JP3639727B2 - Magnetic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic sensor, and more particularly to a high-sensitivity magnetic sensor using a thin film magneto-impedance element.
[0002]
[Prior art]
With the recent rapid development of information equipment and measurement / control equipment, there is an increasing demand for small, low-cost, high-sensitivity, high-speed response magnetic sensors. For example, hard disk drives for computer external storage devices have been improved in performance from bulk-type induction magnetic heads to thin film magnetic heads and magnetoresistive effect (MR) heads. As the number of magnetic poles of the magnet ring increases, a magnetic sensor capable of detecting a weak surface magnetic flux with high sensitivity is required in place of a conventionally used magnetoresistive effect (MR) sensor. There is also a growing demand for high-sensitivity magnetic sensors that can be used for nondestructive inspection and banknote inspection. In addition, there is a growing demand for compact and lightweight automobile orientation sensors, high-definition color televisions, and sensors for active magnetic shields in display tubes of personal computers.
[0003]
Typical magnetic detection elements currently used include an inductive reproducing magnetic head, a magnetoresistive effect (MR) element, a fluxgate sensor, and a Hall element. Recently, a high-sensitivity magnetic sensor using the magneto-impedance effect of an amorphous wire has been proposed (see JP-A-6-176930, JP-A-7-181239, JP-A-7-333305), A high-sensitivity magnetic sensor using the magnetic impedance effect of a magnetic thin film has also been proposed (see Japanese Patent Application Laid-Open No. 8-75835, Journal of Applied Magnetics Society of Japan, vol. 20, 553 (1996)).
[0004]
The induction type reproducing magnetic head requires a coil winding, so that the magnetic head itself becomes large, and if the size is reduced, the relative speed between the magnetic head and the medium is lowered, and the detection sensitivity is remarkably lowered. On the other hand, a magnetoresistive effect (MR) element using a ferromagnetic film has been used. The MR element detects not the time change of the magnetic flux but the magnetic flux itself, and the miniaturization of the magnetic head has been promoted. However, the current MR element has a change rate of about 2%, and even an MR element using a spin valve element has a small change rate of an electric resistance of 6% or less and a resistance change of several%. The external magnetic field required to obtain the value is as large as 1600 A / m or more. Therefore, the magnetoresistive sensitivity is a low sensitivity of 0.001% / (A / m) or less. Recently, a giant magnetoresistance effect (GMR) using an artificial lattice having a magnetoresistance change rate of several tens of percent has been found. However, in order to obtain a resistance change of several tens of percent, an external magnetic field of tens of thousands of A / m is required, and it has not been put into practical use as a magnetic sensor.
[0005]
A fluxgate sensor, which is a conventional high-sensitivity magnetic sensor, measures magnetism by utilizing the fact that the symmetric BH characteristics of a high-permeability magnetic core such as Permalloy are changed by an external magnetic field. High directivity of 1 °. However, in order to increase the detection sensitivity, a large magnetic core with a small demagnetizing field is required, and it is difficult to reduce the overall size of the sensor, and the power consumption is large.
[0006]
A magnetic field sensor using a Hall element utilizes a phenomenon in which, when a magnetic field is applied perpendicularly to the plane of current flow, an electric field is generated in a direction perpendicular to both the current and applied magnetic fields, and an electromotive force is induced in the Hall element. It is a sensor. Although the Hall element is advantageous in terms of cost, it has low magnetic field detection sensitivity, and since it is composed of a semiconductor such as Si or GaAs, electrons or holes are scattered by scattering due to thermal oscillation of the lattice in the semiconductor against temperature changes. Has the disadvantage that the temperature characteristics of the magnetic field sensitivity are poor.
[0007]
As described in JP-A-6-176930, JP-A-7-181239, and JP-A-7-333305, a magneto-impedance element has been proposed to achieve a significant improvement in magnetic field sensitivity. The basic principle of this magneto-impedance element is to detect only the voltage against the time change of the circumferential magnetic flux using the skin effect generated by applying a current that changes rapidly with time to the magnetic wire as a change due to the externally applied magnetic field. It is a magnetic impedance element. FIG. 22 shows an example of the magneto-impedance element. As this magnetic wire, an amorphous wire (wire subjected to tension annealing after drawing) having a diameter of about 30 μm with zero magnetostriction such as (FeCoSiB) is used, and FIG. 23 shows the applied magnetic field dependence of the impedance change of the wire. It is. Even if a wire with a minute dimension of about 1 mm in length is applied with a high frequency current of about 1 MHz, the amplitude of the voltage of the wire changes with a high sensitivity of about 0.1% / (A / m), which is 100 times or more that of the MR element.
[0008]
[Problems to be solved by the invention]
As a magnetic sensor, there is a demand for a high-sensitivity magnetic sensor that is small, low-cost, excellent in output linearity with respect to the detected magnetic field, and excellent in temperature characteristics. A magnetic sensor that uses the magneto-impedance effect of amorphous wire is a highly sensitive magnetic field. The detection characteristics are shown. In addition, in the ones disclosed in Japanese Patent Laid-Open Nos. 6-176930 and 6-347490, the linearity of the applied magnetic field dependency of the impedance change is improved by applying a bias magnetic field, and the amorphous wire is negatively affected. It has been shown that a magnetic sensor having excellent linearity can be provided by winding a feedback coil and applying a current proportional to the voltage across the amorphous wire to the coil to provide negative feedback.
[0009]
However, Japanese Patent Application Laid-Open No. 6-176930 does not mention a drive circuit including an oscillation circuit and a detection circuit, and Japanese Patent Application Laid-Open No. 6-347490 discloses a multivibrator using a pair of switching transistors as an oscillation circuit and a low-pass circuit. Suggests a combination of filters. In addition, IEEJ Transactions E vol. 116-E P435 (1996), 20th Annual Meeting of the Japan Society of Applied Magnetics, 20pB-2 (1996), has proposed an oscillation circuit based on pulse oscillation using a C-MOS multivibrator to reduce power consumption. . By the way, in these pulse oscillation systems, since the magneto-impedance element is an inductance component, a resistor and a differential circuit are formed, and the high-frequency current actually supplied to the magnetic impedance is generated by the transistor and the C-MOS multivibrator. It becomes a differential waveform of the pulse wave and has a higher frequency than the pulse wave. Since the frequency of the differential waveform is determined by the resistance component and the inductance component of the magneto-impedance element, it is difficult to set an appropriate frequency at which the magnetic impedance of the magneto-impedance element exhibits the greatest change rate.
[0010]
In addition, when a circuit that generates a high-frequency current is directly connected to a magnetic impedance element, the impedance of the magnetic impedance element is small, so that the amplitude becomes extremely small and a change in magnetic-impedance cannot be sufficiently extracted. Furthermore, the detection of the amplitude by the pulse wave is unstable because the ripple is generated in the conventional method shown in the IEEJ Transaction E. In Japanese Patent Laid-Open No. 8-75835, a magnetic impedance element using a magnetic thin film has been proposed to reduce the size of the element, but a multivibrator using a switching transistor as an oscillation circuit is used. -It is difficult to maximize the impedance change.
[0011]
The present invention has been made in view of the above circumstances, and is to provide a high-sensitivity magnetic sensor that is small in size and low in cost, excellent in output linearity with respect to a detection magnetic field, and excellent in temperature characteristics, and a driving circuit thereof. .
[0012]
[Means for Solving the Problems]
In order to achieve the object of the present invention as described above, in the invention according to claim 1 of the present application, the bias coil is wound around the magnetic core formed on the non-magnetic substrate via the insulator. In a magnetic sensor using a thin-film magneto-impedance element, an oscillation circuit that applies a high-frequency sine wave current to both ends of the magnetic core, and the oscillation circuit provided between the oscillation circuit and the magnetic core of the thin-film magneto-impedance element A buffer circuit that adjusts the mismatch between the output impedance of the thin film magneto-impedance element and the input impedance of the thin-film magneto-impedance element, and the amount of change in the external magnetic field is detected from the amount of change in the high-frequency current that changes in response to the external magnetic field A magnetic sensor comprising a detection circuit.
In the invention according to claim 2 of the present application, in the invention according to claim 1, the magnetic core formed on the non-magnetic substrate is formed of a ferromagnetic thin film. I will provide a.
In the invention according to claim 3 of the present application, in the invention according to claim 1, the magnetic core formed on the non-magnetic substrate is formed of a ferromagnetic amorphous wire. I will provide a.
The invention according to claim 4 of the present application provides the magnetic sensor according to the invention according to claim 1, wherein the oscillation circuit is a sine wave oscillation circuit including a band-pass filter not including an inductance element.
The invention according to claim 5 of the present application provides the magnetic sensor according to claim 1, wherein the oscillation circuit is configured by a Wien bridge circuit. According to a sixth aspect of the present invention, there is provided a magnetic sensor according to the first aspect of the present invention, wherein the buffer circuit includes a temperature-compensation circuit and includes a push-pull circuit having an impedance conversion function. provide.
The invention according to claim 7 of the present application provides the magnetic sensor according to claim 1, wherein the detection circuit includes a rectifier circuit and a low-pass filter.
The invention according to claim 8 of the present application provides the magnetic sensor according to claim 7, wherein the low-pass filter is a low-pass filter not including an inductance component.
The invention according to claim 9 of the present application provides the magnetic sensor according to claim 7, wherein the detection circuit is constituted by a differential circuit.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a front view schematically showing the structure of a thin film magneto-impedance (MI) element used in an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AB in FIG. FIG. 3 is a cross-sectional view taken along line CD in FIG. The actual thin film MI sensor as a whole is formed on a plate-like body such as a thin film ceramic plate or glass plate, but this is omitted in FIG. 1, 2, and 3, reference numeral 1 denotes an MI sensor plate that is a thin-film magnetic core formed in a thin plate shape having a rectangular planar shape. The thin film magnetic core as the MI sensor plate has a width of 20 μm, a thickness of 5 μm, and a length of 500 μm. A bias coil 4 and a negative feedback coil 5 are wound around the MI sensor plate 1 alternately in the same direction via insulator layers 2 and 3. Although not shown correctly in the figure, each of these coils has 20 turns. Bias and negative feedback coils are wound around a thin film magnetic core alternately on the same surface, so that a bias magnetic field and a negative feedback magnetic field can be evenly applied to each part of the magnetic core. Linearity is improved. Bias coil terminals 6 and 7 are connected to both ends of the bias coil 4, and negative feedback coil terminals 8 and 9 are connected to both ends of the negative feedback coil 5. MI sensor terminals 10 and 11 are connected to both ends of the MI sensor plate 1. These terminals are made of an Au metal thin film and an aluminum metal thin film, and the wide portion at the tip serves as a pad for external wiring. Reference numeral 12 denotes an insulating protective film that covers the entire MI sensor.
[0014]
FIG. 4 shows sensor end electrodes E (E = Z * I) when a magnetic field (Hex) of 0 and 2400 A / m is applied to the thin film magnetic sensor when the thin film magnetic core is made of NiFe plating. It is a current-carrying current frequency characteristic. The difference ΔE in E when Hex = 0 and Hex = 2400 A / m was the maximum near the frequency of the conduction current of 20 MHz. FIG. 5 shows the applied magnetic field (Hex) dependence of the rate of change in impedance when the energizing current frequency is 20 MHz. As the applied magnetic field is increased, the impedance change rate ΔZ / Z0 is increased, ΔZ / Z0 is maximized at the anisotropic magnetic field Hk of the element, and ΔZ / Z0 is decreased when Hex> Hk. Further, the amount of change in the impedance per unit applied magnetic field (magnetic field sensitivity) was maximum around Hex = 1600 A / m, and showed a magnetic field sensitivity of 0.08% / (A / m).
[0015]
FIG. 6 is a block diagram showing a circuit configuration of the magnetic sensor of the present invention. The magnetic sensor includes an oscillation circuit 21, a buffer circuit 23 for impedance matching between the thin film magnetic impedance element 22 and the oscillation circuit 21, a magnetic impedance element 22 having a negative feedback coil 24 and a bias coil 25, a rectifier circuit 26 and a smoothing circuit. It comprises a detection circuit 29 having a low-pass filter 27 and a differential circuit 28 for differential detection, an amplifier circuit 30, and a negative feedback resistor 31.
[0016]
FIG. 7 is a detailed circuit diagram of the oscillation circuit 21 for supplying a high-frequency sine wave current to the thin film magneto-impedance element 22. The oscillation circuit 21 has an oscillation unit 34 by C-MOS oscillation in which an oscillator 32 made of a crystal oscillator or a ceramic oscillator is connected between input and output terminals of a C-MOS circuit 33. Since the oscillation frequency of the oscillation circuit 21 is determined by the frequency of the oscillator 32, the frequency stability is high and a low consumption type oscillation circuit 21 can be obtained. The oscillation output of the oscillating unit 34 is passed through a band pass filter 35 made of a ceramic filter. The waveform of the signal Vc output from the oscillating unit 34 is a rectangular wave as shown in FIG. 8. By passing this through the band-pass filter 35, a sine wave Vf as shown in FIG. 8 is obtained. Then, the oscillation circuit 21 can be set to a frequency at which the magneto-impedance effect can be maximized. The bandpass filter 35 can be used as an LC filter, but in order to eliminate a minute magnetic field (influence of a magnetic field generated from an L (inductance) component) on the magnetic impedance, an inductanceless ceramic filter was used.
[0017]
FIG. 9 is a circuit diagram when the output oscillated by the C-MOS oscillating unit is directly applied to the thin film magneto-impedance element. Although this circuit is different from the circuit shown in the 20th Annual Meeting of the Japan Society of Applied Magnetics 20pB-2 (1996) in C-MOS oscillation mode (RC oscillation), a pulse wave Vc as shown in FIG. 10 is generated. The disadvantage of high-frequency energization when a pulse wave is applied to the thin film magneto-impedance element is that, as shown in FIG. Therefore, as shown in FIG. 10, the pulse wave Vc becomes a differential waveform Vm, and the high-frequency energization frequency shifts to a high region. Taking the frequency characteristics of the thin film magneto-impedance element shown in FIG. 11 as an example, the frequency at which the magneto-impedance characteristic is maximum for this element is 20 MHz (50 ns). This frequency pulse is applied to the thin film magneto-impedance element to conduct high frequency energization. The high-frequency energized pulse wave applied to the thin film magneto-impedance element is output as a differential waveform as shown in FIG. 10, and the frequency shifts to 200 MHz (5 ns). From the graph of FIG. 11, it can be seen that the magneto-impedance change rate at 200 MHz by the thin film magnetic impedance sensor hardly changes. In the present invention, as a solution to this problem, as in the oscillation circuit shown in FIG. 7, the oscillated high-frequency pulse wave is passed through a band-pass filter to eliminate high-frequency components and create a sine wave. Has been proposed to be applied to a thin film magneto-impedance element.
[0018]
FIG. 12 is a circuit diagram showing a Wien bridge oscillation circuit. The Wien bridge oscillation circuit is a sine wave oscillation circuit. When this circuit is used in the oscillation circuit 21 shown in FIG. 6, it is not necessary to add a filter as in the case of using a C-MOS oscillation circuit.
[0019]
FIG. 13 shows details of the buffer circuit 23. The buffer circuit 23 is a circuit that supplies the high-frequency signal oscillated by the oscillation circuit 21 to the thin film magneto-impedance element 22 without loss. For example, in a thin film magnetic impedance element, the impedance at 20 MHz is 5Ω. When R10 in FIG. 13 is 10Ω, the total impedance is 15Ω. When this is connected to the oscillation circuit 21 without a buffer circuit, the load on the oscillation circuit 21 is heavy, so that the voltage output to the thin film magnetic impedance element 22 becomes several tens of mVp-p, and the detection unit of the detection circuit 29 shown in FIG. In the schematic circuit, the voltage is lower than the forward voltage (about 200 mV) of the diode D3 and cannot be detected. In order to solve this problem, a buffer circuit 23 is inserted between the thin film magneto-impedance element and the oscillation circuit. The transistors at the output stage of the buffer circuit 23 constitute a push-bull circuit by Darlington connection (Tr4 and Tr6, Tr3 and Tr5), and the output impedance of the transistor is set to several Ω or less. If R8 and R9 are set to 1Ω or less, the output impedance of the buffer circuit 23 becomes negligible compared to the impedance of the load, and the high-frequency energization output generated by the oscillation circuit 21 is lost to the thin film magnetic impedance element 22 without loss. Can supply.
[0020]
Further, the diodes D1 and D2 of the buffer circuit 23 in FIG. 13 are for correcting the temperature characteristics of the transistor. In FIG. 13, the change in the base-emitter voltage of the transistor due to temperature is represented by ΔVBE. When the diodes D1 and D2 are not inserted in the buffer circuit 23, it can be seen from the equations (1) and (2) shown in FIG. 21 that the transistor voltage changes by ΔVBE. Since ΔVBE generally changes at −2.2 mV / ° C., the collector current Ic of the transistor flows as the temperature rises as shown in FIG. 14, and finally an avalanche phenomenon occurs and the transistor is damaged. As a solution to this, a diode having the same temperature change as that of the transistor can be inserted between Tr2 (Tr1) and Tr4 (Tr3) to cancel the voltage change due to temperature. Equations (3) and (4) in FIG. 21 show this. As a result, the buffer circuit with good temperature characteristics is finished.
[0021]
FIG. 15 is an explanatory circuit diagram for explaining the operation of converting the high-frequency energization output to the thin film magneto-impedance element 22 into a DC voltage. The operation of the circuit shown in FIG. 15 will be described with reference to FIG. 16. The high-frequency output voltage Vo generated at both ends of the thin film magneto-impedance element 22 is half-wave rectified by the diode D3 and becomes the smoothed voltage Ve by the capacitor C6. The ripple generated in order to make it completely DC is eliminated through the low-pass filter 27. The low-pass filter 27 can be used as an LC filter, but is composed of an inductance-less low-pass filter in order to eliminate a minute magnetic field (effect of a magnetic field generated from an L (inductance) component) on the magnetic impedance. Note that the output voltage Vd in FIGS. 15 and 16 varies depending on the amount of magnetism detected by the thin-film impedance element 22.
[0022]
FIG. 17 is a circuit diagram for obtaining the maximum rate of impedance change of the thin film magnetoimpedance element incorporated in the magnetoimpedance sensor. In FIG. 17, the high-frequency output voltage Vo generated at both ends of the thin film magneto-impedance element 22 is half-wave rectified into positive and negative by the diodes D3 and D5, respectively, and converted into DC voltages + Ve and −Ve through a smoothing circuit by capacitors C6 and C10. Then, the ripple is eliminated by a low-pass filter including the resistor R14, the capacitor C7, the resistor 21, and the capacitor C11, and detection outputs + Vd and -Vd are obtained. These waveforms are shown in FIG. The obtained voltage between the positive and negative outputs + Vd and −Vd is differentially detected by an operational amplifier. By this differential detection, a change amount twice as large as the change amount of the magnetic-impedance detected by the circuit shown in FIG. 15 can be obtained. Further, by changing the ratio of R24 and R15, the operational amplifier 36 can be operated as an amplifier.
[0023]
FIG. 19 is a circuit diagram showing an example of a total circuit of a linear magnetic sensor according to the present invention manufactured using a thin film magneto-impedance element having a bias coil and a negative feedback coil. When this is used as a magnetic sensor, the sensor sensitivity can be improved by bringing the operating point to the maximum sensitivity of the thin film magneto-impedance element. For this reason, by applying a current to the bias coil, a bias magnetic field can be applied to change the operating point. By applying a bias magnetic field of 1600 A / m to the magnetic core, the magnetic field sensitivity is maximized at a magnetic field of 0 A / m. I did it.
[0024]
On the other hand, when the operating point is moved so as to bring the maximum sensitivity to the applied magnetic field of 0 A / m using the bias coil, the linearity of the impedance change (output change) with respect to the magnetic field is not very good. As a method of improving this linearity, the output signal is fed back to the thin film magnetic core as a negative feedback magnetic field by feeding back the output signal and correcting the nonlinearity of the output with respect to the magnetic field using a negative feedback coil. A way to get sex is taken. According to the circuit diagram of the linear magnetic sensor shown in FIG. 19, the operating point is moved to the point of maximum sensitivity, the output signal is fed back, and a negative feedback magnetic field is added to the thin film core to improve the linearity of the sensitivity characteristic.
FIG. 20 shows the relationship of the output voltage to the applied magnetic field of the magnetic sensor when negative feedback with a bias coil magnetic field of 1600 A / m and a negative feedback rate of 50% is applied using the circuit shown in FIG. Here, the frequency of the energization current is 20 MHz. As shown in FIG. 20, excellent linearity was exhibited in a measured magnetic field of ± 240 A / m, and a magnetic field resolution of 10 −3 A / m was exhibited. These results are good characteristics as a linear magnetic field sensor.
[0025]
As described above, the present invention has been described with reference to the above embodiment. For example, a thin film magneto-impedance element made of a ferromagnetic amorphous wire is used instead of the thin film magnetic core of the thin film magneto-impedance element. Various modifications and applications are possible, and these modifications and applications are not excluded from the scope of the present invention.
[0026]
【The invention's effect】
As described above in detail, in the inventions according to Claims 1, 2, and 3 of the present application, a highly sensitive magnetic sensor can be provided as a composite element including a thin film magnetoimpedance element, and a sine wave can be input to the thin film magnetoimpedance element. It became possible to draw out the characteristics to the maximum. By providing a buffer circuit between the oscillator and the thin film magneto-impedance element, the influence of the impedance of the thin film magneto-impedance element can be eliminated, and the output of the oscillator can be supplied without loss.
In the invention according to claim 4, since the high-frequency energization current due to the sine wave applied to the thin film magneto-impedance element is configured by a circuit excluding a simple inductance, the influence of the minute magnetic field generated from the magnetic sensor itself on the thin film magneto-impedance element Can be eliminated.
In the invention according to claim 5 of the present application, since the oscillation circuit is composed of a Wien bridge circuit, it is not necessary to provide a band pass filter in the oscillation circuit. Further, since the Wien bridge circuit is an inductanceless circuit, the circuit of the magnetic sensor is provided. The configuration can be easily configured.
In the invention according to claim 6 of the present application, since the buffer circuit has a temperature compensation circuit and is composed of a push-pull circuit having an impedance conversion function, the output impedance of the buffer circuit is ignored compared with the impedance of the load. As a result, the high-frequency energization output generated by the oscillation circuit can be supplied to the thin film magneto-impedance element without loss.
In the invention according to claims 7 and 8 of the present application, since the detection circuit has a rectifier circuit and a low-pass filter, the detection circuit adds the low-pass filter to the rectifier circuit and the smoothing circuit, thereby outputting the output of the thin film magneto-impedance element. A circuit that can be converted into a DC signal and suppresses ripple as much as possible can be supplied. In addition, by providing a differential circuit, not only the positive side but also the negative side of the output of the magnetic impedance sensor can be detected, and the amount of change that is twice as normal can be detected.
In the invention according to claim 8 of the present application, since the low-pass filter is configured by a circuit excluding the inductance, it is possible to eliminate the influence of the minute magnetic field generated from the magnetic sensor itself on the thin film magneto-impedance element.
[Brief description of the drawings]
FIG. 1 is a front view schematically showing the structure of a thin film magneto-impedance element used in the present invention.
FIG. 2 is a cross-sectional view taken along line AB in FIG.
FIG. 3 is a cross-sectional view taken along the line CD in FIG. 1;
FIG. 4 is a frequency characteristic diagram of a conduction current of a thin film magneto-impedance element.
FIG. 5 is an impedance change rate characteristic diagram of a thin film magneto-impedance element.
FIG. 6 is a block diagram of a magnetic sensor according to the present invention.
FIG. 7 is a block diagram of a transmitter and a bandpass filter.
FIG. 8 is an output waveform diagram after passing through a transmission unit and a low-pass filter.
FIG. 9 is a circuit diagram of the main part centering on a thin film magneto-impedance element.
FIG. 10 is an output waveform diagram of the circuit shown in FIG. 9;
FIG. 11 is a frequency characteristic diagram of a thin film magneto-impedance element.
FIG. 12 is a circuit diagram of a Wien bridge.
FIG. 13 is a circuit diagram of a buffer circuit.
FIG. 14 is an emitter-collector characteristic diagram of a transistor.
FIG. 15 is a circuit diagram of a detection circuit.
FIG. 16 is an output waveform diagram of the detection circuit shown in FIG. 15;
FIG. 17 is a circuit diagram of a detection circuit and an amplification unit according to another embodiment.
FIG. 18 is an output waveform diagram of the circuit shown in FIG. 17;
FIG. 19 is a general circuit diagram of the magnetic sensor of the present invention.
FIG. 20 is an output voltage characteristic diagram with respect to an applied magnetic field having a negative feedback rate of 50%.
FIG. 21 is a calculation formula diagram showing a circuit calculation formula of the buffer circuit;
FIG. 22 is a circuit block diagram of a magnetic sensor using a magneto-impedance element made of an amorphous wire.
FIG. 23 is a characteristic diagram of a magneto-impedance element using an amorphous wire.
[Explanation of symbols]
1 ... MI sensor plate
2 ... Insulator layer
3. Insulator layer
4 ... Bias coil
5 ... Negative feedback coil
6 ... Bias coil terminal
7: Bias coil terminal
8 ... Negative feedback coil terminal
9: Negative feedback coil terminal
10 ... MI sensor terminal
11 ... MI sensor terminal
12 ... Insulating protective film
20 ... Non-magnetic substrate
21 ... Oscillator circuit
22 ... Thin film magneto-impedance element
23 ... Buffer circuit
24 ... Negative feedback coil
25 ... Bias coil
26 ... Rectifier circuit
27 ...... Low-pass filter
28 ... Differential circuit
29 ... Detection circuit
30 ... Amplifier circuit
31 ... Negative feedback resistance
32 …… Oscillator
33 ... C-MOS circuit
34 ... Oscillator
35 ... Band pass filter
36 ・ ・ ・ ・ ・ Operational amplifier

Claims (9)

In a magnetic sensor using a thin film magneto-impedance element in which a bias coil and a negative feedback coil via an insulator are wound around a magnetic core formed on a substrate made of a non-magnetic material, high-frequency waves are applied to both ends of the magnetic core. An oscillation circuit for applying a sine wave current; and a buffer circuit provided between the oscillation circuit and the magnetic core of the thin film magneto-impedance element, and adjusting a mismatch between the output impedance of the oscillation circuit and the input impedance of the thin film magneto-impedance element; ,
A detection circuit for direct current detection of the magnetic change amount of the external magnetic field from the change amount of the high-frequency current that changes according to the external magnetic field applied to the magneto-impedance element;
A magnetic sensor comprising: 2. The magnetic sensor according to claim 1, wherein the magnetic core formed on the non-magnetic substrate is formed of a ferromagnetic thin film. 2. The magnetic sensor according to claim 1, wherein the magnetic core formed on the non-magnetic substrate is formed of a ferromagnetic amorphous wire. 2. The magnetic sensor according to claim 1, wherein the oscillation circuit is a sine wave oscillation circuit including a band-pass filter that does not include an inductance element. The magnetic sensor according to claim 1, wherein the oscillation circuit is a Wien bridge circuit. 2. The magnetic sensor according to claim 1, wherein the buffer circuit includes a temperature compensation circuit and includes a push-pull circuit having an impedance conversion function. The magnetic sensor according to claim 1, wherein the detection circuit includes a rectifier circuit and a low-pass filter. The magnetic sensor according to claim 7, wherein the low-pass filter is a low-pass filter that does not include an inductance component. The magnetic sensor according to claim 7, wherein the detection circuit includes a differential circuit.

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