JP3341036B2 - Magnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor, and more particularly to a magnetic impedance sensor which is a high-sensitivity magnetic sensor.

[0002]

2. Description of the Related Art With the rapid development of information devices and measurement / control devices in recent years, there has been an increasing demand for small, low-cost, high-sensitivity, high-speed magnetic sensors. For example, in the hard disk drive of the external storage device of a computer, the performance has been improved from a bulk type inductive magnetic head to a thin film magnetic head and a magnetoresistive effect (MR) head, and a rotary encoder serving as a motor rotation sensor has a magnet. As the number of magnetic poles of the ring increases, a magnetic sensor capable of detecting a weak surface magnetic flux with high sensitivity is required instead of a conventionally used magnetoresistive effect (MR) sensor. In addition, demand for a high-sensitivity magnetic sensor that can be used for nondestructive inspection and banknote inspection is increasing. Further, there is a growing demand for a small and lightweight direction sensor for automobiles, a sensor for active magnetic shield of a display tube of a high-definition color television or a personal computer, and the like.

[0003] Typical magnetic sensors currently used include an inductive reproducing magnetic head, a magnetoresistive (MR) element,
There are a flux gate sensor, a Hall element and the like. Also,
Recently, the magnetic impedance effect of an amorphous wire (see JP-A-6-176930, JP-A-7-181239, and JP-A-7-333305) and the magnetic impedance effect of a magnetic thin film (JP-A-8-75835, Journal of the Japan Society of Applied Magnetics vo
l, 20,553-556 (1996)), a high-sensitivity magnetic sensor has been proposed.

The inductive reproducing magnetic head requires a coil winding, so that the magnetic head itself becomes large. In addition, when the size of the inductive reproducing magnetic head is reduced, the relative speed between the magnetic head and the medium may be reduced, which may cause a problem that the detection sensitivity is significantly reduced. On the other hand, a magnetoresistance (MR) element using a ferromagnetic film has come to be used. The MR element detects the magnetic flux itself rather than the time change of the magnetic flux, and thus the miniaturization of the magnetic head has been promoted. However, the rate of change of the electric resistance of the current MR element is about 2
%, And even the MR element using the spin valve element has a small rate of change in electric resistance of at most 6% or less, and several%.
The external magnetic field required to obtain the resistance change is as large as 1600 A / m or more. Therefore, the magnetoresistive sensitivity is a low sensitivity of 0.001% / (A / m) or less. Recently, the giant magnetoresistance effect (GMR) by an artificial lattice having a magnetoresistance change rate of several tens of percent has been found. However, tens of thousands of A /
Since an external magnetic field of m is required, it has not been put to practical use as a magnetic sensor.

A fluxgate sensor, which is a conventional high-sensitivity magnetic sensor, has a high permeability magnetic core such as permalloy.
It measures the magnetism by using the fact that the BH characteristic changes due to an external magnetic field, and has high resolution and high directivity of ± 1 °. However, this flux gate sensor requires a large magnetic core with a small demagnetizing field in order to increase the detection sensitivity, it is difficult to reduce the size of the entire sensor, and there is a problem that the power consumption is large. The magnetic field sensor using the Hall element utilizes the phenomenon that when a magnetic field is applied perpendicular to the plane where current flows, an electric field is generated in a direction perpendicular to both the current and the applied magnetic field, and an electromotive force is induced in the Hall element. Sensor. Hall elements are advantageous in terms of cost, but have low magnetic field detection sensitivity.Because they are composed of semiconductors such as Si and GaAs, electrons or holes are scattered due to thermal vibration of the lattice in the semiconductor against temperature changes. Has the disadvantage that the temperature characteristics of the magnetic field sensitivity are poor due to the change in the mobility of the magnetic field.

As described in JP-A-6-176930, JP-A-7-181239, and JP-A-7-333305,
Magneto-impedance elements have been proposed to achieve significant improvements in magnetic field sensitivity. The basic principle of this magneto-impedance element is to detect only the voltage with respect to the time change of the circumferential magnetic flux using the skin effect generated by applying a current that changes rapidly with time to a magnetic wire as a change due to an externally applied magnetic field. The magnetic impedance element described above. Amorphous wires with a diameter of about 30 μm with zero magnetostriction such as FeCoSiB (wires that have been drawn and annealed in tension) such as FeCoSiB are used as the magnetic wires. The amplitude of the voltage changes with high sensitivity of about 0.1% / (A / m), which is 100 times or more that of the MR element.

[0007]

By the way, as a magnetic sensor, a small and low-cost magnetic field (external magnetic field) is detected.
There is a demand for a high-sensitivity magnetic sensor having excellent output linearity and temperature characteristics. The magnetic sensor using the magnetic impedance effect of the amorphous wire exhibits high-sensitivity magnetic field detection characteristics. Also, JP-A-6-176930,
Japanese Unexamined Patent Publication No. Hei 6-347489 discloses that the application of a bias magnetic field improves the linearity of the applied magnetic field dependence of the impedance change, and a negative feedback coil is wound around the amorphous wire, and the voltage across the amorphous wire is increased. It is shown that a magnetic sensor with excellent linearity can be provided by amplifying the negative feedback current and flowing a negative feedback current to the negative feedback coil.

Japanese Patent Application Laid-Open No. 6-176930 does not mention a driving circuit including an oscillation circuit and a detection circuit, and Japanese Patent Application Laid-Open No. 6-347489 uses a pair of switching transistors as an oscillation circuit. A combination of a multivibrator and a low-pass filter has been proposed. According to the Japan Society of Applied Magnetics, VOL.21.793-796 (1997), in order to reduce power consumption, high-frequency current is applied to two amorphous wires by pulse driving with a C-MOS multivibrator, and each is detected by a diode. ,
Differential amplification is performed by an operational amplifier. However, in this circuit, the amount of magnetic change of the magneto-impedance element is not maximized, and there is a problem in temperature characteristics. A patent using two amorphous wires is disclosed in Japanese Patent Application Laid-Open No. 7-248365, but does not mention a drive circuit including a detection circuit.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a highly sensitive and compact magnetic sensor having excellent linearity of output with respect to a detected magnetic field and excellent temperature characteristics.

[0010]

According to a first aspect of the present invention, there is provided a magnetic sensor comprising a ferromagnetic material, a first electrode and a second electrode provided at both ends in a longitudinal direction, and a periphery of the ferromagnetic material. And a first and a second two magneto-impedance elements each having a configuration in which a bias coil and a negative feedback coil are wound via an insulator, and a high-frequency current for passing a high-frequency current through the two magneto-impedance elements. An oscillation circuit;
A circuit for flowing a direct current to the bias coil so that magnetic fields of opposite polarities are applied to the two magnetic impedance elements; and a circuit that depends on an impedance change of the two magnetic impedance elements caused by an applied external magnetic field .
A detection circuit that detects both the positive electrode side and the negative electrode side of the AC voltage between the first electrode and the second electrode with a detection diode through which a constant DC current flows, and a peak that holds the peak value of the output voltage of the detection circuit Hold circuit and the peak
Positive electrode side of the first magnetic impedance element of the hold circuit
Output voltage and negative side output of second magneto-impedance element
Voltage and the first magnetic impedance
And a second magneto-impedance element.
Differential amplification of the added voltage obtained by adding the positive output voltage of the
To combine the four output voltages of the peak hold circuit.
And a synthesizing circuit . According to a second aspect of the present invention, in the configuration according to the first aspect, the magneto-impedance element has a ferromagnetic thin-film magnetic core formed on a substrate made of a non-magnetic material, A first electrode and a second electrode are respectively provided at both ends in the longitudinal direction of the thin-film magnetic core, and a bias coil and a negative feedback coil are wound around the ferromagnetic thin-film magnetic core via an insulator. And According to a third aspect of the present invention, in the configuration according to the first aspect, the magneto-impedance element includes a ferromagnetic amorphous wire having a first electrode and a second electrode provided at both ends in a longitudinal direction thereof, A bias coil and a negative feedback coil are wound around the ferromagnetic amorphous wire via an insulator. The invention of a magnetic sensor according to claim 4 of the present application is made of a ferromagnetic material and has first ends at both ends in the longitudinal direction.
First and second two magneto-impedance elements each having a configuration in which an electrode and a second electrode are provided, and a bias coil and a negative feedback coil are wound around the ferromagnetic material via an insulator. An oscillation circuit for supplying a high-frequency current to the two magneto-impedance elements, a circuit for passing a direct current to the bias coil so that magnetic fields of opposite polarities are applied to the two magneto-impedance elements,
An AC voltage between the first electrode and the second electrode, which depends on an impedance change of the two magneto-impedance elements caused by an applied external magnetic field, applies a constant DC voltage to both the positive electrode side and the negative electrode side. a detection circuit for detecting by the detection diode current flows, the peak hold circuit for holding a peak value of the output voltage of the detection wave circuit, the peak hole
Positive output of the first magneto-impedance element of the
And the negative output voltage of the first magneto-impedance element
And a second magneto-impedance element
And the negative output voltage of the second magneto-impedance element.
Differential amplification of the pole side output voltage and the differentially amplified voltage
Combining the output voltages of the two peak hold circuits
And a circuit . According to a fifth aspect of the present invention, in the configuration according to the fourth aspect, the magnetic impedance element has a ferromagnetic thin-film magnetic core formed on a substrate made of a nonmagnetic material, A first electrode and a second electrode are respectively provided at both ends in the longitudinal direction of the thin-film magnetic core, and a bias coil and a negative feedback coil are wound around the ferromagnetic thin-film magnetic core via an insulator. And The invention according to claim 6 of the present application, in the configuration according to claim 4, wherein the magneto-impedance element comprises a ferromagnetic amorphous wire having first and second electrodes provided at both ends in the longitudinal direction, A bias coil and a negative feedback coil are wound around the ferromagnetic amorphous wire via an insulator. The above oscillation circuit can be driven by either a pulse wave or a sine wave, and a circuit that oscillates a rectangular wave as a pulse wave with a C-MOS and supplies a differentiated
There is a circuit that oscillates a square wave with a MOS and an oscillator and generates a sine wave with a low-pass filter or a band-pass filter, a cascaded Colpitts oscillation circuit using a combination of a transistor and an oscillator, and a Wien bridge circuit using an operational amplifier. The above detection circuit is a peak hold circuit that applies a constant current to the detection diode and detects both the positive side and the negative side of the AC voltage, and combines the detection outputs of the two magnetic impedance elements to perform differential amplification. are doing.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. 1 to 18 and FIGS. FIG. 1 is a block diagram showing a circuit configuration of the magnetic sensor 1 of the present invention. The magnetic sensor 1 includes a negative feedback coil 2
Impedance element 4 having a coil and a bias coil 3
Oscillating circuit 5, detecting circuit 6, amplifying circuit 7,
It comprises a negative feedback resistor 8. In FIG. 1, reference numeral 9 denotes a circuit (DC current supply circuit) for flowing a DC current so as to apply magnetic fields of opposite polarities to the bias coils 3 of the two magnetic impedance elements 4, and reference numeral 10 denotes a ferromagnetic material.

As the magnetic impedance element 4, FIG.
Thin-film magneto-impedance (MI) elements 3 and 4 (hereinafter referred to as the thin-film MI element 4 using the same reference numerals) are used. 2 is a diagram schematically showing the structure of the thin-film MI element 4, FIG. 3 is a sectional view taken along the line AA in FIG. 2, and FIG.
FIG. 4 is a cross-sectional view taken along line BB of FIG. The thin film MI element 4 has a ferromagnetic material 10 having a width of 20 μm, a thickness of 3 μm, and a length of 2000 μm.
It is called 0. A ferromagnetic thin film magnetic core according to claim 2 is constituted. ), A thin film coil for negative feedback (hereinafter, referred to as a negative feedback coil 2) serving as a negative feedback coil 2 on a thin film magnetic core 10 via an insulating film 11.
The structure is such that a thin film coil for bias as a thin film coil for negative feedback (hereinafter referred to as a negative feedback thin film coil 2) and a bias coil 3 (hereinafter referred to as a thin film coil for bias 3) are three-dimensionally wound.
The negative feedback and bias thin film coils 2 and 3 are alternately wound around the thin film magnetic core 10, and the number of turns is 42 turns, respectively. Further, Au pads for wire bonding are provided on a part of each electrode portion. 3 and 4, reference numeral 14 denotes a substrate made of a non-magnetic material (constituting the substrate according to claim 2 or 5 );
Reference numeral 15 denotes a first electrode, and reference numeral 16 denotes a second electrode.

Next, characteristics of the manufactured thin film MI element 4 will be described. Here, the dimensions of the thin-film magnetic core 10 are 20 μm in width, 3 μm in thickness, and 2000 μm in length as described above, and the negative feedback and biasing thin-film coils 2 and 3 are alternately wound on the same surface. The number of turns is 42 turns as described above. The structure in which the negative feedback and bias thin film coils 2 and 3 are alternately wound on the same surface of the thin film magnetic core 10 makes it possible to apply a bias magnetic field and a negative feedback magnetic field to each part of the thin film magnetic core 10 evenly. The linearity of the sensitivity characteristic as the thin film MI element 4 (magnetic sensor 1) is improved. FIG. 5 shows the thin film MI element 4 when a magnetic field (Hex) of 0 and 1080 A / m is applied to the thin film MI element 4 in the longitudinal direction when the thin film magnetic core 10 is manufactured by NiFe plating.
7 shows the frequency characteristics of the voltage E between the two end electrodes (first and second electrodes 15 and 16). In this case, Hex = 0 and Hex = 1080
The difference ΔE of E at A / m was the largest around the frequency of the applied current of 20 MHz as shown in FIG. FIG. 7 shows the dependence of the rate of change of impedance on the applied magnetic field (Hex) when the frequency of the flowing current is 20 MHz. As the applied magnetic field increases, the rate of change ΔZ / Z0 of the impedance increases, ΔZ / Z0 becomes maximum at the anisotropic magnetic field Hk of the element, and ΔZ / Z0 decreases when Hex> Hk. In addition, the amount of change in impedance per unit applied magnetic field (magnetic field sensitivity) reaches a maximum at around Hex = 200 A / m and reaches 0.4%.
/ (A / m).

As the oscillation circuit 5, for example, FIG.
Oscillation circuits 5, 9, 10, and 11 are used. FIG.
Reference numerals 9, 10, and 11 denote oscillation circuits 5 for supplying a high-frequency current to the magnetic impedance element 4.
The oscillation circuit 5 in FIG. 8 is a C-MOS oscillation by RC, and is a circuit in which a differentiating circuit 18 is added to the oscillation unit 17.
The oscillation circuit 5 of FIG.
An oscillation circuit 5. The oscillation circuit 5 of FIG. 9 has a high frequency stability and a stable amplitude (amplitude = Vcc). After the CMOS oscillation output, the signal passes through a filter unit 20 including a low-pass filter or a band-pass filter.
A sine wave is obtained. As the low-pass filter, an inexpensive LC filter is used, and a Butterworth-type low-pass filter is shown in the figure, but a Chebyshev-type low-pass filter may be used.
The oscillation circuit 5 in FIG. 10 is a Wien bridge oscillation circuit 5 using the operational amplifier 21. With this circuit, a sine wave is obtained. The oscillation circuit 5 shown in FIG. 11 is a circuit in which a Colpitts oscillation circuit 5 having a common emitter and amplifiers 22 and 23 having a common base are cascaded. The advantage of this circuit is that the influence of the mirror effect can be eliminated, so that the effect of the load fluctuation on the oscillating unit 17 can be suppressed as much as possible, and stable oscillation can be supplied. There is also an advantage that the frequency characteristics can be improved.

In the magnetic sensor 1 configured as described above, the oscillating circuit 5 applies a high-frequency current to the two magnetic impedance elements 4. As shown in FIG. 12, when an external magnetic field is applied to the magnetic impedance element 4, the impedance of the magnetic impedance element 4 changes. The two magnetic impedance elements 4 (hereinafter, for convenience, the lower magnetic impedance element 4 in FIG. 12 is referred to as a first MI element 4a, and the upper magnetic impedance element 4 in FIG.
Is referred to as a second MI element 4b. ) Apply opposite bias magnetic fields. In this case, a positive bias magnetic field is applied to the first MI element 4a, and a negative bias magnetic field is applied to the second MI element 4b. The first MI element 4a by this bias magnetic field
The voltage (voltage amplitude) between the first electrode 15 and the second electrode 16 of the thin film magnetic core 10 has a positive slope as shown in FIG. 13, and the bias magnetic field causes the voltage of the thin film magnetic core 10 of the second MI element 4b to change. The voltage (voltage amplitude) between the first electrode 15 and the second electrode 16 has a negative slope as shown in FIG.

The detecting unit 24 (corresponding to the detection circuit 6 in FIG. 1) is configured to control a voltage (an external magnetic field and a bias magnetic field) between the first electrode 15 and the second electrode 16 of the thin-film magnetic core 10 of the first MI element 4a. ) And the voltage between the first electrode 15 and the second electrode 16 of the thin-film magnetic core 10 of the second MI element 4b (voltage due to an external magnetic field and a bias magnetic field), and the detected signal is output to an operational amplifier 25 (amplifier in FIG. 1). This corresponds to the circuit 7.) By performing differential detection in the [synthesis circuit] , both voltage amplitude changes of the first MI element 4a and the second MI element 4b according to the change of the external magnetic field are added, and the first MI element Changes in characteristics of the 4a and the second MI element 4b due to temperature are canceled out (that is, the temperature characteristics become excellent).

As the detection circuit 6 and the amplification circuit 7 (hereinafter, for convenience, the detection circuit 6 and the amplification circuit 7 are referred to as a detection circuit 26), for example, a detection circuit 26B shown in FIGS. 15 and 16 is used. Prior to the description of the detection circuit 26B shown in FIGS. 15 and 16, the one shown in the Japan Society of Applied Magnetics VOL. 21.793-796 (1997) will be described first. C-MOS by Japan Society of Applied Magnetics VOL.21.793-796 (1997)
The detection circuit 26A of the multivibrator-type magnetic sensor detects one magnetic element (magnetic impedance element) using one diode. This detection circuit 26
FIG. 21 shows a circuit configuration of the magnetic sensor 1 having A.

The detecting method of the detecting section 24 (detecting circuit 26A) is based on the voltage waveforms at both ends of one magnetic impedance element (for convenience, the first MI element 4a) and the other magnetic impedance element (for convenience, the second MI element 4b). (VAi
n, VBin) passes through the diodes 27 and 28, and only the positive polarity side is peak-held and detected. When the detected voltage of the first MI element 4a at this time is VA and the amount of change in the voltage changed by the external magnetic field is ΔVH, when a positive magnetic field is externally applied, as shown in FIGS. 21 and 22, the first MI element 4a Is VA + ΔVH. Similarly, the detection voltage of the second MI element 4b becomes VB-ΔVH. At this time, the output of the operational amplifier 25 is VA = VB, and 2ΔVH is obtained.
In the detection unit 24 (detection circuit 26A) of FIG. 21, the voltage waveform at both ends of the magnetic impedance element 4 is changed to the positive polarity side only.
No detection is performed, and the MI elements (first and second MI elements 4
It cannot be said that the amount of magnetic change due to the external magnetic field in (a, 4b) is detected.

In contrast to the detection circuit 26A shown in FIG. 21, the detection circuit 26B shown in FIG. 15 can detect both positive and negative amplitudes of the voltage waveform at both ends of the MI element by using two detection diodes for one MI element. I did it. The voltage waveforms at both ends of the magneto-impedance element 4 are diodes D1-1, D1-2, D2-
1. After passing through D2-2 (which constitutes the detection circuit 6 of the present invention), the peak output of the voltage which is peak-held on the positive polarity side by the first MI element 4a is VA1 [the first MI element 4a (first
The positive output voltage of the magnetic impedance element) and the negative peak output are set to VA2 [the first MI element 4a (the first magnetic input element).
Negative output voltage of the impedance element) . In addition, the peak output of the positive polarity by the second MI element 4b is VB1 [the second MI element 4b ].
The element 4b (second magneto-impedance element) has a positive electrode
Power Voltage], negative peak output VB2 [First 2MI element 4b
(Negative Output Voltage of the Second Magnetic Impedance Element)
And In the present embodiment, the resistors R6, R7, R8, R
9 and the capacitors C5, C6, C7, C8 constitute a peak hold circuit.

Assuming that the amount of voltage change caused by the external magnetic field is ΔVH, the output when the external magnetic field is applied is VA1 = VA + ΔVH,
VA2 = −VA−ΔVH, VB1 = VB−ΔVH, VB2 = −VB + ΔVH
It is represented by VA1 of peak output as shown in the circuit diagram of FIG.
And VB2 are added to each other to obtain a detection output V1. Similarly VA2
And VB1 are added to each other to obtain a detection output V2. Then, the detection outputs V1 and V2 are differentially detected by the operational amplifier 25 and the four peak outputs are combined, so that the output _Vout can be obtained as 4ΔVH from the equations (1) and (2).

V _out = | ｛(VA2 + VB1) − (VA1 + VB2)｝ | + (1/2) _Vcc = | ｛[(− VA−ΔVH) + (VB−ΔVH)] − [(VA + ΔVH) + (−VB + ΔVH)]｝ | + (1/2) V _cc (1) From VA = VB, V _out = 4ΔVH + (1/2) V _cc (2)

The detection circuit 26B shown in FIG. 15 obtains 4ΔVH as its output _Vout as described above.
Output V _out [shown by equations (3) and (4). As apparent from comparison with FIG. 21, the detection circuit has twice the detection capability of the detection circuit 26A of FIG. V _out = VA + ΔVH− (VB−ΔVH) (3) On the other hand, since VA = VB, V _out = 2ΔVH (4)

In the detection circuit 26B shown in FIG. 15, the detection sensitivity is greatly improved by applying a constant current to the diode.
In C, the detection voltage can be set to (1/2) _Vcc, and the power supply of the operational amplifier 25 can be operated with a single power supply.

Instead of the detection circuit 26B of FIG.
The detection circuit 26C may be configured as shown in FIG. FIG.
15C is different from the detection circuit 26B of FIG. 15 in that VA1 and VA2 are combined with respect to the combination of the peak outputs VA1, VA2, VB1 and VB2, and VB1 and
The difference is that VB2 is combined and both signal values obtained by this combination are differentially combined by an operational amplifier. In FIG. 17, reference numeral 43 denotes an operational amplifier for differentially detecting VA1 and VA2, and reference numeral 44 denotes an operational amplifier for differentially detecting VB1 and VB2. The output V _out is expressed by the equation (5)
As shown in (8), 4ΔVH can be detected, and has a detection capability equivalent to that of the detection circuit 26B of FIG.

V1 = VA2−VA1 = (− VA−ΔVH) − (VA + ΔVH) (5) V2 = VB2−VB1 = (− VB + ΔVH) − (VB−ΔVH) (6) _Vout = | V1−V2 | + (1/2) _Vcc = | (−2VA−2ΔVH) − (− 2VB + 2ΔVH) | + (1/2) _Vcc (7)

From VA = VB, V _out = 4ΔVH + (1/2) V _cc (8)

[0027] However, the detection circuit 26C (detection times in FIG. 17
When determining the temperature characteristics of the road-6 and the amplifier circuit 7) is as shown by the broken line 45 in FIG. 18, the detection circuit 26B of FIG. 15 (test
Compared to the temperature characteristics (solid line 46) of the wave circuit 6 and the amplification circuit 7) , the detection circuit 26B (the detection circuit 6 and the amplification circuit ) of FIG.
The temperature characteristic of the road 7) is better. In the temperature characteristic (dotted line 47) of the detection circuit 26A shown in FIG. 21, the temperature characteristic of the diode appears directly in the output.
Among the two detection circuits 26 (the detection circuit 26B in FIG. 15, the detection circuit 26C in FIG. 17, and the detection circuit 26A in FIG. 21), the characteristics are the worst. The detection circuit 26C of FIG. 17 uses more operational amplifiers than the detection circuit 26B of FIG.
6B is better.

In FIGS. 15 and 17, the detection diodes 30, 31, 32, and 33 use Schottky diodes. However, if there is sufficient output of the voltage between both ends of the magnetic impedance element, a normal silicon diode may be used.

Next, a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, a magnetic sensor 1 actually using the detection circuit 26B of FIG.
FIG. 19 shows the circuit configuration. In the second embodiment, the oscillation circuit 5 uses a CMOS RC oscillator, and a differentiating circuit 18 applies a differential waveform to the MI element. The output of the magnetic sensor 1 is shown in FIG. With this magnetic sensor 1, the magnetic field of the bias coil 3 is set to 320 A / m,
When a negative feedback of 40% was applied, a sensitivity of 0.021 V / (A / m) was obtained within the measurement range of ± 80 A / m, showing excellent linearity. These results show good characteristics as a linear magnetic sensor.

In the above embodiment, the case where the ferromagnetic material of the magnetic impedance element is the ferromagnetic thin film magnetic core 10 has been described as an example. Alternatively, the ferromagnetic material may be formed of a ferromagnetic amorphous wire.

[0031]

According to any one of claims 1 to 3,
The described invention has a configuration in which two magneto-impedance elements are energized at high frequency by an oscillation circuit , their outputs are converted into DC signals by a detection circuit , differentially amplified by an amplification circuit , and the output is fed back to a negative feedback coil. As a result, a circuit capable of stably supplying a high-frequency current to be applied to the magneto-impedance element and efficiently detecting a change in the magnetic field of the magneto-impedance element can be easily configured. In particular, the detection circuit can convert the output of the magneto-impedance element to a DC signal with high sensitivity even when the input amplitude is small, by passing a constant current through the detection diode. In addition, the outputs of the magneto-impedance elements are added to each other and combined, whereby a change over time in the temperature characteristics of the detection diode can be eliminated, and an excellent magnetic sensor module can be provided. This module can be operated with a single power supply. Claim 4 to Claim 6
The invention according to any one of the first to third aspects of the present invention.
In the same manner as the invention described in any of
Stable supply of high-frequency current to be applied to dance elements
And efficiently detects changes in the magnetic field of the magneto-impedance element
Circuits that can be easily configured.
Input current is reduced by flowing a constant current through the
The output of the magneto-impedance element to a DC signal
Can be converted with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically showing a magnetic sensor according to a first embodiment of the present invention.

FIG. 2 is a plan sectional view showing a thin-film magneto-impedance element (thin-film MI element) used in the magnetic sensor of FIG.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a sectional view taken along line BB of FIG. 2;

5 is a diagram showing a current frequency-output voltage characteristic of the MI device of FIG.

FIG. 6 is a diagram showing a current frequency-impedance change rate characteristic of the MI element of FIG. 1;

FIG. 7 is a diagram showing an external magnetic field-impedance change rate characteristic of the MI element of FIG. 1;

FIG. 8 is a circuit diagram showing a first example of the oscillation circuit of FIG. 1;

FIG. 9 is a circuit diagram showing a second example of the oscillation circuit of FIG. 1;

FIG. 10 is a circuit diagram showing a third example of the oscillation circuit of FIG. 1;

FIG. 11 is a circuit diagram showing a fourth example of the oscillation circuit of FIG. 1;

FIG. 12 is a diagram showing a circuit configuration of two MI elements.

FIG. 13 is a diagram showing an external magnetic field-amplitude characteristic of the first MI element of FIG. 1;

FIG. 14 is a diagram showing an external magnetic field-amplitude characteristic of the second MI element of FIG. 1;

FIG. 15 is a circuit diagram illustrating an example of a detection circuit and an amplification circuit (detection circuit) of FIG. 1;

16 is a signal waveform diagram of the detection circuit of FIG.

FIG. 17 is a circuit diagram illustrating another example of the detection circuit and the amplification circuit (detection circuit) of FIG. 1;

FIG. 18 is a diagram showing temperature-output characteristics of the detection circuits of FIGS. 15, 17 and 21;

FIG. 19 is a circuit diagram schematically showing a second embodiment of the present invention.

20 is a diagram showing an external magnetic field-output voltage characteristic of the magnetic sensor of FIG.

FIG. 21 is a circuit diagram illustrating an example of a conventional magnetic sensor.

FIG. 22 is a diagram showing signal waveforms of various parts of the magnetic sensor of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Magnetic sensor 2 Negative feedback thin film coil (negative feedback coil) 3 Bias thin film coil (bias coil) 4 Thin film MI element (magnetic impedance element) 4a, 4b First and second MI element (two magnetic impedance elements) 5 Oscillation circuit 6 Detection circuit 8 Differential amplification circuit 9 DC current supply circuit (circuit for flowing DC current)

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akiyo Yuguchi 173-1 Asana, Asaba-cho, Iwata-gun, Shizuoka Pref. Minebea Co., Ltd. Development Technology Center (56) References JP-A-7-248365 (JP, A) Non Yoshitaka Koji, five others, sputtered thin film micro MI sensor by pulsed current excitation, Journal of the Japan Society of Applied Magnetics, Japan, Japan Society of Applied Magnetics, April 15, 1997, Vol. 21, No. 4-2, 649-652 (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 33/02

Claims (6)

(57) [Claims] 1. A structure comprising a ferromagnetic material, a first electrode and a second electrode provided at both ends in a longitudinal direction , and a bias coil and a negative feedback coil wound around the ferromagnetic material via an insulator. together first with respectively second two magnetic impedance elements, an oscillation circuit for energizing <br/> the high frequency current to the two magnetic impedance elements, said two magnetic impedance elements Reverse polarity magnet
A circuit for flowing a direct current through the bias coil so that an electric field is applied, and a first electrode and a second electrode which depend on an impedance change of the two magnetic impedance elements caused by an applied external magnetic field. AC voltage of each positive electrode and negative electrode
A detection diode through which a constant DC current flows
A detection circuit for detecting in de, a peak hold circuit for holding a peak value of the output voltage of the detection wave circuit, the first magneto-impedance element of said peak-hold circuit
And the negative output voltage of the second magneto-impedance element.
And an added voltage obtained by adding the pole-side output voltage to the first magnetic input.
The negative output voltage of the impedance element and the second magnetic impedance
The added voltage obtained by adding the positive side output voltage of the dance element and
The four output voltages of the peak hold circuit after differential amplification
And a combining circuit for combining the two . 2. The magnetic impedance element has a ferromagnetic thin-film magnetic core formed on a substrate made of a non-magnetic material, and a first electrode and a second electrode at both ends in the longitudinal direction of the ferromagnetic thin-film magnetic core. 2. The magnetic sensor according to claim 1, wherein electrodes are provided, and a bias coil and a negative feedback coil are wound around the ferromagnetic thin film magnetic core via an insulator. 3. The magneto-impedance element comprises a ferromagnetic amorphous wire having a first electrode and a second electrode provided at both ends in the longitudinal direction thereof, and is provided around the ferromagnetic amorphous wire via an insulator. 2. The magnetic sensor according to claim 1, wherein the magnetic sensor has a structure in which a bias coil and a negative feedback coil are wound. 4. A ferromagnetic material having first and second ends at both ends in the longitudinal direction.
A first electrode and a second electrode are provided, respectively, around the ferromagnetic material.
Around the bias coil and negative feedback coil via an insulator
The first and second two magnetic inputs each having the configuration described above.
High-frequency current is applied to the impedance element and the two magnetic impedance elements
An oscillating circuit for performing the operation, and two magnetic impedance elements having opposite polarities.
DC current is applied to the bias coil so that a field is applied.
Flow circuit and the two magnetic impedances generated by the applied external magnetic field.
First electrode dependent on impedance change of dance element
The AC voltage between the positive electrode and the negative electrode
A detection diode through which a constant DC current flows
A detection circuit for detecting the peak value of the output voltage of the detection circuit.
Circuit and a first magnetic impedance element of the peak hold circuit
And the negative output voltage of the first magneto-impedance element.
A voltage obtained by differentially amplifying the pole side output voltage and the second magnetic input.
The positive output voltage of the impedance element and the second magnetic impedance
The differential output of the negative side output voltage of the dance element and the voltage
Differential amplification and output voltages of the four peak hold circuits
And a combining circuit for combining the two . 5. The magnetic impedance element has a ferromagnetic thin-film magnetic core formed on a substrate made of a non-magnetic material, and a first electrode and a second electrode at both ends in the longitudinal direction of the ferromagnetic thin-film magnetic core. 5. The magnetic sensor according to claim 4, wherein electrodes are provided, and a bias coil and a negative feedback coil are wound around the ferromagnetic thin film magnetic core via an insulator. 6. The magneto-impedance element comprises a ferromagnetic amorphous wire having a first electrode and a second electrode provided at both ends in the longitudinal direction thereof, and an insulator is provided around the ferromagnetic amorphous wire via an insulator. The magnetic sensor according to claim 4, wherein the magnetic sensor has a structure in which a bias coil and a negative feedback coil are wound.