JP4808411B2 - Magnetic field detection circuit - Google Patents

Description

  The present invention relates to a magnetic field detection circuit using a magnetic impedance effect element.

As an amorphous alloy wire, an amorphous alloy wire having zero magnetostriction or negative magnetostriction has been developed, which has an outer shell portion in which magnetic domains whose spontaneous magnetization directions are opposite to each other in the circumferential direction of the wire are separated by a domain wall. Yes.
The inductance voltage component in the output voltage between both ends of the wire generated when a high frequency current is applied to the zero magnetostrictive or negative magnetostrictive amorphous magnetic wire is easily increased in the circumferential direction by the circumferential magnetic flux generated in the cross section of the wire. It occurs due to the magnetized outer shell being magnetized in the circumferential direction. Accordingly, the circumferential magnetic permeability μθ depends on the circumferential magnetization of the outer shell.
Therefore, when an external magnetic field is applied to the energized amorphous wire, the magnetic flux acting on the outer shell portion having the easily magnetizable property in the circumferential direction is obtained by synthesizing the circumferential magnetic flux and the external magnetic flux by the energization. Is deviated from the circumferential direction and magnetization in the circumferential direction is less likely to occur, the circumferential permeability μθ is changed, and the inductance voltage is changed.
Thus, this fluctuation phenomenon is called a magnetic inductance effect, and an amorphous wire or the like that exhibits this effect is called a magnetic inductance effect element.

Further, when the frequency of the energization current is in the order of MHz, a high-frequency skin effect appears greatly, and the skin depth δ = (2ρ / wμθ) ^1/2 (μθ is the circumferential permeability, as described above, and ρ is (The electrical resistivity, w indicates the angular frequency, respectively) varies with μθ, and this μθ varies with the external magnetic field as described above, so that the resistance voltage component in the output voltage across the wire also varies with the external magnetic field. Become.
Thus, this fluctuation phenomenon is called a magnetoimpedance effect, and an amorphous wire or the like that exhibits this effect is called a magnetoimpedance effect element.

  Therefore, an external magnetic field detection method using the magneto-impedance effect element (see, for example, Patent Document 1) and an external magnetic field detection method using the magnetic inductance effect (see, for example, Patent Document 2) have been proposed.

  In the above, the positive and negative of the external magnetic field causes the circumferential shift φ of the magnetic field to be positive or negative, but the reduction factor cos (± φ) of the circumferential magnetic field does not change. Does not change. Accordingly, the external magnetic field-output characteristics are almost symmetrical with respect to the y axis when the magnetic field is on the x axis and the output is on the y axis. It is also known to be non-linear.

As shown in FIG. 4A, the magnetic field detection circuit using this magneto-impedance effect element basically includes (1) a high-frequency power source 2 ′ for applying a high-frequency excitation current to the magneto-impedance effect element 1 ′, 2) a magneto-impedance effect element 1 ′, (3) a detection circuit 3 ′ that demodulates a modulated wave obtained by modulating the high-frequency excitation current (carrier wave) with an external magnetic field applied to the magneto-impedance effect element 1 ′, and (4) demodulation. It comprises an amplifier 4 'for amplifying a wave and (5) an output display section 8'.
In FIG. 4B, (a) shows a detected magnetic field _Hex applied to the magnetic impedance effect element 1 ′, (b) shows a high-frequency excitation current wave (carrier wave) Ic passed through the magnetic impedance effect element 1 ′, (C) shows the modulated wave as the magnetic impedance effect element output, (D) shows the envelope waveform of the modulated wave, and (E) shows the demodulated wave. (E) in FIG. 4B shows the output V of the amplifier, and the peak value thereof is adjusted so that + Vcc to 0 and −Vcc to 0 are stored with respect to the power supply voltages + Vcc and −Vcc of the amplifier.

The relationship between the amplitude of the detected magnetic field _{Hex and} the amplitude of the output V in FIG. 4-2 can be expressed as shown in FIG. 5A from the left-right symmetry and nonlinearity.
In the circuit of FIG. 4A, it is well known that the characteristic is linearized as shown in FIG. 5B by applying negative feedback with a negative feedback coil 51 ′. In FIG. 5B, Δw is a range in which the gain A without negative feedback is very large and the gain is determined only by the feedback rate β.
Further, in the circuit shown in FIG. 4A, it is also known to apply a bias magnetic field with a biasing coil as indicated by 6 'to obtain a linear characteristic capable of discriminating polarity as shown in FIG. That is, the characteristic of (b) in FIG. 5 is moved in the direction of the arrow by the bias magnetic field as shown in (c) of FIG. 5, and the maximum range −Hmax to + Hmax of the detected magnetic field is within the range of the oblique line region Δw ′. It is also known to adjust the zero point as shown in FIG.
As the (D) Figure 5 illustrates the relationship between the pulse height H _ex and the peak value V of the amplifier output of the object detection field, and has a V = KH _ex.

As is well known, when a current is passed through a conductor, a magnetic field is generated, and when there is a defect such as a flaw, the magnetic field changes within a certain interval b between the defective portions as shown in FIG.
Therefore, when the magnetic field detection elements are arranged at a predetermined interval and the magnetic field sensor that outputs the difference between the outputs of the two magnetic field detection elements is moved along the conductor, the output is 0 except for the defective part. The flaw information output is detected.
In this case, since the magnetic field sensor is movable and the measuring instrument is normally fixed, the measuring instrument is connected to the output end of the magnetic field sensor via a long cable.
2. Description of the Related Art Conventionally, a magnetic field detection circuit that uses two magnetic impedance effect elements, detects the output of each magnetic impedance effect element, and differentially amplifies it with a differential amplifier is known (Patent Document 3).

JP 7-181239 A JP-A-6-283344 JP 2000-193729 A

In this case, [the the detected magnetic field applied to the magnetic chair are impedance effect element and _{H ex1, H ex2, K} given by _(H ex1 _{-H ex2)]} output of the differential amplifier, level output voltage of the differential amplifier Since H is 0, it is _adjusted so that it falls within the range of + Vcc to 0 for H _ex1 > H _{ex2 and −Vcc} to 0 for H _ex1 <H _ex2 .

When connecting a measuring instrument to the output end of this differential amplifier via a long cable as described above, the input impedance of the measuring instrument including the cable viewed from the differential amplifier is low due to a change in the capacity of the cable, If it changes, accurate measurement is difficult.
In addition, when other electronic and electrical equipment is present at the measurement site, it is inevitable that noise emitted from the equipment enters from the long cable, and this noise flows into the negative feedback circuit and the negative feedback is disturbed and stabilized. It is difficult to obtain a straight line.

  The object of the present invention is to provide a differential amplification type magnetic field detection circuit using two magneto-impedance effect elements, even if a measuring instrument is connected to the output end via a long cable, It is an object of the present invention to provide a magnetic field detection circuit that can stably measure and eliminate the influence of capacitance change and externally induced noise.

The magnetic field detection circuit according to claim 1 includes a first magneto-impedance effect element, a second magneto-impedance effect element, a first bias magnetic field coil for applying a bias magnetic field to the first magneto-impedance effect element, and a second magneto-impedance effect element. A second bias magnetic field coil for applying a bias magnetic field to the magnetic field, an excitation current source for supplying an excitation current to each magneto-impedance effect element, and an excitation current for each magneto-impedance effect element by the detected magnetic field applied to each magneto-impedance effect element. A first detection circuit and a second detection circuit for detecting each magneto-impedance effect element output of the modulated waveform, a differential amplification circuit for differentially amplifying outputs v ₁ and v ₂ of each detection circuit, and a differential amplification circuit a positive phase amplifier circuit connected to the output terminal of the detection target field instruments connected to the output terminal of the positive-phase amplifier circuit, an increase of positive phase And a negative feedback circuit for negatively feeding back the output of the circuit to the first magneto-impedance effect element and the second magneto-impedance effect element via the first negative feedback magnetic field coil and the second negative feedback magnetic field coil. And

A magnetic field detection circuit according to a second aspect is the magnetic field detection circuit according to the second aspect, wherein the differential amplifier circuit is a single power source type or a dual power source type, and the output terminal of the differential amplifier circuit for v ₁ = v ₂ of each detector circuit. A positive-phase circuit that has voltage application means (0.5 + k) Vcc or kVcc (where Vcc is the power supply voltage, 0 <k ≦ 1) attached to the differential amplifier circuit, and the output terminal voltage is the input A bias voltage application circuit for canceling the output voltage V ₀ ′ is attached to the negative feedback circuit.

  A magnetic field detection circuit according to a third aspect is the magnetic field detection circuit according to the first or second aspect, wherein a detected magnetic field measuring instrument is connected to the output terminal of the positive phase amplifier circuit via a cable.

  A magnetic field detection circuit according to a fourth aspect is the magnetic field detection circuit according to any one of the first to third aspects, wherein the first magnetic impedance effect element and the second magnetic impedance effect element are shifted by a predetermined distance, and both magnetic impedance effects are obtained. The element is arranged so that the axial directions of the elements coincide with each other.

  A magnetic field detection circuit according to a fifth aspect is the magnetic field detection circuit according to any one of the first to third aspects, wherein the first magnetic impedance effect element and the second magnetic impedance effect element are arranged in parallel at a predetermined interval. It is characterized by.

  A magnetic field detection circuit according to a sixth aspect is the magnetic field detection circuit according to any one of the first to fifth aspects, wherein each magnetic impedance effect element is attached to one surface of each substrate piece, and the magnetic impedance is provided on the other surface of each substrate piece. An iron core that forms a magnetic circuit with the effect element is attached, and a coil for a bias magnetic field and a coil for a negative feedback magnetic field for each magnetic impedance effect element are wound around each iron core.

(1) Since the positive phase amplifier circuit is connected to the output terminal of the differential amplifier circuit, and the input impedance on the output side of the positive phase amplifier circuit is close to 0, the capacity of the long cable connected to the positive phase amplifier circuit Even if the input impedance of the measuring instrument including the cable viewed from the differential amplifier circuit is low or changes due to a change or the like, accurate measurement is possible. Further, a positive phase amplifier circuit is connected to the output terminal of the differential amplifier circuit, and the output of the positive phase amplifier circuit is negatively fed back. The output side of the positive phase amplifier circuit is parallel feedback and the output side impedance is 0. Therefore, even if external inductive noise enters from the long cable connecting the measuring instrument to the output terminal of the positive phase amplifier circuit, it can be well excluded that the noise flows into the negative feedback circuit. Therefore, the amplification gain can be increased and the output characteristics can be linearized stably.
(2) The output V ₀ ′ of the positive phase circuit when the detected magnetic fields applied to both magneto-impedance elements are equal and the differential output is 0 is sufficiently high, and a measuring instrument is connected to the positive phase amplification end. Even if external inductive noise enters from a long cable, the noise below the cut peak value is eliminated by measuring the output of the positive phase amplifier circuit according to the offset due to the voltage V ₀ ′. The detected magnetic field can be measured by the ratio.
(3) Applying a bias voltage to the negative feedback circuit for negatively feeding back the output of the positive phase amplifier circuit to the first magnetic impedance effect element and the second magnetic impedance effect element, and performing negative feedback in a state where the V ₀ ′ is canceled. because over, eliminating the V _{0 'by} prevents current from flowing in the negative feedback circuit, the V ₀ wastefully DC current flows in the negative feedback _circuit' of power to retain the is wasted it can.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1-1 shows an embodiment of a magnetic field detection circuit according to the present invention.
In FIG. 1-1, 1a and 1b are the 1st magnetic impedance effect element and the 2nd magnetic impedance effect element which were arrange | positioned at predetermined intervals, and the direction of spontaneous magnetization is mutually opposite with respect to the wire circumferential direction. An amorphous alloy ribbon or an amorphous alloy sputtered film is used in addition to a zero magnetostrictive or negative magnetostrictive amorphous alloy wire having an outer shell having a structure in which magnetic domains in directions are alternately separated by domain walls. As these magneto-impedance effect elements, transition metals and non-metal alloys having a non-metal composition of 10 to 30 atomic%, especially transition metals and non-metal alloys account for 10 to 30 atomic%. The transition metal is Fe and Co and the nonmetal is B and Si, or the transition metal is Fe and the nonmetal is B and Si. For example, the composition Co _70.5 B ₁₅ can be used. Si ₁₀ Fe _{4.5 having} a length of 2000 μm to 6000 μm and an outer diameter of 30 μm to 50 μmφ can be used.
Reference numeral 2 denotes a power source for applying a high-frequency excitation current to the first magnetic impedance effect element 1a and the second magnetic impedance effect element 1b, and an equal excitation current is applied to these magnetic impedance effect elements 1a and 1b by the power source 2. It is assembled into a bridge circuit so that it can flow. Reference numerals 3a and 3b denote detection circuits connected to the output terminals of the magnetic impedance effect elements 1a and 1b. As shown in FIG. 1-2, an RC smoothing circuit 32 is connected to the output side of the diode 31, and a DC component is further provided. What connected the capacitor | condenser 33 for cutting can be used.

1-1, if the exciting current flowing through each magnetic impedance effect element is Ic and the detected magnetic field applied to each magnetic impedance effect element is _Hex , the output of the magnetic impedance effect element is as shown in FIG. As shown in (c), the exciting current Ic in (b) of FIG. 4-2 becomes a modulated wave modulated by the detected magnetic field _Hex shown in (b) of FIG. 4-2, and this magnetic impedance effect element The output is demodulated by the detection circuit, and a detected magnetic field signal v shown in FIG.

In FIG. 1, reference numeral 4 denotes an operational differential amplifier circuit, and the demodulated detected magnetic field signal is input to both input terminals of the differential amplifier circuit 4. The detected magnetic field signal based on the detected magnetic field H _ex1 applied to the first magnetic impedance effect element is v ₁ , and the detected magnetic field signal based on the detected magnetic field H _ex2 applied to the second magnetic impedance effect element is v _2. And
1-1, reference numeral 40 denotes offset means for setting the output voltage of the differential amplifier circuit 4 to a predetermined voltage V ₀ when the detected magnetic field signal is v ₁ and v ₂ is v ₁ = v ₂ , The power supply voltage Vcc may be used to apply a voltage of kVcc (k ≦ 1) to the voltage reference terminal.
When the differential amplifier circuit 4 is a dual power supply type using a + Vcc power supply and a -Vcc power supply, V ₀ is V ₀ = kVcc, and when the differential amplifier circuit is a single power supply type using only a + Vcc power supply, ₀ = (0.5 + k) Vcc.

Reference numeral 5 denotes a positive phase amplifier circuit connected to the output terminal of the differential amplifier circuit 4, and the gain G is G = 1 + (R ₂ / R ₁ ).
As described above, the output of the differential amplifier circuit 4 when the inputs v ₁ and v ₂ to both input terminals of the differential amplifier circuit 4 are equal is V ₀ , and V ₀ = kVcc or V ₀ = (0.5 + k). ) Vcc. Accordingly, the output of the positive phase amplifier circuit 5 having the voltage V ₀ as an input, that is, the detected magnetic field H _ex1 applied to the first magnetic impedance effect element 1a and the detected magnetic field H _ex2 applied to the second magnetic impedance effect element 1b. The output V ₀ ′ of the positive phase amplifying circuit 5 when the difference with respect to ₀ is V ₀ ′ = kVcc [1+ (R ₂ / R ₁ )] or V ₀ ′ = (0.5 + k) Vcc [1+ (R ₂ / R ₁ )].

Reference numeral 6 denotes a negative feedback circuit for negatively feeding back the output of the positive phase amplifier circuit 5 to the magnetic impedance effect elements 1a and 1b, and a bias voltage application circuit 60 for canceling the voltage V ₀ ′ is inserted. The bias voltage applying circuit 60 can use a voltage follower that inputs a divided voltage k′Vcc of + Vcc to a non-inverting input terminal, and k ′ = k [1+ (R ₂ / R ₁ )] or ( 0.5 + k) [1+ (R ₂ / R ₁ )]. Therefore, when the inputs v ₁ and v ₂ to the both input terminals of the differential amplifier circuit 4 are equal, it is possible to prevent a direct current from flowing through the negative feedback circuit, and it is possible to prevent waste of + Vcc in the offset means.

Reference numerals 7a and 7b denote a first bias magnetic field coil and a second bias magnetic field coil for applying a bias magnetic field to each of the magnetic impedance effect elements 1a and 1b. As shown in FIG. Hex can be detected by detecting the polarity.
A measuring instrument 8 is connected to the output end of the positive phase amplifier circuit 5 via a long flexible cable 9.

The magnetic field detection circuit according to the present invention is mounted on a substrate as a mobile sensor, and can be used by connecting a fixed measuring instrument to the output end of the positive phase amplifier circuit via a long cable.
When the mobile sensor is moved along a path along which the magnetic field changes in the middle as shown in FIG. 6, the magnetic field H _ex1 and the second magnetic field acting on the first magnetic impedance effect element when passing through the magnetic field changing portion. _There is a difference between the magnetic field H _ex2 acting on the magnetic impedance effect element, and the output V of the positive phase amplifier circuit is a value obtained by offsetting ± K | H _ex1 −H _ex2 | by the voltage V ₀ ′, that is, ± K | H _ex1 −H _ex2 | + V ₀ ′.
That is, when H _ex1 > H _ex2 , it is given by K (H _ex1 −H _ex2 ) + V ₀ ′, and when H _ex2 > H _ex1 , it is given by −K (H _ex2 −H _ex1 ) + V ₀ ′. .
Thus, even if external induction noise enters the long cable 9, V ₀ ′ and K are set so that −K (H _ex2 −H _ex1 ) + V ₀ ′ = E becomes a positive and sufficiently large value. If the output of the positive phase amplifier circuit 5 is measured by cutting the voltage E or less with the measuring instrument 8, noise having a peak value below the voltage E can be cut, and the detection accuracy can be increased accordingly.

The external magnetic field noise acting on the magnetic field sensor including each magnetic impedance effect element is input to the differential amplifier circuit with the same value and the same phase, and the internal noise generated in each detector circuit is also the same value to the differential amplifier circuit, Since they are input in phase, the effects of these noises can be eliminated.

  The magnetic field change shown in FIG. 6 is accompanied by disturbance of the magnetic field generated by the current, and causes a change in the magnetic field component perpendicular to the current direction and a change in the magnetic field component in the current direction. On the other hand, the magnetosensitive direction of the magnetic impedance effect element is the axial direction. Accordingly, as shown in FIG. 2A, the first magneto-impedance effect element 1a and the second magneto-impedance effect element 1b are shifted by a predetermined distance, and the axial direction of both the magnetic impedance effect elements 1a and 1b Can be arranged to match. Further, as shown in FIG. 2B, the first magneto-impedance effect element 1a and the second magneto-impedance effect element 1b can be arranged in parallel at a predetermined interval.

The magnetic field detection circuit according to the present invention is not limited to the above embodiment.
Instead of the peak hold circuit in the detection circuit, an RC low-pass filter may be used. The temperature characteristics can be changed by using a capacitor of these peak hold circuit or RC low-pass filter as a temperature compensation capacitor.

For the magneto-impedance effect element, zero magnetostrictive or negative magnetostrictive amorphous wire, amorphous ribbon, amorphous sputtered film or the like can be used. The frequency of the high frequency excitation current is in the order of MHz.
Even in the case of a carrier wave having a frequency lower than this, the carrier wave can be amplitude-modulated by an external magnetic field due to the above-described magnetic inductance effect, and the present invention can also be implemented using a magnetic inductance effect element.

As the high-frequency carrier wave, a normal high-frequency wave such as a continuous sine wave, a pulse wave, or a triangular wave can be used. For example, a normal oscillation circuit such as a Hartley oscillation circuit, a Colpitts oscillation circuit, a collector-tuned oscillation circuit, or a base-tuned oscillation circuit can be used. In addition, a triangular wave generator that integrates a square wave output of a crystal oscillator through an integration circuit through a DC component cut capacitor and amplifies the triangular wave of the integrated output by an amplifier circuit, and a triangular wave generator that uses a CMOS-IC as an oscillation unit are used. be able to.
It is also possible to use a sine wave, a pulse wave, or a triangular burst wave to reduce power consumption.

  In the above embodiment, the excitation current is a carrier wave, the carrier wave is amplitude-modulated by a detected magnetic field, and the modulated wave is demodulated by a detection circuit to extract a detected magnetic field signal. An appropriate detection circuit can be used as long as the detected magnetic field signal amount corresponding to the detected magnetic field can be extracted from the magnetic field detection signal based on the detected magnetic field.

The negative feedback magnetic field coil 5a (5b) and the bias magnetic field coil 6a (6b) can be wound around the magneto-impedance effect element 1a (1b).
Further, as shown in FIG. 3, a negative feedback magnetic field coil and a bias magnetic field coil can be wound around an iron core constituting a magneto-impedance effect element and a loop magnetic circuit.
3A is a side view showing an example of a magnetic impedance effect unit with an iron core, FIG. 3B is a bottom view, and FIG. 3C is a cross-sectional view of FIG. FIG.
In FIG. 3, reference numeral 100 denotes a substrate piece, for example, a ceramic plate can be used. Reference numeral 101 denotes an electrode provided on one side of the substrate piece, and includes a magneto-impedance effect element connecting projection 102. This electrode can be provided by printing and baking a conductive paste, for example, a silver paste. 1x is a magneto-impedance effect element connected between the protrusions 102 and 102 of the electrodes 101 and 101 by soldering or welding, and an amorphous wire, amorphous ribbon, sputtered film, or the like having zero or negative magnetostriction can be used as described above. 103 is a C-type iron core, 5x is a negative feedback coil wound around the C-type iron core, and 6x is a bias magnetic field coil, and the magneto-impedance effect element 1x and the C-type iron core 103 constitute a loop magnetic circuit. Thus, both ends of the C-shaped iron core 103 are fixed to the other surface of the substrate piece 100 with an adhesive or the like. The iron core material may be a magnetic material having a small residual magnetic flux density. Examples thereof include permalloy, ferrite, iron, amorphous magnetic alloy, magnetic powder mixed plastic, and the like.

It is drawing which shows one Example of the magnetic field detection circuit based on this invention. It is drawing which shows an example of the detection circuit in the circuit of FIGS. 1-2. It is drawing which shows the example of different arrangement | positioning of the magneto-impedance effect element in the magnetic field detection circuit which concerns on this invention. It is drawing which shows an example of the magneto-impedance effect element unit used in the magnetic field detection circuit which concerns on this invention. It is drawing which shows the conventional magnetic field detection circuit. It is drawing which shows the waveform in the circuit of FIGS. It is drawing which shows the output characteristic of a magneto-impedance effect element. It is drawing which shows the distribution state of a to-be-detected magnetic field.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a 1st magneto-impedance effect element 1b 2nd magneto-impedance effect element 2 Excitation current source 3a 1st detection circuit 3b 2nd detection circuit 4 Differential amplification circuit 40 Predetermined voltage offset means 5 Positive phase amplification circuit 6 Negative feedback circuit 6a 1st Negative feedback magnetic field coil 6b Second negative feedback magnetic field coil 60 Bias voltage application circuit 7a First bias magnetic field coil 7b Second bias magnetic field coil 8 Measuring instrument 9 Cable

Claims (6)

The first and second magneto-impedance effect elements, the first bias magnetic field coil for applying a bias magnetic field to the first magneto-impedance effect element, and the second bias magnetic field for applying a bias magnetic field to the second magneto-impedance effect element Coil, excitation current source for supplying excitation current to each magneto-impedance effect element, and each magneto-impedance effect element having a waveform in which the excitation current of each magneto-impedance effect element is modulated by a detected magnetic field applied to each magneto-impedance effect element First detection circuit and second detection circuit for detecting output, differential amplification circuit for differentially amplifying outputs v ₁ and v ₂ of each detection circuit, and positive phase amplification connected to the output terminal of the differential amplification circuit circuit and positive-phase connected to the output terminal of the amplifier circuit and the detected magnetic field measuring instrument, first magnetic Inpi the output of the positive-phase amplifier circuit Field detector characterized by comprising a negative feedback circuit for negatively fed back through the Nsu effect element and the second magneto-impedance effect first negative feedback magnetic field coil and the second negative feedback magnetic field coil in the element. When the differential amplifier circuit is a single power supply type or a dual power supply type, the output terminal voltage of the differential amplifier circuit with respect to v ₁ = v ₂ of each detector circuit is (0.5 + k) Vcc or kVcc (where Vcc is the power supply voltage, 0 <k ≦ 1) is applied to the differential amplifier circuit, and a bias voltage application circuit that cancels the output voltage V ₀ ′ of the positive phase circuit that receives the output terminal voltage is added to the negative feedback circuit. The magnetic field detection circuit according to claim 1. 3. The magnetic field detection circuit according to claim 1, wherein a detected magnetic field measuring instrument is connected to the output terminal of the positive phase amplifier circuit via a cable. The first magneto-impedance effect element and the second magneto-impedance effect element are disposed by being shifted by a predetermined distance, and the axial center directions of the both magneto-impedance effect elements are aligned with each other. The magnetic field detection circuit described. 4. The magnetic field detection circuit according to claim 1, wherein the first magnetic impedance effect element and the second magnetic impedance effect element are arranged in parallel at a predetermined interval. Each magneto-impedance effect element is attached to one surface of each substrate piece, and an iron core that forms a magnetic circuit with the magneto-impedance effect element is attached to the other surface of each substrate piece, and each iron core is attached to each magneto-impedance effect element. 6. The magnetic field detection circuit according to claim 1, wherein a bias magnetic field coil and a negative feedback magnetic field coil are wound.

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