Magnetic sensor

A magnetic sensor includes a radial magnetoresistance element including plural magnetic sensing parts arranged radially from one point, an annular or polygonal magnetoresistance element arranged so as to surround the radial magnetoresistance elements, and at least one half-bridge circuit including the radial magnetoresistance element and the annular or polygonal magnetoresistance element. The radial magnetoresistance element may include a first magnetoresistance element including plural first magnetic sensing parts and a second magnetoresistance element including plural second magnetic sensing parts. The annular or polygonal magnetoresistance element may include an annular or polygonal third magnetoresistance element surrounding the first and second magnetoresistance elements and an annular or polygonal fourth magnetoresistance element surrounding the third magnetoresistance element. Two half-bridge circuits including the first to fourth magnetoresistance elements may be installed in the magnetic sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase of PCT/JP2019/007613 filed on Feb. 27, 2019 claiming priority to Japanese Patent Application No. 2018-054391 filed on Mar. 22, 2018. The disclosure of the PCT Application is hereby incorporated by reference into the present Application.

TECHNICAL FIELD

The present invention relates to a magnetic sensor.

BACKGROUND ART

Angle sensors are known which are provided with a magnetic field sensor element constructed from a MR (Magneto Resistive) sensor in which plural magnetoresistance elements are connected so as to form one or more measuring bridges (see e.g. Patent Literature 1).

The angle sensors can detect an angular position of a measurement target rotating about the rotation axis by detecting a direction of a magnetic vector of a magnetic field.

CITATION LIST

Patent Literature

Patent Literature 1: JP H11/94512 A

SUMMARY OF INVENTION

Technical Problem

A magnetic sensor using the MR sensor is known which determines several states base on the detected angles. The magnetic sensor, when a disturbance magnetic field is applied, may have a difficulty to discriminate whether the detected angle of the magnetic vector is an angle of a magnetic vector of a magnet or an angle of a magnetic vector of the disturbance magnetic field, causing an erroneous determination.

It is an object of the invention to provide a magnetic sensor which is proof against a disturbance magnetic field.

Solution to Problem

According to an embodiment of the invention, a magnetic sensor comprises a radial magnetoresistance element comprising a plurality of magnetic sensing parts arranged radially from one point, an annular or polygonal magnetoresistance element arranged so as to surround the radial magnetoresistance elements, and at least one half-bridge circuit comprising the radial magnetoresistance element and the annular or polygonal magnetoresistance element.

Advantageous Effects of Invention

According to an embodiment of the invention, it is possible to provide a magnetic sensor which is proof against a disturbance magnetic field.

DESCRIPTION OF EMBODIMENTS

Summary of Embodiments

A magnetic sensor of embodiments comprises a magnetic sensor comprises a radial magnetoresistance element comprising a plurality of magnetic sensing parts arranged radially from one point, an annular or polygonal magnetoresistance element arranged so as to surround the radial magnetoresistance elements, and at least one half-bridge circuit comprising the radial magnetoresistance element and the annular or polygonal magnetoresistance element.

Since how the magnetoresistance value changes with respect to a direction of a magnetic field is different between the radial magnetoresistance element and the annular or polygonal magnetoresistance element, the magnetic sensor can easily discriminate between the action of the magnetic field due to a detection target and the action of the disturbance magnetic field and thus can be proof against the disturbance magnetic field, unlike when each magnetoresistance element is arranged in a rotationally symmetric manner.

First Embodiment

General Configuration of Magnetic Sensor1

FIG. 1Ais an explanatory diagram illustrating an arrangement of first to fourth magnetoresistance elements of a magnetic sensor in the first embodiment, andFIG. 1Bis an equivalent circuit diagram illustrating the magnetic sensor in the first embodiment.FIG. 2Ais an explanatory diagram for explaining a positional relation between the magnetic sensor in the first embodiment and a magnet, andFIG. 2Bis an explanatory diagram for explaining a magnetic vector acting on the magnetic sensor in the first embodiment. In each drawing of the embodiment described below, a scale ratio may be different from an actual ratio. In addition, inFIG. 1B, flows of main signal and information are indicated by arrows. Furthermore, wirings6are omitted inFIGS. 2B, 3B and 4A.

A magnetic sensor1detects, e.g., approach or separation of a magnet7to/from the magnetic sensor1. As an example, the magnetic sensor1is used in a non-contact switch which detects ON and OFF, or in a device which detects two states such as an operation device detecting whether or not an operation is performed on an operation part. The magnetic sensor1in the first embodiment is used in a non-contact switch which determines approach of the magnet7as ON and separation as OFF, as an example.

The magnetic sensor1has, e.g., a radial magnetoresistance element having plural magnetic sensing parts arranged radially from one point (a center P), an annular or polygonal magnetoresistance element arranged so as to surround the radial magnetoresistance element, and at least one half-bridge circuit constructed from the radial magnetoresistance element and the annular or polygonal magnetoresistance element, as shown inFIGS. 1A and 1B.

A first magnetoresistance element2having plural first magnetic sensing parts20and a second magnetoresistance element3having plural second magnetic sensing parts30are provided as the radial magnetoresistance elements in the first embodiment. Also, an annular third magnetoresistance element4surrounding the first magnetoresistance element2as well as the second magnetoresistance element3and an annular fourth magnetoresistance element5surrounding the third magnetoresistance element4are provided as the annular or polygonal magnetoresistance elements in the first embodiment. The the magnetic sensor1is provided with, e.g., two half-bridge circuits13aand13bconstructed from the first to fourth magnetoresistance elements2to5, as shown inFIG. 1B.

In the first embodiment, the third magnetoresistance element4and the fourth magnetoresistance element5are formed as the annular magnetoresistance elements, as an example.

The first magnetic sensing parts20and the second magnetic sensing parts30have, e.g., magnetoresistance values which change depending on a magnetic vector71of a magnetic field70generated by the magnet7, as shown inFIGS. 2A and 2B. The first magnetic sensing parts20and the second magnetic sensing parts30have, e.g., a circular-sector shape obtained by dividing a circle centered at the center P, as shown inFIG. 1A.

In addition, the magnetic sensing parts20and the second magnetic sensing parts30are arranged, e.g., alternately in a circumferential direction, as shown inFIG. 1A. When the first magnetoresistance element2and the second magnetoresistance element3are configured to have the same resistance value including the magnetoresistance value, however, the shape, number and circumferential arrangement order, etc., of the magnetic sensing parts are not limited as long as the resistance values are the same.

In addition, the shape and number, etc., of the magnetic sensing parts may be selected so that the resistance values of the first magnetoresistance element2and the second magnetoresistance element3are coordinated with the resistance values of the third magnetoresistance element4and the fourth magnetoresistance element5, i.e., coincide with the resistance values of the annular magnetoresistance elements with which the first magnetoresistance element2and the second magnetoresistance element3constitute the half-bridge circuits.

In the third magnetoresistance element4and the fourth magnetoresistance element5, the magnetic sensing parts have a ring shape (an annular shape) and the magnetoresistance values change depending on the direction of the magnetic vector71.

The magnetic sensor1is configured that the first magnetoresistance element2or the second magnetoresistance element3and the third magnetoresistance element4or the fourth magnetoresistance element5are electrically connected and output a first midpoint potential, and the remaining magnetoresistance elements are electrically connected and output a second midpoint potential. This magnetic sensor1is provided with a bridge circuit13composed of the half-bridge circuit13aand the half-bridge circuit13b.

In detail, the half-bridge circuit13ais formed by electrically connecting, e.g., the first magnetoresistance element2to the third magnetoresistance element4and outputs midpoint potential V1as the first midpoint potential, as shown inFIG. 1B. Also, the half-bridge circuit13ais formed by electrically connecting, e.g., the second magnetoresistance element3to the fourth magnetoresistance element5and outputs midpoint potential V2as the second midpoint potential.

In the bridge circuit13, the combination to form the half-bridge circuit may be other combinations as long as, e.g., the radial magnetoresistance element is connected to the annular magnetoresistance element. Therefore, the half-bridge circuits may be, e.g., the half-bridge circuit13aformed by electrically connecting the first magnetoresistance element2to the fourth magnetoresistance element5and the half-bridge circuit13bformed by electrically connecting the second magnetoresistance element3to the third magnetoresistance element4.

The magnetic sensor1also has, e.g., an op-amp OP and a control unit15, as shown inFIG. 1B. The first to fourth magnetoresistance elements2to5are formed on, e.g., a substrate10, as shown inFIG. 2B. The substrate10is, e.g., a printed circuit board on which the op-amp OP and the control unit15may be arranged in addition to a sensor part12formed of the first to fourth magnetoresistance elements2to5.

Configuration of First to Fourth Magnetoresistance Elements2to5

The first magnetoresistance element2and the second magnetoresistance element3are configured that the first magnetic sensing parts20and the second magnetic sensing parts30have the same shape as the example shown inFIG. 1A. Also, the third magnetoresistance element4and the fourth magnetoresistance element5are configured that magnetic sensing parts thereof have an annular shape but are different in at least a radius.

The first to fourth magnetoresistance elements2to5are formed as, e.g., thin alloy films consisting mainly of a ferromagnetic metal such a Ni or Fe. The first magnetic sensing parts20are arranged in such a manner that, e.g., end portions are alternately connected so as to be connected in series by a metal material such as copper of which resistance value does not change with the change in the direction of the magnetic vector71, and a start point and an end point of the series connection are connected to the wirings6, as shown inFIG. 1A. Likewise, the second magnetic sensing parts30are arranged in such a manner that, e.g., end portions are alternately connected so as to be connected in series, and a start point and an end point of the series connection are connected to the wirings6, as shown inFIG. 1A. Thus, the current in the first magnetic sensing parts20and the second magnetic sensing parts30flows in a radial direction.

The wirings connecting these magnetic sensing parts are formed on a front surface10aand a back surface10bof the substrate10, and the wirings on the front surface10aand the back surface10bare electrically connected via a though-hole which penetrates the substrate10, as an example. The wirings connecting the magnetic sensing parts may be three-dimensionally formed on the front surface10aso as to sandwich an insulation therebetween.

Also, the third magnetoresistance element4and the fourth magnetoresistance element5are, e.g., partially cut out and are electrically connected to the wirings6, as shown inFIG. 1A. The wiring6is formed of a metal material such as copper of which resistance value does not change with the change in the direction of the magnetic vector71. Thus, the current in the third magnetoresistance element4and the fourth magnetoresistance element5flows in a circumferential direction.

As an example, the first magnetic sensing parts20and the second magnetic sensing parts30are circular sector-shaped magnetic sensing parts which have the same shape and are arranged at equal intervals with a rotation by 10° about the center P. In other words, the first magnetic sensing parts20and the second magnetic sensing parts30are arranged rotationally symmetrically about the center P.

The first to fourth magnetoresistance elements2to5constitute the bridge circuit13and thus preferably have equal resistance values including magnetoresistance values when not under the action of the magnetic vector71. In other words, the first to fourth magnetoresistance elements2to5preferably have equal resistance values including resistance components which do not change even under the action of the magnetic vector71and magnetoresistance components which change under the action of the magnetic vector71. When the magnetic sensor1has such a configuration and the magnet7is located directly above the sensor part12, the midpoint potential V1and the midpoint potential V2become equal to each other and an output signal S1becomes zero.

Therefore, the first magnetoresistance element2and the second magnetoresistance element3are formed so that the same numbers of the first magnetic sensing parts20and the second magnetic sensing parts30having the same area are formed of the same material.

The third magnetoresistance element4and the fourth magnetoresistance element5also preferably have equal resistance values. However, the third magnetoresistance element4and the fourth magnetoresistance element5have different radii and thus have different shapes. Therefore, it is preferable to adjust widths, lengths and materials, etc., so that their resistance values become equal. For the first to fourth magnetoresistance elements2to5in the first embodiment, the materials, etc., are selected so that their resistance values become equal.

As a modification, the magnetic sensor1may be configured so that at least the resistance values of the radial magnetoresistance element and the annular magnetoresistance element constituting the half-bridge circuit are equal. In detail, for example, the resistance values of the first magnetoresistance element2and the third magnetoresistance element4constituting the half-bridge circuit13aare equal, and the resistance values of the second magnetoresistance element3and the fourth magnetoresistance element5constituting the half-bridge circuit13bare equal.

As another modification, the magnetic sensor1may have, e.g., a configuration in which a difference between midpoint potentials due to a difference between the resistance values of the first to fourth magnetoresistance elements2to5is offset when the magnet7is located directly above the sensor part12, or a configuration in which ON or OFF is determined by adjusting a threshold value Th.

A node11aas a connecting point between the second magnetoresistance element3and the third magnetoresistance element4is electrically connected to a power source voltage Vcc, as shown inFIG. 1B. A node11cas a connecting point between the first magnetoresistance element2and the fourth magnetoresistance element5is electrically connected to GND.

The midpoint potential V1at a node11bbetween the third magnetoresistance element4and the first magnetoresistance element2is output from the half-bridge circuit13a, as described above. The midpoint potential V1is input to anon-inverting (+side) input terminal of the op-amp OP.

The midpoint potential V2at a node11dbetween the second magnetoresistance element3and the fourth magnetoresistance element5is output from the half-bridge circuit13b, as described above. The midpoint potential V2is input to an inverting (−side) input terminal of the op-amp OP. The op-amp OP outputs the output signal S1, which is obtained by differentially amplifying the midpoint potential V1input to the non-inverting input terminal and the midpoint potential V2input to the inverting input terminal, to the control unit15.

Configuration of the Magnet7

The magnet7has, e.g., a pillar shape, such as column or quadrangular prism, which generates the radial magnetic vector71, as shown inFIGS. 2A and 2B. The magnet7in the first embodiment has, e.g., a columnar shape.

The magnet7is magnetized to have, e.g., an N-pole on the first to fourth magnetoresistance elements2to5side and an S-pole on the other side, as shown inFIG. 2A. The magnet7generates, e.g., the radial magnetic field70toward the substrate10so that the radial magnetic vector71acts on the first to fourth magnetoresistance elements2to5, as shown inFIG. 2B. The magnetic poles of the magnet7may be located the other way round.

The magnet7is obtained by, e.g., shaping a permanent magnet such as alnico magnet, ferrite magnet or neodymium magnet into a desired shape, or by mixing a magnetic material based on ferrite, neodymium, samarium-cobalt or samarium-iron-nitrogen, etc., with a synthetic resin material and shaping into a desired shape. The magnet7in the first embodiment is a permanent magnet, as an example. Alternatively, the magnet7may be an electromagnet.

As an example, the magnet7in the first embodiment moves from a position at which a center line72shown inFIG. 2Acoincides with the center P of the magnetic sensor1, to outside a boundary120of the magnetic sensor1. The center line72is, e.g., a line which connects the centers of an end face7aon the N-pole side and an end face7bon the S-pole side and is extended. Also, the boundary120is, e.g., an outer periphery of the sensor part12, i.e., an outer periphery of the fourth magnetoresistance element5.

The control unit15is configured to determine it is ON when the center line72of the magnet7is located in an ON region80, and to determine it is OFF when located in an OFF region81, where, e.g., a region from the center P to the boundary120is defined as the ON region80and a region outside the boundary120is defined as the OFF region81.

Configuration of the Control Unit15

FIG. 3Ais an explanatory diagram illustrating the magnet located at a distance from the magnetic sensor in the first embodiment, andFIG. 3Bis an explanatory diagram illustrating a magnetic vector of the magnet located at a distance from the magnetic sensor in the first embodiment.FIG. 4Ais an explanatory diagram illustrating a disturbance magnetic field acting on the magnetic sensor in the first embodiment,FIG. 4Bis a graph showing a relation between a magnetoresistance value of the magnetic sensor in the first embodiment and a distance from the center, andFIG. 4Cis an explanatory diagram illustrating an example of the output signal output from the magnetic sensor. InFIG. 4B, the vertical axis indicates the magnetoresistance value and the horizontal axis indicates a distance from the center P to the magnet7. InFIG. 4C, the vertical axis indicates voltage and the horizontal axis indicates the distance from the center P to the magnet7. The distance to the magnet7is a distance (the shortest distance) from the center P to the center line72of the magnet7.

The control unit15is, e.g., a microcomputer composed of a CPU (Central Processing Unit) performing calculation and processing, etc., of the acquired data according to a stored program, and a RAM (Random Access Memory) and a ROM (Read Only Memory) which are semiconductor memories, etc. The ROM stores, e.g., a program for operation of the control unit15, and the threshold value Th. The RAM is used as, e.g., a storage area for temporarily storing calculation results, etc.

The control unit15compares, e.g., the output signal S1output from the op-amp OP with the threshold value Th and determines whether or not the magnet7approaches. The threshold value Th is set based on the output signal S1, i.e., a voltage difference between the midpoint potential V1and the midpoint potential V2when the magnet7is located on the boundary120. The magnet7located on the boundary120means that the center line72of the magnet7is located on the boundary120.

The control unit15determines that the magnet7is located in the ON region80and it is thus ON when the voltage of the output signal S1is not less than the threshold value Th, and that the magnet7is located in the OFF region81and it is thus OFF when less than the threshold value Th. When determining that it is ON, the control unit15generates detection information S2indicating ON and outputs it to a connected electronic device.

When the magnet7is far enough away, magnetoresistance values R12of the first magnetoresistance element2and the second magnetoresistance element3and magnetoresistance values R34of the third magnetoresistance element4and the fourth magnetoresistance element5converge to substantially the same value, and the threshold value Th thus becomes a value close to zero.

The Case That the Center Line72of the Magnet7is Located in ON Region80

When the magnet7is located directly above the center P of the magnetic sensor1, i.e., when the center line72of the magnet7coincides with the center P of the sensor part12as shown inFIGS. 2A and 2B, the magnetic vector71radially extending from the center P acts on the sensor part12.

As to the first magnetoresistance element2and the second magnetoresistance element3, the magnetoresistance value R12does not change, i.e., remain at the maximum value Rmaxsince the magnetic vector71acts, e.g., parallelly on the first magnetic sensing parts20and the second magnetic sensing parts30, as shown inFIGS. 2A, 2B and 4B. In other words, since the magnetic vector71acts parallelly on the current flowing through the first magnetoresistance element2and the second magnetoresistance element3, the magnetoresistance values R12do not change.

Meanwhile, the magnetoresistance values R12are the magnetoresistance values represented by a solid line inFIG. 4Bwhich is shown as an example and indicates both the magnetoresistance values of the first magnetoresistance element2and the second magnetoresistance element3to depict that the magnetoresistance values are equal.

As to the third magnetoresistance element4and the fourth magnetoresistance element5, the magnetoresistance value R34become the minimum value Rmin, since the magnetic vector71acts, e.g., perpendicularly, as shown inFIGS. 2A, 2B and 4B. In other words, since the magnetic vector71acts perpendicularly on the current flowing through the third magnetoresistance element4and the fourth magnetoresistance element5, the magnetoresistance values R34become the minimum.

Meanwhile, the magnetoresistance values R34are the magnetoresistance values represented by a thick dotted line inFIG. 48which is shown as an example and indicates both the magnetoresistance values of the third magnetoresistance element4and the fourth magnetoresistance element5to depict that the magnetoresistance values are equal.

Thus, the midpoint potential V1becomes the maximum and the midpoint potential V2becomes the minimum. Therefore, the output signal S1output from the op-amp OP becomes the maximum value, as shown in, e.g.,FIG. 4C. That is, when the magnet7is located on the center P, the output signal S1becomes the maximum.

Then, when the magnet7moves from the center P toward the boundary120, the magnetoresistance value R12and the magnetoresistance value R34of the first to fourth magnetoresistance elements2to5increase and decrease toward, e.g., a resistance value Rm, as shown inFIG. 4B. The control unit15compares, e.g., the output signal S1, which is obtained by amplifying a difference between the midpoint potential V1and the midpoint potential V2, with the threshold value Th and determines that the magnet7is located in the ON region80until the output signal S1becomes smaller than the threshold value Th, as shown inFIG. 4C.

The Case That the Center Line72of the Magnet7is Located in OFF Region81

When the magnet7is located outside the magnetic sensor1, i.e., when the center line72of the magnet7is located outside the boundary120as shown inFIGS. 3A and 3B, a portion of the magnetic vector71radially extending from a center72aacts on the sensor part12.

As to the first magnetoresistance element2and the second magnetoresistance element3, the magnetic vector71within, e.g., an angle θ1formed by two lines (solid lines inFIG. 3B) extending from the center72aof the radial magnetic vector71and tangent to the first magnetic sensing parts20and the second magnetic sensing parts30acts thereon from outside the boundary120, as shown inFIGS. 3A, 3B and 4B.

The magnetic vector71acts on the first magnetoresistance element2and the second magnetoresistance element3, e.g., symmetrically with respect to the horizontal direction on the paper ofFIG. 3Band also intersects with the current, causing a decrease from the maximum value Rmaxand convergence. The magnetoresistance values R12converge to a value close to the resistance value Rm, as an example.

Also, as to the third magnetoresistance element4, the magnetic vector71within, e.g., an angle θ2formed by two lines (dashed-dotted lines inFIG. 3B) extending from the center72aof the radial magnetic vector71and tangent to the third magnetoresistance element4acts thereon, as shown inFIGS. 3A, 3B and 4B.

Likewise, as to the fourth magnetoresistance element5, the magnetic vector71within, e.g., an angle θ3formed by two lines (dash-dot-dot lines inFIG. 3B) extending from the center72aof the magnetic vector71and tangent to the fourth magnetoresistance element5acts thereon, as shown inFIGS. 3A, 3B and 4B. These angles satisfy θ1<θ2<θ3.

These magnetic vectors71act on the third magnetoresistance element4and the fourth magnetoresistance element5, e.g., symmetrically with respect to the horizontal direction on the paper ofFIG. 3Band intersects with the current at an angle off the perpendicular, causing an increase from the maximum value Rmaxand convergence. The magnetoresistance values R34converge to a value close to the resistance value Rm, as an example.

When, for example, it is configured that the magnetoresistance values of the first to fourth magnetoresistance elements2to5converge to a value close to the resistance value Rm, the midpoint potential V1and the midpoint potential V2become a value closed to zero. Therefore, the output signal S1output from the op-amp OP becomes a value closed to zero. That is, when the magnet7is located outside the boundary120, the output signal S1becomes a value closed to zero.

The Case That the Disturbance Magnetic Field9Acts Thereon

When a disturbance magnetic field9acts on the magnetic sensor1, for example, magnetic vectors90in the same direction act on the first to fourth magnetoresistance elements2to5, as shown inFIG. 4A.

In this case, the magnetoresistance values R12of the first magnetoresistance element2and the second magnetoresistance element3converge to a value close to the resistance value Rm, in the same manner as when the magnet7is located outside the boundary120. The magnetoresistance values R34of the third magnetoresistance element4and the fourth magnetoresistance element5also converge to a value close to the resistance value Rm, in the same manner as when the magnet7is located outside the boundary120.

The above-mentioned configuration allows the control unit15to detect ON and OFF by comparing the output signal S1with the threshold value Th. In addition, under the action of the disturbance magnetic field9, the control unit15does not determine that the magnet7is located in the ON region80. Therefore, it is possible to prevent such an erroneous determination that it is determined ON when the disturbance magnetic field9is applied.

Next, an example of an operation of the magnetic sensor1in the first embodiment will be described below along with the flowchart inFIG. 5.

Operation

When the power is turned on, the control unit15of the magnetic sensor1monitors the output signal S1. When it is “Yes” in Step1, i.e., when the output signal S1is not less than threshold value Th (Step1: Yes), the control unit15determines that the magnet7is located in the ON region80, i.e., it is ON (Step2).

Based on the determination result, the control unit15generates the detection information S2indicating determination of “ON” and outputs it to the connected electronic device (Step3).

Effects of the First Embodiment

The magnetic sensor1in the first embodiment is proof against the disturbance magnetic field9. In detail, since how the magnetoresistance value changes with respect to the direction of the magnetic field70is different between the radial magnetoresistance elements (the first magnetoresistance element2and the second magnetoresistance element3) and the annular magnetoresistance elements (the third magnetoresistance element4and the fourth magnetoresistance element5), the magnetic sensor1can easily discriminate between the action of the magnetic field70of the magnet7and the action of the disturbance magnetic field9and thus can be proof against the disturbance magnetic field9, unlike when each magnetoresistance element is arranged in a rotationally symmetric manner.

Since the direction of the magnetic vector71which causes a change in the magnetoresistance value is different for the radial magnetoresistance elements and the annular magnetoresistance elements, the magnetic sensor1does not determine “ON” even when the disturbance magnetic field9acts. Therefore, unlike when such a configuration is not adopted, it is suitable for use in an environment in which the disturbance magnetic field9is likely to be generated, such as in vehicle.

Second Embodiment

The second embodiment is different from other embodiments in having one radial magnetoresistance element and one annular magnetoresistance element.

FIG. 6Ais an explanatory diagram illustrating an arrangement of a radial magnetoresistance element and an annular magnetoresistance element of a magnetic sensor in the second embodiment, andFIG. 6Bis an equivalent circuit diagram illustrating the magnetic sensor. In the embodiment described below, portions having the same functions and the configurations as those in the first embodiment are denoted by the same reference numerals as the first embodiment and the explanation thereof will be omitted.

The magnetic sensor1in the second embodiment has, e.g., a radial magnetoresistance element2ahaving plural magnetic sensing parts (the first magnetic sensing parts20) arranged radially from one point (the center P), an annular magnetoresistance element4aarranged so as to surround the magnetoresistance element2a, and a half-bridge circuit14constructed from the radial magnetoresistance element2aand the annular magnetoresistance element4a, as shown inFIGS. 6A and 6B.

In the second embodiment, the magnetoresistance element4ais formed as an annular magnetoresistance element, as an example.

In this magnetic sensor1, the magnetoresistance element2ais formed by arranging the first magnetic sensing parts20at equal intervals with a rotation by 10° about the center P, as an example. Then, the magnetoresistance element4ais formed so as to surround the magnetoresistance element2a. The radial magnetoresistance element2aand the annular magnetoresistance element4apreferably have equal resistance values.

A node14aas a connecting point between the radial magnetoresistance element2aand the annular magnetoresistance element4ais electrically connected to the power source voltage Vcc, as shown inFIG. 6B. A node14cas a connecting point between the radial magnetoresistance element2aand the annular magnetoresistance element4ais electrically connected to the GND.

A midpoint potential Vaat the node14abetween the radial magnetoresistance element2aand the annular magnetoresistance element4ais output from the half-bridge circuit14. The midpoint potential Vais output to, e.g., the control unit15.

The control unit15compares the midpoint potential Vawith the threshold value Th and determines that the magnet7is located in the ON region80, i.e., it is ON, when the midpoint potential Vais not less than the threshold value Th. Then, the control unit15generates the detection information S2indicating “ON” and outputs it to the connected electronic device.

Effects of the Second Embodiment

Since how the magnetoresistance value changes with respect to the direction of the magnetic field70is different between the radial magnetoresistance element2aand the annular magnetoresistance element4a, the magnetic sensor1in the second embodiment can easily discriminate between the action of the magnetic field70of the magnet7and the action of the disturbance magnetic field9and thus can be proof against the disturbance magnetic field9, unlike when each magnetoresistance element is arranged in a rotationally symmetric manner.

Third Embodiment

The third embodiment is different from the other embodiments in having one radial magnetoresistance element and one polygonal magnetoresistance element.

FIG. 7is an explanatory diagram illustrating an example of an arrangement of a radial magnetoresistance element and a polygonal magnetoresistance element of a magnetic sensor in the third embodiment.

The magnetic sensor1in the third embodiment has, e.g., the radial magnetoresistance element2ahaving plural magnetic sensing parts (the first magnetic sensing parts20) arranged radially from one point (the center P), and a polygonal magnetoresistance element4barranged so as to surround the magnetoresistance element2a, as shown inFIG. 7.

In this magnetic sensor1, for example, a half-bridge circuit is constructed from the radial magnetoresistance element2aand the polygonal magnetoresistance element4b, in the same manner as, e.g., the half-bridge circuit14shown inFIG. 6B. Alternatively, the magnetic sensor1may have a full-bridge circuit constructed from two radial magnetoresistance elements and two polygonal magnetoresistance elements as in the first embodiment.

The magnetoresistance element4bhas a regular polygonal shape with N vertices.FIG. 7shows N=12, i.e., the magnetoresistance element4bhaving a regular dodecagonal shape, as an example. When N=infinity, the magnetoresistance element4bhas approximately an annular shape. Therefore, by appropriately selecting N, it is possible to obtain the same detection results as those by the annular magnetoresistance element. The shape of the polygonal magnetoresistance element is not limited to a regular polygon as long as it is a polygonal shape with which the same detection results as those by the annular magnetoresistance element are obtained.

Although some embodiments and modifications of the invention have been described, the embodiments and modifications are merely examples and the invention according to claims is not to be limited thereto. These new embodiments and modifications may be implemented in various other forms, and various omissions, substitutions and changes, etc., can be made without departing from the gist of the invention. In addition, all combinations of the features described in the embodiments and modifications are not necessary to solve the problem of the invention. Further, these embodiments and modifications are included within the scope and gist of the invention and also within the invention described in the claims and the range of equivalency.

REFERENCE SIGNS LIST