Magnetic sensor

Abstract

To reduce the amount of current required for modulation in a magnetic sensor capable of sensitively detecting a magnetic field in a low-frequency region.SOLUTION: A magnetic sensor 1 includes: a sensor chip 100 having magnetic sensing elements R1 to R4; compensation coils C1 and C2 for generating a cancel magnetic field on the basis of an output signal ▵V of the magnetic sensing elements R1 to R4; a switch SW1 connected in series to the compensation coil C1; a control circuit 130 for periodically turning on and off the switch SW1; and a resistor 143 for converting a compensation current i2 flowing through the compensation coil C2 into a voltage.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a magnetic sensor, and more particularly to a magnetic sensor capable of detecting magnetic fields in a low frequency range with high sensitivity. [Background technology]

[0002] Currently, magnetic sensors using magneto-sensitive elements are used in a variety of fields, but to detect extremely weak magnetic fields, magnetic sensors with a high S / N ratio are required. One factor that reduces the S / N ratio of magnetic sensors is 1 / f noise. 1 / f noise becomes more pronounced the lower the frequency component of the magnetic field being measured. Therefore, reducing 1 / f noise is important for highly sensitive detection of magnetic fields in the low-frequency range, for example, below 1 kHz.

[0003] A known magnetic sensor that reduces 1 / f noise is the magnetic sensor described in Patent Document 1. The magnetic sensor described in Patent Document 1 reduces 1 / f noise by periodically saturating the magnetic sensing element using modulation means. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2020-522696 Summary of the Invention [Problem to be solved by the invention]

[0005] 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.

[0006] This disclosure describes a technology for reducing the amount of current required for modulation in a magnetic sensor that can detect magnetic fields in the low frequency range with high sensitivity. [Means for solving the problem]

[0007] A magnetic sensor according to one aspect of the present disclosure comprises a sensor chip having a magnetic sensing element, first and second compensation coils that generate a canceling magnetic field based on an output signal of the magnetic sensing element, a first switch connected in series to the first compensation coil, a control circuit that periodically turns the first switch on and off, and a detection circuit that detects a compensation current flowing through the second compensation coil. [Effects of the Invention]

[0008] According to the present disclosure, a technique is provided for reducing the amount of current required for modulation in a magnetic sensor capable of detecting magnetic fields in the low frequency range with high sensitivity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 1 according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic perspective view of the sensor chip 100. As shown in FIG. [Figure 3] FIG. 3 is a schematic plan view of the sensor chip 100. As shown in FIG. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line AA in FIG. [Figure 5] FIG. 5 is a circuit diagram of the magnetic sensor 1. [Figure 6] FIG. 6 is a graph for explaining the effect of the magnetic sensor 1. In FIG. [Figure 7] FIG. 7 is a circuit diagram of a magnetic sensor 2 according to the second embodiment of the present disclosure. [Figure 8] FIG. 8 is a schematic perspective view showing the appearance of a magnetic sensor 3 according to the third embodiment of the present disclosure. [Figure 9] FIG. 9 is a schematic perspective view showing the appearance of a magnetic sensor 4 according to the fourth embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the technology according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0011] FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 1 according to a first embodiment of the present disclosure.

[0012] 1, the magnetic sensor 1 according to the first embodiment includes a sensor chip 100 having a magnetic sensing element, magnetic collectors 110 and 120 that collect a magnetic field to the magnetic sensing element provided on the sensor chip 100, and a compensation coil C1 wound around the magnetic collector 110. The magnetic collectors 110 and 120 are both blocks made of a high-permeability material such as ferrite. The magnetic collector 110 is a rod-shaped body with its longitudinal direction in the Z direction, and its end in the -Z direction faces the sensor chip 100.

[0013] A compensation coil C1 with its axial direction aligned in the Z direction is wound around the magnetic collector 110. The magnetic collector 120 has a main body 121 with its longitudinal direction aligned in the Z direction, a pair of protrusions 122 and 123 that protrude further in the +Z direction from an end of the main body 121 in the +Z direction and have a thickness in the X direction that is thinner than that of the main body 121, an overhang 124 that protrudes in the +X direction from the end of the protrusion 122 in the +Z direction, and an overhang 125 that protrudes in the -X direction from the end of the protrusion 123 in the +Z direction. The sensor chip 100 is disposed in a space surrounded by the main body 121, the protrusions 122 and 123, and the overhangs 124 and 125.

[0014] FIG. 2 is a schematic perspective view of the sensor chip 100. As shown in FIG.

[0015] 2, the sensor chip 100 has an element forming surface 101 and a back surface 102 which are located opposite each other and form an XY plane, side surfaces 103 and 104 which are located opposite each other and form a YZ plane, and side surfaces 105 and 106 which are located opposite each other and form an XZ plane. A magnetic sensing element and magnetic layers M1 to M3, which will be described later, are formed on the element forming surface 101 of the sensor chip 100.

[0016] FIG. 3 is a schematic plan view of the sensor chip 100, and FIG. 4 is a schematic cross-sectional view taken along line AA in FIG.

[0017] As shown in FIGS. 3 and 4, four magnetically sensitive elements R1 to R4 are formed on the element forming surface 101 of the sensor chip 100. The magnetically sensitive elements R1 to R4 are not particularly limited as long as they are elements whose electrical resistance changes depending on the direction of magnetic flux, and for example, MR elements can be used. The fixed magnetization directions of the magnetically sensitive elements R1 to R4 are aligned in the same direction (for example, the positive side in the X direction). The magnetically sensitive elements R1 to R4 are provided on the surface of an insulating layer 107 that covers the element forming surface 101. The magnetically sensitive elements R1 to R4 are covered with an insulating layer 108, and magnetic layers M1 to M3 made of permalloy or the like are formed on the surface of the insulating layer 108. The magnetic layers M1 to M3 are covered with an insulating layer 109. The magnetic layer M1 is disposed approximately in the center of the element forming surface 101 in the X direction. The magnetic layers M2 and M3 are disposed on both sides of the element forming surface 101 in the X direction so as to sandwich the magnetic layer M1 in the X direction.

[0018] The magnetic layers M1 and M2 form two gaps G1 and G2 that extend in the Y direction and have the X direction as their width direction. The positions of the gaps G1 and G2 in the X direction coincide with each other, and they are aligned in the Y direction. The magnetic layers M1 and M3 form two gaps G3 and G4 that extend in the Y direction and have the X direction as their width direction. The positions of the gaps G3 and G4 in the X direction coincide with each other, and they are aligned in the Y direction. Furthermore, the gaps G1 and G3 are aligned in the X direction, and the gaps G2 and G4 are aligned in the X direction. The magnetic sensing elements R1 to R4 are positioned so as to overlap with the gaps G1 to G4, respectively, in a plan view seen from the Z direction. As a result, the magnetic field in the X direction passing through the magnetic gaps G1 to G4 is applied to the magnetic sensing elements R1 to R4, respectively.

[0019] 3 and 4, the region indicated by reference numeral 110a indicates a region covered from the Z direction by the XY plane located at one end of the magnetic collector 110 in the Z direction, and the regions indicated by reference numerals 124a and 125a indicate regions covered from the Z direction by the overhanging portions 124 and 125 of the magnetic collector 120, respectively. Furthermore, the side surface 103 of the sensor chip 100 is covered from the X direction by the protruding portion 122 of the magnetic collector 120, and the side surface 104 of the sensor chip 100 is covered from the X direction by the protruding portion 123 of the magnetic collector 120. Furthermore, the back surface 102 of the sensor chip 100 is covered by the main body portion 121 of the magnetic collector 120.

[0020] The regions 110a, 124a, and 125a overlap the magnetic layers M1 to M3, respectively. As a result, the magnetic layer M1 is covered from the Z direction by the magnetic collector 110, the magnetic layer M2 is covered from the Z direction by the overhanging portion 124 of the magnetic collector 120, and the magnetic layer M3 is covered from the Z direction by the overhanging portion 125 of the magnetic collector 120. The magnetic field in the Z direction, which is the magnetic field to be detected, is collected by the magnetic collector 110 and applied to the magnetic layer M1 via the magnetic collector 110. The magnetic field applied to the magnetic layer M1 is bent in the +X direction and the −X direction in the magnetic layer M1. The magnetic flux component bent in the −X direction in the magnetic layer M1 is supplied to the magnetic layer M2 via the gaps G1 and G2, and then flows to the overhanging portion 124 of the magnetic collector 120, the protrusion 122, and the main body portion 121. At this time, part of the magnetic flux passing through gaps G1 and G2 in the -X direction is applied to magnetic sensing elements R1 and R2. Meanwhile, the magnetic flux component bent in the +X direction in magnetic layer M1 is supplied to magnetic layer M3 through gaps G3 and G4, and then flows to overhang portion 125, protrusion 123, and main body portion 121 of magnetic collector 120. At this time, part of the magnetic flux passing through gaps G3 and G4 in the +X direction is applied to magnetic sensing elements R3 and R4.

[0021] Although it is not essential to provide the overhanging portions 124, 125 on the magnetic collector 120, by covering the magnetic layers M2, M3 with the overhanging portions 124, 125, respectively, it is possible to significantly reduce the magnetic resistance between the magnetic collector 110 and the magnetic collector 120. Furthermore, even if the magnetic collector 120 does not have the overhanging portions 124, 125, it is possible to reduce the magnetic resistance between the magnetic collector 110 and the magnetic collector 120 by covering the side surfaces 103, 104 of the sensor chip 100 with the protruding portions 122, 123 of the magnetic collector 120. Furthermore, by covering the back surface 102 of the sensor chip 100 with the main body portion 121 of the magnetic collector 120, it is possible to efficiently apply the magnetic field in the Z direction to be detected to the magnetic sensing elements R1 to R4.

[0022] As shown in FIGS. 2 and 4, the sensor chip 100 is provided with a compensation coil C2. The compensation coil C2 is provided, for example, at a position overlapping 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. In the example shown in FIG. 4, the compensation coil C2 is provided on the element formation surface 101. Because the compensation coil C2 is integrated into the sensor chip 100, the distance between the compensation coil C2 and the magnetic sensing elements R1 to R4 is significantly shorter than the distance between the compensation coil C1 and the magnetic sensing elements R1 to R4. However, it is not essential that the compensation coil C2 be provided at a position overlapping the magnetic sensing elements R1 to R4; for example, the compensation coil C2 may be wound around the magnetic layers M2 and M3. Even in this case, the distance between the compensation coil C2 and the magnetic sensing elements R1 to R4 is significantly shorter than the distance between the compensation coil C1 and the magnetic sensing elements R1 to R4.

[0023] FIG. 5 is a circuit diagram of the magnetic sensor 1 according to the first embodiment.

[0024] As shown in Figure 5, magnetic sensing elements R1 to R4 are bridge-connected between the power supply Vcc and ground GND. That is, magnetic sensing elements R1 and R4 are connected in series between the power supply Vcc and ground GND, and magnetic sensing elements R3 and R2 are connected in series between the power supply Vcc and ground GND. The potential difference between the potential Va appearing at the connection point between magnetic sensing elements R1 and R4 and the potential Vb appearing at the connection point between magnetic sensing elements R3 and R2 is used as the output signal ΔV (= Va - Vb). In this way, magnetic sensing elements R1 to R4 form a differential bridge circuit, and the change in the electrical resistance of magnetic sensing elements R1 to R4 according to the magnetic flux density appears as the level of the output signal ΔV.

[0025] The output signal ΔV is supplied in common to the operational amplifiers 141 and 142. The compensation current i1 output from the 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, while the switch SW1 is on, the compensation current i1 flows to ground GND via the compensation coil C1, whereas while the switch SW1 is off, the compensation current i1 does not flow to the compensation coil C1. When the compensation current i1 flows to the compensation coil C1, a canceling magnetic field is generated. As a result, 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 to the compensation coil C1, generating a canceling magnetic field in the opposite direction, and canceling the magnetic field to be detected flowing through the magnetic collector 110. In other words, the magnetic field to be detected is no longer applied to the magnetic sensing elements R1 to R4.

[0026] The on / off of the switch SW1 is controlled by the control circuit 130. The control circuit 130 periodically turns the switch SW1 on and off. The frequency at which the switch SW1 is turned on and off is set to be sufficiently higher than the frequency of the magnetic field to be detected.

[0027] The compensation current i2 output from the operational amplifier 142 is supplied to the compensation coil C2. The compensation coil C2 is integrated on the sensor chip 100 as shown in FIGS. 2 and 4. When the compensation current i2 output from the operational amplifier 142 flows through the compensation coil C2, a canceling magnetic field is generated. As a result, an output signal ΔV corresponding to the magnetic flux density of the magnetic field to be detected is generated. The corresponding compensation current i2 flows through the compensation coil C2, generating a canceling magnetic field in the opposite direction, and the magnetic field to be detected applied to the magnetic sensing elements R1 to R4 is canceled on the sensor chip 100. Then, by converting the compensation current i2 from current to voltage using a resistor 143 to generate an output signal Vout, it becomes possible to detect the strength of the magnetic field to be detected. In this case, the resistor 143 forms a detection circuit that detects the compensation current i2 flowing through the compensation coil C2.

[0028] As described above, the magnetic sensor 1 according to this embodiment includes two compensation coils C1 and C2. The compensation coil C1, which is far from the magnetic sensitive elements R1 to R4, cancels the magnetic field to be detected that flows through the magnetic collector 110, while the compensation coil C2, which is close to the magnetic sensitive elements R1 to R4, cancels the magnetic field to be detected on the sensor chip 100. The switch SW1, which is periodically turned on and off, is connected in series to the compensation coil C1. Therefore, while the switch SW1 is off, the magnetic field to be detected that flows through the magnetic collector 110 is not canceled, and the magnetic field to be detected is applied to the magnetic sensitive elements R1 to R4, and a corresponding output signal Vout is obtained. Meanwhile, while the switch SW1 is on, the magnetic field to be detected that flows through the magnetic collector 110 is canceled, and the magnetic field to be detected is no longer applied to the magnetic sensitive elements R1 to R4, and the output signal Vout becomes approximately zero.

[0029] In other words, the magnetic field to be detected that is applied to the magnetic sensing elements R1 to R4 is modulated by the on / off frequency of the switch SW1. This significantly reduces 1 / f noise, even when the frequency of the weak magnetic field to be detected is low. Furthermore, because the magnetic field to be detected is modulated rather than the characteristics of the magnetic sensing elements R1 to R4, the noise of the magnetic sensing elements R1 to R4 themselves is not modulated.

[0030] Furthermore, the compensation current i1 that needs to flow through the compensation coil C1 is a current amount that cancels the magnetic field to be detected, and is significantly smaller than the current amount required to magnetically saturate the magnetic collector 110 and the magnetic sensing elements R1 to R4. This reduces the amount of compensation current i1 supplied from the operational amplifier 141, thereby not only reducing current consumption but also suppressing heat generation due to the compensation current. Furthermore, the compensation current i2 that generates the output signal Vout flows through the compensation coil C2 integrated on the sensor chip 100, making it possible to obtain a more accurate output signal Vout.

[0031] 6 is a graph illustrating the effect of the magnetic sensor 1 according to this embodiment, where the solid line indicates the frequency characteristics of noise in the magnetic sensor 1 according to this embodiment and the dashed line indicates the frequency characteristics of noise in a conventional magnetic sensor that does not have the amplifier 141, the compensation coil C1, and the switch SW1. As shown in FIG. 6, in the magnetic sensor 1 according to this embodiment, the magnetic field to be detected is modulated by the on / off frequency of the switch SW1, and therefore it can be seen that 1 / f noise, particularly in the low frequency range, is significantly reduced.

[0032] FIG. 7 is a circuit diagram of a magnetic sensor 2 according to the second embodiment of the present disclosure.

[0033] 7, the magnetic sensor 2 according to the second embodiment differs from the magnetic sensor 1 according to the first embodiment in that it further includes a switch SW2 connected in series to the compensation coil C2. Since the other basic configurations are the same as those of the magnetic sensor 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0034] The switch SW2 is controlled to be turned on and off by the control circuit 130. The control circuit 130 turns on the switch SW2 while the switch SW1 is off, and turns off the switch SW2 while the switch SW1 is on. That is, during the period when the magnetic sensing elements R1 to R4 can detect the magnetic field to be detected, an output signal Vout corresponding to the strength of the magnetic field to be detected is obtained, whereas during the period when the magnetic field to be detected is no longer applied to the magnetic sensing elements R1 to R4, the output signal Vout is fixed to ground level. In this way, in the magnetic sensor 2 according to the second embodiment, it is possible to reliably maintain the output signal Vout at ground level during the period when the magnetic field to be detected flowing through the magnetic collector 110 is canceled by the compensation coil C1.

[0035] FIG. 8 is a schematic perspective view showing the appearance of a magnetic sensor 3 according to the third embodiment of the present disclosure.

[0036] 8, the magnetic sensor 3 according to the third embodiment differs from the magnetic sensor 1 according to the first embodiment in that a compensation coil C1 is wound around a magnetic collector 120. Since the other basic configurations are the same as those of the magnetic sensor 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0037] As exemplified by the magnetic sensor 3 according to the third embodiment, when the two magnetic collectors 110 and 120 are arranged so that at least a part of the magnetic field flowing from one magnetic collector (for example, magnetic collector 110) to the other magnetic collector (for example, magnetic collector 120) passes through the magnetic sensing elements R1 to R4, the compensation coil C1 may be wound around either of the magnetic collectors. Alternatively, the compensation coil C1 may be wound around both of the magnetic collectors 110 and 120.

[0038] Also, as shown in FIG. 8, even when the compensation coil C1 is wound around the magnetic collector 120, a switch SW2 that turns on and off in conjunction with the switch SW1 may be connected in series to the compensation coil C2, as described with reference to FIG. 7.

[0039] FIG. 9 is a schematic perspective view showing the appearance of a magnetic sensor 4 according to the fourth embodiment of the present disclosure.

[0040] 9, the magnetic sensor 4 according to the fourth embodiment differs from the magnetic sensor 1 according to the first embodiment in that a compensation coil C2 is wound around a magnetic collector 120. Since the other basic configurations are the same as those of the magnetic sensor 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0041] In this embodiment, there is no need for a compensation coil C2 integrated on the sensor chip 100. Therefore, a sensor chip 100 without a compensation coil C2 may be used, and even when a sensor chip 100 including a compensation coil C2 is used, a compensation current i2 is not supplied to the compensation coil C2 on the sensor chip 100. In this embodiment, the compensation current i2 is supplied to the compensation coil C2 wound around the magnetic collector 120.

[0042] As exemplified by the magnetic sensor 4 according to the fourth embodiment, when two magnetic collectors 110, 120 are arranged so that at least a portion of the magnetic field flowing from one magnetic collector (e.g., magnetic collector 110) to the other magnetic collector (e.g., magnetic collector 120) passes through the magnetic sensing elements R1 to R4, the compensation coil C1 may be wound around one magnetic collector and the compensation coil C2 may be wound around the other magnetic collector.

[0043] Also in this embodiment, as described with reference to FIG. 7, a switch SW2 that turns on and off in conjunction with the switch SW1 may be connected in series to the compensation coil C2.

[0044] The above describes the embodiments of the present disclosure, but the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the present disclosure, and it goes without saying that these modifications are also included within the scope of the present disclosure.

[0045] The technology according to the present disclosure includes, but is not limited to, the following configuration examples.

[0046] A magnetic sensor according to one aspect of the present disclosure includes a sensor chip having a magnetic sensing element, first and second compensation coils that generate a canceling magnetic field based on an output signal of the magnetic sensing element, a first switch connected in series to the first compensation coil, a control circuit that periodically turns on and off the first switch, and a detection circuit that detects a compensation current flowing through the second compensation coil. With this, the magnetic field to be detected that is applied to the magnetic sensing element is modulated by the on / off frequency of the first switch, thereby significantly reducing 1 / f noise.

[0047] In the magnetic sensor described above, the distance between the second compensation coil and the magnetic sensing element may be shorter than the distance between the first compensation coil and the magnetic sensing element, which allows the modulated magnetic field to be detected, applied to the magnetic sensing element, to be canceled in the vicinity of the magnetic sensing element, thereby achieving higher sensitivity.

[0048] The magnetic sensor may further include a first magnetic collector that collects the magnetic field to the magnetic sensing element, and the first compensation coil may be wound around the first magnetic collector, thereby modulating the magnetic field to be detected that flows through the first magnetic collector.

[0049] In the magnetic sensor, the second compensation coil may be integrated on the sensor chip, which allows the modulated magnetic field to be detected on the sensor chip to be converted into an output signal by closed-loop control.

[0050] The magnetic sensor may further include a second magnetic collector that collects the magnetic field to the magnetic sensing element, the sensor chip may be disposed between the first magnetic collector and the second magnetic collector, and the second compensation coil may be wound around the second magnetic collector. This allows the modulated magnetic field to be detected on the second magnetic collector to be converted into an output signal by closed-loop control.

[0051] The magnetic sensor may further include a second switch connected in series to the second coil, and the control circuit may turn on the second switch while the first switch is off and turn off the second switch while the first switch is on. This makes it possible to fix the output signal during the period when the magnetic field to be detected is canceled. [Explanation of symbols]

[0052] 1~4 Magnetic sensors 100 sensor chips 101 Element formation surface 102 Back side 103~106 Side 107~109 Insulating layer 110,120 Magnetic collector 110a,124a,125a area 121 Main body 122,123 Protrusion 124,125 Overhang 130 control circuit 141,142 operational amplifiers 143 Resistance C1, C2 compensation coil G1~G4 Gap M1~M3 magnetic layer R1~R4 magnetic sensing element SW1, SW2 switches i1,i2 Compensation current

Claims

1. a sensor chip having a magnetic sensing element; first and second compensation coils for generating a canceling magnetic field based on the output signal of the magnetic sensing element; a first switch connected in series with the first compensation coil; a control circuit that periodically turns on and off the first switch; a detection circuit that detects a compensation current flowing through the second compensation coil; Equipped with Magnetic sensor.

2. the distance between the second compensation coil and the magnetic sensing element is shorter than the distance between the first compensation coil and the magnetic sensing element; The magnetic sensor according to claim 1 .

3. Further provided is a first magnetic collector that collects a magnetic field at the magnetic sensing element; the first compensation coil is wound around the first magnetic flux collector; The magnetic sensor according to claim 1 .

4. the second compensation coil is integrated on the sensor chip; The magnetic sensor according to claim 3 .

5. Further provided is a second magnetic collector that collects a magnetic field at the magnetic sensing element; the sensor chip is disposed between the first magnetic collector and the second magnetic collector; the second compensation coil is wound around the second magnetic collector. The magnetic sensor according to claim 2 .

6. a second switch connected in series with the second coil; the control circuit turns on the second switch during a period in which the first switch is off, and turns off the second switch during a period in which the first switch is on; The magnetic sensor according to claim 1 .

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