Magnetic sensor

Abstract

The technical problem of the present invention is to reduce the amount of current required for modulation in a magnetic sensor capable of detecting a magnetic field in a low-frequency region with high sensitivity. This magnetic sensor (1) is provided with: a sensor chip (100) having magnetosensitive elements (R1 to R4); compensation coils (C1, C2) for generating a cancelling magnetic field on the basis of the output signals ([delta] V) of the magnetosensitive elements (R1-R4); a switch (SW1) connected in series with the compensation coil (C1); a control circuit (130) that periodically turns on and off the switch (SW1); and a resistor (143) for performing current-voltage conversion on the compensation current (i2) flowing through the compensation coil (C2).

Description

Technical Field

[0001] The present disclosure relates to a magnetic sensor, and in particular to a magnetic sensor capable of detecting a magnetic field in a low-frequency region with high sensitivity. Background Art

[0002] Magnetic sensors using magnetosensitive elements are currently used in a wide variety of fields. Detecting extremely weak magnetic fields requires magnetic sensors with a high signal-to-noise ratio (S / N) ratio. 1 / f noise is a major factor that reduces the S / N ratio of magnetic sensors. The lower the frequency components of the magnetic field being measured, the more pronounced this 1 / f noise becomes. Therefore, reducing 1 / f noise is crucial for highly sensitive detection of magnetic fields in low-frequency regions, such as those below 1 kHz.

[0003] As a magnetic sensor that reduces 1 / f noise, there is known a magnetic sensor described in Patent Document 1. The magnetic sensor described in Patent Document 1 reduces 1 / f noise by periodically saturating a magnetic sensor using a modulation method.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2020-522696 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, the magnetic sensor described in Patent Document 1 has a problem in that a large current is required to saturate the magnetic sensing element.

[0009] In the present disclosure, a technology for reducing the amount of current required for modulation in a magnetic sensor capable of detecting a magnetic field in a low-frequency region with high sensitivity will be described.

[0010] Means used to solve problems

[0011] A magnetic sensor according to one aspect of the present disclosure includes: a sensor chip having a magnetic sensitive element; first and second compensation coils for generating a canceling magnetic field based on an output signal of the magnetic sensitive element; a first switch connected in series with the first compensation coil; a control circuit for periodically turning the first switch on and off; and a detection circuit for detecting a compensation current flowing in the second compensation coil.

[0012] Effects of the Invention

[0013] According to the present disclosure, a technology is provided for reducing the amount of current required for modulation in a magnetic sensor capable of detecting a magnetic field in a low-frequency region with high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic perspective view showing the appearance of the magnetic sensor 1 according to the first embodiment of the present disclosure.

[0015] Figure 2 It is a schematic perspective view of the sensor chip 100 .

[0016] Figure 3 FIG. 1 is a schematic top view of the sensor chip 100 .

[0017] Figure 4 It is along Figure 3 Rough cross-section diagram of line AA.

[0018] Figure 5 is a circuit diagram of the magnetic sensor 1.

[0019] Figure 6 It is a graph for explaining the effect of the magnetic sensor 1 .

[0020] Figure 7 1 is a circuit diagram of a magnetic sensor 2 according to a second embodiment of the present disclosure.

[0021] Figure 8 It is a schematic perspective view showing the appearance of a magnetic sensor 3 according to a third embodiment of the present disclosure.

[0022] Figure 9 It is a schematic perspective view showing the appearance of a magnetic sensor 4 according to a fourth embodiment of the present disclosure.

[0023] Description of Reference Signs

[0024] 1 to 4 magnetic sensors

[0025] 100 sensor chips

[0026] 101 component forming surface

[0027] 102 back

[0028] 103-106 side

[0029] 107~109 insulation layer

[0030] 110, 120 sets of magnets

[0031] Areas 110a, 124a, and 125a

[0032] 121 Main Body

[0033] 122, 123 protrusions

[0034] 124, 125 overhang

[0035] 130 control circuit

[0036] 141, 142 operational amplifiers

[0037] 143 resistor

[0038] C1, C2 compensation coils

[0039] G1~G4 gap

[0040] M1 to M3 magnetic layers

[0041] R1~R4 magnetic sensitive elements

[0042] SW1, SW2 switches

[0043] i1, i2 compensation current DETAILED DESCRIPTION

[0044] Hereinafter, embodiments of the technology according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0045] Figure 1 It is a schematic perspective view showing the appearance of the magnetic sensor 1 according to the first embodiment of the present disclosure.

[0046] like Figure 1 As shown, the magnetic sensor 1 of the first embodiment includes a sensor chip 100 having a magnetic sensor element; magnetic flux collectors 110 and 120 for concentrating the magnetic field on the magnetic sensor element provided on the sensor chip 100; and a compensation coil C1 wound around the magnetic flux collector 110. Both magnetic flux collectors 110 and 120 are blocks made of a high-permeability material such as ferrite. The magnetic flux collector 110 is a rod-shaped structure with its longitudinal side oriented in the Z direction, with its end in the -Z direction facing the sensor chip 100.

[0047] A compensation coil C1 is wound around the magnetic flux collector 110, with the Z direction as its axial direction. The magnetic flux collector 120 comprises a main body 121 with its longitudinal side oriented in the Z direction; a pair of protrusions 122 and 123 that protrude further in the +Z direction from the +Z end of the main body 121 and are thinner in the X direction than the main body 121; an overhang 124 that protrudes from the +Z end of the protrusion 122 in the +X direction; and an overhang 125 that protrudes from the +Z end of the protrusion 123 in the -X direction. The sensor chip 100 is positioned in the space enclosed by the main body 121, the protrusions 122 and 123, and the overhangs 124 and 125.

[0048] Figure 2 It is a schematic perspective view of the sensor chip 100 .

[0049] like Figure 2As shown, sensor chip 100 has an element-forming surface 101 and a back surface 102, which form the XY plane and are located on opposite sides of each other; side surfaces 103 and 104, which form the YZ plane and are located on opposite sides of each other; and side surfaces 105 and 106, which form the XZ plane and are located on opposite sides of each other. The magnetic sensing element and magnetic layers M1 to M3, described later, are formed on element-forming surface 101 of sensor chip 100.

[0050] Figure 3 is a rough top view of the sensor chip 100. Figure 4 It is along Figure 3 Rough cross-section diagram of line AA.

[0051] like Figure 3 and Figure 4 As shown, four magnetic sensing elements R1 to R4 are formed on the element forming surface 101 of the sensor chip 100. There are no particular limitations on the types of magnetic sensing elements R1 to R4, as long as their resistance changes depending on the direction of magnetic flux; for example, MR elements can be used. The fixed magnetization directions of the magnetic sensing elements R1 to R4 are aligned and face the same direction (e.g., the positive direction in the X direction). The magnetic sensing elements R1 to R4 are disposed on the surface of an insulating layer 107 covering the element forming surface 101. The magnetic sensing elements R1 to R4 are covered by an insulating layer 108, on which magnetic layers M1 to M3 made of permalloy or the like are formed. The magnetic layers M1 to M3 are covered by an insulating layer 109. Magnetic layer M1 is positioned approximately in the center of the element forming surface 101 in the X direction. Magnetic layers M2 and M3 are positioned on either side of the element forming surface 101 in the X direction, sandwiching magnetic layer M1 in the X direction.

[0052] The magnetic layers M1 and M2 form two slits (gaps) G1 and G2, extending in the Y direction with the X direction as their width. The X-direction positions of slits G1 and G2 coincide with each other, and the two are aligned in the Y direction. The magnetic layers M1 and M3 form two slits G3 and G4, extending in the Y direction with the X direction as their width. The X-direction positions of slits G3 and G4 coincide with each other, and the two are aligned in the Y direction. Furthermore, slits G1 and G3 are aligned in the X direction, while slits G2 and G4 are aligned in the X direction. Furthermore, magnetic sensors R1 to R4 are positioned so as to overlap with slits G1 to G4 when viewed from above in the Z direction. Consequently, the X-direction magnetic field passing through magnetic gaps G1 to G4 is applied to magnetic sensors R1 to R4, respectively.

[0053] exist Figure 3 and Figure 4In the figure, the area indicated by reference numeral 110a represents the area covered in the Z direction by the XY plane located at one end of the magnet collector 110 in the Z direction. The areas indicated by reference numerals 124a and 125a represent the areas covered in the Z direction by the overhanging portions 124 and 125 of the magnet collector 120, respectively. Furthermore, the side surface 103 of the sensor chip 100 is covered in the X direction by the protruding portion 122 of the magnet collector 120, and the side surface 104 of the sensor chip 100 is covered in the X direction by the protruding portion 123 of the magnet collector 120. Furthermore, the back surface 102 of the sensor chip 100 is covered by the main body 121 of the magnet collector 120.

[0054] Regions 110a, 124a, and 125a overlap with magnetic layers M1 to M3, respectively. Consequently, magnetic layer M1 is covered by magnetism collector 110 from the Z direction, magnetic layer M2 is covered by overhanging portion 124 of magnetism collector 120 from the Z direction, and magnetic layer M3 is covered by overhanging portion 125 of magnetism collector 120 from the Z direction. Furthermore, the Z-direction magnetic field, which serves as the magnetic field to be detected, is collected by magnetism collector 110 and applied to magnetic layer M1 via magnetism collector 110. The magnetic field applied to magnetic layer M1 is bent in the +X and -X directions within magnetic layer M1. The magnetic flux component bent in the -X direction within magnetic layer M1 is supplied to magnetic layer M2 through slits G1 and G2, then flows toward overhanging portion 124, protrusion 122, and main body 121 of magnetism collector 120. At this time, a portion of the magnetic flux passing through slits G1 and G2 in the -X direction is applied to magnetic sensors R1 and R2. Meanwhile, the magnetic flux component bent in the +X direction by magnetic layer M1 is supplied to magnetic layer M3 via slits G3 and G4, then flows toward overhang 125, protrusion 123, and main body 121 of magnetism collector 120. At this time, a portion of the magnetic flux passing through slits G3 and G4 in the +X direction is applied to magnetic sensors R3 and R4.

[0055] While it's not essential to have overhangs 124 and 125 on the magnetism collector 120, covering the magnetic layers M2 and M3 with the overhangs 124 and 125, respectively, significantly reduces the magnetic resistance between the magnetism collector 110 and the magnetism collector 120. Furthermore, even when the magnetism collector 120 doesn't have overhangs 124 and 125, the protrusions 122 and 123 of the magnetism collector 120 can cover the side surfaces 103 and 104 of the sensor chip 100, thereby reducing the magnetic resistance between the magnetism collector 110 and the magnetism collector 120. Furthermore, the main body 121 of the magnetism collector 120 can cover the back surface 102 of the sensor chip 100, effectively applying the Z-direction magnetic field to be detected to the magnetosensitive elements R1 to R4.

[0056] like Figure 2 and Figure 4As shown, a compensation coil C2 is provided in the sensor chip 100. The compensation coil C2 is provided, for example, at a position overlapping with the magnetic sensing elements R1 to R4. When a compensation current flows through the compensation coil C2, a canceling magnetic field is applied to the magnetic sensing elements R1 to R4. Figure 4 In the example shown, compensation coil C2 is provided on element forming surface 101. Since compensation coil C2 is integrated into sensor chip 100, the distance between compensation coil C2 and magnetic sensors R1-R4 is significantly shorter than the distance between compensation coil C1 and magnetic sensors R1-R4. However, compensation coil C2 does not necessarily need to be located overlapping with magnetic sensors R1-R4; for example, it can be wound around magnetic layers M2 and M3. In this case, the distance between compensation coil C2 and magnetic sensors R1-R4 is significantly shorter than the distance between compensation coil C1 and magnetic sensors R1-R4.

[0057] Figure 5 1 is a circuit diagram of the magnetic sensor 1 according to the first embodiment.

[0058] like Figure 5 As shown, magnetic sensors R1-R4 are connected as a bridge between power supply Vcc and ground GND. Specifically, magnetic sensors R1 and R4 are connected in series between power supply Vcc and ground GND, while magnetic sensors R3 and R2 are connected in series between power supply Vcc and ground GND. Furthermore, the potential difference between the potential Va at the connection point between magnetic sensors R1 and R4 and the potential Vb at the connection point between magnetic sensors R3 and R2 is used as the output signal ΔV (=Va-Vb). Thus, magnetic sensors R1-R4 form a differential bridge circuit, and changes in the resistance of magnetic sensors R1-R4 corresponding to the magnetic flux density are reflected as the level of the output signal ΔV.

[0059] The output signal ΔV is supplied to both operational amplifiers 141 and 142. The compensation current i1 output from operational amplifier 141 is supplied to the compensation coil C1. In this embodiment, a switch SW1 is connected in series with the compensation coil C1. Therefore, when the switch SW1 is on, the compensation current i1 flows through the compensation coil C1 to ground GND. Conversely, when the switch SW1 is off, the compensation current i1 does not flow through the compensation coil C1. When the compensation current i1 flows through the compensation coil C1, a canceling magnetic field is generated. Therefore, when an output signal ΔV corresponding to the magnetic flux density of the magnetic field to be detected is generated, the corresponding compensation current i1 flows through the compensation coil C1, generating a canceling magnetic field in the opposite direction, thereby canceling the magnetic field to be detected flowing through the magnetic flux collector 110. In other words, the magnetic field to be detected is not applied to the magnetic sensors R1 to R4.

[0060] The switch SW1 is turned on and off by the control circuit 130. The control circuit 130 periodically turns the switch SW1 on and off. The frequency of turning the switch SW1 on and off is set to be much higher than the frequency of the magnetic field to be detected.

[0061] The compensation current i2 output from the operational amplifier 142 is supplied to the compensation coil C2. Figure 2 and Figure 4 As shown, the sensor chip 100 is integrated with the compensating current i2 output by the operational amplifier 142. When the compensating current i2 flows through the compensating coil C2, a cancelling magnetic field is generated. Consequently, when an output signal ΔV corresponding to the magnetic flux density of the target magnetic field is generated, the corresponding compensating current i2 flows through the compensating coil C2, generating a cancelling magnetic field in the opposite direction. The target magnetic field applied to the magnetic sensors R1 to R4 is canceled on the sensor chip 100. Furthermore, the compensating current i2 is converted to voltage by resistor 143 to generate the output signal Vout, enabling detection of the target magnetic field's intensity. In this case, resistor 143 constitutes the detection circuit for detecting the compensating current i2 flowing through the compensating coil C2.

[0062] Thus, the magnetic sensor 1 of this embodiment includes two compensation coils C1 and C2. Compensation coil C1, located farther from magnetic sensors R1 to R4, cancels the magnetic field to be detected flowing through magnetic flux collector 110, while compensation coil C2, located closer to magnetic sensors R1 to R4, cancels the magnetic field to be detected on sensor chip 100. Furthermore, a switch SW1, which periodically switches on and off, is connected in series with compensation coil C1. Therefore, when switch SW1 is off, the magnetic field to be detected flowing through magnetic flux collector 110 is not canceled, and the magnetic field to be detected is applied to magnetic sensors R1 to R4, resulting in an output signal Vout corresponding thereto. On the other hand, when switch SW1 is on, the magnetic field to be detected flowing through magnetic flux collector 110 is canceled, and the magnetic field to be detected is not applied to magnetic sensors R1 to R4, resulting in an output signal Vout that is substantially zero.

[0063] In other words, the magnetic field to be detected, applied to magnetic sensors R1-R4, is modulated by the on-off frequency of switch SW1. This significantly reduces 1 / f noise, even when the frequency of the weak magnetic field being detected is low. Furthermore, since the characteristics of magnetic sensors R1-R4 are modulated, not the magnetic field being detected, the noise of magnetic sensors R1-R4 themselves is not modulated.

[0064] Furthermore, the compensation current i1 required to flow through compensation coil C1 is sufficient to offset the magnetic field of the target object and is significantly smaller than the current required to magnetically saturate magnetic collector 110 and magnetic sensors R1-R4. This reduces the amount of compensation current i1 supplied by operational amplifier 141, thereby reducing current consumption and suppressing heat generation caused by the compensation current. Furthermore, since compensation current i2, which generates output signal Vout, flows through compensation coil C2 integrated into sensor chip 100, a more accurate output signal Vout can be obtained.

[0065] Figure 6 1 is a graph for explaining the effect of the magnetic sensor 1 of this embodiment. The solid line represents the frequency characteristics of the noise of the magnetic sensor 1 of this embodiment, and the dotted line represents the frequency characteristics of the noise of a conventional magnetic sensor without the amplifier 141, the compensation coil C1, and the switch SW1. Figure 6 As shown, it can be seen that in the magnetic sensor 1 of this embodiment, the detection target magnetic field is modulated by the on-off frequency of the switch SW1 , so that the 1 / f noise is significantly reduced, especially in the low-frequency region.

[0066] Figure 7 1 is a circuit diagram of a magnetic sensor 2 according to a second embodiment of the present disclosure.

[0067] like Figure 7 As shown, the magnetic sensor 2 of the second embodiment differs from the magnetic sensor 1 of the first embodiment in that it further includes a switch SW2 connected in series with the compensation coil C2. The rest of the basic structure is the same as that of the magnetic sensor 1 of the first embodiment. Therefore, the same reference numerals are used to designate the same elements, and duplicate descriptions are omitted.

[0068] Switch SW2 is controlled on and off by the control circuit 130. The control circuit 130 turns on switch SW2 when switch SW1 is off, and turns off switch SW2 when switch SW1 is on. Specifically, during the period in which the target magnetic field passing through the magnetic sensors R1 to R4 is being detected, an output signal Vout corresponding to the strength of the target magnetic field is obtained. Conversely, during the period in which the target magnetic field is not being applied to the magnetic sensors R1 to R4, the output signal Vout is fixed at ground level. In this way, the magnetic sensor 2 of the second embodiment reliably maintains the output signal Vout at ground level during the period in which the compensation coil C1 cancels the target magnetic field flowing through the magnetic flux collector 110.

[0069] Figure 8 It is a schematic perspective view showing the appearance of a magnetic sensor 3 according to a third embodiment of the present disclosure.

[0070] like Figure 8As shown, the magnetic sensor 3 of the third embodiment differs from the magnetic sensor 1 of the first embodiment in that the compensation coil C1 is wound around the magnetic flux collector 120. The rest of the basic structure is the same as that of the magnetic sensor 1 of the first embodiment, and therefore, the same reference numerals are used to designate the same elements, and duplicate descriptions are omitted.

[0071] As illustrated in the magnetic sensor 3 of the third embodiment, when two magnetic field collectors 110 and 120 are arranged so that at least a portion of the magnetic field flowing from one magnetic field collector (e.g., magnetic field collector 110) to the other magnetic field collector (e.g., magnetic field collector 120) passes through the magnetosensitive elements R1 to R4, the compensation coil C1 can be wound around either magnetic field collector. Alternatively, the compensation coil C1 can be wound around both magnetic field collectors 110 and 120.

[0072] In addition, if Figure 8 As shown, when the compensation coil C1 is wound around the magnetic collecting body 120, it is also possible to use Figure 7 As described above, the switch SW2 that turns on and off in conjunction with the switch SW1 is connected in series with the compensation coil C2.

[0073] Figure 9 It is a schematic perspective view showing the appearance of a magnetic sensor 4 according to a fourth embodiment of the present disclosure.

[0074] like Figure 9 As shown, the magnetic sensor 4 of the fourth embodiment differs from the magnetic sensor 1 of the first embodiment in that the compensation coil C2 is wound around the magnetic flux collector 120. The rest of the basic structure is the same as that of the magnetic sensor 1 of the first embodiment, and therefore, the same reference numerals are used to designate the same elements, and duplicate descriptions are omitted.

[0075] In this embodiment, the compensation coil C2 integrated into the sensor chip 100 is not required. Therefore, a sensor chip 100 without the compensation coil C2 can be used. Alternatively, when using a sensor chip 100 equipped with the compensation coil C2, the compensation current i2 may not be supplied to the compensation coil C2 on the sensor chip 100. In this embodiment, the compensation current i2 is not supplied to the compensation coil C2 wound around the magnetic flux collector 120.

[0076] As illustrated by the magnetic sensor 4 of the fourth embodiment, when two magnetic collectors 110 and 120 are configured in such a manner that at least a portion of the magnetic field flows from one magnetic collector (for example, magnetic collector 110) to another magnetic collector (for example, magnetic collector 120) through magnetic sensitive elements R1 to R4, the compensation coil C1 can be wound around one magnetic collector and the compensation coil C2 can be wound around the other magnetic collector.

[0077] In addition, in this embodiment, it is also possible to use Figure 7 As described above, the switch SW2 that turns on and off in conjunction with the switch SW1 is connected in series with the compensation coil C2.

[0078] While the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present disclosure. Such modifications are naturally included in the scope of the present disclosure.

[0079] The technology according to the present disclosure includes the following configuration examples, but is not limited thereto.

[0080] A magnetic sensor according to one aspect of the present disclosure includes: a sensor chip having a magnetic sensor; first and second compensation coils that generate canceling magnetic fields based on an output signal from the magnetic sensor; a first switch connected in series with the first compensation coil; a control circuit that periodically turns the first switch on and off; and a detection circuit that detects the compensation current flowing through the second compensation coil. This allows the magnetic field applied to the magnetic sensor to be modulated by the on / off frequency of the first switch, significantly reducing 1 / f noise.

[0081] In the magnetic sensor described above, the distance between the second compensation coil and the magnetic sensor may be shorter than the distance between the first compensation coil and the magnetic sensor. This allows the modulated magnetic field to be offset near the magnetic sensor, thereby achieving higher sensitivity.

[0082] The magnetic sensor may further include a first magnetic flux collector that collects magnetic fields on the magnetic sensing element, and a first compensation coil wound around the first magnetic flux collector.

[0083] In the magnetic sensor described above, the second compensation coil may be integrated into the sensor chip, thereby enabling the modulated detection target magnetic field on the sensor chip to be converted into an output signal through closed-loop control.

[0084] The magnetic sensor may further include a second magnetic collector for concentrating the magnetic field on the magnetic sensitive element, the sensor chip being disposed between the first and second magnetic collectors, and a second compensation coil being wound around the second magnetic collector. This allows the modulated magnetic field of the detection target on the second magnetic collector to be converted into an output signal through closed-loop control.

[0085] The magnetic sensor may further include a second switch connected in series with the second compensation coil, wherein the control circuit turns on the second switch when the first switch is off and turns off the second switch when the first switch is on. This allows the output signal to be fixed during the period when the magnetic field of the detection target is canceled.

Claims

1. A magnetic sensor, wherein: have: A sensor chip having a magnetic sensitive element; generating a first compensation coil and a second compensation coil to cancel the magnetic field based on the output signal of the magnetic sensitive element; a first switch connected in series with the first compensation coil; a control circuit for periodically turning the first switch on and off; and A detection circuit detects a compensation current flowing through the second compensation coil.

2. The magnetic sensor according to claim 1, wherein Compared with the distance between the first compensation coil and the magnetic sensitive element, the distance between the second compensation coil and the magnetic sensitive element is shorter.

3. The magnetic sensor according to claim 1, wherein It also includes: a first magnetizer for focusing the magnetic field on the magnetic sensitive element, The first compensation coil is wound around the first magnetic flux collector.

4. The magnetic sensor according to claim 3, wherein The second compensation coil is integrated with the sensor chip.

5. The magnetic sensor according to claim 2, wherein It also includes: a second magnetizer for focusing the magnetic field on the magnetic sensitive element, The sensor chip is arranged between the first magnetic collecting body and the second magnetic collecting body. The second compensation coil is wound around the second magnetic flux collector.

6. The magnetic sensor according to any one of claims 1 to 5, wherein further comprising: a second switch connected in series with the second compensation coil, The control circuit turns on the second switch while the first switch is off, and turns off the second switch while the first switch is on.

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