JP2003177167A - Magnetic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To heighten the accuracy of a magnetic sensor utilizing a magnetic impedance effect. <P>SOLUTION: This magnetic sensor for detecting an external magnetic field by the magnetic impedance effect is a magnetic sensor capable of detecting a differential voltage vector between a back electromotive force vector generated on the terminal of a magnetic sensor element and a required reference voltage vector, and measuring the external magnetic field and/or the polarity, and the sensor is constituted in a three-terminal or bridge circuit, to thereby improve furthermore the accuracy. Especially, the magnetic sensor has such a characteristic that, assuming that a vector locus of the back electromotive force generated by the change of the external magnetic field is drawn on a complex plane, and that the starting point of the reference voltage vector is placed on the origin of the complex plane, the end point thereof is in a circle when the circle having a radius of curvature on the vector locus is arranged on a required position. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor capable of measuring a low magnetic field below a geomagnetic level, and more particularly to a magnetic sensor.
^{The present invention} relates to a magnetic sensor utilizing a magnetic impedance effect capable of measuring an external magnetic field of ⁻⁴ to 10 ⁻¹⁰ T with high accuracy.

[0002]

2. Description of the Related Art Heretofore, a magnetic sensor has been known which detects the magnitude of an external magnetic field as a change in impedance by passing a high-frequency current that causes a skin effect in a magnetic body. For example, the magnetic sensor described in Japanese Patent Application Laid-Open No. 7-181239 utilizes that the counter electromotive voltage with respect to the time change of the circumferential magnetic flux generated by flowing a high frequency current in the magnetic wire varies depending on the externally applied magnetic field. The sensor is based on the magnetic impedance effect. In addition, JP-A-200
In JP-A 1-276664, two magnetic sensor elements each having a magnetic film formed in a strip shape are connected to a three-terminal bridge circuit, and a three-terminal bridge is provided while applying a reverse biasing magnetic field to each magnetic sensor element. A method for detecting changes in the midpoint potential of a circuit is described. 12A and 12B are a top view and a sectional view of the magnetic sensor. The operation of this sensor will be briefly described.

In FIG. 12 (a), a magnetic sensor 90 comprises magnetic detection cores 92 and 93 formed on a substrate 91 and an insulated spiral coil 99. The magnetic detection cores 92 and 93 are three-terminal bridge circuits which are composed of strip-shaped magnetic films and whose adjacent ends are connected by output electrodes 96. When a bias voltage is applied between the bias electrodes 97 and 98, the magnetic detection cores 92 and 93 are biased by the DC magnetic fields H _bias in mutually opposite directions as shown in FIG. When a high frequency voltage source is applied between the drive voltage applying electrode 94 and the ground electrode 95, a voltage corresponding to the component of the external magnetic field H _ext that coincides with the longitudinal direction of the magnetic detection core is applied between the terminals of the magnetic detection cores 92 and 93. Occurs. Since the voltage variation due to H _ext between the terminals of each magnetic detection core has an opposite phase relationship, the voltage obtained from the output electrode 96 is double that of the case where it is used alone, thus increasing the detection sensitivity.

[0004]

By the way, the conventional magnetic sensor is not sufficiently sensitive for measuring a low magnetic field. In recent years, magnetic field detection in a living body, which has rapidly increased needs, requires high resolution of 10 ⁻⁸ T order or higher. Although the above-mentioned Japanese Patent Laid-Open No. 2001-27664 describes that an output of about 10 ⁻⁶ T per mV is obtained, the required performance cannot be satisfied with such a sensor sensitivity.

On the other hand, in order to improve the sensitivity of the magnetic sensor, "1
0 there is a ^-10 T stage high frequency carrier type thin film magnetic field sensor having a magnetic field detection decomposition ability of "(Institute of Electrical Engineers magnetic Tech Research Group materials MAG-00-133 1-6P) papers such as. This document describes a method of narrowing the sensor element width while maintaining the uniaxial anisotropy of the sensor element while forming the magnetic film in multiple layers. Further, all of the above-mentioned documents are methods for converting the impedance change of the magnetic sensor element into a voltage change. However, the above-described sensor detection method of capturing an impedance change with respect to the external magnetic field as a voltage variation, the thermal noise of the sensor itself, the resolution by the gain versus frequency characteristics of the amplifier is limited, ^10-8
It has been difficult to obtain a resolution exceeding T order.

On the other hand, as an example in which the change in the amplitude of the sensor output voltage is not used as the detection amount, the method disclosed in Japanese Patent Application Laid-Open No. 8-320362 uses a single sensor element to detect the impedance fluctuation as a phase change. Is. This magnetic sensor element has a laminated structure including a conductor layer formed on a substrate and a magnetic layer provided around the conductor layer. The easy axis of magnetization is set in the direction orthogonal to the current flowing through the sensor element, and the resistance change of the sensor element reduces the impedance change of the magnetic sensor element due to the external magnetic field as phase fluctuation even in the drive frequency range that is two orders of magnitude lower than the conventional element. It states that it can be detected. The frequency of the driving voltage is reduced to 0.1 to 10 MHz, and it is considered that the manufacturing tolerance increases as the driving frequency decreases.

Further, it is described that the sensitivity of this magnetic sensor element is 27 mV / 10 ⁻⁴ T without an amplifier, which is a sensitivity corresponding to about 10 ⁻⁵ T. This sensitivity is almost the same as the above-mentioned output voltage amplification method, and the target sensitivity is not obtained even by this method. In addition, referring to FIGS. 18 and 21 of the publication, data indicating a dead zone in which the phase and the inductance do not change with respect to the magnetic field is described in the low magnetic field region where the detected magnetic field is 10 ⁻³ T (10 Oe) or less. However, this method is clearly unsuitable for measurement of 10 ⁻⁸ T or less.

[0008]

To achieve high sensitivity of a magnetic sensor, (1) a method of increasing the sensor output by realizing high sensitivity of the sensor element itself, and (2) There is a method of improving the weak output of the signal by signal processing or resolution on the detection circuit side, but the present invention is considered to belong to the latter. Further, it can be applied to a general magnetic sensor regardless of the structure of the magnetic sensor element, and has high sensitivity and excellent characteristics.

In the external magnetic field measurement by the conventional magnetic sensor, the impedance change is detected as a change ΔV in the output voltage of a single magnetic sensor element or a three-terminal bridge circuit, and made to correspond to the external magnetic field. That is, this is a method in which the magnetic sensor used up to now uses the voltage amplitude value of the sensor output as the detection amount. Due to the characteristics of the sensor, ΔV is generally very small, so a considerable amount of amplifier processing is required, and the magnetic sensor that utilizes the magnetic impedance effect is 1
Since it operates with a high-frequency signal of about 00 MHz or more, use of an expensive amplifier and advanced design technology were indispensable to obtain stable operation. For this reason, in the external magnetic field measurement using the conventional method, the operating range or sensitivity is theoretically limited, and it has been difficult to overcome this limit value. However, the present invention is a method in which the conventional limiting requirements are basically not entered. Hereinafter, the solving means of the present invention will be described in detail. Although an example of a magnetic sensor using a magnetic film is shown in the drawings or the description, the present invention can be implemented without any change even when using a magnetic wire of a soft magnetic material,
The same effect is obtained.

FIG. 1 shows the principle of the present invention. In this figure, the vector locus of the back electromotive force e of the magnetic sensor element is drawn on the complex plane, and the parameter is the magnitude of the external magnetic field H. As shown in FIG. 2A, a high frequency power supply 23 is connected to a series circuit of a resistance 50Ω and a magnetic sensor element 21, and while applying an external magnetic field H in the longitudinal direction of the magnetic sensor element 21, a reverse generated in the magnetic sensor element 21 occurs. The vector of the electromotive voltage E is measured. The starting point of the reverse voltage vector is selected as the origin, and the locus of the ending point of the vector is shown.

The magnetic sensor 21 has a resistance R and a reactance X.
Can be treated as an equivalent circuit connected in series, and changes with respect to the external magnetic field H as shown in FIGS. 2B and 2C. The figure shows the case of 100 and 500 MHz. The higher the frequency of the high-frequency power supply 23, the larger the changes of R and X with respect to H, and the higher frequency is more convenient in view of the S / N of the sensor. However, since the frequency is close to GHz, the influence of stray capacitance etc. Is large, and the configuration of a high-frequency signal processing circuit becomes difficult. Therefore, 100 MHz is considered to be suitable for practical use, and thereafter, the explanation will be focused on the case of 100 MHz.

Before referring to the principles of the invention, the minimum conditions that a magnetic sensor has will be described first. Since the high frequency current flowing through the magnetic sensor element is 100 MHz, it is necessary to select the magnetic sensor element near the characteristic impedance of 50Ω in consideration of impedance matching. Therefore, the structure, size, etc. of the magnetic sensor element may be manufactured and adjusted so as to satisfy this regulation. Figure 2 (a)
Then, in order to satisfy this condition, the series resistance is selected to be 50Ω. Incidentally, the magnetic sensor 21 is Co-Nd-Zr.
3 mm long, 50 μm wide, and 3 μm thick. A ferromagnetic film such as permalloy is suitable as the material of the magnetic film, but if it is a ferromagnetic material that can obtain the skin effect, it does not hinder the practice of the present invention.

FIG. 1 schematically shows the positional relationship among the vector loci A-B-C, the back electromotive force vector E and the reference voltage vector E ₀ . First, the vector locus A-B-
C is a figure obtained when the external magnetic field H is changed from 0 to ∞, and the points plotted on the curve are the external magnetic field H = 0, 1.5 × 10 ⁻⁴ T (1.5 Oe) and 3 × 10, respectively.
^-4 T (3 Oe), 4.5 x 10 ^-4 T (4.5 O
e), 6x10 ^-4 T (6Oe), 15x10 ^-4 T
It is the end point position of the back electromotive force vector E with respect to (15 Oe) and ∞. The bias magnetic field is 3 × 10 ⁻⁴ T. As shown, the vector locus A-B-C has H = 0.
And H = ∞ form a substantially closed curve, and a flat elliptical shape is formed. H of R and X shown in FIGS. 2 (b) and 2 (c)
As is clear from the change situation with respect to, considering that R and X change with the same tendency with respect to H, have one peak value, and saturate at H = ∞ and return to the initial value almost, It is understood that it becomes flat and elliptical. Further, even if the external magnetic field H is reversed, R and X have axial symmetry, so that the vector locus has the same result as in FIG.

The point B on the locus curve corresponds to the peak values of R and X. At this time, H is a physical property constant indicated by the anisotropic magnetic field H _k of the magnetic film, which is a value naturally determined by the material used, and H at the point B in FIG. 1 is 6 × 10 ⁻⁴ T. The present invention will be described for the low magnetic field region from point A to point B, but in principle it can be applied to the high magnetic field region, and any point or range from point B to point C can be set as the operating range. However, it is necessary to solve the binary problem when the operating range is from A to C.

Now, one of the important points in the present invention is how to determine the reference voltage vector E ₀ . In FIG. 1, after the midpoint M of the line segment connecting the points A and B is obtained, a straight line drawn from the origin O toward the point M is the reference voltage vector E ₀ . The amount changed by the external magnetic field is the difference voltage vector ΔE obtained by vector-wise subtracting E ₀ from E ₀ as shown in the figure. For example, when H changes from H = 0 to H = 6 × 10 ⁻⁴ T, ΔE changes by nearly 180 degrees and the direction is reversed. The phase changes by nearly 180 degrees with a change of 6 × 10 ⁻⁴ T. However, according to the method disclosed in Japanese Unexamined Patent Publication No. 8-320362, since the deviation angle φ of the counter electromotive voltage E shown in FIG. 1 is detected, only a phase change of about 20 to 30 degrees can be obtained on the drawing.

As can be understood from the above description, the point of the present invention is how to take the reference voltage vector E ₀ . Although FIG. 1 shows an example in which the point M is provided at the midpoint between the minimum and maximum values of the external magnetic field or on the perpendicular line passing through the midpoint, it should be determined in consideration of the shape of the reverse voltage vector locus of the magnetic sensor element. In this case, not only can the measurement range, accuracy, etc. be improved, but also the way to apply the magnetic sensor of the present invention to a peculiar application is opened up. Some typical ways of taking the reference voltage vector E ₀ are shown in FIG.

First, the reference voltage vector E₀₁If outside
For covering a relatively narrow range of the partial magnetic field H near zero
And M₁The point was located close to H = 0 and in front. Be
Calculate the radius of curvature on the cuttle locus and₁Decide
It is possible to use Then E₀₂Is H_kTarget the neighborhood
This is the case. The previous examples are from inside the trajectory curve
However, in the present invention, as shown in the figure,
M outside the trajectory curve_TwoEven if you put points, it is the same as the previous example
The effect of the invention can be obtained. Furthermore, E ₀₃so
Is the end point M of the vector_ThreeIs set on the locus curve,
It Like this_{0 Three}The operating principle,
As can be seen, the differential voltage vector ΔE is M _ThreeTo
External magnetic field (1.5 x 10 here)^-4Outside on T)
The magnetic field is in the direction of decreasing magnetic field, but M_ThreeExceeds
Facing the increasing direction of the external magnetic field, which means the reversal of ΔE
It That is, a magnetic switch or relay with a threshold set or
Can be applied to the polarity judgment of the external magnetic field.

What should be emphasized here is that the phase of the reference voltage vector has only a function of inverting the phase with respect to the output, and is not an essential problem. For example,
The problem is whether to output a large positive voltage when the external magnetic field to be measured is large, or to make it negative when the magnetic field is low. The same applies to the case of analog output, and the polarity of the output voltage or zero can be selected depending on the magnitude of the measured magnetic field. Further, it is clear from the measurement principle of the present application that the soft magnetic material used for the magnetic sensor element has only to obtain the magnetic impedance effect and is not related to the magnitude of the effect. In addition, a thin film or a linear shape can be used as the form of the detecting portion of the magnetic sensor element, but the thin film method is preferably more advantageous in size reduction or manufacturing.

(Operation) According to the present invention, since only the change of the magnetic impedance with respect to the change of the external magnetic field can be magnified and detected, it can be used not only as a highly sensitive sensor, but also for detecting a slight change of the magnetic field. It can be applied as a relay that performs on-off operation. Furthermore, the sensor can be integrated by using a magnetic thin film or the like. In addition to this, the present invention identifies the position of a metal buried object in the ground from the distribution of magnetism on the surface of the earth, detects and tracks the mixing or movement of a magnetic body (iron or iron alloy), and fixes a plurality of objects fixed on the human body. It can be considered to be applied to a method of knowing the movement of a person or muscle from the fluctuation of the magnetic field due to individual permanent magnet pieces or the like.

The magnetic sensor of the present invention has a magnetic sensor element having a magnetic film or a magnetic wire made of a soft magnetic material and a bias coil, and is supplied with a high-frequency current to the outside to generate a skin effect on the magnetic sensor element. A magnetic sensor for detecting a magnetic field is characterized by detecting a differential voltage vector between a counter electromotive voltage vector generated between the magnetic sensor element terminals and a required reference voltage vector to measure an external magnetic field and / or a polarity. . In this magnetic sensor, a vector locus of the back electromotive force generated by a change in an external magnetic field is drawn on a complex plane, and when the origin of the reference plane is the starting point of the complex plane, the end point has a radius of curvature on the vector locus. It is characterized by being inside the circle when the circle is placed at the required position. Further, the end point of the reference voltage vector is in a circle including a part or all of the vector locus.

Another magnetic sensor of the present invention has a magnetic sensor element having a magnetic film or a magnetic wire made of a soft magnetic material and a bias coil, and has a high-frequency current to the extent that a skin effect is produced in the magnetic sensor element. In a magnetic sensor for detecting an external magnetic field through a magnetic sensor element, a differential voltage vector between a counter electromotive voltage vector generated between the magnetic sensor element terminals and a required reference voltage vector is detected to measure the external magnetic field and / or the polarity. The end point of the reference voltage vector is set on the vector locus of the counter electromotive voltage.

In any one of the above-mentioned configurations of the present invention, the magnetic sensor element is connected to at least one side of a three-terminal or a bridge circuit, and is provided with phase detection means for inputting an output voltage and the reference voltage. To do. The output voltage can be the output voltage of the three terminals having the magnetic sensor element or the output voltage of the bridge circuit including the magnetic sensor element.

Another magnetic sensor of the present invention has a magnetic sensor element having a magnetic film or magnetic wire made of a soft magnetic material and a bias coil, and supplies a current to the magnetic sensor element to the extent that a skin effect is produced. In a magnetic sensor having a high-frequency power supply and a processing circuit for processing the output of the magnetic sensor element, the magnetic sensor element is connected alone or as at least one side of three terminals or a bridge, and a differential voltage between a sensor output voltage vector and a reference voltage vector. It is characterized by detecting a vector and measuring an external magnetic field of 10 ⁻⁴ to 10 ⁻¹⁰ T. Further, the external magnetic field is 0 to 50
It is desirable to include frequency components up to about kHz.

Another magnetic sensor of the present invention is a magnetic sensor for detecting an external magnetic field using a magnetic sensor element, wherein a phase difference between a counter electromotive force vector generated between the magnetic sensor element terminals and a required reference voltage vector is determined. It is characterized by sensing and measuring the external magnetic field and / or the polarity. Further, it is preferable that the magnetic sensor element is connected to at least one side of a three-terminal or bridge circuit, and is provided with a phase detection unit that receives the output voltage of the three-terminal or bridge circuit and the reference voltage as inputs.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments based on the principle of the present invention described above will be described in detail, but the present invention is not limited to these embodiments. From this point onward, the numbers in the reference drawings are parts having the same function, and the same numbers are used.
FIG. 4 is a circuit diagram showing the basic configuration of the magnetic sensor according to the present invention. As shown in the figure, the magnetic sensor comprises a detection unit 20 for detecting an external magnetic field and a reference voltage generation circuit 40, and the respective outputs are input to the phase comparison circuit 47. Further, the output of the phase comparison circuit 47 is input to a processing circuit 49 for converting it into an analog output or a digital output as required.

Characteristic points of the embodiment shown in FIG. 4 are as follows: (1) The output of the detecting section 20 is a differential voltage.
(2) The reference voltage generation circuit 40 includes the attenuator 43 and the phase shifter 45, and the high frequency power supply 23 ′ is completely synchronized with the high frequency power supply 23 on the detection side by the synchronization circuit 41.
(3) The output of the processing circuit 45 is not only analog but also A /
It is also possible to obtain a digital output without using a D converter.

In the present invention, since the phase difference between the reference voltage vector and the back electromotive force vector of the sensor is detected, it is possible to eliminate the non-linear portion in the small signal region due to the rectification circuit (detection circuit) which has been conventionally required. Therefore, it is possible to detect the magnetic field with high sensitivity while simplifying the circuit because it is not necessary to consider the circuit such as inserting the correction circuit. Particularly, in the conventional method of directly rectifying the high frequency voltage, the pulsating voltage of the fundamental wave component of the carrier frequency is large, and it is very difficult to obtain a high S / N due to the processing of minute signals. However, the present invention only needs to amplify the sensor output to the extent that the circuit processing can be performed, and in principle, the accuracy does not decrease due to the amplitude value. Therefore, since there is no portion where a small signal is likely to be mixed with noise, stable measurement can be performed. Normally, in order to amplify linearly at high frequency,
Although high-level electronic circuit technology is required, since the high frequency amplification in the present invention focuses on the phase, it can be easily implemented without paying particular attention to the linearity of the circuit and the element.
Moreover, since the amplified signal has a large amplitude, noise is less mixed.

Next, the detection resolution of the magnetic field to be measured in the present invention will be described. Factors that determine the detection limit are thermal noise of the magnetic film forming the magnetic sensor element, thermal noise of the amplifier, noise current propagating from the DC power source of the bias coil, noise of the high frequency oscillator, and the like. However, since the detection signal is differentially output in a high frequency range, the influence of the above noise can be sufficiently reduced. Further, the noise of the bias coil power source can be reduced to a negligible level because a DC current with a sufficiently attenuated AC component can be obtained by using a carefully set low-pass filter or the like. Further, noise components due to the high frequency oscillator are differentially calculated by the detection unit 20, so most of the errors are canceled out, and the influence thereof is minimized.

On the other hand, the noise generated by the amplifier can be reduced without any problems because an inexpensive and high-performance integrated circuit can be used with the recent remarkable progress of semiconductors for communication equipment and satellite broadcasting. The measurement limit is 10 ⁻¹⁰ T / Hz ^1/2 , which is limited by thermal noise as the resistance of the magnetic sensor element. This value means a resolution of 10 ^-10 T per Hz,
The resolution decreases as the frequency band becomes wider. Furthermore, as shown in FIG. 4, since the magnetic field component is not a voltage amplitude but a phase change as a detection signal, it is natural that it can be converted into an analog signal voltage, but it is possible to directly obtain a digital signal as a signal output along the time axis. Is also possible.

As an example, a method of generating a digital signal will be described. The reference voltage and the detection voltage from the magnetic sensor element are amplified and input to the waveform shaping circuit, shaped into a rectangular wave, and then the exclusive OR is calculated. As the output of the exclusive OR, a pulse train having a pulse width proportional to the phase difference between both inputs is obtained. By gating the clock pulse with this pulse train, the number of clock pulses proportional to the pulse width, that is, the phase difference can be obtained. An analog voltage can be directly converted into a digital value by counting the number of pulses with a counter. Since it is not common to count pulses with a frequency higher than the frequency applied to the sensor, a common local oscillator output is usually used for both the high frequency signal voltage and the comparison signal. A frequency converter is used to convert to a lower frequency to improve accuracy. The above waveform example is shown in FIG.
1 (a). An example of a method for obtaining an analog voltage is shown in FIG. After waveform shaping of the reference voltage and the detection voltage, the exclusive OR is taken. By smoothing this waveform, 0 V with a phase difference of 0 degrees and a power supply voltage (5 V) with a phase difference of 180 degrees can be obtained.

FIG. 5 is a conceptual plan view showing the configuration of the magnetic sensor in the second embodiment and a conceptual diagram showing the connection with the accessory parts. The magnetic sensor elements 21-1 and 21-2 are 3-terminal bridge-coupled as shown in the figure and connected to the secondary coil of the transformer 19. Since the middle point of the secondary coil of the transformer 19 is grounded, high-frequency currents having phases different by 180 degrees flow. Further, the magnetic sensor elements 21-1 and 2
Since 1-2 is arranged on the bias coil 13 via the insulating sheets 15-1 and 15-2, a bias magnetic field is applied in the longitudinal direction of the magnetic sensor. In this example,
The reference voltage is a voltage in phase with the voltage applied to the magnetic sensor element 21-2.

The third embodiment shown in FIG. 6A is a case where the generation of the reference voltage vector is realized by a simple method. The magnetic sensor element 21 is inserted in the bridge-side left series circuit to obtain an output from the middle point, and the right side is connected with a series circuit of a resistor and a capacitor. A reference voltage of phase and magnitude is obtained.

Even in the voltage amplitude differential output of the conventional method, the relationship between the external magnetic field and the voltage output exhibits a V-shaped characteristic as shown in FIG. 6B. When a low magnetic field close to the origin is detected, an error is likely to be mixed because the detected voltage is very small, and accurate measurement is considerably difficult. On the other hand, since the present invention focuses on the phase change, it is possible to perform detection with constant accuracy regardless of the magnitude of the amplitude of the detection voltage. FIG. 6C shows the relationship between the external magnetic field and the phase difference. This data is 3x10
^The circuit constants are collectively shown in FIG. 6D, which were measured by using the circuit of FIG. 6A with a bias magnetic field of ⁻⁴ T applied. It can be seen from the characteristic curves (1) to (3) in the figure that the phase changes by nearly 180 degrees with a slight change in the external magnetic field.
The characteristic curves of are when the gain is changed. This is equivalent to adjusting the midpoint potential of FIG.
The point M in Fig. 1 will be moved. Therefore, it is obvious that a larger sensitivity can be obtained by setting the M point closer to the P point (H = 3Oe (3 × 10 ⁻⁴ T)). It should be noted that the curve is a case where a point near the origin of FIG. 6B is folded back, and an infinite gain when passing through the origin,
That is, a switching operation can be obtained.

A practical circuit is shown in FIGS. First,
In the embodiment shown in FIG. 7, the magnetic sensor elements 21-1 and 21-2 shown in FIG. 5 in which electrodes are provided on a substrate and a strip-shaped magnetic film are connected to a three-terminal bridge circuit to measure an external magnetic field. Is. This is a method of applying a high frequency voltage of opposite phase to each of the magnetic sensor elements 21-1 and 21-2 and detecting the phase of the midpoint voltage of the three-terminal bridge circuit. So-called
Although a bridge structure with a transformer is used, the above-described transformer structure is not necessarily used as long as a high frequency voltage having an opposite phase can be obtained.

In this embodiment, two magnetic sensor elements 2 are used.
In 1-1 and 21-2, a voltage proportional to the external magnetic field H coinciding with the longitudinal direction is obtained from the middle point of the three-terminal bridge circuit. When the voltages applied to the magnetic sensors are in phase, the impedance of the magnetic sensors on the upper and lower sides changes simultaneously with the strength of the external magnetic field, so the midpoint potential does not fluctuate, and as a result, the voltage changes commensurate with the external magnetic field. I can't get it. Further, by obtaining the differential output of the two magnetic sensor elements 21-1 and 21-2, the output per unit magnetic flux density change can be doubled, and the noise included in the high frequency oscillator has a negative phase. , The S / N ratio is improved and the resolution is improved. Therefore, if a sensor is installed at the measurement location, such as when measuring the difference in magnetic field between two points, the differential voltage of each magnetic sensor output can be obtained, and the magnetic field difference and change amount of the external magnetic field can be easily known. be able to.

FIG. 8 shows a bridge using two resistors and a magnetic sensor element, which is a method of using a transformer for inputting to a one-input amplifier. Since a general-purpose IC can be used in this configuration, the cost of the configuration circuit can be reduced.

FIG. 9 shows a circuit configuration when a differential amplifier having two input terminals is used. The transformer used in FIGS. 7 and 8 can be omitted, and the cost can be reduced because an expensive transformer is not used.

FIG. 10 shows an example in which one magnetic sensor element 21 is used. The relationship between the magnetic sensor element 21 and its load resistance, that is, the relationship between the magnetic sensor element having a reactor component and the load of a pure resistance component. The phase change caused by this is detected as the voltage between the pure resistors in series with the parallel circuit of the pure resistor and the capacitor, and is input to the differential amplifier.

[0039]

According to the structure of the present invention, a weak output from the sensor element can be improved and a highly sensitive magnetic sensor can be obtained. At the same time, the measurement range can be greatly expanded, so it can be applied to various applications.

[Brief description of drawings]

FIG. 1 is a principle diagram for explaining the present invention.

FIG. 2 is a characteristic diagram of a magnetic sensor with respect to an external magnetic field.

FIG. 3 is an example of setting a reference voltage vector.

FIG. 4 is a basic conceptual diagram of the present invention.

FIG. 5 is a plan view of the magnetic sensor element according to the first embodiment of the present invention.

FIG. 6 is a circuit diagram and characteristics showing a second embodiment of the present invention.

FIG. 7 is a circuit configuration diagram showing a third embodiment of the present invention.

FIG. 8 is a circuit configuration diagram showing a fourth embodiment of the present invention.

FIG. 9 is a circuit configuration diagram showing a fifth embodiment of the present invention.

FIG. 10 is a circuit configuration diagram showing a sixth embodiment of the present invention.

FIG. 11 is an example of a voltage waveform of each part.

FIG. 12 is a configuration diagram of a conventional magnetic sensor.

[Explanation of symbols]

11: substrate, 13: bias coil, 14: electrode, 1
5: Insulation sheet, 16: Midpoint electrode, 17: Amplifier, 1
9: transformer, 20: detector, 21: magnetic sensor element,
23: high frequency power supply, 25: amplifier, 40: reference voltage generation circuit, 41: tuning circuit, 43: phase comparison circuit, 45: processing circuit, 47: attenuator, 49: phase shifter, 90: magnetic sensor, 91: Substrate, 92, 93: Magnetic detection core, 94:
Drive voltage applying electrode, 95: ground electrode, 96: output electrode,
97 and 98: bias electrodes, 99: spiral coil.

Claims (9)

[Claims] 1. A magnetic sensor having a magnetic film or a magnetic wire made of a soft magnetic material and a bias coil, for detecting an external magnetic field through a high-frequency current that causes a skin effect on the magnetic sensor element. In the sensor, the external magnetic field and / or the polarity is measured by detecting a differential voltage vector between a counter electromotive voltage vector generated between the magnetic sensor element terminals and a required reference voltage vector. 2. The vector locus of the back electromotive force generated by a change of an external magnetic field according to claim 1, drawn on a complex plane, and when the reference voltage vector has an origin of the complex plane as a starting point, an end point is on the vector locus. A magnetic sensor characterized by being within a circle when a circle having a radius of curvature of is arranged at a required position. 3. The magnetic sensor according to claim 2, wherein the end point of the reference voltage vector is within a circle including a part or all of the vector locus. 4. The magnetic sensor according to claim 1, wherein an end point of the reference voltage vector is set on a vector locus of the counter electromotive voltage. 5. The magnetic sensor element according to any one of claims 1 to 4, wherein the magnetic sensor element is connected as at least one side of a three-terminal or a bridge circuit, and is provided with a phase detection means for inputting an output voltage and the reference voltage. And a magnetic sensor. 6. A magnetic sensor element comprising a magnetic film or a magnetic wire made of a soft magnetic material and a bias coil, a high frequency power source for supplying a current to the magnetic sensor element to the extent that a skin effect is produced, and the magnetic sensor. In a magnetic sensor having a processing circuit for the output of a sensor element, the magnetic sensor element is connected alone or as at least one side of a three terminal or a bridge, and a difference voltage vector between a sensor output voltage vector and a reference voltage vector is detected to detect 10 A magnetic sensor which measures an external magnetic field of ^-4 to 10 ^-10 T. 7. The magnetic sensor according to claim 6, wherein the external magnetic field includes a frequency component of about 0 to 50 kHz. 8. A magnetic sensor for detecting an external magnetic field using a magnetic sensor element, which detects a phase difference between a counter electromotive voltage vector generated between the magnetic sensor element terminals and a required reference voltage vector to detect an external magnetic field and A magnetic sensor characterized by measuring polarity. 9. The magnetic sensor element according to claim 8, further comprising phase detection means connected to at least one side of the three-terminal or bridge circuit, and receiving the output voltage of the three-terminal or bridge circuit and the reference voltage as input. Magnetic sensor characterized by.