magnetic sensor

Abstract

The present invention provides a magnetic sensor capable of eliminating the AC component contained in an ambient magnetic field. The magnetic sensor (1) comprises: an ambient magnetic field sensor (S0) that generates an ambient magnetic field signal (F0), a detection magnetic field sensor (S1) that generates a detection magnetic field signal (F1), a capacitor (C) that extracts the DC component by removing the AC component of a predetermined frequency band from the ambient magnetic field signal (F0), a compensation coil (31) that applies magnetic field elimination to the detection magnetic field sensor (S1) based on the DC component, a compensation coil (41) that applies magnetic field elimination to the detection magnetic field sensor (S1) based on the detection magnetic field signal (F1), and a bandpass filter (91) that removes at least the AC component of a predetermined frequency band from the detection magnetic field signal (F1). Thus, the AC component contained in the ambient magnetic field can be eliminated regardless of the positions of the ambient magnetic field sensor and the detection magnetic field sensor.

Description

Technical Field

[0001] This invention relates to magnetic sensors, and more particularly to magnetic sensors capable of eliminating the influence of ambient magnetic fields. Background Technology

[0002] Magnetic sensors, especially those detecting weak magnetic fields, are strongly affected by ambient magnetic fields such as the Earth's magnetism. Therefore, to accurately detect the magnetic field of the target object, it is necessary to eliminate the influence of the ambient magnetic field. As a magnetic sensor capable of eliminating the influence of the ambient magnetic field, the magnetic sensor described in Patent Document 1 is known. The magnetic sensor described in Patent Document 1 includes: a first magnetic field detection unit for detecting the ambient magnetic field, a second magnetic field detection unit for detecting the magnetic field of the target object, and a magnetic field generating unit that applies a magnetic field elimination signal corresponding to the output signal of the first magnetic field detection unit to the second magnetic field detection unit. As a result, the ambient magnetic field applied to the second magnetic field detection unit is eliminated; therefore, only the magnetic field of the target object is applied to the second magnetic field detection unit.

[0003] However, sometimes the ambient magnetic field contains not only DC components such as geomagnetism, but also AC components such as power supply noise. Since the phase of the AC component of the ambient magnetic field varies depending on the spatial position, the magnetic sensor described in Patent Document 1 may not be able to correctly eliminate the AC component of the ambient magnetic field. In the case where the AC component of the ambient magnetic field is amplified according to the positions of the first magnetic field detection unit and the second magnetic field detection unit, it may overlap with the detected magnetic field signal.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2015-087228 Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a magnetic sensor that can eliminate the AC component contained in the ambient magnetic field regardless of the position of the magnetic field sensor.

[0008] The magnetic sensor of the present invention comprises: an ambient magnetic field sensor that generates an ambient magnetic field signal by detecting an ambient magnetic field; a detection magnetic field sensor that generates a detection magnetic field signal by detecting a detection object's magnetic field; a first filter that extracts a DC component by removing an AC component of a predetermined frequency band from the ambient magnetic field signal; a first compensation coil that applies a first elimination magnetic field to the detection magnetic field sensor based on the DC component; a second compensation coil that applies a second elimination magnetic field to the detection magnetic field sensor based on the detection magnetic field signal; and a second filter that removes at least a predetermined frequency band of AC component from the detection magnetic field signal.

[0009] According to the present invention, the AC component of a specified frequency band is removed from the ambient magnetic field signal by a first filter, and the AC component of a specified frequency band is removed from the detection magnetic field signal by a second filter. Therefore, the AC component contained in the ambient magnetic field can be eliminated regardless of the positions of the ambient magnetic field sensor and the detection magnetic field sensor.

[0010] In this invention, the magnetic field sensor may also include an external magnetizer that collects the magnetic field, with a first compensation coil wound around the external magnetizer. Accordingly, a larger current can flow through the first compensation coil, thus eliminating the magnetic field even in environments with strong magnetic fields.

[0011] In this invention, the magnetic field sensor may also include a magnetic sensing element formed on a sensor chip, and the second compensation coil may be composed of a thin-film coil formed on the sensor chip. Accordingly, the number of components can be reduced, and the detected magnetic field signal can be eliminated with high precision.

[0012] The magnetic sensor of the present invention can also comprise multiple unit sensors, each consisting of a magnetic field detection sensor and corresponding first and second compensation coils. Accordingly, the magnetic field of the target object can be detected at multiple locations. In this case, the first compensation coils contained in the multiple unit sensors can also be connected in series. Accordingly, the same elimination current can flow through all the first compensation coils.

[0013] Thus, according to the present invention, a magnetic sensor capable of eliminating the AC component contained in the ambient magnetic field can be provided. Attached Figure Description

[0014] Figure 1 This is a general perspective view showing the appearance of a magnetic sensor 1 according to one embodiment of the present invention.

[0015] Figure 2 This is a roughly exploded three-dimensional diagram used to illustrate the structure of the magnetic field sensor S1.

[0016] Figure 3 This is a general three-dimensional diagram showing the state after the magnetic thin films M1 to M3 have been removed from the sensor chip 10.

[0017] Figure 4 This is the circuit diagram of magnetic sensor 1.

[0018] Figure 5 This is a circuit diagram of an active filter.

[0019] Explanation of symbols

[0020] 1. Magnetic sensor

[0021] 2. Circuit board

[0022] 3 Cables

[0023] 4. Sensor substrate

[0024] 10 Sensor Chips

[0025] 11 Component Forming Surface

[0026] 21~24 External magnet collector

[0027] Compensation coils 30-32, 41, 42

[0028] 51 Power Terminal

[0029] 52 Grounding terminal

[0030] 53, 54 signal terminals

[0031] 55, 56 Coil Terminals

[0032] 60-62 Amplifier

[0033] 71, 71 resistors

[0034] 81, 82 Voltage Sensors

[0035] 91, 92 bandpass filters

[0036] C capacitor

[0037] F0 Ambient magnetic field signal

[0038] F1 and F2 detect magnetic field signals

[0039] M1~M3 Magnetic Thin Film

[0040] R1~R4 magnetic sensing elements

[0041] S0 Ambient Magnetic Field Sensor

[0042] S1 and S2 are magnetic field sensors. Detailed Implementation

[0043] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0044] Figure 1 This is a general perspective view showing the appearance of a magnetic sensor 1 according to one embodiment of the present invention.

[0045] like Figure 1 As shown, the magnetic sensor 1 of this embodiment includes an ambient magnetic field sensor S0 and detection magnetic field sensors S1 and S2 mounted on the circuit board 2. The ambient magnetic field sensor S0 is used to detect the ambient magnetic field, and the detection magnetic field sensors S1 and S2 are used to detect the magnetic field of the object being detected. Figure 1In the example shown, two magnetic field sensors, S1 and S2, are used, but the number of magnetic field sensors is not particularly limited; it can be one or more. The environmental magnetic field sensor S0 and the magnetic field sensors S1 and S2 have essentially the same structure, and their magnetic field detection sensitivities are also the same.

[0046] Figure 2 This is a roughly exploded three-dimensional diagram used to illustrate the structure of the magnetic field sensor S1.

[0047] like Figure 2 As shown, the magnetic field sensor S1 includes a sensor chip 10 mounted on a sensor substrate 4 with the xz plane as its main surface, and external magnets 21-24. The sensor chip 10 has an element forming surface 11 constituting the xy plane. Magnetic thin films M1-M3 made of a high-permeability material such as permalloy are formed on the element forming surface 11. When viewed from the z-direction, a magnetic sensing element is formed between the magnetic thin film M1 and the magnetic thin films M2 and M3. The external magnets 21-24 are blocks made of a high-permeability material such as ferrite, which function to concentrate the magnetic field in the z-direction onto the sensor chip 10. The external magnets 21-23 are positioned at locations that overlap with the magnetic thin films M1-M3 when viewed from the z-direction. The external magnets 21 and 22, 23 are separated, and the magnetic field in the z-direction collected by the external magnet 21 is applied to the magnetic thin film M1. The magnetic field applied to the magnetic thin film M1 bends in the x-direction and flows through the magnetic sensing element to the magnetic thin films M2 and M3. The magnetic fields applied to the magnetic films M2 and M3 are collected by the external magnet collectors 22 and 23, respectively, and flow to the external magnet collector 24 covering the yz side and xy back of the sensor chip 10.

[0048] Figure 3 This is a general three-dimensional diagram showing the state after the magnetic thin films M1 to M3 have been removed from the sensor chip 10.

[0049] like Figure 3 As shown, magnetic sensing elements R1 to R4 are formed on the element forming surface 11 of the sensor chip 10. The fixed magnetization direction of magnetic sensing elements R1 to R4 is consistent with the +x direction. Here, viewed from the z-direction, magnetic sensing elements R1 and R2 are disposed between magnetic thin film M1 and magnetic thin film M2, and magnetic sensing elements R3 and R4 are disposed between magnetic thin film M1 and magnetic thin film M3. In addition, magnetic sensing elements R1 and R3 are connected in series between power supply terminal 51 and ground terminal 52, and magnetic sensing elements R4 and R2 are connected in series between power supply terminal 51 and ground terminal 52. Thus, the connection point of magnetic sensing elements R1 and R3 is connected to signal terminal 53, and the connection point of magnetic sensing elements R4 and R2 is connected to signal terminal 54.

[0050] Furthermore, a compensation coil 41 is formed along the magnetic sensing elements R1 to R4 on the element forming surface 11 of the sensor chip 10. The compensation coil 41 is a thin-film coil formed by a conductor pattern on the element forming surface 11, with one end connected to the coil terminal 55 and the other end connected to the coil terminal 56. Thus, when current flows between the coil terminals 55 and 56, a magnetic field eliminating generated by the compensation coil 41 is applied to the magnetic sensing elements R1 to R4.

[0051] Figure 4 This is a circuit diagram of the magnetic sensor 1 in this embodiment.

[0052] like Figure 4 As shown, the magnetic sensing elements R1 to R4 in the ambient magnetic field sensor S0 are connected in a full-bridge configuration, and their differential signal component is amplified by amplifier 60. The ambient magnetic field signal F0 output from amplifier 60 flows through the compensation coil 30 wound around the external magnetizer 21 of the ambient magnetic field sensor S0. The compensation coil 30 generates a canceling magnetic field to cancel the ambient magnetic field applied to the ambient magnetic field sensor S0. Through this closed-loop control, the ambient magnetic field applied to the magnetic sensing elements R1 to R4 of the ambient magnetic field sensor S0 is always canceled.

[0053] Here, compensation coils 31 and 32 are also wound around the external magnetizers 21 of the magnetic field sensors S1 and S2, respectively. These compensation coils 30-32 are connected via... Figure 1 The cables 3 shown are connected in series. A capacitor C is connected in parallel with the compensation coils 31 and 32. The capacitor C is mounted on... Figure 1 The circuit board 2 shown functions as a filter to remove the AC component of a specified frequency band from the ambient magnetic field signal F0 flowing through the compensation coil 30. The specified frequency band includes at least the AC component contained in the ambient magnetic field. The AC component in the ambient magnetic field is power supply noise, etc., and in most cases, this frequency band is known. Therefore, the DC component of the ambient magnetic field signal F0 flowing to the compensation coil 30 flows through the compensation coils 31 and 32. That is, the compensation coils 31 and 32 generate a canceling magnetic field based on the DC component in the ambient magnetic field, thereby canceling the DC component of the ambient magnetic field.

[0054] The magnetic sensing elements R1 to R4 contained in the magnetic field sensor S1 are also connected by a full bridge. Figure 3The differential signal components represented by signal terminals 53 and 54 are amplified by amplifier 61. The detection magnetic field signal F1 output from amplifier 61 flows through compensation coil 41 formed in sensor chip 10. Thus, a detection magnetic field composed of AC components and an ambient magnetic field composed of AC components are applied to the magnetic sensing elements R1-R4 of the detection magnetic field sensor S1. The frequency bands of the detection magnetic field and the ambient magnetic field are different. Through this dual closed-loop control, the DC component of the ambient magnetic field is canceled by compensation coil 31, and the AC component of the ambient magnetic field and the detection magnetic field are canceled by compensation coil 41. Therefore, the detection magnetic field signal F1 corresponds to the composite component of the AC component of the ambient magnetic field and the detection magnetic field. The detection magnetic field signal F1 is converted from current to voltage using resistor 71. After the voltage across resistor 71 is detected by voltage sensor 81, the frequency band of the detection magnetic field is extracted using bandpass filter 91. The frequency band of the AC component contained in the ambient magnetic field is removed by bandpass filter 91. Therefore, the detection signal OUT1 output from the bandpass filter 91 only represents the magnetic field of the object being detected at the location where the detection magnetic field sensor S1 is set.

[0055] Similarly, the magnetic field sensor S2 feeds back the detected magnetic field signal F2 output from amplifier 62 to compensation coil 42, and performs current-to-voltage conversion through resistor 72. The voltage across resistor 72 is detected by voltage sensor 82, and then the frequency band of the detected magnetic field is extracted by bandpass filter 92. The frequency band of the AC component contained in the ambient magnetic field is removed by bandpass filter 92. Therefore, the detection signal OUT2 output from bandpass filter 92 only represents the detected magnetic field at the location where the magnetic field sensor S2 is installed.

[0056] Thus, the magnetic sensor 1 of this embodiment uses a filter composed of a capacitor C to remove the AC component from the ambient magnetic field signal F0, thereby eliminating the influence of the AC component of the ambient magnetic field whose phase differs due to spatial location. Consequently, the AC component of the ambient magnetic field overlapping with the detection magnetic field signals F1 and F2 is removed by bandpass filters 91 and 92, thus removing the ambient magnetic field component from the detection signals OUT1 and OUT2. Therefore, even when DC and AC components are mixed in the ambient magnetic field, the magnetic field of the target object at the location where the detection magnetic field sensors S1 and S2 are set can be accurately detected. Furthermore, this embodiment includes multiple unit sensors composed of a magnetic sensing element and two compensation coils, thus enabling the detection of the target magnetic field at multiple locations.

[0057] The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. Various modifications can be made without departing from the spirit of the present invention, and these modifications are also included within the scope of the present invention.

[0058] For example, in the above embodiment, an LC filter is constructed by connecting a capacitor C between the connection point of the compensation coils 30 and 31 and the ground wire. However, an LR filter can also be constructed by using a resistor instead of the capacitor C. Alternatively, an LR filter can be constructed using... Figure 5 The active filter shown removes the AC component of the ambient magnetic field.

[0059] In addition, in the above embodiments, bandpass filters 91 and 92 are used to remove the AC component of the ambient magnetic field, but as long as the AC component of the ambient magnetic field is removed, high-pass filters, low-pass filters, etc. can also be used.

Claims

1. A magnetic sensor, characterized in that, have: An environmental magnetic field sensor generates an environmental magnetic field signal by detecting the environmental magnetic field, which includes a DC component and an AC component in a known frequency band. A magnetic field sensor generates a detection magnetic field signal by detecting the magnetic field of the object being detected. A first filter extracts the DC component by removing the AC component from the ambient magnetic field signal; A first compensation coil applies a first elimination magnetic field to the detection magnetic field sensor based on the DC component; The second compensation coil applies a second elimination magnetic field to the detection magnetic field sensor based on the detected magnetic field signal; and A second filter removes at least the AC component from the detected magnetic field signal. The magnetic field of the target object and the AC component are applied to the detection magnetic field sensor. The detected magnetic field signal corresponds to the composite component of the AC component and the magnetic field of the detected object.

2. The magnetic sensor according to claim 1, characterized in that, The magnetic field sensor includes an external magnet collector that gathers the magnetic field. The first compensation coil is wound around the external magnet.

3. The magnetic sensor according to claim 2, characterized in that, The magnetic field sensor includes a magnetic sensing element formed on a sensor chip. The second compensation coil is composed of a thin-film coil formed on the sensor chip.

4. The magnetic sensor according to any one of claims 1 to 3, characterized in that, It has multiple unit sensors consisting of the magnetic field sensor and the corresponding first and second compensation coils.

5. The magnetic sensor according to claim 4, characterized in that, The first compensation coils contained in the multiple unit sensors are connected in series with each other.

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