discharge circuit 3 is given to the input side Vin. As a result, the upper and lower limits of the voltage level of the output side Vc of the charge / discharge circuit 3 (Vcmin,
Vcmax) coincides with the upper and lower limit values (Vhmin, Vhmax) of the hysteresis of the Schmitt inverter circuit 2. Here, when the magnetoresistance value of the magnetoresistance element 1 has a predetermined finite value, a current also flows through the input resistance 4 via the magnetoresistance element 1 with the output inversion of the Schmitt inverter circuit 2. Thus, the input side V of the Schmitt inverter circuit 2
in is supplied with a voltage signal (Vc-Vr) obtained by subtracting a shared voltage Vr corresponding to a voltage drop in the input resistor 4 from the voltage V1 of the output side Vc when the charging / discharging circuit 3 discharges.
Voltage V1 and the shared voltage Vr of the input resistor 4 (Vc +
Vr). This means that the Schmitter inverter circuit 2 performs the inverting operation before the charge / discharge circuit 3 reaches the above-described upper and lower limit values (Vcmin, Vcmax). With such a configuration, it becomes possible to change the phase of the output signal of the Schmitt inverter circuit according to the magnetic resistance value of the magnetic resistance element.

<Invention of Claim 3> According to the configuration of Claim 3, the input side of the Schmitt inverter circuit for detection is also provided on the input side.
A voltage signal on the output side of the charge / discharge circuit that repeats charge / discharge according to the output inversion of the reference Schmitt inverter circuit is provided, and an output signal on the output side of the reference Schmitt inverter circuit is input via the magnetoresistive element. It is configured to receive on the side. With such a configuration, the inversion operations of both Schmitt inverter circuits can be matched as long as the magnetoresistive value of the magnetoresistive element does not change with respect to the reference magnetoresistive element. Only when a difference occurs, the phase shifts, and more accurate magnetic detection becomes possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIG.
It will be explained by. The magnetic sensor according to the present embodiment includes, for example, a pair of semiconductor magnetoresistive elements whose magnetoresistance changes when a magnetic field is applied in a direction perpendicular to the element surface of InSb, and converts the change in the magnetoresistance into a predetermined signal. And a detecting means for performing a detecting operation based on an output signal of the converting means, so that it is possible to accurately detect even minute magnetism.

In FIG. 2, reference numerals 15A and 15B are
A pair of semiconductor magneto-resistive elements, wherein one of the semiconductor magneto-resistive elements is arranged so that its element surface is perpendicular to the direction of the magnetic field to be detected;
5B, and the other semiconductor magnetoresistive element is a reference magnetoresistive element 15A formed in the same package while being arranged such that the element surfaces are at an angle of 90 degrees with respect to the detecting magnetoresistive element 15B. It is. The magnetoresistive elements 15A and 15B in the present embodiment use a type in which a magnetic field is applied to the element surface to reduce the magnetoresistance value.

Next, the conversion means includes the two magnetoresistive elements 15
A pair of oscillating circuits for outputting a signal corresponding to a change in the magnetoresistive value of each of the magnetoresistive elements 15A, 15B.
Have the same hysteresis and both magnetoresistive elements 15A,
A time-constant circuit 13 (a charge / discharge circuit according to claim 3) comprising a pair of reference and detection Schmitt inverter CMOS gates 10 </ b> A and 10 </ b> B corresponding to 15 B and a resistor 11 and a capacitor 12 connected in series. ").

The time constant circuit 13 has one end of the resistor 11 connected to the output side of the reference CMOS gate 10A, and the connection point of the resistor 11 and the capacitor 12 connected to the reference CMOS gate 10A.
The input side of the gate 10A is connected via an input resistor 14A, and the input side of the detection CMOS gate 10B is connected via input resistors 14Ba and 14Bb. As a result, the time constant circuit 13 repeats charging and discharging with the output inversion of the reference CMOS gate 10A. Further, a reference magnetic resistance element 15A is connected in a feedback manner to the reference CMOS gate 10A. As a result, a voltage signal (Vc-Vr) lower than the voltage shared by the capacitor 12 by the voltage drop Vr in the input resistor 14A is applied to the input side of the reference CMOS gate 10A when the time constant circuit 13 is discharged, while charging is performed. Sometimes, a voltage signal (Vc + Vr) higher than the shared voltage Vc of the capacitor 12 by the voltage drop Vr of the input resistor 14A is provided. This means that the reference voltage Cc before the shared voltage Vc of the capacitor 12 of the time constant circuit 13 reaches the upper and lower limit values (Vhmin, Vhmax) of the hysteresis of the reference CMOS gate 10A, respectively.
This means that the MOS gate 10A performs an inversion operation. This makes it possible to reflect the change in the magnetic resistance of the reference magnetic resistance element 15A as the change in the phase of the oscillation signal from the reference CMOS gate 10A. At this time, the shared voltage Vc of the capacitor 12 of the time constant circuit 13 is lower than the lower limit value (Vhm
(in + Vr) and an upper limit (Vhmax-Vr).

On the other hand, the detection CMOS gate 10B is connected to the input side of the capacitor 12 sharing voltage Vc of the time constant circuit 13 via the input resistors 14Ba and 14Bb as described above, and to the reference CMOS gate. The output side of the gate 10A is connected via the detecting magnetoresistive element 15B.
This makes it possible to reflect a change in the magnetic resistance value of the detection magnetoresistive element 15B as a change in the phase of the oscillation signal from the detection CMOS gate 10B. Note that the detection magnetic resistance element 15B includes a diode 16 as a reference CMOS.
The outputs are connected in parallel with the direction from the output side of the gate 10A to the input side of the detection CMOS gate 10B being the forward direction. This is because before the inversion operation of the detection CMOS gate 10B, the reference CMOS gate
This is so that the detection CMOS gate 10B can perform the inversion operation even when the gate 10A is in the state of performing the inversion operation. Further, the resistance value of the input resistor 14A and the total resistance value of the input resistors 14Ba and 14Bb are set to be the same value.

The oscillation signal from the reference CMOS gate 10A is given to the CLK terminal of the D flip-flop circuit 17, and the oscillation signal from the detection CMOS gate 10B is given to the D terminal. The Q terminal is connected to a detection operation unit (not shown), and the QBAR terminal is connected to both input resistors 14Ba and 14Ba on the detection side.
It is connected to the connection point of Bb via the resistor 20. Note that the resistor 18 and the capacitor 19 are a power-on reset of the D flip-flop circuit 17.

Next, the operation of the magnetic sensor of this embodiment will be described. When there is no magnetic field, both detection and reference magnetoresistive elements 10A and 10B formed on the same chip are used.
Are the same, and the resistance of the input resistor 14A and the total resistance of the input resistors 14Ba and 14Bb are set to the same value. Therefore, the oscillations of the same phase are output from both the CMOS gates 10A and 10B. A signal is output. Therefore, the D flip-flop circuit 17 initially in the reset state holds the reset state as it is, and the Q terminal outputs a low level.

On the other hand, when a magnetism having a magnetic field in a direction perpendicular to the element surface of the detecting magnetoresistive element 15B is generated,
The magnetoresistive value of the reference magnetoresistive element 15A in which the detection magnetoresistive element 15B and the element surface are arranged at an angle of 90 degrees does not change, and only the magnetoresistive value of the detecting magnetoresistive element 15B changes. Will be. That is, the magnetic resistance of the detection magnetic resistance element 15B is changed to the reference magnetic resistance element 15A.
Is smaller than the magnetic resistance value of. Then, the shared voltage of the input resistors 14Ba and 14Bb of the detection CMOS gate 10B is
It becomes higher than that of the input resistance 14A of the reference CMOS gate 10A. As a result, the phase of the oscillation signal from the detection CMOS gate 10B becomes faster than the phase of the oscillation signal from the reference CMOS gate 10A, so that the D flip-flop circuit 17 is inverted from the reset state and the Hi level is output from the Q terminal. Then, a predetermined detection operation is performed. In addition,
At this time, the output level of the QBAR terminal of the D flip-flop circuit 17 is also inverted from Hi level to Low level. That is, at the time of the Hi level before the magnetic detection operation, a voltage signal higher than the shared voltage Vc of the capacitor 12 by the shared voltage of the input resistor 14Ba is applied to the input side of the detection CMOS gate 10B. At times, a voltage signal lower than the shared voltage Vc of the capacitor 12 by the shared voltage of the input resistor 14Ba is applied via the input resistor 14Bb. This means that the hysteresis of the magnetic sensor as a whole is provided for the difference between the magnetoresistance values of the two magnetoresistance elements 15A and 15B, and the magnetoresistance values of the two magnetoresistance elements 15A and 15B do not correspond to the magnetic detection. Is adjusted so that the magnetic sensor does not perform the detection operation up to the difference of
Thus, a stable detection operation is performed for the magnetism to be detected.

When a magnetic field having a magnetic field in a direction perpendicular to the element surface of the reference magnetoresistive element 15A is generated,
Contrary to the above, the magnetic resistance of the reference magnetic resistance element 15A becomes smaller than the magnetic resistance of the detection magnetic resistance element 15B, and the phase of the oscillation signal from the reference CMOS gate 10A changes to the detection CMOS gate 10B. , And the reset state of the D flip-flop circuit 17 is maintained. That is, in the magnetic sensor of the present embodiment, the detection magnetoresistive element 15B detects magnetism,
The detection operation is performed only when the magnetic resistance value is relatively smaller than that of the reference magnetic resistance element 15A.

As described above, separately from the detection magneto-resistive element 15B, the reference surfaces are set at an angle of 90 degrees with respect to the detection magneto-resistive element 15B so as not to be affected by the magnetism to be detected. By providing a magnetoresistive element 15A,
The CMOS gates 10A and 10B are configured to output oscillation signals having phases corresponding to the magnetoresistance values of the respective magnetoresistance elements. Thus, for example, if the ambient temperature changes within a predetermined range, only the magnitude of each of the magnetoresistive values of the magnetoresistive elements 15A and 15B changes, and the relative difference between the magnetoresistive values does not change. No effect occurs. In addition, since the D flip-flop circuit 17 detects the phase shift of the transmission signals from both the CMOS gates 10A and 10B and performs the magnetic detection operation based on the detection, the sensitivity can be maintained even when a small magnetic field is detected. Magnetic detection can be performed well.

In general, the hysteresis of the Schmitt inverter circuit is inherent and cannot be changed. However, by configuring the pair of oscillation circuits as described above, the CMOS gate 10 serving as the Schmitt inverter circuit can be used.
The phase of the square wave output from A and 10B can be changed according to the magnetoresistance values of the detection and reference magnetoresistance elements 15A and 15B. This makes it possible to accurately detect the difference between the phases of the two oscillation signals with a simple circuit configuration.

Furthermore, a signal of the NO voltage Vc for the capacitor 12 of the time constant circuit 13 that repeats charging and discharging in accordance with the output inversion of the reference CMOS gate 10A is also supplied to the input side of the detection CMOS gate 10B. CMOS gate for reference 1
The output signal of 0A on the output side is configured to be received on the input side via the detection magnetoresistive element 15B. With such a configuration, both CMOSs are used as long as the magnetoresistance value of the detection magnetoresistance element 15B does not change with respect to the reference magnetoresistance element 15A.
The inversion operations of the gates 10A and 10B can be matched, and the phase is shifted only when a difference occurs between the magnetoresistive values of the two magnetoresistive elements, thereby enabling more accurate magnetic detection.

<Other Embodiments> The present invention is not limited to the above embodiments. For example, the following embodiments are also included in the technical scope of the present invention.
In addition to the following, various changes can be made without departing from the scope of the invention. (1) In the above embodiment, the oscillation circuit is configured by the CMOS gates 10A and 10B that output a square wave. However, the invention is not limited to this, and a Wien bridge oscillation circuit may be used as long as the oscillation circuit is used. In this case, by configuring the positive feedback circuit including the magnetoresistive element, it becomes possible to output an oscillation signal having a phase corresponding to the magnetoresistance value of the magnetoresistive element.

(2) In the above embodiment, a pair of oscillation circuits are supplied from one time constant circuit 13 to both the reference CM and the detection CM.
A signal is supplied to the OS gates 10A and 10B, and a reference
The output side of the CMOS gate 10A detects the magnetoresistive element 15B
Is connected to the input side of the detection CMOS gate 10B through the gate, but is not limited to this configuration. For example, each CMOS
The reference and detection magnetoresistive elements 15A and 15B are connected to the gates 10A and 10B by feedback, respectively, and a pair of time constant circuits 13 corresponding to each of the magnetoresistive elements 15A and 15B are provided (corresponding to claim 2). ).

(3) In the above embodiment, the semiconductor magnetoresistive element has been described as an example. However, the present invention is not limited to this, and any magnetoresistive element whose magnetoresistance changes when a magnetic field in a predetermined direction is applied. For example, a ferromagnetic thin film element may be used.

(4) In the above embodiment, the magnetoresistive element has a configuration in which the magnetoresistance value is reduced by applying a magnetic field. However, the present invention is not limited to this, and a configuration in which the magnetoresistance value is increased by the application of a magnetic field. By changing the predetermined circuit configuration, the same effect as in the above embodiment can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram for explaining the operation and effect of the present invention.

FIG. 2 is a circuit diagram of a magnetic sensor according to one embodiment of the present invention.

[Explanation of symbols]

 10A: Reference CMOS gate 10B: Detection CMOS gate 13: Time constant circuit 14A, 14Ba, 14Bb: Input resistance 15A: Reference magnetic resistance element 15B: Detection magnetic resistance element 17: Flip-flop circuit

Claims (3)

[Claims] 1. A magnetoresistive element whose magnetic resistance changes when a magnetic field in a predetermined direction is applied, conversion means for converting the change in the magnetic resistance into a predetermined signal, and detection based on an output signal of the conversion means. A magnetic sensor provided with a detecting means for performing an operation, wherein a reference magnetoresistive element arranged such that magnetic detection directions form an angle of 90 degrees with respect to the magnetoresistive element for detection, The conversion means is constituted by a pair of oscillation circuits each including the two magnetoresistive elements, and the detection means performs a detection operation based on a difference in oscillation phase between the pair of oscillation circuits. Characteristic magnetic sensor. 2. The pair of oscillation circuits repeat a charge / discharge operation in response to a pair of detection and reference Schmitt inverter circuits and an output inversion of each of the Schmitt inverter circuits, and have an output side of each of the Schmitt inverter circuits. A pair of detection and reference charging / discharging circuits connected to the input side via an input resistor, respectively, so as to perform an oscillating operation, wherein the magnetoresistive element and the reference magnetoresistive element are each of the Schmitt elements. The magnetic sensor according to claim 1, wherein the magnetic sensor is configured to be connected to the inverter circuit by feedback. 3. The pair of oscillation circuits repeat a charge / discharge operation in response to output inversion of a pair of detection and reference Schmitt inverter circuits and an output side of the Schmitt inverter circuits. The input side of the circuit is configured to perform an oscillating operation with a charging / discharging circuit connected via an input resistor to the input side, and the reference magnetoresistance element is connected back to the reference Schmitt inverter circuit, and The magnetic sensor according to claim 1, wherein a magnetoresistive element is connected between an output side of the Schmitt inverter circuit for reference and an input side of the Schmitt inverter circuit for detection.