JP2001264361A - Current sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current sensor which uses a magnetic impedance element (MI element) and a low-cost and subminiatured. SOLUTION: The MI element 1 is installed on a conductive substrate 8 for a current to be sensed. A DC bias coil 2 for magnetic-flux cancellation and negative-feedback bias coil 3 are wound on the MI element 1. Both ends of the MI element 1 are connected to the bias coil 3 through sensing circuit 4. The terminating end of the bias coil 3 is connected to one end of an element 5 for output sensing. Its output is sensed across both ends of the element 5 for output sensing. Alternatively, the MI element 1 is installed on the conductive substrate 8 for the current to be sensed. Both ends of the MI element 1 are connected to the bias coil 3, wound on the MI element 1, through an initial offset circuit 7. The terminating end of the bias coil 3 is connected to one end of the element 5 for output sensing. Its output is sensed across both ends of the element 5 for output sensing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor and, more particularly, to a control device for an MI device capable of detecting output over a wide range similarly to a Hall device with high sensitivity.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a magnetic sensor having a small size, a low cost, a high sensitivity and a high speed response. Accordingly, MI that can detect a weak external magnetic field with high sensitivity
Devices are becoming necessary. In addition, demand for high-sensitivity sensors that can be used for nondestructive inspection and banknote inspection has been increasing. Further, there is an increasing demand for a current sensor having high sensitivity and capable of sensing over a wide range of a detected magnetic field as a current sensor for an automobile.

Here, the MI effect will be briefly described. The MI effect is an electromagnetic phenomenon in which when a high-frequency current or a pulse current of several MHz that causes a skin effect on a highly permeable magnetic material is applied, the magnitude of the impedance changes greatly due to an external magnetic field. A highly sensitive MI device utilizing this phenomenon was proposed in 1993 by Professor Mori of Nagoya University. The MI element utilizing the MI effect is an amorphous magnetic wire type shown below.
When a high-frequency current of the order of Hz is applied, not only the amplitude of the induced voltage but also the amplitude between both ends of the wire significantly changes due to the external magnetic field Hex in the wire length direction. This is H
The reason for this is that, in addition to the inductance inside the wire, the ohmic resistance due to the skin effect also changes at the same time.
The use of the zero magnetostrictive or negative magnetostrictive amorphous wire also makes the MI effect remarkable even in a sample having a small size of several tens of μm and a length of 1 to 2 mm, and no coil for excitation or detection is required at all. Further, the MI effect does not require a circuit for canceling the ohmic voltage, so that the sensor configuration can be simplified, and the excitation frequency can be up to several hundred MHz, so that a high-frequency device can be configured.

As a feature, since a change in magnetic flux in the circumferential direction (closed magnetic path) is used due to energization, there is no demagnetizing field due to excitation, not only the head becomes micro-sized, but also no magnetic flux due to excitation is generated outside. No coil is required for excitation and detection, and there is no problem of stray capacitance in high-frequency excitation. It is possible to suppress a characteristic change due to a temperature change of the magnetic wire. Since the detection sensitivity is high, it is expected to be applied to a magnetic head or a high-precision magnetic head for a rotary encoder of an HDD or FDD spindle motor.

[0005] In order to reduce the size and weight of the MI element, an MI element using a thin magnetic thin film has been proposed.
In order to configure a magnetic field sensor with this MI element, since the MI effect is symmetric with respect to the positive and negative of the external magnetic field, it is necessary to make the characteristics asymmetric using a DC bias magnetic field generated by a coil or a permanent magnet. In particular, the magnetic thin film MI element generally has a magnetic field detection sensitivity of 1/3 of that of an amorphous wire.
Since the DC bias magnetic field is generated by the coil current, the power consumption is increased because the current is as low as １ ／. Further, there is a problem that the element becomes large by winding a coil or disposing a permanent magnet. Further, the above-mentioned MI element is improved by using Co
A laminated crossed magnetic anisotropic film MI element in which two soft magnetic thin films such as FeB films are laminated has also been proposed.

[0006] The latter cross-type magnetic thin film MI element is a cross-type magnetic anisotropic film MI element having a magnetic anisotropy that crosses using the easy axis of magnetization of the soft magnetic thin film.
The MI effect that is asymmetric with respect to the sign of the external magnetic field can be obtained. This makes it possible to construct a magnetic field sensor without using a DC bias magnetic field at all. Since a coil for generating a DC bias magnetic field is not required, low power consumption and ultra-miniaturization have become possible. Further, since the magnitude of the magnetic field at which the magnitude of the impedance is maximum is 1/5 of that of the magnetic thin film MI element, it is expected that a sensor with higher sensitivity can be manufactured.

However, although the above-described MI element has high sensitivity, linearity cannot be obtained over a wide range of the detected magnetic field, and thus the control device has to be improved.
FIG. 17 is a block diagram showing a conventional control device 30 for the MI element 31. A bias magnetic field is applied by a DC bias coil 32, amplified by an amplifier 35 through a detection circuit 34, a negative feedback resistor 37, and a wound negative feedback bias coil 33
The output 36 is obtained by applying a negative feedback via. The external magnetic field H _ex [Oe] −the output voltage E _OUT [V] has obtained linearity as shown in FIG.

As described above, in the current sensor, the conventional MI
Even with the element controller 30, linearity could be obtained only in the range of ± 3 [Oe] as shown in FIG. The MI element has high sensitivity but an external magnetic field Hex-
Looking at the MI characteristics such as the impedance change rate [%], the peak of the impedance change rate [%] is ± several [O].
e] and the characteristics are symmetric, so that the bias magnetic field H _b
The output could be detected only in the linear region where the characteristics were shifted and asymmetric as a result of applying. For example, as shown in FIG. 18, a linear region could be obtained only in the range of ± 3 [Oe]. ± 4 [O
e] and ± 5 [Oe], the output was in the saturation region, and the output could not be detected.

The MI element 31 has higher sensitivity than the ball element, but the current sensor using the ball element has an advantage that the current can be detected over a wide range. The mainstream is a current sensor using a. FIG.
FIG. 2 is a simplified view of a conventional current sensor using a ball element. In such a current sensor using a ball element, a method is used in which a magnetic core using a member such as ferrite is used to measure a current flowing in a conductive substrate for a current to be detected. Not only is the cost high, but it is not suitable for downsizing the current sensor.

The applicant of the present invention has proposed that, in a current sensor, the output of a MI element having any MI characteristics is not saturated and a hole can be obtained with high sensitivity by using a new MI element control device. Using a control device of the MI element capable of detecting a magnetic field over a wide range (infinitely) like the element, a small and low-sized device capable of detecting the current flowing through the conductive substrate for the current to be detected similarly to FIG. 19 without using a magnetic core. This makes it possible to provide a cost-effective current sensor.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a current sensor using a control device for an MI element which has solved the above-mentioned problems enables high-sensitivity output detection for any MI element having any characteristic. An object of the present invention is to provide a current sensor using a control device for an MI element capable of linear output detection over a wide range of magnetic field even with an MI element which can be applied only for detecting a magnetic field in a narrow range. It is another object of the present invention to provide a current sensor using a control device that achieves the same effect without requiring a DC bias coil. This allows
An object of the present invention is to provide an ultra-compact and low-cost current sensor that does not use a magnetic core and solve the above-mentioned problem.

[0012]

According to a first aspect of the present invention, in a current sensor, a magnetic impedance is provided on a conductive substrate for a current to be detected.
A dance element (MI element) is provided, a DC bias coil for magnetic flux cancellation and a negative feedback bias coil are wound around the MI element, and both ends of the MI element are connected to the negative feedback bias coil via a detection circuit. 3. The current sensor according to claim 2, wherein the terminal is connected to one end of an output detection element, and an output is detected at both ends of the output detection element. A magnetic impedance element (MI element) is provided on a conductive substrate, and both ends of the MI element are connected to a negative feedback bias coil wound around the MI element via a detection circuit and an initial offset circuit. Is connected to one end of an output detection element, and an output is detected at both ends of the output detection element. In claim 3,
In the current sensor, the conductive substrate for the current to be detected
A negative feedback bias coil wound around the MI element from both ends of the MI element via a detection circuit, and a terminating end of the negative feedback bias coil is connected to one end of an output detection element to detect output. The above-mentioned problem is solved by providing a current sensor characterized in that outputs are detected at both ends of a device.

According to a fourth aspect of the present invention, in the MI element, a voltage across the MI element, which is changed by an external magnetic field, is read by the detection circuit to generate a current, and the current is supplied to the negative feedback bias coil. The problem is solved by providing a current sensor according to any one of claims 1 to 3, wherein a magnetic field is generated to balance the current. According to claim 5, the MI element is configured such that a magnetic field generated by a magnetic field through which a current of the conductive substrate flows through the conductive substrate for the current to be detected coincides with the highest direction of the magnetic field sensitivity of the MI element. The above problem is solved by providing a current sensor according to claims 1 to 4, wherein According to a sixth aspect of the present invention, in the current sensor according to the first or second aspect, the MI element has a symmetric MI characteristic. In the seventh aspect, the MI element has an asymmetric MI characteristic. The problem is solved by providing a current sensor according to claim 3.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an embodiment of the current sensor of the present invention will be described using an MI element using a magnetic thin film, but the same effect can be obtained with any MI element. Each embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a magnetic thin film M according to a first embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of an I element 1. FIG. 2A is a diagram showing MI characteristics of the MI element when an external magnetic field Hex [Oe] is applied from the plus side and when an external magnetic field Hex [Oe] is applied from the minus side. FIG. 2B is a diagram showing MI characteristics of MI elements having different MI characteristics. In FIG. 2b, for the sake of simplicity, the external magnetic field Hex is applied from the plus side.
MI is obtained only by the impedance change rate when [Oe] is applied.
Represents the characteristics. FIG. 3 shows a configuration diagram of the magnetic thin film MI element when the bias magnetic field _Hb is applied. FIG. 4a
6 is a characteristic diagram of the thin-film MI element when a bias magnetic field _Hb is applied. FIG. 4B shows a thin film M when a bias magnetic field _Hb is applied to MI elements having different MI characteristics.
It is a characteristic view of an I element. FIG. 5 is a diagram schematically showing a current sensor to which the control device 10 of the MI element is applied as a first embodiment according to the present invention. 6a and 6b
It is a figure showing an example which modeled an electronic circuit of a current sensor concerning the present invention with a block. FIG. 7A shows an external magnetic field H _ex [Oe] -output voltage E _OUT [V] of a current sensor to which the control device of the MI element 1 is applied as a first embodiment according to the present invention.
6 is a graph showing the relationship of. FIG. 7B shows a detected current value I _ex [A] _-output voltage E of the current sensor to which the control device of the MI element is applied as the first embodiment according to the present invention.
₇ is a graph showing the relationship of _OUT [V].

FIG. 1 shows a thin-film MI element 1, and the substrate is omitted in the figure. The thin-film MI element 1
Al ₂ 0 ₃ ceramic wafer, Si wafer, on a non-magnetic substrate having enhanced surface smoothness such as glass wafer is soft magnetic thin film CoFeNi, a plating film such as NiFe or FeCoSiB,, CoZrNb, FeSiB, CoSi
When a soft magnetic thin film such as an amorphous sputtered film such as B or a NiFe sputtered film is formed, and then heat-treated in a rotating magnetic field or a static magnetic field, the magnetic properties can be improved. Further, a non-magnetic substrate may be used without increasing the surface smoothness.

An electrode made of aluminum wire bonding, Au wire or the like or a lead is directly soldered to both ends of the thin-film MI element 1 for obtaining a skin effect by applying a time-varying current.
Tens [MHz] (10 to 40 [MH]
z]) is applied to both ends. At this time,
FIG. 2A shows the relationship (MI characteristic) between the external magnetic field Hex [Oe] and the impedance change rate (%). In FIG. 3, DC
A bias magnetic field H _b [Oe] is applied to shift the operating point where the maximum sensitivity is obtained by winding the bias coil 2 N times. FIG. 4A shows the MI characteristics at this time. In this case, the DC bias coil 2 wound around the thin-film MI element 1 is coated with insulation or the outer periphery of the coil is coated with insulation, and the negative feedback bias coil 3 is replaced by the same amount as the DC bias coil. It is wound N times. Next, assuming that a current flowing through a conductive substrate (hereinafter referred to as a detected current bar) 8 made of a conductive material such as a copper plate is _Iex , an external magnetic field is generated. Assuming that the external magnetic field is H _ex [Oe], H
_ex [Oe] changes the voltage of the thin-film MI element 1. Read the voltage V has changed by the detection circuit 4 from both ends of the MI element 1 described above, to generate a current to be I _1, a thin film MI
The negative feedback bias coil 3 wound around the element 1 is supplied to the
To generate H ₁ which barrel magnetic field is zero at all times to balance the I _1. The H ₁ via the detection element 5 (resistance R ₁₎ to measure the output. The DC bias coil 2 and the negative feedback bias coil 3 are disclosed in the main part of the MI element 1 in FIG. An example of the electronic circuit at this time is schematically shown in blocks in FIGS. 6A and 6B.

Since the external magnetic field H _ex and the total magnetic field of H ₁ generated by the current I _ex flowing through the detected current bar 8 become zero, the voltage change of the thin film MI element 1 with respect to the external magnetic field H _ex is saturated. Even a magnetic field in the region can be detected linearly. Therefore, conventionally, detection was possible only in a narrow magnetic field range of ± several [Oe] as shown in FIG. 4A. However, as shown in FIG. 7A, a wide range (physically infinite) of the external magnetic field _Hex was detected. The control device 10 of the magnetic field equilibrium type that obtains a linear output over the entirety can be obtained. This makes it possible to obtain the relationship between the output voltage [V] and the detected current value [A] as shown in FIG. 7B. Next, the different MIs shown in FIG.
The control device having the characteristic a and the MI characteristic b and the current sensor using the control device using the MI device were examined. MI of MI element
Since characteristics varied somewhat depending on the device, an experiment was conducted using MI devices having such different characteristics. FIG. 4B is a diagram in which a bias magnetic field H _b [Oe] is applied to each of the MI characteristics a and b in FIG. 2B and shifted. Although not described in detail because it has been described above, both the MI characteristic a shown by a solid line and the MI characteristic b shown by a dotted line have a completely similar (physically infinite) external magnetic field H _ex as shown in FIG. 7A.
Field-balanced control device 10 that obtains a linear output over a
Has been verified. The same applies to FIG. 7b. As described above, it has been verified that the current sensor is a magnetic field balanced type MI element control device that can detect a linear output over a wide range (physical infinity) of current measurement. In configuring the current sensor as shown in FIG. 5, the MI element 1 is arranged so that the magnetic field generated by the current bar 8 to be detected and the external magnetic field having the highest sensitivity of the MI element 1 match. Is preferred. This is because the magnetic field generated by the energizing current becomes an external magnetic field of the MI element 1, and therefore, the sensitivity is better.
Further, in the figure, the MI element 1 is provided above the current bar 8 to be detected, but may be below the current bar 8, and may not necessarily be provided above or below the current bar 8 to detect the magnetic field generated by the current bar 8 to be detected. What is necessary is just to be in the position of the range which can be performed.

Next, as a second embodiment according to the present invention, a current sensor to which a control device for a thin film MI element is applied will be described with reference to the drawings. FIG. 8 is a diagram showing a configuration of a thin-film MI device using the MI effect according to the present invention. FIG. 9a
Is the MI when the external magnetic field Hex [Oe] is applied from the plus side and when the external magnetic field Hex [Oe] is applied from the minus side.
FIG. 3 is a diagram showing MI characteristics of the element. FIG. 9B is a diagram showing MI characteristics c and d of MI elements having different MI characteristics. In FIG. 9B, for simplicity of description, the MI characteristic is expressed only by the impedance change rate when the external magnetic field Hex [Oe] is applied from the plus side. FIG.
A characteristic diagram is shown in which an initial offset circuit 7 causes a current to flow through the negative feedback bias coil 3 in advance and shifts ΔH [Oe] to make the MI characteristic asymmetric. FIG. 10B is a characteristic diagram in which a current is previously passed through the negative feedback bias coil 3 by the initial offset circuit 7 to MI elements having different MI characteristics c and d, and the MI characteristics are asymmetric. FIG. 11 is a diagram schematically showing a current sensor to which the thin-film MI element control device 10 according to the present invention is applied.
12A and 12B are diagrams schematically illustrating an example of an electronic circuit of the current sensor according to the present invention by using blocks. Further, the control device 10 for the MI element 1 according to the present invention
Magnetic field H _ex [Oe] -output voltage E of current sensor applying
_{Since the} graph showing the relationship between _OUT [V] and the relationship between the detected current value I _ex [A] and the output voltage E _OUT [V] is the same as that of the first embodiment, the graphs of FIGS. 7A and 7B are used. I will explain using.

FIG. 11 shows a current sensor to which a control device 10 for a thin-film MI element 1 using an MI element 1 for obtaining a skin effect by applying a time-varying current in a second embodiment according to the present invention. FIG. 2 is a diagram schematically showing the structure of FIG. 1, and more specifically, a principle diagram of current detection by an MI element. FIG. 9a
When using the MI element 1 in which the voltage changes symmetrically with respect to the direction of the magnetic field as shown in FIG. 10A, the current generated by the initial offset circuit 7 is passed through a negative feedback bias coil in advance, and as shown in FIG. The characteristic is shifted by ΔH [Oe] to be asymmetric. The external magnetic field generated by the current I _ex [A] flowing through the detected current bar 18 is represented by H
_ex [Oe], the voltage of the MI element 1 changes according to _Hex [Oe]. Read the voltage V has changed by the detection circuit 4 from both ends of the MI element 1 described above, to generate a current to be I _1, a negative feedback bias coil 3 wound on the MI element 1
Supplied to, bets - to generate H ₁ which barrel magnetic field is zero,
Let I ₁ always be in equilibrium. This I ₁ is used as an output detecting element 5
The output is measured via (resistance R ₁ ). FIGS. 12A and 12B schematically show an example of an electronic circuit at this time by using blocks.

Therefore, conventionally, ± number [O] as shown in FIG.
e] could be detected only in the narrow magnetic field range,
As shown in FIG. 7A, it was possible to obtain the magnetic field balanced control device 10 that obtains a linear output voltage over a wide range of the external magnetic field H _ex [Oe]. As a result, as shown in FIG. 7B, the sensitivity is higher than that of the ball element, such as the detected current value _Iex [A] _-output voltage E _OUT [V]. 2), and a low-cost and ultra-compact current sensor can be obtained by not using a magnetic core. Further, an asymmetric characteristic as shown in FIG. 10A can be obtained without the need for a DC bias coil, and the voltage V changed by the detection circuit 4 from both ends of the thin-film MI element 1 is read only by the negative feedback bias coil 3. I
To generate a current of _1, and supplied to the negative feedback bias coil 3 wound in the thin film MI elements 1, bets - to generate H ₁ which barrel magnetic field becomes zero, the cost since always set to balance the I ₁ It does not reduce the number of steps and does not complicate the process. next,
The control device 10 was verified with MI elements having different MI characteristics c and d shown in FIG. 9B. Although not described in detail because it has been described above, the MI characteristic c shown by a solid line and the M characteristic shown by a dotted line
Initial offset circuit 7 for both I characteristic d
A current is caused to flow through and shift by ΔH [Oe] as shown in FIG. Different MI characteristics c, d
Control device 1 for MI element 1 used for current sensor
The graph showing the relationship between the external magnetic field H _ex [Oe] and the output voltage E _OUT [V] and the relationship between the detected current value I _ex [A] and the output voltage E _OUT [V] are the same as those of the first embodiment. The same was verified. In constituting the current sensor, as shown in FIG. 11, the MI element 1, a magnetic field generated by the applied current I _ex of the current to be detected bar -18, to match the magnetic field direction of the best sensitivity MI element 1 It is more preferable to arrange them. This is because the magnetic field generated by the energizing current is the external magnetic field of the MI element 1, and the sensitivity is further improved. Further, although the MI element 1 is provided above the current bar 18 to be detected in the drawing, it may be provided below, and it is not always necessary to provide it above or below the range where the magnetic field generated by the current bar 18 can be detected. It is sufficient if it is provided in.

Next, a third embodiment according to the present invention will be described with reference to the drawings. FIG. 13 is a diagram showing a configuration of a cross-type magnetic anisotropic thin film MI element 21 according to the present invention, which is stacked so as to cross the direction of magnetic anisotropy of the soft magnetic thin film. FIG.
FIG. 4 is a diagram showing MI characteristics of the cross-type magnetic anisotropic thin-film MI element 21 when an external magnetic field Hex [Oe] is applied from the plus side and when an external magnetic field Hex [Oe] is applied from the minus side. FIG. 14B shows the MI characteristics e and f of the crossed magnetic anisotropic thin film MI elements having different variations. FIG.
4b is an external magnetic field H from the plus side for simplicity of explanation.
FIG. 7 is a diagram showing MI characteristics when ex [Oe] is applied. FIG. 15 is a diagram schematically showing the structure of a current sensor to which the control device 20 for the cross-type magnetic anisotropic thin-film MI element 21 is applied. FIGS. 16A and 16B are diagrams schematically illustrating an example of an electronic circuit of a current sensor to which the control device 20 of the cross-type magnetic anisotropic thin-film MI element 21 according to the present invention is applied. Further, the relationship between the external magnetic field H _ex [Oe] —the output voltage E _OUT [V] of the control device 20 of the cross-type magnetic anisotropic thin film MI element 21 used in the current sensor according to the present invention, and the detected current value I _ex [ Since the graph showing the relationship between A] and the output voltage E _OUT [V] was the same as that of the first embodiment, FIG.
This will be described with reference to FIG.

The thin film MI elements 21 of the structure to cross direction of the magnetic anisotropy of the soft magnetic thin film as shown in FIG. 13, not specifically shown but Al ₂ 0 ₃ ceramic wafer, Si wafer, a substrate such as a glass wafer On top of the soft magnetic thin film C
oFeNi, NiFe, etc. plating film or FeCoS
The films are laminated so that the directions of the magnetic anisotropy of soft magnetic thin films such as amorphous sputtered films such as iB, CoZrNb, FeSiB and CoSiB, and NiFe sputtered films are crossed.

In the cross-type thin-film MI element 21 which obtains a skin effect by applying a time-varying current, since the MI characteristic is asymmetric as shown in FIG. 14A, a DC bias or an initial offset circuit is used. Not only does it have the advantage of not being necessary, but its detection sensitivity is very good. FIG. 15 shows a cross type magnetic anisotropic thin film MI according to the present invention.
FIG. 2 is a diagram schematically showing a structure of a current sensor to which a control device 20 of an element 21 is applied, and more specifically, a principle diagram of current detection by a cross-type magnetic anisotropic thin film MI element 21.

FeCoSiB, CoZrNb, FeSi
B, CoSiB or other amorphous sputtered film, NiFe
Although not shown, the cross-type MI element 21 utilizing the easy axis of the soft magnetic thin film made of a sputtered film or the like is connected to an electrode made of aluminum wire bonding at both ends, an Au wire or the like, or to a lead wire by direct soldering. Connect and dozens [MH
z] or more, and preferably a high-frequency current of 10 to 40 [MHz] is applied to both ends. The external magnetic field Hex [O
FIG. 14A shows the relationship between [e] and the impedance change rate [%]. As shown in FIG. 14A, when using a cross-type magnetically anisotropic thin-film MI element 21 in which the voltage changes asymmetrically with respect to the direction of the magnetic field, the MI characteristics are made asymmetric by a DC bias or an initial offset circuit. No need.

Referring to FIG. 15, the detected current bar
The external magnetic field generated by the current _Iex flowing through
_{Assuming ex} [Oe], the voltage of the cross-type magnetic anisotropic thin-film MI element 21 changes depending on _Hex [Oe]. The voltage V changed by the detection circuit 24 is read from both ends of the MI element 1 to generate a current I ₁ , which is supplied to the negative feedback bias coil 23 wound around the cross-type magnetic anisotropic thin film MI element 21, DOO - to generate H ₁ which barrel magnetic field becomes zero, I ₁
Is always balanced. This I ₁ is used as an output detecting element 25.
It is measured as output via (resistance R ₁ ). The external magnetic field H _ex generated by the current flowing through the detected current bar 28
And H ₁ bets - barrel magnetic fields can be detected linearly in the magnetic field in the region where the voltage change to the magnetic field in the cross-type magnetic anisotropic thin film MI elements 21 is saturated by zero. FIGS. 16A and 16B schematically show an example of an electronic circuit at this time by using blocks.

Accordingly, the magnetic field can be detected only in a narrow magnetic field range of ± several [Oe] as shown in FIG.
the current to be detected bar as shown in a - generated by the current I _ex flowing through the external magnetic field H _ex can be obtained a magnetic equilibrium type control device to obtain a linear output voltage over a wide range of detection magnetic field H _ex current It could be applied as the sensor 20. Also, D
14A can be obtained without the need for the C bias coil and the initial offset circuit, and the detection circuit 24 can be obtained from both ends of the cross-type magnetic anisotropic thin-film MI element 21 using only the negative feedback bias coil 23. To read the voltage V changed, and generate a current that becomes I ₁ ,
Supplying a negative feedback bias coil 23 wound on MI element 21, bets - to generate H ₁ which barrel magnetic field becomes zero, since all times is an equilibrium I ₁ reduces the cost, leading to complicated process Not even. Next, a crossed magnetic anisotropic thin film M having different MI characteristics e and f shown in FIG.
The verification was performed by applying the control device 20 for the I element and the MI element as a current sensor. Although not described in detail because it has been described above, the MI characteristic e shown by a solid line and the MI characteristic f shown by a dotted line are also asymmetrical characteristics. Even in this case, FIG.
As shown in FIG. 7B, the relationship between the external magnetic field H _ex [Oe] and the output voltage E _OUT [V] of the control device 20 of the MI element 21 used for the current sensor and the detected current value I are also obtained for different MI characteristics e and f. _The graph showing the relationship between _ex [A] and output voltage E _OUT [V] shows that a linear output is obtained over a wide range (physically infinite) of the external magnetic field _Hex just like the first embodiment. This is a magnetic field balance type control device. Even when applied to the current sensor 20, the detected current value I _ex [A] _−the output voltage E _OUT [V]
Could be verified to be the same. In configuring the current sensor as shown in FIG.
It is preferable that the direction of the magnetic field generated by the current flowing through the detected current bar 28 and the direction of the magnetic field having the maximum sensitivity of the MI element 21 be aligned. This is because the magnetic field generated by the energizing current becomes an external magnetic field of the MI element 21 and the sensitivity is better. Further, although the MI element 21 is provided above the detected current bar 28 in the drawing, it may be provided below, or may be provided not necessarily above or below the range in which the magnetic field generated by the detected current bar 28 can be detected. It is sufficient if it is provided in. It is self-evident that the coil is used with an insulative coating or the element is insulated and the coil is wound. Although not specifically shown, stabilizing the characteristics by using an initial offset circuit for the cross-type magnetic anisotropic thin-film MI element 21 is also included in the present application. In this case, it is preferable to supply a current in advance by the initial offset and shift the current to the position of the maximum sensitivity.

Therefore, the above-described MI element and its MI characteristics have been verified. However, the MI element control device used in the current sensor according to the present invention always generates a magnetic field that makes the total magnetic field zero, thereby detecting the MI element. Even a magnetic field in a region where the voltage change with respect to the external magnetic field _Hex generated by the current bar is saturated can be detected linearly. This is a current sensor that can obtain linearity over a wide range of detection magnetic fields (physically infinite) as in the case of the ball element with ultra-high sensitivity compared to the ball element, and without applying a bias magnetic field. Can also be achieved. Further, output detection can be performed without being affected by variations in MI characteristics of the MI element.

[0028]

As described above, according to the present invention, a magnetic field in which the total magnetic field is always zero is generated by using the control device of any MI element having any MI characteristics in the current sensor. By maintaining the equilibrium state at all times, linearity can be obtained over a wide range of the detected magnetic field (physically infinite) as in the case of the Hall element with ultra-high sensitivity. Further, similar effects can be achieved without applying a bias magnetic field. Further, since a magnetic core is not used, a current sensor that is ultra-compact and low-cost can be obtained as compared with a current sensor using a ball element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a magnetic thin film MI element using an MI effect in a first embodiment of a current sensor according to the present invention.

FIG. 2A is a view showing MI characteristics when an external magnetic field is applied from the plus side and when an external magnetic field is applied from the minus side to the magnetic thin film MI element in the first embodiment of the current sensor according to the present invention. .

FIG. 2B is a diagram showing MI characteristics when a magnetic thin film MI element having different characteristics in the first embodiment of the current sensor according to the present invention is applied with an external magnetic field from the plus side.

FIG. 3 shows a magnetic thin film M when a bias magnetic field _Hb is applied in the first embodiment of the current sensor according to the present invention.
1 shows a configuration diagram of an I element.

FIG. 4a is a characteristic diagram of the magnetic thin film MI element when a bias magnetic field _Hb is applied to the magnetic thin film MI element in the first embodiment of the current sensor according to the present invention.

FIG. 4b is a characteristic diagram of the magnetic thin film MI element when a bias magnetic field _Hb is applied to the magnetic thin film MI elements having different MI characteristics in the first embodiment of the current sensor according to the present invention.

FIG. 5 is a diagram schematically illustrating a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film is applied as a first embodiment of the current sensor according to the present invention.

FIG. 6a is a block diagram schematically illustrating an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film is applied as a first embodiment of the current sensor according to the present invention; FIG.

FIG. 6b is a block diagram schematically illustrating an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film is applied as a first embodiment of the current sensor according to the present invention. FIG.

FIG. 7a shows an external magnetic field H _ex [Oe] -output voltage E _OUT [V] of the control device of the MI element in the current sensor according to the present invention.
6 is a graph showing the relationship of.

FIG. 7B is a diagram showing a detected current value I _ex [A] _-output voltage E _OUT of the control device for the MI element in the current sensor according to the present invention;
It is a graph which shows the relationship of [V].

FIG. 8 is a diagram showing a configuration of a magnetic thin film MI element using the MI effect in a second embodiment of the current sensor according to the present invention.

FIG. 9a is a diagram showing MI characteristics when a magnetic thin film MI element according to a second embodiment of the present invention is applied with an external magnetic field from the plus side and when an external magnetic field is applied from the minus side.

FIG. 9b is a diagram showing MI characteristics of magnetic thin film MI elements having different characteristics in the second embodiment of the current sensor according to the present invention.

FIG. 10a is a characteristic diagram of the thin film MI element when a bias magnetic field _HΔ is applied to the magnetic thin film MI element in the second embodiment of the current sensor according to the present invention by an initial offset circuit.

FIG. 10b is a characteristic diagram of a thin film MI element according to a second embodiment of the current sensor according to the present invention when a bias magnetic field _HΔ is applied to magnetic thin film MI elements having different MI characteristics at an initial offset. .

FIG. 11 is a diagram schematically showing a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film in a second embodiment of the current sensor according to the present invention is applied.

FIG. 12a is a diagram showing an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film in a second embodiment of the current sensor according to the present invention is applied.

FIG. 12b is a diagram showing an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film in a second embodiment of the current sensor according to the present invention is applied.

FIG. 13 is a diagram showing a configuration of a cross-type magnetic thin film MI element stacked so as to cross the direction of magnetic anisotropy of a soft magnetic thin film in a third embodiment of the current sensor according to the present invention.

FIG. 14A is a diagram showing a third embodiment of the current sensor according to the present invention in which an external magnetic field is applied from the plus side to a cross-type magnetic thin film MI element stacked so as to cross the direction of magnetic anisotropy of a soft magnetic thin film. FIG. 9 is a diagram illustrating MI characteristics when the external magnetic field is applied from the minus side and when an external magnetic field is applied from the minus side.

FIG. 14b is a diagram showing characteristics of a current sensor according to a third embodiment of the present invention when an external magnetic field is applied from the plus side to crossed magnetic thin film MI elements having different MI characteristics.

FIG. 15 schematically illustrates a current sensor to which a control device of a cross-type magnetic thin film MI element which is stacked so as to cross the magnetic anisotropy of a soft magnetic thin film in a third embodiment of the current sensor according to the present invention is applied. FIG.

FIG. 16a is an example of a diagram schematically showing, in a block diagram, an electronic circuit of a current sensor to which a control device for a cross-type magnetic thin film MI element in a third embodiment of the current sensor according to the present invention is applied.

FIG. 16b is an example of a diagram schematically showing a block diagram of an electronic circuit of a current sensor to which a control device for a cross-type magnetic thin film MI element according to a third embodiment of the present invention is applied.

FIG. 17 is a block diagram showing an electronic circuit of a conventional MI element control device.

FIG. 18 shows an external magnetic field H generated by a conventional MI element controller.
FIG. 9 is a diagram showing _ex -output (voltage) E _OUT characteristics.

FIG. 19 is a diagram showing a simplified structure of a current sensor using a conventional ball element.

[Explanation of symbols]

1, 21, 31 ... MI element 2, 32 ... DC biasing coil 3,23,33 ... negative feedback bias coil 4,24,34 ... detection circuit 5,25 ... output detection element (resistor R ₁₎ 6, 26, 36 output 7, initial offset circuit 8, 18, 28 conductive substrate for detected current (detected current bar) 35 amplifier 37 negative feedback resistor 10, 20, 30 control of MI element device H _b ... bias field H _ex ... external magnetic field I ₁ ... negative feedback current (balanced current) I _ex · · · the current to be detected bar - applied current H ₁ ... capital of an external magnetic field of - equilibrium barrel magnetic field is zero Magnetic field (negative feedback magnetic field)

[Procedure amendment]

[Submission date] March 14, 2001 (2001.3.1.
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Detailed description of the invention

[Correction method] Change

[Correction contents]

DETAILED DESCRIPTION OF THE INVENTION

[0012]

According to a first aspect of the present invention, in a current sensor, a magnetic impedance is provided on a conductive substrate for a current to be detected.
A dance element (MI element) is provided, a negative feedback bias coil for magnetic flux cancellation and a DC bias coil are wound around the MI element, and both ends of the MI element are passed through a detection circuit.
3. The current sensor according to claim 2, wherein said negative feedback bias coil is connected, a terminal thereof is connected to one end of an output detection element, and an output is detected at both ends of said output detection element.
In the current sensor, a magnetic impedance element (MI element) is provided on a conductive substrate for a current to be detected.
From both ends of the element, through a detection circuit and an initial offset circuit, connect to a negative feedback bias coil wound around the MI element, connect the end of the negative feedback bias coil to one end of an output detection element, This is a current sensor characterized by detecting an output at both ends of the element. According to a third aspect of the present invention, in the current sensor, the MI element is provided on the conductive substrate for the current to be detected, and both ends of the MI element are connected to a negative feedback bias coil wound around the MI element via a detection circuit. The above-mentioned problem is solved by providing a current sensor characterized in that a terminal of a negative feedback bias coil is connected to one end of an output detection element and an output is detected at both ends of the output detection element.

According to a fourth aspect of the present invention, in the MI element, a voltage across the MI element, which is changed by an external magnetic field, is read by the detection circuit to generate a current, and the current is supplied to the negative feedback bias coil. The problem is solved by providing a current sensor according to any one of claims 1 to 3, wherein a magnetic field is generated to balance the current. According to claim 5, the MI element is configured such that a magnetic field generated by a magnetic field through which a current of the conductive substrate flows through the conductive substrate for the current to be detected coincides with the highest direction of the magnetic field sensitivity of the MI element. The above problem is solved by providing a current sensor according to claims 1 to 4, wherein According to a sixth aspect of the present invention, in the current sensor according to the first or second aspect, the MI element has a symmetric MI characteristic. In the seventh aspect, the MI element has an asymmetric MI characteristic. The problem is solved by providing a current sensor according to claim 3.

[Procedure amendment]

[Submission date] April 25, 2001 (2001.4.2
5)

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Detailed description of the invention

[Correction method] Change

[Correction contents]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current sensor and, more particularly, to a control device for an MI device capable of detecting output over a wide range similarly to a Hall device with high sensitivity.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a magnetic sensor having a small size, a low cost, a high sensitivity and a high speed response. Accordingly, MI that can detect a weak external magnetic field with high sensitivity
Devices are becoming necessary. In addition, demand for high-sensitivity sensors that can be used for nondestructive inspection and banknote inspection has been increasing. Further, there is an increasing demand for a current sensor having high sensitivity and capable of sensing over a wide range of a detected magnetic field as a current sensor for an automobile.

Here, the MI effect will be briefly described. The MI effect is an electromagnetic phenomenon in which when a high-frequency current or a pulse current of several MHz that causes a skin effect on a highly permeable magnetic material is applied, the magnitude of the impedance changes greatly due to an external magnetic field. A highly sensitive MI device utilizing this phenomenon was proposed in 1993 by Professor Mori of Nagoya University. The MI element utilizing the MI effect is an amorphous magnetic wire type shown below.
When a high-frequency current of the order of Hz is applied, not only the amplitude of the induced voltage but also the amplitude between both ends of the wire significantly changes due to the external magnetic field Hex in the wire length direction. This is H
The reason for this is that, in addition to the inductance inside the wire, the ohmic resistance due to the skin effect also changes at the same time.
The use of the zero magnetostrictive or negative magnetostrictive amorphous wire also makes the MI effect remarkable even in a sample having a small size of several tens of μm and a length of 1 to 2 mm, and no coil for excitation or detection is required at all. Further, the MI effect does not require a circuit for canceling the ohmic voltage, so that the sensor configuration can be simplified, and the excitation frequency can be up to several hundred MHz, so that a high-frequency device can be configured.

As a feature, since a change in magnetic flux in the circumferential direction (closed magnetic path) is used due to energization, there is no demagnetizing field due to excitation, not only the head becomes micro-sized, but also no magnetic flux due to excitation is generated outside. No coil is required for excitation and detection, and there is no problem of stray capacitance in high-frequency excitation. It is possible to suppress a characteristic change due to a temperature change of the magnetic wire. Since the detection sensitivity is high, it is expected to be applied to a magnetic head or a high-precision magnetic head for a rotary encoder of an HDD or FDD spindle motor.

[0005] In order to reduce the size and weight of the MI element, an MI element using a thin magnetic thin film has been proposed.
In order to configure a magnetic field sensor with this MI element, since the MI effect is symmetric with respect to the positive and negative of the external magnetic field, it is necessary to make the characteristics asymmetric using a DC bias magnetic field generated by a coil or a permanent magnet. In particular, the magnetic thin film MI element generally has a magnetic field detection sensitivity of 1/3 of that of an amorphous wire.
Since the DC bias magnetic field is generated by the coil current, the power consumption is increased because the current is as low as １ ／. Further, there is a problem that the element becomes large by winding a coil or disposing a permanent magnet. Further, the above-mentioned MI element is improved by using Co
A laminated crossed magnetic anisotropic film MI element in which two soft magnetic thin films such as FeB films are laminated has also been proposed.

[0006] The latter cross-type magnetic thin film MI element is a cross-type magnetic anisotropic film MI element having a magnetic anisotropy that crosses using the easy axis of magnetization of the soft magnetic thin film.
The MI effect that is asymmetric with respect to the sign of the external magnetic field can be obtained. This makes it possible to construct a magnetic field sensor without using a DC bias magnetic field at all. Since a coil for generating a DC bias magnetic field is not required, low power consumption and ultra-miniaturization have become possible. Further, since the magnitude of the magnetic field at which the magnitude of the impedance is maximum is 1/5 of that of the magnetic thin film MI element, it is expected that a sensor with higher sensitivity can be manufactured.

However, although the above-described MI element has high sensitivity, linearity cannot be obtained over a wide range of the detected magnetic field, and thus the control device has to be improved.
FIG. 17 is a block diagram showing a conventional control device 30 for the MI element 31. A bias magnetic field is applied by a DC bias coil 32, amplified by an amplifier 35 through a detection circuit 34, a negative feedback resistor 37, and a wound negative feedback bias coil 33
The output 36 is obtained by applying a negative feedback via. The external magnetic field H _ex [Oe] −the output voltage E _OUT [V] has obtained linearity as shown in FIG.

As described above, in the current sensor, the conventional MI
Even with the element controller 30, linearity could be obtained only in the range of ± 3 [Oe] as shown in FIG. The MI element has high sensitivity but an external magnetic field Hex-
Looking at the MI characteristics such as the impedance change rate [%], the peak of the impedance change rate [%] is ± several [O].
e] and the characteristics are symmetric, so that the bias magnetic field H _b
The output could be detected only in the linear region where the characteristics were shifted and asymmetric as a result of applying. For example, as shown in FIG. 18, a linear region could be obtained only in the range of ± 3 [Oe]. ± 4 [O
e] and ± 5 [Oe], the output was in the saturation region, and the output could not be detected.

The MI element 31 has higher sensitivity than the ball element, but the current sensor using the ball element has an advantage that the current can be detected over a wide range. The mainstream is a current sensor using a. FIG.
FIG. 2 is a simplified view of a conventional current sensor using a ball element. In such a current sensor using a ball element, a method is used in which a magnetic core using a member such as ferrite is used to measure a current flowing in a conductive substrate for a current to be detected. Not only is the cost high, but it is not suitable for downsizing the current sensor.

The applicant of the present invention has proposed that, in a current sensor, the output of a MI element having any MI characteristics is not saturated and a hole can be obtained with high sensitivity by using a new MI element control device. Using a control device of the MI element capable of detecting a magnetic field over a wide range (infinitely) like the element, a small and low-sized device capable of detecting the current flowing through the conductive substrate for the current to be detected similarly to FIG. 19 without using a magnetic core. This makes it possible to provide a cost-effective current sensor.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a current sensor using a control device for an MI element which has solved the above-mentioned problems enables high-sensitivity output detection for any MI element having any characteristic. An object of the present invention is to provide a current sensor using a control device for an MI element capable of linear output detection over a wide range of magnetic field even with an MI element which can be applied only for detecting a magnetic field in a narrow range. It is another object of the present invention to provide a current sensor using a control device that achieves the same effect without requiring a DC bias coil. This allows
An object of the present invention is to provide an ultra-compact and low-cost current sensor that does not use a magnetic core and solve the above-mentioned problem.

[0012]

According to a first aspect of the present invention, in a current sensor, a magnetic impedance is provided on a conductive substrate for a current to be detected.
A dance element (MI element) is provided, a negative feedback bias coil and a DC bias coil for magnetic flux cancellation are wound around the MI element, and both ends of the MI element are connected to the negative feedback bias coil via a detection circuit. 3. The current sensor according to claim 2, wherein the terminal is connected to one end of an output detection element, and an output is detected at both ends of the output detection element. A magnetic impedance element (MI element) is provided on a conductive substrate, and both ends of the MI element are connected to a negative feedback bias coil wound around the MI element via a detection circuit and an initial offset circuit. Is connected to one end of an output detection element, and an output is detected at both ends of the output detection element. In claim 3,
In the current sensor, the conductive substrate for the current to be detected
A negative feedback bias coil wound around the MI element from both ends of the MI element via a detection circuit, and a terminating end of the negative feedback bias coil is connected to one end of an output detection element to detect output. The above-mentioned problem is solved by providing a current sensor characterized in that outputs are detected at both ends of a device.

According to a fourth aspect of the present invention, in the MI element, a voltage across the MI element, which is changed by an external magnetic field, is read by the detection circuit to generate a current, and the current is supplied to the negative feedback bias coil. The problem is solved by providing a current sensor according to any one of claims 1 to 3, wherein a magnetic field is generated to balance the current. According to claim 5, the MI element is configured such that a magnetic field generated by a magnetic field through which a current of the conductive substrate flows through the conductive substrate for the current to be detected coincides with the highest direction of the magnetic field sensitivity of the MI element. The above problem is solved by providing a current sensor according to claims 1 to 4, wherein According to a sixth aspect of the present invention, in the current sensor according to the first or second aspect, the MI element has a symmetric MI characteristic. In the seventh aspect, the MI element has an asymmetric MI characteristic. The problem is solved by providing a current sensor according to claim 3.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an embodiment of the current sensor of the present invention will be described using an MI element using a magnetic thin film, but the same effect can be obtained with any MI element. Each embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a magnetic thin film M according to a first embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of an I element 1. FIG. 2A is a diagram showing MI characteristics of the MI element when an external magnetic field Hex [Oe] is applied from the plus side and when an external magnetic field Hex [Oe] is applied from the minus side. FIG. 2B is a diagram showing MI characteristics of MI elements having different MI characteristics. In FIG. 2b, for the sake of simplicity, the external magnetic field Hex is applied from the plus side.
MI is obtained only by the impedance change rate when [Oe] is applied.
Represents the characteristics. FIG. 3 shows a configuration diagram of the magnetic thin film MI element when the bias magnetic field _Hb is applied. FIG. 4a
6 is a characteristic diagram of the thin-film MI element when a bias magnetic field _Hb is applied. FIG. 4B shows a thin film M when a bias magnetic field _Hb is applied to MI elements having different MI characteristics.
It is a characteristic view of an I element. FIG. 5 is a diagram schematically showing a current sensor to which the control device 10 of the MI element is applied as a first embodiment according to the present invention. 6a and 6b
It is a figure showing an example which modeled an electronic circuit of a current sensor concerning the present invention with a block. FIG. 7A shows an external magnetic field H _ex [Oe] -output voltage E _OUT [V] of a current sensor to which the control device of the MI element 1 is applied as a first embodiment according to the present invention.
6 is a graph showing the relationship of. FIG. 7B shows a detected current value I _ex [A] _-output voltage E of the current sensor to which the control device of the MI element is applied as the first embodiment according to the present invention.
₇ is a graph showing the relationship of _OUT [V].

FIG. 1 shows a thin-film MI element 1, and the substrate is omitted in the figure. The thin-film MI element 1
Al ₂ 0 ₃ ceramic wafer, Si wafer, on a non-magnetic substrate having enhanced surface smoothness such as glass wafer is soft magnetic thin film CoFeNi, a plating film such as NiFe or FeCoSiB,, CoZrNb, FeSiB, CoSi
When a soft magnetic thin film such as an amorphous sputtered film such as B or a NiFe sputtered film is formed, and then heat-treated in a rotating magnetic field or a static magnetic field, the magnetic properties can be improved. Further, a non-magnetic substrate may be used without increasing the surface smoothness.

An electrode made of aluminum wire bonding, Au wire or the like or a lead is directly soldered to both ends of the thin-film MI element 1 for obtaining a skin effect by applying a time-varying current.
Tens [MHz] (10 to 40 [MH]
z]) is applied to both ends. At this time,
FIG. 2A shows the relationship (MI characteristic) between the external magnetic field Hex [Oe] and the impedance change rate (%). In FIG. 3, DC
A bias magnetic field H _b [Oe] is applied to shift the operating point where the maximum sensitivity is obtained by winding the bias coil 2 N times. FIG. 4A shows the MI characteristics at this time. In this case, the DC bias coil 2 wound around the thin-film MI element 1 is coated with insulation or the outer periphery of the coil is coated with insulation, and the negative feedback bias coil 3 is replaced by the same amount as the DC bias coil. It is wound N times. Next, assuming that a current flowing through a conductive substrate (hereinafter referred to as a detected current bar) 8 made of a conductive material such as a copper plate is _Iex , an external magnetic field is generated. Assuming that the external magnetic field is H _ex [Oe], H
_ex [Oe] changes the voltage of the thin-film MI element 1. Read the voltage V has changed by the detection circuit 4 from both ends of the MI element 1 described above, to generate a current to be I _1, a thin film MI
The negative feedback bias coil 3 wound around the element 1 is supplied to the
To generate H ₁ which barrel magnetic field is zero at all times to balance the I _1. The H ₁ via the detection element 5 (resistance R ₁₎ to measure the output. The DC bias coil 2 and the negative feedback bias coil 3 are disclosed in the main part of the MI element 1 in FIG. An example of the electronic circuit at this time is schematically shown in blocks in FIGS. 6A and 6B.

Since the external magnetic field H _ex and the total magnetic field of H ₁ generated by the current I _ex flowing through the detected current bar 8 become zero, the voltage change of the thin film MI element 1 with respect to the external magnetic field H _ex is saturated. Even a magnetic field in the region can be detected linearly. Therefore, conventionally, detection was possible only in a narrow magnetic field range of ± several [Oe] as shown in FIG. 4A. However, as shown in FIG. 7A, a wide range (physically infinite) of the external magnetic field _Hex was detected. The control device 10 of the magnetic field equilibrium type that obtains a linear output over the entirety can be obtained. This makes it possible to obtain the relationship between the output voltage [V] and the detected current value [A] as shown in FIG. 7B. Next, the different MIs shown in FIG.
The control device having the characteristic a and the MI characteristic b and the current sensor using the control device using the MI device were examined. MI of MI element
Since characteristics varied somewhat depending on the device, an experiment was conducted using MI devices having such different characteristics. FIG. 4B is a diagram in which a bias magnetic field H _b [Oe] is applied to each of the MI characteristics a and b in FIG. 2B and shifted. Although not described in detail because it has been described above, both the MI characteristic a shown by a solid line and the MI characteristic b shown by a dotted line have a completely similar (physically infinite) external magnetic field H _ex as shown in FIG. 7A.
Field-balanced control device 10 that obtains a linear output over a
Has been verified. The same applies to FIG. 7b. As described above, it has been verified that the current sensor is a magnetic field balanced type MI element control device that can detect a linear output over a wide range (physical infinity) of current measurement. In configuring the current sensor as shown in FIG. 5, the MI element 1 is arranged so that the magnetic field generated by the current bar 8 to be detected and the external magnetic field having the highest sensitivity of the MI element 1 match. Is preferred. This is because the magnetic field generated by the energizing current becomes an external magnetic field of the MI element 1, and therefore, the sensitivity is better.
Further, in the figure, the MI element 1 is provided above the current bar 8 to be detected, but may be below the current bar 8, and may not necessarily be provided above or below the current bar 8 to detect the magnetic field generated by the current bar 8 to be detected. What is necessary is just to be in the position of the range which can be performed.

Next, as a second embodiment according to the present invention, a current sensor to which a control device for a thin film MI element is applied will be described with reference to the drawings. FIG. 8 is a diagram showing a configuration of a thin-film MI device using the MI effect according to the present invention. FIG. 9a
Is the MI when the external magnetic field Hex [Oe] is applied from the plus side and when the external magnetic field Hex [Oe] is applied from the minus side.
FIG. 3 is a diagram showing MI characteristics of the element. FIG. 9B is a diagram showing MI characteristics c and d of MI elements having different MI characteristics. In FIG. 9B, for simplicity of description, the MI characteristic is expressed only by the impedance change rate when the external magnetic field Hex [Oe] is applied from the plus side. FIG.
A characteristic diagram is shown in which an initial offset circuit 7 causes a current to flow through the negative feedback bias coil 3 in advance and shifts ΔH [Oe] to make the MI characteristic asymmetric. FIG. 10B is a characteristic diagram in which a current is previously passed through the negative feedback bias coil 3 by the initial offset circuit 7 to MI elements having different MI characteristics c and d, and the MI characteristics are asymmetric. FIG. 11 is a diagram schematically showing a current sensor to which the thin-film MI element control device 10 according to the present invention is applied.
12A and 12B are diagrams schematically illustrating an example of an electronic circuit of the current sensor according to the present invention by using blocks. Further, the control device 10 for the MI element 1 according to the present invention
Magnetic field H _ex [Oe] -output voltage E of current sensor applying
_{Since the} graph showing the relationship between _OUT [V] and the relationship between the detected current value I _ex [A] and the output voltage E _OUT [V] is the same as that of the first embodiment, the graphs of FIGS. 7A and 7B are used. I will explain using.

FIG. 11 shows a current sensor to which a control device 10 for a thin-film MI element 1 using an MI element 1 for obtaining a skin effect by applying a time-varying current in a second embodiment according to the present invention. FIG. 2 is a diagram schematically showing the structure of FIG. 1, and more specifically, a principle diagram of current detection by an MI element. FIG. 9a
When using the MI element 1 in which the voltage changes symmetrically with respect to the direction of the magnetic field as shown in FIG. 10A, the current generated by the initial offset circuit 7 is passed through a negative feedback bias coil in advance, and as shown in FIG. The characteristic is shifted by ΔH [Oe] to be asymmetric. The external magnetic field generated by the current I _ex [A] flowing through the detected current bar 18 is represented by H
_ex [Oe], the voltage of the MI element 1 changes according to _Hex [Oe]. Read the voltage V has changed by the detection circuit 4 from both ends of the MI element 1 described above, to generate a current to be I _1, a negative feedback bias coil 3 wound on the MI element 1
Supplied to, bets - to generate H ₁ which barrel magnetic field is zero,
Let I ₁ always be in equilibrium. This I ₁ is used as an output detecting element 5
The output is measured via (resistance R ₁ ). FIGS. 12A and 12B schematically show an example of an electronic circuit at this time by using blocks.

Therefore, conventionally, ± number [O] as shown in FIG.
e] could be detected only in the narrow magnetic field range,
As shown in FIG. 7A, it was possible to obtain the magnetic field balanced control device 10 that obtains a linear output voltage over a wide range of the external magnetic field H _ex [Oe]. As a result, as shown in FIG. 7B, the sensitivity is higher than that of the ball element, such as the detected current value _Iex [A] _-output voltage E _OUT [V]. 2), and a low-cost and ultra-compact current sensor can be obtained by not using a magnetic core. Further, an asymmetric characteristic as shown in FIG. 10A can be obtained without the need for a DC bias coil, and the voltage V changed by the detection circuit 4 from both ends of the thin-film MI element 1 is read only by the negative feedback bias coil 3. I
To generate a current of _1, and supplied to the negative feedback bias coil 3 wound in the thin film MI elements 1, bets - to generate H ₁ which barrel magnetic field becomes zero, the cost since always set to balance the I ₁ It does not reduce the number of steps and does not complicate the process. next,
The control device 10 was verified with MI elements having different MI characteristics c and d shown in FIG. 9B. Although not described in detail because it has been described above, the MI characteristic c shown by a solid line and the M characteristic shown by a dotted line
Initial offset circuit 7 for both I characteristic d
A current is caused to flow through and shift by ΔH [Oe] as shown in FIG. Different MI characteristics c, d
Control device 1 for MI element 1 used for current sensor
The graph showing the relationship between the external magnetic field H _ex [Oe] and the output voltage E _OUT [V] and the relationship between the detected current value I _ex [A] and the output voltage E _OUT [V] are the same as those of the first embodiment. The same was verified. In constituting the current sensor, as shown in FIG. 11, the MI element 1, a magnetic field generated by the applied current I _ex of the current to be detected bar -18, to match the magnetic field direction of the best sensitivity MI element 1 It is more preferable to arrange them. This is because the magnetic field generated by the energizing current is the external magnetic field of the MI element 1, and the sensitivity is further improved. Further, although the MI element 1 is provided above the current bar 18 to be detected in the drawing, it may be provided below, and it is not always necessary to provide it above or below the range where the magnetic field generated by the current bar 18 can be detected. It is sufficient if it is provided in.

Next, a third embodiment according to the present invention will be described with reference to the drawings. FIG. 13 is a diagram showing a configuration of a cross-type magnetic anisotropic thin film MI element 21 according to the present invention, which is stacked so as to cross the direction of magnetic anisotropy of the soft magnetic thin film. FIG.
FIG. 4 is a diagram showing MI characteristics of the cross-type magnetic anisotropic thin-film MI element 21 when an external magnetic field Hex [Oe] is applied from the plus side and when an external magnetic field Hex [Oe] is applied from the minus side. FIG. 14B shows the MI characteristics e and f of the crossed magnetic anisotropic thin film MI elements having different variations. FIG.
4b is an external magnetic field H from the plus side for simplicity of explanation.
FIG. 7 is a diagram showing MI characteristics when ex [Oe] is applied. FIG. 15 is a diagram schematically showing the structure of a current sensor to which the control device 20 for the cross-type magnetic anisotropic thin-film MI element 21 is applied. FIGS. 16A and 16B are diagrams schematically illustrating an example of an electronic circuit of a current sensor to which the control device 20 of the cross-type magnetic anisotropic thin-film MI element 21 according to the present invention is applied. Further, the relationship between the external magnetic field H _ex [Oe] —the output voltage E _OUT [V] of the control device 20 of the cross-type magnetic anisotropic thin film MI element 21 used in the current sensor according to the present invention, and the detected current value I _ex [ Since the graph showing the relationship between A] and the output voltage E _OUT [V] was the same as that of the first embodiment, FIG.
This will be described with reference to FIG.

The thin film MI elements 21 of the structure to cross direction of the magnetic anisotropy of the soft magnetic thin film as shown in FIG. 13, not specifically shown but Al ₂ 0 ₃ ceramic wafer, Si wafer, a substrate such as a glass wafer On top of the soft magnetic thin film C
oFeNi, NiFe, etc. plating film or FeCoS
The films are laminated so that the directions of the magnetic anisotropy of soft magnetic thin films such as amorphous sputtered films such as iB, CoZrNb, FeSiB and CoSiB, and NiFe sputtered films are crossed.

In the cross-type thin-film MI element 21 which obtains a skin effect by applying a time-varying current, since the MI characteristic is asymmetric as shown in FIG. 14A, a DC bias or an initial offset circuit is used. Not only does it have the advantage of not being necessary, but its detection sensitivity is very good. FIG. 15 shows a cross type magnetic anisotropic thin film MI according to the present invention.
FIG. 2 is a diagram schematically showing a structure of a current sensor to which a control device 20 of an element 21 is applied, and more specifically, a principle diagram of current detection by a cross-type magnetic anisotropic thin film MI element 21.

FeCoSiB, CoZrNb, FeSi
B, CoSiB or other amorphous sputtered film, NiFe
Although not shown, the cross-type MI element 21 utilizing the easy axis of the soft magnetic thin film made of a sputtered film or the like is connected to an electrode made of aluminum wire bonding at both ends, an Au wire or the like, or to a lead wire by direct soldering. Connect and dozens [MH
z] or more, and preferably a high-frequency current of 10 to 40 [MHz] is applied to both ends. The external magnetic field Hex [O
FIG. 14A shows the relationship between [e] and the impedance change rate [%]. As shown in FIG. 14A, when using a cross-type magnetically anisotropic thin-film MI element 21 in which the voltage changes asymmetrically with respect to the direction of the magnetic field, the MI characteristics are made asymmetric by a DC bias or an initial offset circuit. No need.

Referring to FIG. 15, the detected current bar
The external magnetic field generated by the current _Iex flowing through
_{Assuming ex} [Oe], the voltage of the cross-type magnetic anisotropic thin-film MI element 21 changes depending on _Hex [Oe]. The voltage V changed by the detection circuit 24 is read from both ends of the MI element 1 to generate a current I ₁ , which is supplied to the negative feedback bias coil 23 wound around the cross-type magnetic anisotropic thin film MI element 21, DOO - to generate H ₁ which barrel magnetic field becomes zero, I ₁
Is always balanced. This I ₁ is used as an output detecting element 25.
It is measured as output via (resistance R ₁ ). The external magnetic field H _ex generated by the current flowing through the detected current bar 28
And H ₁ bets - barrel magnetic fields can be detected linearly in the magnetic field in the region where the voltage change to the magnetic field in the cross-type magnetic anisotropic thin film MI elements 21 is saturated by zero. FIGS. 16A and 16B schematically show an example of an electronic circuit at this time by using blocks.

Accordingly, the magnetic field can be detected only in a narrow magnetic field range of ± several [Oe] as shown in FIG.
the current to be detected bar as shown in a - generated by the current I _ex flowing through the external magnetic field H _ex can be obtained a magnetic equilibrium type control device to obtain a linear output voltage over a wide range of detection magnetic field H _ex current It could be applied as the sensor 20. Also, D
14A can be obtained without the need for the C bias coil and the initial offset circuit, and the detection circuit 24 can be obtained from both ends of the cross-type magnetic anisotropic thin-film MI element 21 using only the negative feedback bias coil 23. To read the voltage V changed, and generate a current that becomes I ₁ ,
Supplying a negative feedback bias coil 23 wound on MI element 21, bets - to generate H ₁ which barrel magnetic field becomes zero, since all times is an equilibrium I ₁ reduces the cost, leading to complicated process Not even. Next, a crossed magnetic anisotropic thin film M having different MI characteristics e and f shown in FIG.
The verification was performed by applying the control device 20 for the I element and the MI element as a current sensor. Although not described in detail because it has been described above, the MI characteristic e shown by a solid line and the MI characteristic f shown by a dotted line are also asymmetrical characteristics. Even in this case, FIG.
As shown in FIG. 7B, the relationship between the external magnetic field H _ex [Oe] and the output voltage E _OUT [V] of the control device 20 of the MI element 21 used for the current sensor and the detected current value I are also obtained for different MI characteristics e and f. _The graph showing the relationship between _ex [A] and output voltage E _OUT [V] shows that a linear output is obtained over a wide range (physically infinite) of the external magnetic field _Hex just like the first embodiment. This is a magnetic field balance type control device. Even when applied to the current sensor 20, the detected current value I _ex [A] _−the output voltage E _OUT [V]
Could be verified to be the same. In configuring the current sensor as shown in FIG.
It is preferable that the direction of the magnetic field generated by the current flowing through the detected current bar 28 and the direction of the magnetic field having the maximum sensitivity of the MI element 21 be aligned. This is because the magnetic field generated by the energizing current becomes an external magnetic field of the MI element 21 and the sensitivity is better. Further, although the MI element 21 is provided above the detected current bar 28 in the drawing, it may be provided below, or may be provided not necessarily above or below the range in which the magnetic field generated by the detected current bar 28 can be detected. It is sufficient if it is provided in. It is self-evident that the coil is used with an insulative coating or the element is insulated and the coil is wound. Although not specifically shown, stabilizing the characteristics by using an initial offset circuit for the cross-type magnetic anisotropic thin-film MI element 21 is also included in the present application. In this case, it is preferable to supply a current in advance by the initial offset and shift the current to the position of the maximum sensitivity.

Therefore, the above-described MI element and its MI characteristics have been verified. However, the MI element control device used in the current sensor according to the present invention always generates a magnetic field that makes the total magnetic field zero, thereby detecting the MI element. Even a magnetic field in a region where the voltage change with respect to the external magnetic field _Hex generated by the current bar is saturated can be detected linearly. This is a current sensor that can obtain linearity over a wide range of detection magnetic fields (physically infinite) as in the case of the ball element with ultra-high sensitivity compared to the ball element, and without applying a bias magnetic field. Can also be achieved. Further, output detection can be performed without being affected by variations in MI characteristics of the MI element.

[0028]

As described above, according to the present invention, a magnetic field in which the total magnetic field is always zero is generated by using the control device of any MI element having any MI characteristics in the current sensor. By maintaining the equilibrium state at all times, linearity can be obtained over a wide range of the detected magnetic field (physically infinite) as in the case of the Hall element with ultra-high sensitivity. Further, similar effects can be achieved without applying a bias magnetic field. Further, since a magnetic core is not used, a current sensor that is ultra-compact and low-cost can be obtained as compared with a current sensor using a ball element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a magnetic thin film MI element using an MI effect in a first embodiment of a current sensor according to the present invention.

FIG. 2A is a view showing MI characteristics when an external magnetic field is applied from the plus side and when an external magnetic field is applied from the minus side to the magnetic thin film MI element in the first embodiment of the current sensor according to the present invention. .

FIG. 2B is a diagram showing MI characteristics when a magnetic thin film MI element having different characteristics in the first embodiment of the current sensor according to the present invention is applied with an external magnetic field from the plus side.

FIG. 3 shows a magnetic thin film M when a bias magnetic field _Hb is applied in the first embodiment of the current sensor according to the present invention.
1 shows a configuration diagram of an I element.

FIG. 4a is a characteristic diagram of the magnetic thin film MI element when a bias magnetic field _Hb is applied to the magnetic thin film MI element in the first embodiment of the current sensor according to the present invention.

FIG. 4b is a characteristic diagram of the magnetic thin film MI element when a bias magnetic field _Hb is applied to the magnetic thin film MI elements having different MI characteristics in the first embodiment of the current sensor according to the present invention.

FIG. 5 is a diagram schematically illustrating a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film is applied as a first embodiment of the current sensor according to the present invention.

FIG. 6a is a block diagram schematically illustrating an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film is applied as a first embodiment of the current sensor according to the present invention; FIG.

FIG. 6b is a block diagram schematically illustrating an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film is applied as a first embodiment of the current sensor according to the present invention. FIG.

FIG. 7a shows an external magnetic field H _ex [Oe] -output voltage E _OUT [V] of the control device of the MI element in the current sensor according to the present invention.
6 is a graph showing the relationship of.

FIG. 7B is a diagram showing a detected current value I _ex [A] _-output voltage E _OUT of the control device for the MI element in the current sensor according to the present invention;
It is a graph which shows the relationship of [V].

FIG. 8 is a diagram showing a configuration of a magnetic thin film MI element using the MI effect in a second embodiment of the current sensor according to the present invention.

FIG. 9a is a diagram showing MI characteristics when a magnetic thin film MI element according to a second embodiment of the present invention is applied with an external magnetic field from the plus side and when an external magnetic field is applied from the minus side.

FIG. 9b is a diagram showing MI characteristics of magnetic thin film MI elements having different characteristics in the second embodiment of the current sensor according to the present invention.

FIG. 10a is a characteristic diagram of the thin film MI element when a bias magnetic field _HΔ is applied to the magnetic thin film MI element in the second embodiment of the current sensor according to the present invention by an initial offset circuit.

FIG. 10b is a characteristic diagram of a thin film MI element according to a second embodiment of the current sensor according to the present invention when a bias magnetic field _HΔ is applied to magnetic thin film MI elements having different MI characteristics at an initial offset. .

FIG. 11 is a diagram schematically showing a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film in a second embodiment of the current sensor according to the present invention is applied.

FIG. 12a is a diagram showing an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film in a second embodiment of the current sensor according to the present invention is applied.

FIG. 12b is a diagram showing an example of an electronic circuit of a current sensor to which a control device for a magnetic thin film MI element using a soft magnetic thin film in a second embodiment of the current sensor according to the present invention is applied.

FIG. 13 is a diagram showing a configuration of a cross-type magnetic thin film MI element stacked so as to cross the direction of magnetic anisotropy of a soft magnetic thin film in a third embodiment of the current sensor according to the present invention.

FIG. 14A is a diagram showing a third embodiment of the current sensor according to the present invention in which an external magnetic field is applied from the plus side to a cross-type magnetic thin film MI element stacked so as to cross the direction of magnetic anisotropy of a soft magnetic thin film. FIG. 9 is a diagram illustrating MI characteristics when the external magnetic field is applied from the minus side and when an external magnetic field is applied from the minus side.

FIG. 14b is a diagram showing characteristics of a current sensor according to a third embodiment of the present invention when an external magnetic field is applied from the plus side to crossed magnetic thin film MI elements having different MI characteristics.

FIG. 15 schematically illustrates a current sensor to which a control device of a cross-type magnetic thin film MI element which is stacked so as to cross the magnetic anisotropy of a soft magnetic thin film in a third embodiment of the current sensor according to the present invention is applied. FIG.

FIG. 16a is an example of a diagram schematically showing, in a block diagram, an electronic circuit of a current sensor to which a control device for a cross-type magnetic thin film MI element in a third embodiment of the current sensor according to the present invention is applied.

FIG. 16b is an example of a diagram schematically showing a block diagram of an electronic circuit of a current sensor to which a control device for a cross-type magnetic thin film MI element according to a third embodiment of the present invention is applied.

FIG. 17 is a block diagram showing an electronic circuit of a conventional MI element control device.

FIG. 18 shows an external magnetic field H by a conventional MI element control device.
FIG. 6 is a diagram showing _ex -output (voltage) E _OUT characteristics.

FIG. 19 is a diagram showing a simplified structure of a current sensor using a conventional ball element.

[Description of Signs] 1, 21, 31, MI element 2, 32, DC bias coil 3, 23, 33 Negative feedback bias coil 4, 24, 34 Detection circuit 5, 25, Output detection element (resistance R ₁ ) 6 , 26, 36, output 7, initial offset circuit 8, 18, 28 conductive substrate for detected current (detected current bar) 35, amplifier 37, negative feedback resistor 10, 20, 30, MI device control device H _b , bias magnetic field H _ex , external magnetic field I ₁ , negative feedback current (balanced current) I _ex , conduction current H ₁ of the detected current bar, balanced magnetic field (negative) where the total magnetic field with the external magnetic field becomes zero Return magnetic field)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaaki Hatsumi 1-3-1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Inside Stanley Electric Co., Ltd. Yokohama Technical Center (72) Inventor Chihiro Funaoka Eda, Aoba-ku, Yokohama-shi, Kanagawa 1-3-1 Nishi, Stanley Electric Co., Ltd. Technical Research Institute (72) Inventor Katsura Tsukada 1-3-1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Stanley Electric Co., Ltd. Technical Research Institute (72) Inventor Hiroyuki Sano Yokohama, Kanagawa Prefecture 1-3-1 Eda Nishi, Aoba-ku, Tokyo Stanley Electric Co., Ltd. (72) Inventor Hiroo Yokoyama 1-3-1 Eda Nishi, Aoba-ku, Aoba-ku, Yokohama-shi, Kanagawa Pref. Stanley Electric Co., Ltd. (72) Inventor Iritono Kimihiro 1-33-1 Edanishi, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Stanley Electric Co., Ltd. Technology Research house F-term (reference) 2G017 AA01 AB07 AC09 AD51 BA01 BA05 2G025 AA16 AB01 AC01

Claims (7)

[Claims] In a current sensor, a magnetic impedance element (MI element) is provided on a conductive substrate for a current to be detected, and a DC bias coil for magnetic flux cancellation and a negative feedback bias coil are wound around the MI element. Then, both ends of the MI element are connected to the negative feedback bias coil via a detection circuit, the terminal of the negative feedback bias coil is connected to one end of an output detection element, and the output is output at both ends of the output detection element. A current sensor characterized by detecting the following. In a current sensor, a magnetic impedance element (MI element) is provided on a conductive substrate for a current to be detected, and both ends of the MI element are connected to the MI element via a detection circuit and an initial offset circuit. A current sensor, wherein the current sensor is connected to a wound negative feedback bias coil, a terminal of the negative feedback bias coil is connected to one end of an output detection element, and an output is detected at both ends of the output detection element. 3. A current sensor, wherein a magnetic impedance element (MI element) is provided on a conductive substrate for a current to be detected, and a negative electrode wound around the MI element from both ends of the MI element via a detection circuit. Connected to the feedback bias coil, the end of the negative feedback bias coil is connected to one end of the output detection element,
A current sensor for detecting an output at both ends of the output detecting element. 4. The MI element reads a voltage across the MI element, which is varied by an external magnetic field, by using the detection circuit to generate a current and supplies the current to the negative feedback bias coil, thereby generating a magnetic field that reduces the total magnetic field to zero. 4. The current sensor according to claim 1, wherein the current is balanced. 5. The MI element is disposed on the conductive substrate for the current to be detected such that a magnetic field generated by a current flowing through the conductive substrate coincides with a magnetic direction with good sensitivity in the MI element. The current sensor according to any one of claims 1 to 4, wherein 6. The current sensor according to claim 1, wherein the MI element has a symmetric MI characteristic. 7. The current sensor according to claim 3, wherein the MI element has an asymmetric MI characteristic.