Magnetic field sensor and magnetic field detection method

Abstract

A magnetic field sensor according to the present invention comprises: a first element having a resistance value that changes in response to a magnetic field; a first readout circuit that outputs a first voltage corresponding to the resistance value of the first element; a second element having a resistance value that changes in response to a magnetic field; a second readout circuit that outputs a second voltage corresponding to the resistance value of the second element; wiring provided for the first element and the second element; and a control circuit that controls the current flowing through the wiring on the basis of the first voltage. The ratio of the amount of change in the first voltage with respect to the amount of change in the magnetic field and the ratio of the amount of change in the second voltage with respect to the amount of change in the magnetic field are different from each other.

Description

Magnetic field sensor and magnetic field detection method

[0001] The present disclosure relates to a magnetic field sensor and a magnetic field detection method.

[0002] For example, Patent Document 1 discloses a technique for detecting a target magnetic field in a state where a disturbance magnetic field (environmental magnetic field) is reduced by using two magnetoresistance elements.

[0003] Japanese Patent Application Laid-Open No. 2017-187502

[0004] For example, in a situation where the magnitude of the disturbance magnetic field and the target magnetic field differ, the detection accuracy may decrease.

[0005] One aspect of the present disclosure is to suppress a decrease in detection accuracy.

[0006] A magnetic field sensor according to one aspect of the present disclosure comprises a first element whose resistance value changes in response to a magnetic field, a first readout circuit that outputs a first voltage in response to the resistance value of the first element, a second element whose resistance value changes in response to a magnetic field, a second readout circuit that outputs a second voltage in response to the resistance value of the second element, wiring provided for the first element and the second element, and a control circuit that controls the current flowing through the wiring based on the first voltage, wherein the ratio of the change in the first voltage to the change in the magnetic field and the ratio of the change in the second voltage to the change in the magnetic field are different from each other.

[0007] A magnetic field detection method according to one aspect of the present disclosure includes obtaining a first voltage corresponding to the resistance value of a first element whose resistance value changes according to a magnetic field, controlling a current flowing through wiring provided to the first element and a second element whose resistance value changes according to the magnetic field based on the first voltage, and obtaining a second voltage corresponding to the resistance value of the second element, wherein the ratio of the change in the first voltage to the change in the magnetic field and the ratio of the change in the second voltage to the change in the magnetic field are different from each other.

[0008] 1 is a diagram showing an example of a schematic configuration of a magnetic field sensor 1 according to an embodiment; FIG. 2 is a diagram showing an example of a schematic configuration of a readout circuit 3; FIG. 3 is a diagram showing an example of a schematic configuration of a control circuit 4; FIG. 4 is a diagram schematically showing a magnetic field H; FIG. 5 is a diagram showing an example of control of a current I1; FIG. 6 is a diagram showing the principle of saturation suppression; FIG. 7 is a diagram showing the principle of saturation suppression; FIG. 8 is a flowchart showing an example of processing (magnetic field detection method) performed in the magnetic field sensor 1; FIG. 9 is a diagram showing an example of the configuration of an element 2; FIG. 10 is a diagram showing an example of the configuration of wiring 5; FIG. 11 is a diagram showing an example of a schematic configuration of the magnetic field sensor 1; FIG. 12 is a diagram showing an example of the appearance of the magnetic field sensor 1; FIG. 13 is a diagram showing a first modified example; FIG. 14 is a flowchart showing an example of processing (magnetic field detection method) performed in the magnetic field sensor 1; FIG. 15 is a diagram showing an example of the appearance of the magnetic field sensor 1; FIG. 16 is a diagram showing an example of the appearance of the magnetic field sensor 1;

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following embodiments, the same elements are designated by the same reference numerals, and redundant description will be omitted.

[0010] The present disclosure will be described in the following order: 0. Introduction 1. Embodiment 2. Modifications 2.1 First Modification 2.2 Second Modification 3. Conclusion

[0011] 0. Introduction: Magnetoresistive elements are known as elements for detecting magnetic fields. To improve detection accuracy, it is necessary to reduce the influence of disturbance magnetic fields. To achieve this, a method using two magnetoresistive elements can be considered. For example, a first magnetoresistive element is used to detect the disturbance magnetic field, and a second magnetoresistive element is used to detect the magnetic field resulting from the cancellation of the disturbance magnetic field. However, if the disturbance magnetic field is larger than the target magnetic field, the detection accuracy may be reduced due to reasons such as saturation of the voltage indicating the detection result.

[0012] According to one aspect of the disclosed technology, two detection systems with different sensitivities (for example, a set of an element and a readout circuit corresponds to one detection system) are used. Based on the result of the low-sensitivity detection system, the disturbance magnetic field is canceled so that the high-sensitivity detection system does not become saturated. The high-sensitivity detection system detects the magnetic field with high accuracy.

[0013] 1. Embodiment FIG. 1 is a diagram showing an example of the schematic configuration of a magnetic field sensor 1 according to an embodiment. Note that the term "sensor" may be interpreted as meaning an apparatus, equipment, device, etc., and these terms may be interpreted as appropriate. Furthermore, the term "detection" may be interpreted as meaning "sensing," and these terms may be interpreted as appropriate. The magnetic field sensor 1 includes an element 2, a readout circuit 3, a control circuit 4, and wiring 5.

[0014] The element 2 is a magnetoresistive element whose resistance value changes in response to a magnetic field. For example, the resistance value of the element 2 changes due to a magnetoresistive effect such as a tunnel magnetoresistive effect (TMR) or a giant magnetoresistive effect (GMR). The specific element configuration is not particularly limited, and various known configurations may be adopted.

[0015] The magnetic field sensor 1 is used with the element 2 positioned at or near a detection target location. The magnetic field present at the location of the element 2 at this time is referred to as a magnetic field H and is shown in the figure.

[0016] The magnetic field sensor 1 includes a plurality of elements 2, and two elements 2 are shown in Fig. 1. The first element 2 is referred to as element 2-1 and shown in the figure. The second element 2 is referred to as element 2-2 and shown in the figure. When there is no particular distinction between these elements, they will simply be referred to as elements 2.

[0017] The readout circuit 3 outputs a voltage according to the resistance value of the element 2. Various known readout technologies may be used. There are a plurality of readout circuits 3 corresponding to a plurality of elements 2, and two readout circuits 3 are illustrated in FIG. 1. The first readout circuit 3 is referred to as readout circuit 3-1 and is shown in the figure. The second readout circuit 3 is referred to as readout circuit 3-2 and is shown in the figure. When there is no particular distinction between these, they are simply referred to as readout circuits 3.

[0018] The read circuit 3-1 outputs a voltage (first voltage) corresponding to the resistance value of the element 2-1. This first voltage is referred to as voltage V1. The read circuit 3-2 outputs a voltage (second voltage) corresponding to the resistance value of the element 2-2. This second voltage is referred to as voltage V2.

[0019] In one embodiment, the voltages V1 and V2 may be output as digital voltage values. In this case, the readout circuit 3 also has an AD conversion function. This will be described with reference to FIG. 2.

[0020] 2 is a diagram showing an example of a schematic configuration of the readout circuit 3. Each of the readout circuit 3-1 and the readout circuit 3-2 includes an AD conversion unit 31.

[0021] The AD conversion unit 31 of the readout circuit 3-1 is used to output the voltage V1 as a digital value. The digital value after AD conversion by the AD conversion unit 31 corresponds to the voltage V1.

[0022] The AD conversion unit 31 of the readout circuit 3-2 is used to output the voltage V2 as a digital value. The digital value after AD conversion by the AD conversion unit 31 corresponds to the voltage V2.

[0023] Unless otherwise specified, hereinafter, it is assumed that the voltages V1 and V2 are digital values.

[0024] 1, the control circuit 4 controls the current flowing through the wiring 5 based on the voltage V1. This current is referred to as a current I1. An example of the configuration of the control circuit 4 will be described with reference to FIG. 3 as well.

[0025] 3 is a diagram showing an example of a schematic configuration of the control circuit 4. The control circuit 4 includes a signal processing unit 41 and a DA conversion unit 42.

[0026] The signal processing unit 41 processes the voltage V1. The processed voltage V1 will continue to be referred to as voltage V1. Examples of processing of the voltage V1 by the signal processing unit 41 include amplitude adjustment, phase adjustment, and frequency filtering (e.g., high-pass filter, band-pass filter, low-pass filter), etc. Various known signal processing techniques may be used. The amplitude adjustment, phase adjustment, frequency filtering, etc. of the voltage V1 by the signal processing unit 41 lead to the amplitude adjustment, phase adjustment, frequency filtering, etc. of the current I1 by the control circuit 4, which in turn lead to the amplitude adjustment, phase adjustment, frequency filtering, etc. of the canceling magnetic field H2c, which will be described later. Further explanation will be given below.

[0027] The DA conversion unit 42 generates a current I1 based on the voltage V1 and supplies it to the wiring 5. Various known DA conversion circuits, current generation circuits, etc. may be used. Note that the signal processing unit 41 may be omitted, in which case the voltage V1 from the readout circuit 3-1 may be input directly to the DA conversion unit 42.

[0028] 1 , the wiring 5 is connected to the control circuit 4 so that a current I1 flows from the control circuit 4. In this example, the wiring 5 is connected between the control circuit 4 and ground GND. Ground GND has a reference potential (e.g., 0 V).

[0029] The wiring 5 is provided for the element 2. The wiring 5 is arranged so that at least a part of the magnetic field generated by a current flowing through the wiring 5 passes through the element 2.

[0030] The wiring 5 includes wiring 5-1 and wiring 5-2. Wiring 5-1 is a portion of the wiring 5 that is provided for element 2-1. Wiring 5-2 is a portion of the wiring 5 that is provided for element 2-2. In the example shown in FIG. 1, the wiring 5-1 and wiring 5-2 are connected in series with each other, and therefore, the current I1 from the control circuit 4 flows through the wiring 5-1 and wiring 5-2 in this order.

[0031] The wiring 5 may include a coil. In the example shown in Fig. 1, the wiring 5-1 and the wiring 5-2 are both coils.

[0032] In the magnetic field sensor 1 according to the embodiment, the ratio of the change in voltage V1 to the change in magnetic field H is different from the ratio of the change in voltage V2 to the change in magnetic field H. The former ratio can also be referred to as the sensitivity of element 2-1 and readout circuit 3-1 to the magnetic field H, or the sensitivity of voltage V1 to the magnetic field H. The latter ratio can also be referred to as the sensitivity of element 2-2 and readout circuit 3-2 to the magnetic field H, or the sensitivity of voltage V2 to the magnetic field H. Hereinafter, these will also be simply referred to as the sensitivity of voltage V1 and the sensitivity of voltage V2.

[0033] The sensitivity of the voltage V2 is higher than the sensitivity of the voltage V1. The highly sensitive voltage V2 is output as the sensor value SV. This improves detection accuracy compared to when the low-sensitivity voltage V1 is output as the sensor value SV.

[0034] One method for differentiating the sensitivity to voltage V1 and the sensitivity to voltage V2 is to design the size (e.g., dimensions, area, volume, etc.) of element 2. Because the characteristics of the magnetoresistive elements themselves are different, the sensitivity to voltage V1 and the sensitivity to voltage V2 also differ. In this case, element 2-1 and element 2-2 may have different sizes. More specifically, element 2-2 may have a size larger than element 2-1, thereby making the sensitivity to voltage V2 higher than the sensitivity to voltage V1.

[0035] Another approach is to design the gain of the readout circuit 3. When the circuit gains are different, the sensitivity to voltage V1 and the sensitivity to voltage V2 also differ. In this case, the readout circuit 3-1 and the readout circuit 3-2 may have different gains. More specifically, the readout circuit 3-2 may have a gain greater than the gain of the readout circuit 3-1, thereby making the sensitivity to voltage V2 higher than the sensitivity to voltage V1.

[0036] Either of the two above-mentioned techniques may be used alone, or both may be used in combination.

[0037] The trade-off with sensitivity is the dynamic range. The dynamic range of the high-sensitivity voltage V2 is narrower than the dynamic range of the low-sensitivity voltage V1. The range (of magnitude) of the magnetic field H that can be detected as the voltage V2 is narrower than the range of the magnetic field H that can be detected as the voltage V1.

[0038] The magnetic field H includes not only the magnetic field to be detected but also a disturbance magnetic field (environmental magnetic field). The influence of the disturbance magnetic field can cause the voltage V2, which has a narrow dynamic range, to saturate, thereby reducing the detection accuracy. This problem becomes particularly apparent when the disturbance magnetic field is strong.

[0039] 4 is a diagram schematically illustrating a magnetic field H. The magnetic field to be detected is referred to as a target magnetic field H1 and illustrated. The disturbance magnetic field is referred to as a disturbance magnetic field H2 and illustrated. The magnetic field H includes the magnetic field obtained by adding (combining) the target magnetic field H1 and the disturbance magnetic field H2.

[0040] The target magnetic field H1 and the disturbance magnetic field H2 may have, for example, different amplitudes, frequency components, etc., which may allow the target magnetic field H1 and the disturbance magnetic field H2 to be distinguished by the magnetic field sensor 1. The types of the target magnetic field H1 and the disturbance magnetic field H2 are not particularly limited. Various magnetic fields depending on the application of the magnetic field sensor 1 can become the target magnetic field H1, and any magnetic field that may exist in the environment in which the magnetic field sensor 1 is placed can become the disturbance magnetic field H2. An example of a source of the disturbance magnetic field H2 is the current of a commercial power supply.

[0041] In the magnetic field sensor 1 according to the embodiment, the current I1 flowing through the wiring 5 is controlled so as to cancel the disturbance magnetic field H2. This will be described with reference to FIG.

[0042] 5 is a diagram showing an example of control of the current I1. The control circuit 4 controls the current I1 flowing through the wiring 5 so that the magnetic field generated by the current I1 flowing through the wiring 5 cancels at least a portion of the disturbance magnetic field H2 at the position of the element 2. The magnetic field generated by this current I1 is referred to as a canceling magnetic field H2c and is shown in the figure. The direction of the canceling magnetic field H2c at the position of the element 2 may be opposite to the direction of the disturbance magnetic field H2.

[0043] One of the purposes of the canceling magnetic field H2c is to prevent the voltage V2 from saturating. The control circuit 4 controls the current I1 flowing through the wiring 5 so that the voltage V2 does not exceed a threshold value (corresponding to the upper limit value in FIGS. 6 and 7, which will be described later). The canceling magnetic field H2c generated by the current I1 cancels at least a portion of the disturbance magnetic field H2.

[0044] 5, a canceling magnetic field H2c is generated by the current I1 flowing through the wiring 5-1 to cancel out the disturbance magnetic field H2 contained in the magnetic field H at the position of the element 2-1. A canceling magnetic field H2c is generated by the current I1 flowing through the wiring 5-2 to cancel out the disturbance magnetic field H2 contained in the magnetic field H at the position of the element 2-2.

[0045] As described above, the current I1 is supplied from the control circuit 4. The signal processing unit 41 of the control circuit 4, which was previously described with reference to FIG. 3, processes the voltage V1 so that an appropriate canceling magnetic field H2c capable of canceling the disturbance magnetic field H2 is generated by the current I1.

[0046] For example, the amplitude adjustment of the voltage V1 by the signal processing unit 41 corresponds to the amplitude adjustment of the current I1, and therefore to the amplitude adjustment of the canceling magnetic field H2c. By such amplitude adjustment, it is possible to generate a canceling magnetic field H2c having a magnitude sufficient to cancel out the disturbance magnetic field H2.

[0047] The phase adjustment of the voltage V1 by the signal processing unit 41 corresponds to the phase adjustment of the current I1, and therefore to the phase adjustment of the canceling magnetic field H2c. By this phase adjustment, it is possible to generate a canceling magnetic field H2c having a phase that cancels out the disturbance magnetic field H2.

[0048] The frequency filtering of the voltage V1 by the signal processing unit 41 passes, for example, only a voltage having the same frequency component as the disturbance magnetic field H2 out of the target magnetic field H1 and the disturbance magnetic field H2, thereby generating a cancellation magnetic field H2c having a frequency component that cancels out only the disturbance magnetic field H2 out of the target magnetic field H1 and the disturbance magnetic field H2.

[0049] Feedback control is performed so that an appropriate canceling magnetic field H2c continues to be generated. The canceling magnetic field H2c generated by the current I1 flowing through the wiring 5-1 cancels out at least a portion of the disturbance magnetic field H2 contained in the magnetic field H at the position of the element 2-1. The element 2-1 has a resistance value corresponding to the magnetic field H in which at least a portion of the disturbance magnetic field H2 has been canceled out. The readout circuit 3-1 outputs a voltage corresponding to the resistance value of the element 2-1 as a voltage V1. The control circuit 4 controls the current I1 based on this voltage V1, so that feedback to the current control can be completed within the magnetic field sensor 1. Dynamic (almost real-time) feedback control is possible.

[0050] On the other hand, a canceling magnetic field H2c generated by the current I1 flowing through the wiring 5-2 cancels out at least a portion of the disturbance magnetic field H2 contained in the magnetic field H at the position of the element 2-2. The element 2-2 has a resistance value corresponding to the magnetic field H in which at least a portion of the disturbance magnetic field H2 has been canceled out. The readout circuit 3-2 outputs a voltage corresponding to the resistance value of the element 2-2 as a voltage V2.

[0051] The voltage V2 is output as the sensor value SV. The highly sensitive voltage V2 is used to detect the magnetic field H without saturating the voltage V2. This prevents a decrease in detection accuracy due to saturation of the voltage V2. This will be described with reference to FIGS. 6 and 7.

[0052] 6 and 7 are diagrams illustrating the principle of saturation suppression. The horizontal axis of each graph represents time. The vertical axis of the graph in FIG. 6A schematically represents the magnitude of the magnetic field H when the canceling magnetic field H2c is not generated. The vertical axis of the graph in FIG. 6B schematically represents the magnitude of the voltages V1 and V2. The lower and upper limits of the range in which the voltages V1 and V2 change appropriately (e.g., linearly) in response to changes in the magnetic field H are also shown.

[0053] When the magnetic field H changes, the high-sensitivity voltage V2 falls below the lower limit or exceeds the upper limit (saturates). In contrast, the low-sensitivity voltage V1 changes within the range between the lower limit and the upper limit. The magnetic field H, including the disturbance magnetic field H2, is detected accurately by the voltage V1. The control circuit 4 controls the current I1 based on this voltage V1. An appropriate canceling magnetic field H2c is generated, and at least a portion of the disturbance magnetic field H2 contained in the magnetic field H is canceled out.

[0054] The vertical axis of the graph in Fig. 7A schematically shows the magnitude of the magnetic field H when the canceling magnetic field H2c is generated. The vertical axis of the graph in Fig. 7B shows the voltage V2. Compared to Fig. 6 described above, the magnetic field fluctuation and voltage fluctuation are reduced because at least a portion of the disturbance magnetic field H2 is canceled out by the canceling magnetic field H2c. The voltage V2 varies within a range between a lower limit and an upper limit. The magnetic field H can be detected accurately by the voltage V2 that does not saturate.

[0055] According to the above principle, it is possible to avoid saturation of the voltage V2, thereby suppressing a decrease in detection accuracy.

[0056] 8 is a flowchart showing an example of a process (magnetic field detection method) executed in the magnetic field sensor 1. Description of content that overlaps with the above will be omitted where appropriate.

[0057] In step S1, the voltage V1 is acquired. The readout circuit 3-1 outputs the voltage V1 according to the resistance value of the element 2-1.

[0058] In step S2, the current I1 is controlled based on the voltage V1. The control circuit 4 controls the current I1 flowing through the wiring 5 based on the voltage V1. For example, the DA converter 42 of the control circuit 4 generates the current I1 based on the voltage V1. The current I1 generates a canceling magnetic field H2c that cancels out at least a portion of the disturbance magnetic field H2. Although not essential, the signal processor 41 may perform processes such as amplitude adjustment, phase adjustment, and frequency filtering adjustment on the voltage V1 before the DA converter 42 generates the current I1.

[0059] In step S3, the voltage V2 is acquired. The readout circuit 3-2 outputs the voltage V2 according to the resistance value of the element 2-2. This voltage V2 corresponds to the detection result of the magnetic field H in which at least a part of the disturbance magnetic field H2 is canceled by the cancel magnetic field H2c.

[0060] In step S4, it is determined whether the voltage V2 is saturated. For example, the control circuit 4 determines that the voltage V2 is saturated when the voltage V2 exceeds the upper limit value described above with reference to FIG. 6. If the voltage V2 is saturated (step S4: Yes), the process proceeds to step S1. If not (step S4: No), the process proceeds to step S5.

[0061] In step S5, the voltage V2 is output as the sensor value SV. The magnetic field H is detected with high accuracy by the non-saturated voltage V2. This voltage V2 is output as the sensor value SV. Then, the process returns to step S1.

[0062] While the magnetic field sensor 1 is detecting a magnetic field (while the magnetic field sensor 1 is in use), the processes of steps S1 to S5 are repeatedly executed. In particular, the processes of steps S1 to S4 are repeatedly executed until the voltage V2 is no longer saturated, and the voltage V2 is output as the sensor value SV. This makes it possible to suppress a decrease in detection accuracy due to saturation of the voltage V2.

[0063] Some examples of more specific configurations of the magnetic field sensor 1 based on the techniques described above will be described with reference to FIGS.

[0064] <Example of Element and Wiring Configuration> In one embodiment, the element 2 may be configured to detect a plurality of magnetic field components in different directions. This will be described with reference to FIGS.

[0065] 9 is a diagram showing an example of the configuration of element 2. In this example, element 2 includes a plurality of elements that are sensitive in mutually different directions. The mutually different directions may include two orthogonal directions, and more particularly may include three orthogonal directions. In the example shown in FIG. 9, element 2 includes three elements, element 21, element 22, and element 23, provided on base 20 so as to correspond to the three orthogonal directions. The direction in which each element is sensitive is schematically shown by a white arrow.

[0066] 10 is a diagram showing an example of the configuration of the wiring 5. The wiring 5 includes three wirings: a wiring 51, a wiring 52, and a wiring 53. A current I1 flowing through each wiring is schematically shown by a white arrow.

[0067] Wiring 51 is provided to face element 21. Current I1 flowing through wiring 51 generates a canceling magnetic field H2c that cancels out the disturbance magnetic field H2 that can be detected by element 21. Wiring 52 is provided to face element 22. Current I1 flowing through wiring 52 generates a canceling magnetic field H2c that cancels out the disturbance magnetic field H2 that can be detected by element 22. Wiring 53 is provided to face element 23. Current I1 flowing through wiring 53 generates a canceling magnetic field H2c that cancels out the disturbance magnetic field H2 that can be detected by element 23.

[0068] The above-described configuration of the element 2 and the wiring 5 allows for accurate detection of magnetic field components in various directions, thereby achieving both improved detection accuracy and improved directivity.

[0069] <Example of On-Chip Configuration> In one embodiment, the element 2, readout circuit 3, and control circuit 4 may be provided on the same semiconductor chip. This will be described with reference to FIGS.

[0070] 11 is a diagram showing an example of the schematic configuration of the magnetic field sensor 1. The magnetic field sensor 1 includes one semiconductor chip 6. The semiconductor chip 6 is provided (formed) with the elements 2-1, 2-2, readout circuits 3-1, 3-2, and control circuit 4 described above.

[0071] 12 and 13 are diagrams showing examples of the external appearance of the magnetic field sensor 1. Some of the elements described so far are indicated by reference numerals. In the example shown in Fig. 12, the wiring 5 is a coil wound around the element 2 provided on the semiconductor chip 6 so as to include the element 2 inside. In the example shown in Fig. 13, the wiring 5 extends from the control circuit 4 to the element 2 so as to face the element 2 and the control circuit 4 provided on the semiconductor chip 6.

[0072] For example, by integrating the element 2, readout circuit 3, and control circuit 4 onto a single semiconductor chip 6 as described above, the configuration of the magnetic field sensor 1 can be simplified, and the magnetic field sensor 1 can be made smaller, lighter, and less expensive.

[0073] 2. Modifications The disclosed technology is not limited to the above-described embodiment. Some modifications will be described.

[0074] 2.1 First Modification Figure 14 shows a first modification. In this example, the magnetic field sensor 1 further includes a reference element 2ref, a reference readout circuit 3ref, a reference control circuit 4ref, a reference wiring 5ref, and a correction circuit 7. The basic configuration of these is the same as that of the element 2, readout circuit 3, control circuit 4, and wiring 5 described so far. The differences will be particularly described below.

[0075] The reference element 2ref is disposed at a position away from the elements 2-1 and 2-2. For example, the distance from the element 2-1 to the reference element 2ref and the distance from the element 2-2 to the reference element 2ref are both greater than the distance between the elements 2-1 and 2-2.

[0076] When the magnetic field sensor 1 detects a magnetic field, the reference element 2ref is located away from the detection target location. At the position of the reference element 2ref, the target magnetic field H1 is negligibly small, and a disturbance magnetic field H2 exists.

[0077] The reference read circuit 3ref outputs a voltage corresponding to the resistance value of the reference element 2ref, which is referred to as a reference voltage Vref.

[0078] The reference control circuit 4ref controls the current flowing through the reference wiring 5ref based on the reference voltage Vref. This current is referred to as the reference current Iref. The reference control circuit 4ref controls the reference current Iref flowing through the wiring 5 so as to generate a canceling magnetic field H2c. This canceling magnetic field H2c cancels at least a portion of the disturbance magnetic field H2 at the position of the reference element 2ref. The magnitude of this canceling magnetic field H2c may be the same as the magnitude of the canceling magnetic field H2c at the elements 2-1 and 2-2.

[0079] The reference voltage Vref is a voltage corresponding to the resistance value of the reference element 2ref. The reference voltage Vref corresponds to a voltage corresponding to the resistance value of the reference element 2ref in a state in which at least a portion of the disturbance magnetic field H2 is canceled by the cancellation magnetic field H2c, or more specifically, a voltage corresponding to the resistance values ​​of the elements 2-1 and 2-2. This reference voltage Vref can indicate a minute magnetic field that remains separate from the target magnetic field H1 among the magnetic fields contained in the magnetic field H. This minute magnetic field is also referred to as a residual magnetic field.

[0080] The correction circuit 7 corrects the voltage V2 based on the reference voltage Vref. The correction of the voltage V2 by the correction circuit 7 includes subtracting the reference voltage Vref from the voltage V2. The subtraction process can be schematically expressed by a formula, for example, as shown in the following formula (1). Corrected voltage V2=Uncorrected voltage V2−Reference voltage Vref (1)

[0081] The correction circuit 7 may perform processing, such as amplitude adjustment, phase adjustment, and frequency filtering, on the reference voltage Vref, similar to the processing performed by the signal processing unit 41 of the control circuit 4 in the previous embodiment. The amplitude adjustment allows the magnitude of the reference voltage Vref to be subtracted from the voltage V2 to be appropriately adjusted, and then the reference voltage Vref can be subtracted from the voltage V2. The phase adjustment allows the phases of the voltage V2 and the reference voltage Vref to be aligned, and then the reference voltage Vref can be subtracted from the voltage V2. The frequency filtering allows the component of the reference voltage Vref to be subtracted from the voltage V2 to be appropriately extracted, and then the reference voltage Vref can be subtracted from the voltage V2.

[0082] This correction can remove the residual magnetic field contained in the magnetic field H. This corrected voltage V2 is output as the sensor value SV, further improving detection accuracy.

[0083] 15 is a flowchart showing an example of processing (magnetic field detection method) executed in the magnetic field sensor 1. The processing in steps S11 and S12 is similar to the processing in steps S1 and S2 in Fig. 8 described above. The voltage V1 is acquired, and the current I1 is controlled based on the voltage V1.

[0084] In step S13, the voltage V2 and the reference voltage Vref are acquired. The read circuit 3-2 outputs the voltage V2 according to the resistance value of the element 2-2. The reference read circuit 3ref outputs the reference voltage Vref according to the resistance value of the reference element 2ref.

[0085] The process of step S14 is the same as the process of step S4 in Fig. 8 described above. If the voltage V2 is saturated (step S14: Yes), the process returns to step S11. If not (step S14: No), the process proceeds to step S15.

[0086] In step S15, the voltage V2 is corrected based on the reference voltage Vref. The correction circuit 7 subtracts the reference voltage Vref from the voltage V2.

[0087] In step S16, the corrected voltage V2 is output as the sensor value SV. The unsaturated voltage V2 accurately detects the magnetic field H after the residual magnetic field has been removed, and the result is output as the sensor value SV. Then, the process returns to step S11.

[0088] While the magnetic field sensor 1 is detecting the magnetic field, the above-described processing of steps S11 to S16 is repeatedly executed. In particular, the processing of steps S11 to S14 is repeatedly executed until the voltage V2 is no longer saturated, and the magnetic field H from which the residual magnetic field has been removed is detected by the voltage V2. This makes it possible to suppress a decrease in detection accuracy due to saturation of the voltage V2, and further improve detection accuracy by virtue of the absence of the influence of the residual magnetic field.

[0089] 16 and 17 are diagrams showing examples of the appearance of the magnetic field sensor 1. Some of the elements described so far are indicated by reference numerals.

[0090] The control circuit 4 and wiring 5 are shown with reference numerals as peripheral elements of the element 2. Although not shown in the figure, the readout circuit 3 (FIG. 1) may also be included in the peripheral elements of the element 2, and the element 2 and its peripheral elements will be referred to as the element 2, etc., herein. The element 2, etc. are provided on a semiconductor chip 6.

[0091] The peripheral elements of the reference element 2ref are indicated by reference symbols as a reference control circuit 4ref and a reference wiring 5ref. Although not shown in the figure, a reference read circuit 3ref (FIG. 14) may also be included in the peripheral elements of the reference element 2ref, and the reference element 2ref and its peripheral elements are collectively referred to as the reference element 2ref, etc. The reference element 2ref, etc. are provided on a reference semiconductor chip 6ref.

[0092] The location detected by the magnetic field sensor 1 is shown schematically as a detection location 9. The detection location 9 is a location where the target magnetic field H1 is generated, such as an object, and the type, shape, etc. of the object are not particularly limited.

[0093] While the magnetic field sensor 1 is detecting a magnetic field, the elements 2 (elements 2-1 and 2-2) are located near the detection point 9. The reference element 2ref is farther away from the detection point 9 than the element 2. In the example shown in FIG. 16, the reference semiconductor chip 6ref is placed on the opposite side of the semiconductor chip 6 from the detection point 9. In addition, a member 8 is provided between the semiconductor chip 6 and the reference semiconductor chip 6ref to space them and fix them. In the example shown in FIG. 17, the reference semiconductor chip 6ref is placed near the reference detection point 9ref. The reference detection point 9ref may be any location other than the detection point 9.

[0094] 2.2 Second Modification Up to this point, an example has been described in which two elements 2, element 2-1 and element 2-2, are used as the elements 2. However, three or more elements 2 may be used, and in that case the number of elements 2-1 may be two or more. An example will be described with reference to FIG. 18.

[0095] 18 is a diagram showing a second modified example. There are two elements 2-1, which are illustrated as elements 2-1a and 2-1b. There are two readout circuits 3-1, which are illustrated as readout circuits 3-1a and 3-1b. There are two wirings 5-1, which are illustrated as wirings 5-1a and 5-1b.

[0096] The read circuit 3-1a outputs a voltage according to the resistance value of the element 2-1a. This voltage is referred to as voltage V1a. The read circuit 3-1b outputs a voltage according to the resistance value of the element 2-1b. This voltage is referred to as voltage V1b. The control circuit 4 controls the current I1 based on voltage V1a, and also controls the current I1 based on voltage V1b.

[0097] The sensitivity of voltage V1a, the sensitivity of voltage V1b, and the sensitivity of voltage V2 are different from one another. More specifically, the sensitivity of voltage V1a is higher than the sensitivity of voltage V1b. The sensitivity of voltage V2 is higher than the sensitivity of voltage V1b. For example, the sensitivities of voltage V1a, voltage V1b, and voltage V2 can be made different by varying the sizes of elements 2-1a, 2-1b, and 2-2, or by varying the gains of readout circuits 3-1a, 3-1b, and 3-2.

[0098] The dynamic range narrows in the order of voltage V1a, voltage V1b, and voltage V2. The dynamic range of voltage V1a is the largest, and the dynamic range of voltage V2 is the smallest. The dynamic range of voltage V1b is intermediate between these two.

[0099] First, the control circuit 4 controls the current I1 based on the voltage V1a with the widest dynamic range. The current I1 can be appropriately controlled based on the voltage V1a that does not saturate. The canceling magnetic field H2c generated by the current I1 cancels at least a portion of the disturbance magnetic field H2.

[0100] Next, the control circuit 4 controls the current I1 based on the voltage V1b. Although the dynamic range of the voltage V1b is narrower than that of the voltage V1a, the voltage V1b does not saturate because at least a portion of the disturbance magnetic field H2 has already been canceled. The current I1 can be appropriately controlled based on the voltage V1b. The canceling magnetic field H2c generated by the current I1 further cancels at least a portion of the disturbance magnetic field H2.

[0101] In this state, the readout circuit 3-2 reads out a voltage V2 corresponding to the resistance value of the element 2-2. The voltage V2 is output as the sensor value SV. In this way, current control and magnetic field detection can be performed using three detection systems (elements 2 and readout circuit 3) configured to have different levels of sensitivity. In particular, even when the disturbance magnetic field H2 is much larger than the target magnetic field H1, the current I1 can be controlled in stages to prevent saturation of the detection system, making it possible to detect the magnetic field H with high accuracy.

[0102] Naturally, four or more detection systems may be used, in which case three or more elements 2-1, three or more readout circuits 3-1, and three or more wirings 5-1 may be used. Generally speaking, the magnetic field sensor 1 includes two or more elements 2-1, two or more readout circuits 3-1, and two or more wirings 5-1. The ratios (sensitivities) of the amount of change in voltage corresponding to the resistance value of each of the two or more elements 2-1 to the amount of change in the magnetic field H are different from each other. The magnetic field H is detected in order from the detection system with the lowest sensitivity, and the current I1 is controlled in stages based on the detection results. Increasing the number of detection systems increases the possibility of avoiding saturation.

[0103] 3. Summary The techniques described above can be specified, for example, as follows. One of the techniques disclosed is a magnetic field sensor 1. As described with reference to FIGS. 1 to 18 , the magnetic field sensor 1 includes an element 2-1 (first element) whose resistance value changes in response to a magnetic field H, a readout circuit 3-1 (first readout circuit) that outputs a voltage V1 (first voltage) corresponding to the resistance value of the element 2-1, an element 2-2 (second element) whose resistance value changes in response to the magnetic field H, a readout circuit 3-2 (second readout circuit) that outputs a voltage V2 (second voltage) corresponding to the resistance value of the element 2-2, wiring 5 (e.g., a coil) provided for the elements 2-1 and 2-2, and a control circuit 4 that controls a current I1 flowing through the wiring 5 based on the voltage V1. The ratio of the amount of change in voltage V1 to the amount of change in magnetic field H (sensitivity of voltage V1) and the ratio of the amount of change in voltage V2 to the amount of change in magnetic field H (sensitivity of voltage V2) are different from each other. For example, the control circuit 4 may control the current I1 flowing through the wiring 5 so that the canceling magnetic field H2c generated by the current I1 flowing through the wiring 5 cancels out the disturbance magnetic field H2 at the position of the element 2-2. The sensitivity of the voltage V2 may be greater than the sensitivity of the voltage V1. The voltage V2 may be output as the sensor value SV. The control circuit 4 may control the current I1 flowing through the wiring 5 so that the voltage V2 does not exceed a threshold value (upper limit value).

[0104] According to the magnetic field sensor 1, the current I1 flowing through the wiring 5 is controlled based on the voltage V1 so that the voltage V2 does not saturate. The canceling magnetic field H2c generated by the current I1 cancels out at least a portion of the disturbance magnetic field H2 contained in the magnetic field H, and this magnetic field H is detected as a voltage V2 with higher sensitivity than the voltage V1. The voltage V2 is output as the sensor value SV. This makes it possible to suppress a decrease in detection accuracy due to saturation of the voltage V2.

[0105] 11 to 13, the magnetic field sensor 1 may include one semiconductor chip 6 on which the elements 2-1, 2-2, readout circuits 3-1, 3-2, and control circuit 4 are provided. This simplifies the configuration of the magnetic field sensor 1, and enables the magnetic field sensor 1 to be made smaller, lighter, and less expensive.

[0106] As described with reference to Figures 9 and 10, element 2 (element 2-1, element 2-2) may include a plurality of elements having sensitivity in mutually different directions, for example, element 21, element 22, and element 23. The mutually different directions may include two orthogonal directions, or may include three orthogonal directions. In this case, the wiring may include a plurality of wirings extending in mutually different directions, for example, wiring 51, wiring 52, and wiring 53, corresponding to the plurality of elements having sensitivity in mutually different directions, for example, element 21, element 22, and element 23. Magnetic field components in various directions can be detected with high accuracy. This makes it possible to achieve both improved detection accuracy and improved directivity.

[0107] 18 and other figures, the magnetic field sensor 1 includes two or more elements 2-1 (e.g., element 2-1a, element 2-1b) and two or more readout circuits 3-1 (e.g., readout circuit 3-1a, readout circuit 3-1b), and the ratios of the amount of change in voltage corresponding to the resistance value of each of the two or more elements 2-1 to the amount of change in the magnetic field H (e.g., the sensitivities of voltage V1a and voltage V1b) may be different from one another. This allows the magnetic field H to be detected using three or more detection systems (elements 2 and readout circuits 3) configured to have gradually different sensitivities.

[0108] 1 etc., the elements 2-1 and 2-2 may have different sizes, and the readout circuits 3-1 and 3-2 may have different gains, etc. In this way, for example, the sensitivity to voltage V1 and the sensitivity to voltage V2 can be made different.

[0109] 1 to 3, the readout circuit 3-1 may include an AD conversion unit 31 for outputting the voltage V1 as a digital value, and the control circuit 4 may include a DA conversion unit 42 for generating the current I1 based on the voltage V1, which is a digital value. In this way, for example, the current I1 flowing through the wiring 5 can be controlled based on the voltage V1.

[0110] 3 and other figures, the control circuit 4 includes a signal processing unit 41 that processes the voltage V1, which is a digital value, and the processing by the signal processing unit 41 may include at least one of amplitude adjustment, phase adjustment, and frequency filtering. For example, by controlling the current I1 flowing through the wiring 5 based on the voltage V1 processed in this manner, it is possible to generate a canceling magnetic field H2c appropriate for canceling the disturbance magnetic field H2.

[0111] As described with reference to Figures 14 to 17, the magnetic field sensor 1 includes a reference element 2ref, whose resistance value changes in response to the magnetic field H; a reference read circuit 3ref, which outputs a reference voltage Vref corresponding to the resistance value of the reference element 2ref; a reference wiring 5ref provided for the reference element 2ref; a reference control circuit 4ref, which controls a reference current Iref flowing through the reference wiring 5ref based on the reference voltage Vref; and a correction circuit 7, which corrects a voltage V2 based on the reference voltage Vref. The distance from element 2-1 to the reference element 2ref and the distance from element 2-2 to the reference element 2ref may both be greater than the distance between elements 2-1 and 2-2. The correction by the correction circuit 7 may include subtracting the reference voltage Vref from the voltage V2. By correcting the voltage V2 in this manner, the influence of residual magnetic fields can be eliminated, further improving detection accuracy.

[0112] The magnetic field detection method described with reference to FIGS. 1 to 18 is also one of the disclosed techniques. The magnetic field detection method includes acquiring a voltage V1 (first voltage) corresponding to the resistance value of an element 2-1 (first element) whose resistance value changes in response to a magnetic field H (steps S1 and S11), controlling a current I1 flowing through wiring 5 provided for element 2-1 and element 2-2 whose resistance value changes in response to the magnetic field H based on the voltage V1 (steps S2 and S12), and acquiring a voltage V2 corresponding to the resistance value of element 2-2 (steps S3 and S13). The ratio of the change in voltage V1 to the change in magnetic field H (sensitivity of voltage V1) and the ratio of the change in voltage V2 to the change in magnetic field H (sensitivity of voltage V2) may be different from each other. As described above, this magnetic field detection method can also suppress a decrease in detection accuracy.

[0113] The effects described in this disclosure are merely examples and are not limited to the disclosed contents. Other effects may also be obtained.

[0114] Although the embodiments of the present disclosure have been described above, the technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present disclosure. Furthermore, components of different embodiments and modifications may be combined as appropriate.

[0115] The present technology can also be configured as follows: (1) A magnetic field sensor comprising: a first element whose resistance value changes in response to a magnetic field; a first readout circuit that outputs a first voltage in response to the resistance value of the first element; a second element whose resistance value changes in response to the magnetic field; a second readout circuit that outputs a second voltage in response to the resistance value of the second element; wiring provided for the first element and the second element; and a control circuit that controls a current flowing through the wiring based on the first voltage, wherein a ratio of a change in the first voltage to a change in the magnetic field and a ratio of a change in the second voltage to a change in the magnetic field are different from each other. (2) The magnetic field sensor according to (1), wherein the control circuit controls the current flowing through the wiring so that a magnetic field generated by the current flowing through the wiring cancels out a disturbance magnetic field at the position of the second element. (3) The magnetic field sensor according to (1) or (2), comprising a single semiconductor chip on which the first element, the second element, the first readout circuit, the second readout circuit, and the control circuit are provided. (4) The magnetic field sensor according to any one of (1) to (3), wherein the first element includes a plurality of elements having sensitivity in mutually different directions, and the second element also includes a plurality of elements having sensitivity in mutually different directions, and the mutually different directions include two orthogonal directions. (5) The magnetic field sensor according to (4), wherein the mutually different directions include three orthogonal directions. (6) The magnetic field sensor according to (4) or (5), wherein the wiring includes a plurality of wirings extending in mutually different directions corresponding to the multiple elements having sensitivity in mutually different directions. (7) The magnetic field sensor according to any one of (1) to (6), comprising two or more of the first elements and two or more of the first readout circuits, and wherein ratios of amounts of change in voltage corresponding to amounts of change in the magnetic field corresponding to resistance values ​​of the two or more first elements are different from each other. (8) The magnetic field sensor according to any one of (1) to (7), wherein the first element and the second element have different sizes. (9) The magnetic field sensor according to any one of (1) to (8), wherein the first readout circuit and the second readout circuit have different gains.(10) The magnetic field sensor according to any one of (1) to (9), wherein the first readout circuit includes an AD conversion unit for outputting the first voltage as a digital value, and the control circuit includes a DA conversion unit for generating the current based on the first voltage which is the digital value. (11) The magnetic field sensor according to (10), wherein the control circuit includes a signal processing unit that processes the first voltage which is the digital value, and the processing by the signal processing unit includes at least one of amplitude adjustment, phase adjustment, and frequency filtering. (12) The magnetic field sensor according to any one of (1) to (11), wherein the wiring includes a coil. (13) The magnetic field sensor according to any one of (1) to (12), comprising: a reference element whose resistance value changes in response to the magnetic field; a reference readout circuit that outputs a reference voltage in response to the resistance value of the reference element; a reference wiring provided for the reference element; a reference control circuit that controls a reference current flowing through the reference wiring based on the reference voltage; and a correction circuit that corrects the second voltage based on the reference voltage, wherein a distance from the first element to the reference element and a distance from the second element to the reference element are both greater than a distance between the first element and the second element. (14) The magnetic field sensor according to (13), wherein the correction by the correction circuit includes subtracting the reference voltage from the second voltage. (15) The magnetic field sensor according to any one of (1) to (14), wherein a ratio of a change in the second voltage to a change in the magnetic field is greater than a ratio of a change in the first voltage to a change in the magnetic field. (16) The magnetic field sensor according to (15), wherein the second voltage is output as a sensor value. (17) The magnetic field sensor according to (15) or (16), wherein the control circuit controls the current flowing through the wiring so that the second voltage does not exceed a threshold value.(18) A magnetic field detection method, comprising: acquiring a first voltage corresponding to a resistance value of a first element whose resistance value changes according to a magnetic field; controlling, based on the first voltage, a current flowing through wiring provided for the first element and a second element whose resistance value changes according to the magnetic field; and acquiring a second voltage corresponding to the resistance value of the second element, wherein a ratio of a change in the first voltage to a change in the magnetic field and a ratio of a change in the second voltage to a change in the magnetic field are different from each other.

[0116] 1 magnetic field sensor 2 element 2-1 element 2-1a element 2-1b element 2-2 element 20 base 21 element 22 element 23 element 2ref reference element 3 readout circuit 3-1 readout circuit 3-1a readout circuit 3-1b readout circuit 3-2 readout circuit 31 AD conversion unit 3ref reference readout circuit 4 control circuit 41 signal processing unit 42 DA conversion unit 4ref reference control circuit 5 wiring 5-1 wiring 5-1a wiring 5-1b wiring 5-2 wiring 51 wiring 52 wiring 53 wiring 5ref reference wiring 6 semiconductor chip 6ref reference semiconductor chip 7 correction circuit 8 member 9 detection point 9ref reference detection point H magnetic field H1 target magnetic field H2 disturbance magnetic field H2c Cancellation magnetic field I1 Current Iref Reference current SV Sensor value V1 Voltage V1a Voltage V1b Voltage V2 Voltage Vref Reference voltage

Claims

1. A magnetic field sensor comprising: a first element whose resistance value changes in response to a magnetic field; a first readout circuit that outputs a first voltage in response to the resistance value of the first element; a second element whose resistance value changes in response to the magnetic field; a second readout circuit that outputs a second voltage in response to the resistance value of the second element; wiring provided for the first element and the second element; and a control circuit that controls the current flowing through the wiring based on the first voltage, wherein the ratio of the amount of change in the first voltage to the amount of change in the magnetic field and the ratio of the amount of change in the second voltage to the amount of change in the magnetic field are different from each other.

2. The magnetic field sensor according to claim 1, wherein the control circuit controls the current flowing through the wiring so that the magnetic field generated by the current flowing through the wiring cancels out the disturbance magnetic field at the position of the second element.

3. The magnetic field sensor according to claim 1, comprising a single semiconductor chip on which the first element, the second element, the first readout circuit, the second readout circuit, and the control circuit are provided.

4. The magnetic field sensor according to claim 1, wherein the first element includes a plurality of elements having sensitivity in mutually different directions, the second element also includes a plurality of elements having sensitivity in mutually different directions, and the mutually different directions include two orthogonal directions.

5. The magnetic field sensor according to claim 4, wherein the different directions include three orthogonal directions.

6. The magnetic field sensor according to claim 4, wherein the wiring includes a plurality of wirings extending in different directions corresponding to the plurality of elements having sensitivity in different directions.

7. A magnetic field sensor according to claim 1, comprising two or more of the first elements and two or more of the first readout circuits, wherein the ratios of the amount of change in voltage corresponding to the resistance value of each of the two or more first elements to the amount of change in the magnetic field are different from each other.

8. The magnetic field sensor of claim 1, wherein the first element and the second element have different sizes.

9. The magnetic field sensor according to claim 1, wherein the first readout circuit and the second readout circuit have different gains.

10. The magnetic field sensor according to claim 1, wherein the first readout circuit includes an AD conversion unit for outputting the first voltage as a digital value, and the control circuit includes a DA conversion unit for generating the current based on the first voltage which is the digital value.

11. The magnetic field sensor according to claim 10, wherein the control circuit includes a signal processing unit that processes the first voltage, which is the digital value, and the processing by the signal processing unit includes at least one of amplitude adjustment, phase adjustment, and frequency filtering.

12. The magnetic field sensor according to claim 1, wherein the wiring includes a coil.

13. A magnetic field sensor as described in claim 1, comprising: a reference element whose resistance value changes depending on the magnetic field; a reference readout circuit that outputs a reference voltage depending on the resistance value of the reference element; a reference wiring provided for the reference element; a reference control circuit that controls a reference current flowing through the reference wiring based on the reference voltage; and a correction circuit that corrects the second voltage based on the reference voltage, wherein the distance from the first element to the reference element and the distance from the second element to the reference element are both greater than the distance between the first element and the second element.

14. The magnetic field sensor according to claim 13, wherein the correction by the correction circuit includes subtracting the reference voltage from the second voltage.

15. The magnetic field sensor according to claim 1, wherein a ratio of the amount of change in the second voltage to the amount of change in the magnetic field is greater than a ratio of the amount of change in the first voltage to the amount of change in the magnetic field.

16. The magnetic field sensor according to claim 15, wherein the second voltage is output as a sensor value.

17. The magnetic field sensor according to claim 15, wherein the control circuit controls the current flowing through the wiring so that the second voltage does not exceed a threshold value.

18. A magnetic field detection method comprising: acquiring a first voltage corresponding to the resistance value of a first element, the resistance value of which changes according to a magnetic field; controlling, based on the first voltage, a current flowing through wiring provided for the first element and a second element, the resistance value of which changes according to the magnetic field; and acquiring a second voltage corresponding to the resistance value of the second element, wherein a ratio of a change in the first voltage to a change in the magnetic field and a ratio of a change in the second voltage to a change in the magnetic field are different from each other.

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