JP2015021790A - Method and device for detecting fault in bridge circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a fault in a bridge circuit of a mode in which the potentials of two output contacts do not change.SOLUTION: A bridge circuit 14 comprises contacts J11, J12, J13, J14 and resistors R11, R12, R13, R14. Both ends of the resistor R11 are connected to the contacts J11, J12; both ends of the resistor R12 are connected to the contacts J12, J13; both ends of the resistor R13 are connected to the contacts J13, J14; and both ends of the resistor R14 are connected to the contacts J14, J11. A method for detecting a fault in the bridge circuit involves measuring the potential of the contact J12 and the potential of the contact J14 by applying a voltage between the contacts J11, J13, measuring the potential of the contact J11 and the potential of the contact J13 by applying a voltage between the contacts J12, J14, and, if all of the potentials of the contacts J11-J14 are within a normal range, determines that the bridge circuit 14 is working properly, and, if otherwise, determining that the bridge circuit 14 is faulty.

Description

  The present invention relates to a failure detection method and apparatus for detecting a failure of a bridge circuit used in a magnetic sensor or the like.

  In recent years, magnetic sensors have been widely used to detect the rotational position of an object in various applications such as detection of the rotational position of an automobile steering. In a system in which such a magnetic sensor is used, generally, means (for example, a magnet) that generates an external magnetic field whose direction rotates in conjunction with the rotation of an object is provided. For example, the magnetic sensor detects an angle formed by the direction of the external magnetic field with respect to the reference direction. Thereby, the rotational position of the object is detected.

  As a magnetic sensor, as described in Patent Documents 1 and 2, a sensor having two bridge circuits (Wheatstone bridge circuits) is known. One bridge circuit includes first to fourth contacts and first to fourth magnetic detection elements. Both ends of the first magnetic detection element are connected to the first contact and the second contact, respectively. Both ends of the second magnetic detection element are connected to the second contact and the third contact, respectively. Both ends of the third magnetic detection element are connected to a third contact and a fourth contact, respectively. Both ends of the fourth magnetic detection element are connected to the fourth contact and the first contact, respectively. The first to fourth magnetic detection elements are elements whose resistance values change according to the external magnetic field. The resistance value of the first and third magnetic detection elements and the resistance value of the second and fourth magnetic detection elements change in opposite directions with respect to the change in the intensity of the component in one direction of the external magnetic field. In this bridge circuit, a predetermined voltage is applied between the first contact and the third contact, and the difference between the potential of the second contact and the potential of the fourth contact is the unidirectional component of the external magnetic field. Corresponds to strength.

  Hereinafter, the second contact and the fourth contact are also referred to as output contacts. The difference between the potential of the second contact and the potential of the fourth contact in one bridge circuit is called an output signal of the bridge circuit. In a magnetic sensor having two bridge circuits, when the direction of the external magnetic field rotates, the output signals of the two bridge circuits change periodically with the same period. However, the phases of the output signals of the two bridge circuits differ by ¼ of the period of the output signal of each bridge circuit. The angle formed by the direction of the external magnetic field with respect to the reference direction is calculated based on the output signals of the two bridge circuits.

  As a magnetic detection element, for example, as described in Patent Document 1, a structure in which a plurality of magnetoresistive elements (hereinafter referred to as MR elements) are connected in series is known. The plurality of MR films in Patent Document 1 correspond to a plurality of MR elements referred to here, and the MR element in Patent Document 1 corresponds to a magnetic detection element referred to herein.

Japanese Patent No. 5110134 JP 2003-194598 A

  In the magnetic sensor having the two bridge circuits as described above and detecting the angle formed by the direction of the external magnetic field with respect to the reference direction, if at least one of the bridge circuits is faulty, the calculated angle is not accurate. Disappear. Therefore, at the time of manufacturing the magnetic sensor, it is necessary to detect a failure of the bridge circuit in order not to use the failed bridge circuit for manufacturing the magnetic sensor.

  Patent Documents 1 and 2 describe a method of detecting a failure in a bridge circuit by monitoring the potentials of two output contacts (second and fourth contacts) of the bridge circuit in a state incorporated in a magnetic sensor. Has been. However, there are failure modes that cannot be detected by this method. Hereinafter, this aspect will be described. In the following description, variations in the resistance value of the magnetic detection element that are not caused by a failure are ignored.

  In a bridge circuit including four magnetic detection elements each formed by connecting a plurality of MR elements in series, as a failure mode, in one of the four magnetic detection elements, a plurality of MR elements There is a mode in which at least one of these is short-circuited and the resistance value of the magnetic detection element deviates from a desired value. Hereinafter, this aspect is referred to as a first aspect. Further, as a failure mode, in two of the four magnetic detection elements, at least one of the plurality of MR elements is short-circuited, and the resistance value of the magnetic detection element is a desired value. There is an aspect that deviates. Hereinafter, this aspect is referred to as a second aspect. Further, as a failure mode, in three of the four magnetic detection elements, at least one of the plurality of MR elements is short-circuited, and the resistance value of the magnetic detection element is a desired value. There is an aspect that deviates. Hereinafter, this aspect is referred to as a third aspect. As an aspect of the failure, an aspect in which at least one of a plurality of MR elements included in the magnetic detection element is short-circuited in all four magnetic detection elements is conceivable. There is almost no failure.

  Here, in the first and second magnetic detection elements of the second aspect described above, one of the plurality of MR elements is short-circuited, and the resistance value of the first and second magnetic detection elements, respectively. However, consider the case where each deviates from the desired value by the same value. In this case, the potential of the second contact is the same as when the resistance values of the first and second magnetic detection elements are both desired values. Similarly, in each of the third and fourth magnetic sensing elements, one of the plurality of MR elements is short-circuited, and the resistance values of the third and fourth magnetic sensing elements are the same from the desired values, respectively. Even in the case of a deviation, the potential of the fourth contact is not different from the case where the resistance values of the third and fourth magnetic detection elements are both desired values. Therefore, in these two aspects, it is impossible to detect a failure of the bridge circuit by monitoring the potentials of the two output contacts (second and fourth contacts) of the bridge circuit.

  As described above, the method of detecting the failure of the bridge circuit by monitoring the potential of the two output contacts of the bridge circuit has a problem in that it is not possible to detect a failure in which the potential of the two output contacts does not change. It was.

  Up to this point, the problem in the case of detecting a failure of a bridge circuit including four magnetic detection elements has been described. However, the above problem applies to all bridge circuits including the first to fourth resistors not limited to the first to fourth magnetic detection elements.

  SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object thereof is to provide a bridge circuit failure detection method and apparatus capable of detecting a failure of a bridge circuit in a mode in which the potentials of two output contacts do not change. There is.

  A fault detection method and apparatus for a bridge circuit according to the present invention is a method and apparatus for detecting a fault in a bridge circuit including first to fourth contacts and first to fourth resistors. In the bridge circuit, both ends of the first resistor are connected to the first contact and the second contact, respectively, and both ends of the second resistor are connected to the second contact and the third contact, respectively. Both ends of the resistor are connected to the third contact and the fourth contact, respectively, and both ends of the fourth resistor are connected to the fourth contact and the first contact, respectively.

The fault detection method of the bridge circuit of the present invention is
A first measurement procedure in which a voltage is applied between the first contact and the third contact to measure the potential of the second contact and the potential of the fourth contact;
A second measurement procedure for measuring a potential of the first contact and a potential of the third contact by applying a voltage between the second contact and the fourth contact;
When the potentials of the first to fourth contacts measured by the first and second measurement procedures are all within the normal range, the bridge circuit is determined to be normal, and otherwise, the bridge circuit is determined to be normal. The circuit includes a determination procedure for determining that the circuit has failed.

The fault detection device for the bridge circuit of the present invention is
A voltage source for generating a voltage;
An electric potential measuring device for measuring electric potential;
A switching device for switching a connection relationship between the voltage source and the potential measuring device and the first to fourth contacts;
And a control device that controls the switching device and determines whether or not the bridge circuit is out of order.

The control device
The switching device is controlled to connect the voltage source to the first and third contacts, and the potential measuring device is connected to the second and fourth contacts, and the voltage source connects the first contact and the third contact. A first measurement operation in which a voltage is applied between them and the potential of the second contact and the potential of the fourth contact are measured by a potential measurement device;
The switching device is controlled to connect the voltage source to the second and fourth contacts, and the potential measuring device is connected to the first and third contacts, and the voltage source connects the second contact and the fourth contact. A second measurement operation in which a voltage is applied between the first contact point and the potential of the first contact point and the potential of the third contact point by a potential measuring device;
When the potentials of the first to fourth contacts measured by the first and second measurement operations are all within the normal range, the bridge circuit is determined to be normal, and otherwise, the bridge circuit is determined to be normal. A determination operation for determining that the circuit has failed is executed.

  In the bridge circuit failure detection method and apparatus according to the present invention, each of the first to fourth resistors may be a magnetic detection element whose resistance value changes according to an external magnetic field. The magnetic detection element may include a plurality of magnetoresistance effect elements connected in series. Each of the plurality of magnetoresistive elements includes a magnetization fixed layer whose magnetization direction is fixed, a free layer whose magnetization changes in response to an external magnetic field, a nonmagnetic layer disposed between the magnetization fixed layer and the free layer, You may have. The nonmagnetic layer may be a tunnel barrier layer.

  In the fault detection method and apparatus of the bridge circuit according to the present invention, not only the potentials of the second and fourth contacts corresponding to the two output contacts are measured, but also the voltage between the second contact and the fourth contact is measured. And the potentials of the first and third contacts are also measured. In the present invention, when all the measured potentials of the first to fourth contacts are within the normal range, it is determined that the bridge circuit is normal. In other cases, the bridge circuit fails. It is determined that As a result, according to the present invention, it is possible to detect a failure of the bridge circuit in a mode in which the potentials of the two output contacts do not change.

1 is a perspective view showing a magnetic sensor system including a bridge circuit to which a failure detection method and apparatus according to an embodiment of the present invention is applied. It is explanatory drawing which shows the definition of the direction and angle in the magnetic sensor shown in FIG. It is a circuit diagram which shows the structure of the magnetic sensor shown in FIG. FIG. 4 is a perspective view showing a part of one resistor in FIG. 3. It is a top view which shows the foundation structure containing a some bridge circuit. It is a top view which shows the area | region in which the two bridge circuits were formed in the foundation structure shown in FIG. It is explanatory drawing which shows the failure detection apparatus of the bridge circuit which concerns on one embodiment of this invention. It is explanatory drawing which shows the other state of the failure detection apparatus shown in FIG. It is a functional block diagram which shows the function structure of the control apparatus of the failure detection apparatus shown in FIG. It is a block diagram which shows the hardware constitutions of the control apparatus of the failure detection apparatus shown in FIG. It is a flowchart which shows operation | movement of the failure detection apparatus of the bridge circuit which concerns on one embodiment of this invention. It is explanatory drawing for demonstrating the 1st measurement operation | movement in the flowchart shown in FIG. It is explanatory drawing for demonstrating the 2nd measurement operation | movement in the flowchart shown in FIG. 12 is a histogram showing an example of a potential distribution measured by the first or second measurement operation in the flowchart shown in FIG. 11.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an example of a device including a bridge circuit to which a bridge circuit failure detection method and device according to an embodiment of the present invention is applied will be described. Here, the magnetic sensor 1 will be described as an example of a device including the bridge circuit. FIG. 1 is a perspective view showing a magnetic sensor system including a magnetic sensor 1. FIG. 2 is an explanatory diagram showing definitions of directions and angles in the magnetic sensor 1.

  As shown in FIG. 1, the magnetic sensor 1 detects the angle formed by the direction of the external magnetic field MF at the reference position with respect to the reference direction. The direction of the external magnetic field MF at the reference position rotates as viewed from the magnetic sensor 1. In FIG. 1, a cylindrical magnet 2 is shown as an example of means for generating the external magnetic field MF. The magnet 2 has an N pole and an S pole that are arranged symmetrically about a virtual plane including the central axis of the cylinder. The magnet 2 rotates around the central axis of the cylinder. Thereby, the direction of the external magnetic field MF generated by the magnet 2 rotates around the rotation center C including the central axis of the cylinder.

  The reference position is located in a virtual plane (hereinafter referred to as a reference plane) parallel to one end face of the magnet 2. In this reference plane, the direction of the external magnetic field MF generated by the magnet 2 rotates around the reference position. The reference direction is located in the reference plane and intersects the reference position. In the following description, the direction of the external magnetic field MF at the reference position refers to the direction located in the reference plane. The magnetic sensor 1 is disposed so as to face the one end surface of the magnet 2.

  The configuration of the means for generating the external magnetic field MF and the magnetic sensor 1 is not limited to the example shown in FIG. The means for generating the external magnetic field MF and the magnetic sensor 1 have a relative positional relationship between the means for generating the external magnetic field MF and the magnetic sensor 1 such that the direction of the external magnetic field MF at the reference position rotates when viewed from the magnetic sensor 1. It only needs to change. For example, in the magnet 2 and the magnetic sensor 1 arranged as shown in FIG. 1, the magnet 2 may be fixed and the magnetic sensor 1 may rotate, or the magnet 2 and the magnetic sensor 1 may rotate in opposite directions. Alternatively, the magnet 2 and the magnetic sensor 1 may rotate at different angular velocities in the same direction.

  Further, instead of the magnet 2, a magnet in which one or more sets of N poles and S poles are alternately arranged in a ring shape may be used, and the magnetic sensor 1 may be disposed in the vicinity of the outer periphery of the magnet. In this case, at least one of the magnet and the magnetic sensor 1 may be rotated.

  Even in the configuration of the above-described means for generating various external magnetic fields MF and the magnetic sensor 1, there is a reference plane having a predetermined positional relationship with the magnetic sensor 1, and the direction of the external magnetic field MF is magnetic in the reference plane. As viewed from the sensor 1, it rotates around the reference position.

  Here, with reference to FIG. 1 and FIG. 2, the definition of the direction and angle in the magnetic sensor system shown in FIG. 1 will be described. First, a direction parallel to the rotation center C shown in FIG. 1 and extending from bottom to top in FIG. 1 is defined as a Z direction. In FIG. 2, the Z direction is represented as a direction from the back to the front in FIG. Next, two directions perpendicular to the Z direction and orthogonal to each other are defined as an X direction and a Y direction. In FIG. 2, the X direction is represented as a direction toward the right side, and the Y direction is represented as a direction toward the upper side. In addition, a direction opposite to the X direction is defined as -X direction, and a direction opposite to the Y direction is defined as -Y direction.

  The reference position PR is a position where the magnetic sensor 1 detects the external magnetic field MF. The reference direction DR is the X direction. The angle formed by the direction DM of the external magnetic field MF at the reference position PR with respect to the reference direction DR is represented by the symbol θ. The direction DM of the external magnetic field MF is assumed to rotate counterclockwise in FIG. The angle θ is represented by a positive value when viewed counterclockwise from the reference direction DR, and is represented by a negative value when viewed clockwise from the reference direction DR.

  The magnetic sensor 1 includes a first detection unit 10 and a second detection unit 20. The first and second detection units 10 and 20 each include a bridge circuit to which the bridge circuit failure detection method and apparatus according to the present embodiment is applied. The first detection unit 10 detects a component in the X direction of the external magnetic field MF at the reference position PR, and generates a first signal corresponding to the intensity of the component. The second detection unit 20 detects a component in the Y direction of the external magnetic field MF at the reference position PR, and generates a second signal corresponding to the intensity of the component.

  The first and second signals periodically change with a signal period T equal to each other. The phase of the second signal is different from the phase of the first signal. The phase of the second signal is preferably different from the phase of the first signal by an odd multiple of 1/4 of the signal period T. However, the phase difference between the first signal and the second signal may be slightly shifted from an odd multiple of ¼ of the signal period T from the viewpoint of the accuracy of manufacturing the magnetic detection element. Here, it is assumed that the phase of the second signal differs from the phase of the first signal by ¼ of the signal period T. The waveforms of the first and second signals are ideally sinusoidal curves (including a sine waveform and a cosine waveform).

  Next, the configuration of the magnetic sensor 1 will be described in detail with reference to FIG. FIG. 3 is a circuit diagram showing a configuration of the magnetic sensor 1. The first detection unit 10 includes a bridge circuit 14, a difference detector 15, a voltage source V1, and two output ports E11 and E12. Specifically, the bridge circuit 14 is a Wheatstone bridge circuit. The bridge circuit 14 includes first to fourth contacts J11, J12, J13, J14 and first to fourth resistors R11, R12, R13, R14. Both ends of the first resistor R11 are connected to the first contact J11 and the second contact J12, respectively. Both ends of the second resistor R12 are connected to the second contact J12 and the third contact J13, respectively. Both ends of the third resistor R13 are connected to the third contact J13 and the fourth contact J14, respectively. Both ends of the fourth resistor R14 are connected to the fourth contact J14 and the first contact J11, respectively.

  The first and third contacts J11 and J13 are connected to the voltage source V1. The second contact J12 is connected to the output port E11. The fourth contact J14 is connected to the output port E12. The voltage source V1 applies a voltage having a predetermined magnitude between the contacts J11 and J13. The difference detector 15 outputs a signal corresponding to the potential difference between the output ports E11 and E12.

  The circuit configuration of the second detection unit 20 is the same as that of the first detection unit 10. That is, the second detection unit 20 includes a bridge circuit 24, a difference detector 25, a voltage source V2, and two output ports E21 and E22. The bridge circuit 24 includes first to fourth contacts J21, J22, J23, J24 and first to fourth resistors R21, R22, R23, R24. Both ends of the first resistor R21 are connected to the first contact J21 and the second contact J22, respectively. Both ends of the second resistor R22 are connected to the second contact J22 and the third contact J23, respectively. Both ends of the third resistor R23 are connected to the third contact J23 and the fourth contact J24, respectively. Both ends of the fourth resistor R24 are connected to the fourth contact J24 and the first contact J21, respectively.

  The first and third contacts J21 and J23 are connected to the voltage source V2. The second contact J22 is connected to the output port E21. The fourth contact J24 is connected to the output port E22. The voltage source V2 applies a voltage having a predetermined magnitude between the contacts J21 and J23. The difference detector 25 outputs a signal corresponding to the potential difference between the output ports E21 and E22.

  The resistors R11 to R14 and R21 to R24 are all magnetic detection elements whose resistance values change according to the external magnetic field MF. The magnetic detection element includes a plurality of MR elements connected in series. In this embodiment, a spin valve MR element, particularly a TMR element is used as the MR element. A GMR element may be used instead of the TMR element. The TMR element or GMR element includes a magnetization fixed layer whose magnetization direction is fixed, a free layer whose magnetization direction changes according to the direction DM of the external magnetic field MF, and a non-magnetic layer arranged between the magnetization fixed layer and the free layer. And a magnetic layer.

  In the TMR element, the nonmagnetic layer is a tunnel barrier layer. In the GMR element, the nonmagnetic layer is a nonmagnetic conductive layer. In the TMR element or the GMR element, the resistance value changes according to the angle formed by the magnetization direction of the free layer with respect to the magnetization direction of the magnetization fixed layer, and when this angle is 0 °, the resistance value becomes the minimum value. When the angle is 180 °, the resistance value becomes the maximum value. In FIG. 3, a solid arrow indicates the magnetization direction of the magnetization fixed layer in the MR element, and a white arrow indicates the magnetization direction of the free layer in the MR element.

  In the bridge circuit 14 of the first detection unit 10, the magnetization direction of the magnetization fixed layer in the plurality of MR elements included in the resistors R11 and R13 is the X direction, and the plurality of MR elements included in the resistors R12 and R14. The magnetization direction of the magnetization pinned layer at − is the −X direction. In FIG. 2, the arrow denoted by reference numeral DP1 represents the direction of magnetization of the magnetization fixed layer in the plurality of MR elements included in the resistors R11 and R13. In this case, the resistance values of the resistors R11 and R13 and the resistance values of the resistors R12 and R14 change in opposite directions with respect to the change in the intensity of the component in the X direction of the external magnetic field MF. In this bridge circuit 14, a predetermined voltage is applied between the first contact J11 and the third contact J13, and the difference in potential between the second contact J12 and the fourth contact J14 is the X of the external magnetic field MF. Corresponds to the intensity of the direction component. The first detection unit 10 outputs a signal corresponding to the potential difference between the output ports E11 and E12, that is, the potential difference between the second and fourth contacts J12 and J14, as the first signal S1. The second and fourth contacts J12 and J14 are two output contacts of the bridge circuit 14.

  In the bridge circuit 24 of the second detection unit 20, the magnetization direction of the magnetization fixed layer in the plurality of MR elements included in the resistors R21 and R23 is the Y direction, and the plurality of MR elements included in the resistors R22 and R24. The magnetization direction of the magnetization fixed layer at is in the -Y direction. In FIG. 2, the arrow denoted by reference numeral DP2 represents the magnetization direction of the magnetization fixed layer in the plurality of MR elements included in the resistors R21 and R23. In this case, the resistance values of the resistors R21 and R23 and the resistance values of the resistors R22 and R24 change in opposite directions with respect to the change in the intensity of the component in the Y direction of the external magnetic field MF. In this bridge circuit 24, a predetermined voltage is applied between the first contact J21 and the third contact J23, and the difference in potential between the second contact J22 and the fourth contact J24 is the Y of the external magnetic field MF. Corresponds to the intensity of the direction component. The second detection unit 20 outputs a signal corresponding to the potential difference between the output ports E21 and E22, that is, the potential difference between the second and fourth contacts J22 and J24, as the second signal S2. The second and fourth contacts J22 and J24 are two output contacts of the bridge circuit 14.

  In addition, the magnetization direction of the magnetization fixed layer in the plurality of MR elements in the detection units 10 and 20 may be slightly deviated from the above-mentioned direction from the viewpoint of the accuracy of manufacturing the MR element.

  Here, with reference to FIG. 4, an example of a configuration of the magnetic detection elements as the resistors R11 to R14, R21 to R24 will be described. FIG. 4 is a perspective view showing a part of one magnetic detection element (resistor) in the magnetic sensor 1 shown in FIG. In this example, one magnetic detection element includes a plurality of lower electrodes 42, a plurality of MR elements 50, and a plurality of upper electrodes 43. The plurality of lower electrodes 42 are disposed on a substrate (not shown). Each lower electrode 42 has an elongated shape. A gap is formed between two lower electrodes 42 adjacent to each other in the longitudinal direction of the lower electrode 42. As shown in FIG. 4, MR elements 50 are arranged on the upper surface of the lower electrode 42 in the vicinity of both ends in the longitudinal direction. The MR element 50 includes a free layer 51, a nonmagnetic layer 52, a magnetization fixed layer 53, and an antiferromagnetic layer 54, which are stacked in this order from the lower electrode 42 side. The free layer 51 is electrically connected to the lower electrode 42. The antiferromagnetic layer 54 is made of an antiferromagnetic material and causes exchange coupling with the magnetization fixed layer 53 to fix the magnetization direction of the magnetization fixed layer 53. The plurality of upper electrodes 43 are disposed on the plurality of MR elements 50. Each upper electrode 43 has an elongated shape, and is disposed on two lower electrodes 42 adjacent to each other in the longitudinal direction of the lower electrode 42 to electrically connect the antiferromagnetic layers 54 of the two adjacent MR elements 50. To do. With such a configuration, the magnetic detection element shown in FIG. 4 includes a plurality of MR elements 50 connected in series by a plurality of lower electrodes 42 and a plurality of upper electrodes 43. It should be noted that the arrangement of the layers 51 to 54 in the MR element 50 may be reversed upside down from the arrangement shown in FIG.

  As shown in FIG. 3, the magnetic sensor 1 further includes a calculation unit 30. The calculation unit 30 calculates a detection value θs that is a value of the angle θ detected by the magnetic sensor 1. The computing unit 30 can be realized by a microcomputer, for example.

  Hereinafter, a method for calculating the detection value θs will be described. In the example shown in FIG. 3, ideally, the magnetization direction of the magnetization fixed layer 53 of the MR element 50 in the bridge circuit 24 is orthogonal to the magnetization direction of the magnetization fixed layer 53 of the MR element 50 in the bridge circuit 14. . In this case, ideally, the waveform of the first signal S1 is a cosine waveform depending on the angle θ, and the waveform of the second signal S2 is a sine waveform depending on the angle θ. Become. In this case, the phase of the second signal S2 differs from the phase of the first signal S1 by ¼ of the signal period T, that is, π / 2 (90 °).

  When the angle θ is greater than or equal to 0 ° and less than 90 °, and greater than 270 ° and less than or equal to 360 °, the first signal S1 is a positive value, and the angle θ is greater than 90 ° and smaller than 270 ° The first signal S1 has a negative value. When the angle θ is larger than 0 ° and smaller than 180 °, the second signal S2 is a positive value. When the angle θ is larger than 180 ° and smaller than 360 °, the second signal S2 is positive. S2 is a negative value.

  The computing unit 30 calculates a detection value θs having a correspondence relationship with the angle θ based on the first and second signals S1 and S2. Specifically, for example, the calculation unit 30 calculates θs by the following equation (1). “Atan” represents an arc tangent.

  θs = atan (S2 / S1) (1)

  Atan (S2 / S1) in Equation (1) represents arctangent calculation for obtaining θs. In the range where θs is 0 ° or more and less than 360 °, the solution of θs in Equation (1) has two values that differ by 180 °. However, it is possible to determine which of the two solutions of θs in Equation (1) is the true value of θs by the positive / negative combination of S1 and S2. That is, when S1 is a positive value, θs is in the range of 0 ° to less than 90 ° and greater than 270 ° to 360 °. When S1 is a negative value, θs is greater than 90 ° and smaller than 270 °. When S2 is a positive value, θs is larger than 0 ° and smaller than 180 °. When S2 is a negative value, θs is greater than 180 ° and smaller than 360 °. The computing unit 30 obtains θs within a range of 0 ° or more and less than 360 ° by determining the combination of the expression (1) and the positive / negative combination of S1 and S2.

  Next, a failure detection method for the bridge circuit according to the present embodiment will be described. The failure detection method according to the present embodiment is a method of detecting a failure of the bridge circuits 14 and 24 when the magnetic sensor 1 is manufactured.

  First, a method of forming the bridge circuits 14 and 24 will be briefly described with reference to FIGS. FIG. 5 is a plan view showing the substructure 60 manufactured in the manufacturing process of the magnetic sensor 1. The foundation structure 60 includes a plurality of sets of bridge circuits 14 and 24. FIG. 6 shows a set of bridge circuits 14 and 24 in the substructure 60 shown in FIG. In the method of forming the bridge circuits 14 and 24, for example, a plurality of sets of bridge circuits 14 and 24 are collectively formed on a substrate having a semiconductor substrate and an insulating layer, and the foundation structure 60 is manufactured. 5 and 6, reference numeral 61 indicates a region where a pair of bridge circuits 14 and 24 are formed. In FIG. 5, the region 61 is drawn larger than the substructure 60 for easy understanding. In the foundation structure 60, the regions 61 are arranged in a plurality of rows.

  In each region 61, pad-shaped terminals T11, T12, T13, T14, T21, T22, T23, and T24 are formed in addition to the bridge circuits 14 and 24. The first to fourth contacts J11, J12, J13, J14 of the bridge circuit 14 are connected to terminals T11, T12, T13, T14, respectively. The first to fourth contacts J21, J22, J23, J24 of the bridge circuit 24 are connected to terminals T21, T22, T23, T24, respectively.

  The plurality of bridge circuits 14 and 24 included in the foundation structure 60 are inspected by a failure detection method according to the present embodiment, which will be described later, and whether or not each bridge circuit has a failure is determined. Determined. Thereafter, the foundation structure 60 is cut so that the plurality of sets of bridge circuits 14 and 24 are separated from each other. Only the set of the bridge circuits 14 and 24 in which both the bridge circuits 14 and 24 are not in failure is used for manufacturing the magnetic sensor 1.

  Next, with reference to FIG. 6 thru | or FIG. 8, the failure detection apparatus used for implementation of the failure detection method which concerns on this Embodiment is demonstrated. FIG. 7 is an explanatory diagram showing the failure detection apparatus according to the present embodiment. FIG. 8 is an explanatory diagram showing another state of the failure detection apparatus shown in FIG.

  As shown in FIGS. 7 and 8, the failure detection device 70 includes a voltage source 71 that generates a voltage, a potential measurement device 72 that measures a potential, a switching device 73, and a control device 74. The switching device 73 includes four first ports P11 to P14, four second ports P21 to P24, and 16 switches S11 to S14, S21 to S24, S31 to S34, and S41 arranged in a matrix. To S44.

  The 16 switches are connected to one of the four first ports P11 to P14 and one of the four second ports P21 to P24, respectively, and the connected first port and second A conduction state and a non-conduction state between the two ports are selected. Specifically, the switches S11 to S14 are connected to the first port P11, the switches S21 to S24 are connected to the first port P12, the switches S31 to S34 are connected to the first port P13, and the switches S41 to S41 are connected. S44 is connected to the first port P14. The switches S11, S21, S31, and S41 are connected to the second port P21, the switches S12, S22, S32, and S42 are connected to the second port P22, and the switches S13, S23, S33, and S43 are connected to the second port P22. Connected to the port P23, the switches S14, S24, S34, S44 are connected to the second port P24.

  The voltage source 71 is connected to the ports P21 and P22. The potential measuring device 72 is connected to the ports P23 and P24. The failure detection apparatus 70 includes four probes 75 (see FIG. 6) connected to the ports P11 to P14, respectively. By bringing the four probes 75 into contact with the terminals T11 to T14, the ports P11 to P14 are connected to the terminals T11, T14, T13, and T12, respectively. Further, by bringing the four probes 75 into contact with the terminals T21 to T24, the ports P11 to P14 are connected to the terminals T21, T24, T23, and T22, respectively.

  When the ports P11 to P14 are connected to the terminals T11, T14, T13, and T12, respectively, the ports P11 to P14 are respectively connected to the contacts J11, J14, J13, and J12 via the T11, T14, T13, and T12. Connected. When the ports P11 to P14 are connected to the terminals T21, T24, T23, and T22, the ports P11 to P14 are connected to the contacts J21, J24, J23, and J22 via the terminals T21, T24, T23, and T22, respectively. Connected to. 7 and 8 show examples in which the ports P11 to P14 are connected to the contacts J11, J14, J13, and J12 through T11, T14, T13, and T12, respectively.

  The switching device 73 switches the connection relationship between the voltage source 71 and the potential measuring device 72 and the contacts J11 to J14 or the contacts J21 to J24 by controlling the conduction state and non-conduction state of the 16 switches. In the example shown in FIGS. 7 and 8, the filled circle represents a conductive switch, and the white circle represents a non-conductive switch. The control device 74 controls the switching device 73 as described above, and determines whether or not the bridge circuit 14 or the bridge circuit 24 has failed based on the measurement result of the potential measurement device 72.

  The failure detection device 70 may include two sets of voltage sources 71, a potential measurement device 72, and a switching device 73. In this case, as shown in FIG. 6, the failure detection apparatus 70 includes eight probes 75 that are in contact with the terminals T11 to T14 and T21 to T24. In this case, the bridge circuit 14 is inspected using one set of voltage source 71, potential measuring device 72 and switching device 73, and another set of voltage source 71, potential measuring device 72 and switching device 73 is used. Thus, the bridge circuit 24 can be inspected. In this case, the control device 74 controls the two switching devices 73 and determines whether or not the bridge circuits 14 and 24 are out of order based on the measurement results of the two potential measuring devices 72.

  Alternatively, one switching device 73 may include eight first ports, four second ports P21 to P24, and 32 switches arranged in a matrix. Each of the 32 switches is connected to one of the eight first ports and one of the four second ports P21 to P24, and is connected to the connected first port and second port. A conduction state and a non-conduction state are selected. In this case, the failure detection apparatus 70 includes eight probes 75 connected to the eight first ports. In this case, as shown in FIG. 6, the eight first ports are connected to the terminals T11 to T14 and T21 to T24 by bringing the eight probes 75 into contact with the terminals T11 to T14 and T21 to T24. Is done. The switching device 73 switches the connection relationship between the voltage source 71 and the potential measuring device 72 and the contacts J11 to J14 and J21 to J24 by controlling the conduction and non-conduction states of the 32 switches. The control device 74 controls the switching device 73 as described above, and determines whether or not the bridge circuits 14 and 24 are out of order based on the measurement result of the potential measuring device 72.

  The failure detection device 70 further includes a drive device (not shown) that changes the relative positional relationship between the foundation structure 60 and the plurality of probes 75. A drive device (not shown) moves at least one of the foundation structure 60 and the plurality of probes 75 to move the plurality of probes 75 to terminals T11 to T14 and terminals T21 to T24 in an arbitrary region 61 of the foundation structure 60. At least one of them. The control device 74 may control a driving device (not shown).

  Next, the functional configuration and hardware configuration of the control device 74 will be described in detail with reference to FIGS. 9 and 10. FIG. 9 is a functional block diagram showing a functional configuration of the control device 74. FIG. 10 is a block diagram illustrating a hardware configuration of the control device 74.

  As shown in FIG. 9, the control device 74 includes a sequence control unit 81, a measurement control unit 82 that controls the voltage source 71 and the potential measurement device 72, a switching control unit 83 that controls the switching device 73, and a potential measurement. A storage unit 84 that stores the measurement result of the device 72; and a determination unit 85 that determines whether or not the bridge circuits 14 and 24 are out of order based on the measurement result of the potential measurement device 72 stored in the storage unit 84. Have. The sequence control unit 81 controls the measurement control unit 82, the switching control unit 83, the storage unit 84, and the determination unit 85 to control a series of operations of the failure detection device 70 when detecting a failure of the bridge circuits 14 and 24. To do.

  The control device 74 is realized, for example, by a computer 90 having a hardware configuration as shown in FIG. The computer 90 includes a main control unit 91, an input device 92, an output device 93, a storage device 94, and a bus 95 that connects them to each other. The main control unit 91 has a CPU (central processing unit) and a RAM (random access memory). The input device 92 is used for inputting various parameters and instructing various operations of the failure detection device 70 when performing an inspection by the failure detection method according to the present embodiment. The output device 93 is used to output (including display) various information related to the examination.

  The storage device 94 may be of any form as long as it can store information. For example, the storage device 94 is a hard disk device or an optical disk device. The storage device 94 records information on a computer-readable recording medium 96 and reproduces information from the recording medium 96. The recording medium 96 is, for example, a hard disk or an optical disk. The recording medium 96 may be a recording medium that records a control program for the failure detection device 70.

  The main control unit 91 performs various functions shown in FIG. 9 by executing a program recorded in the recording medium 96 of the storage device 94, for example. Note that the sequence control unit 81, the measurement control unit 82, the switching control unit 83, and the determination unit 85 illustrated in FIG. 9 are realized by software, not physically separate elements. The storage unit 84 is realized by the RAM of the main control unit 91 or the recording medium 96 of the storage device 94.

  Next, the operation of the failure detection apparatus 70 will be described with reference to FIGS. 7, 8, and 11. FIG. 11 is a flowchart showing the operation of the failure detection apparatus 70. The following description includes a description of the failure detection method according to the present embodiment. Here, a case where inspection is performed on the bridge circuit 14 will be described as an example.

  As shown in FIG. 11, the control device 74 first executes a first measurement operation in step S101. The first measurement operation corresponds to the first measurement procedure of the failure determination method according to the present embodiment. FIG. 7 shows the state of the failure detection apparatus 70 in the first measurement operation. As shown in FIG. 7, in the first measurement operation, the control device 74 controls the switching device 73 by the switching control unit 83 so that the voltage source 71 is connected to the first and third contacts J11, J11 of the bridge circuit 14. In addition to connecting to J13, the potential measuring device 72 is connected to the second and fourth contacts J12 and J14 of the bridge circuit 14. In this state, the control device 74 controls the voltage source 71 and the potential measuring device 72 by the measurement control unit 82 and applies a predetermined voltage between the first contact J11 and the third contact J13 by the voltage source 71. Then, the potential measuring device 72 measures the potential of the second contact J12 and the potential of the fourth contact J14. The measurement result of the potential measuring device 72 is stored in the storage unit 84.

  Next, in step S102, the control device 74 executes a second measurement operation. The second measurement operation corresponds to the second measurement procedure of the failure determination method according to the present embodiment. FIG. 8 shows the state of the failure detection apparatus 70 in the second measurement operation. As shown in FIG. 8, in the second measurement operation, the control device 74 controls the switching device 73 by the switching control unit 83 so that the voltage source 71 is connected to the second and fourth contacts J12, J12 of the bridge circuit 14. In addition to being connected to J14, the potential measuring device 72 is connected to the first and third contacts J11 and J13 of the bridge circuit 14. In this state, the control device 74 controls the voltage source 71 and the potential measuring device 72 by the measurement control unit 82, and causes the voltage source 71 to apply a predetermined voltage between the second contact J12 and the fourth contact J14. Then, the potential measuring device 72 measures the potential of the first contact J11 and the potential of the third contact J13. The measurement result of the potential measuring device 72 is stored in the storage unit 84.

  Next, the control device 74 executes a determination operation including steps S103, S104, and S105. This determination operation corresponds to the determination procedure of the failure determination method according to the present embodiment. In the determination operation, in step S103, the potentials of the first to fourth contacts J11 to J14 measured by the first and second measurement operations (steps S101 and S102) and stored in the storage unit 84 are within the normal range. It is determined whether or not. If the potentials of the first to fourth contacts J11 to J14 are all within the normal range (Yes), the control device 74 determines that the bridge circuit 14 is normal in step S104, and otherwise In the case of (No), in step S105, it is determined that the bridge circuit 14 has failed, and the inspection for the bridge circuit 14 is terminated.

  In step S103, when determining whether or not the potentials of the first to fourth contacts J11 to J14 are within the normal range, the measured values of the potentials of the first to fourth contacts J11 to J14 are used as they are. A value obtained by subtracting a predetermined value from the measured value may be used. As this predetermined value, for example, the potential values of the first to fourth contacts J11 to J14 when the first and fourth resistors R11 to R14 are both assumed to be desired values (hereinafter referred to as the following values) Called ideal value). In this case, the normal range is defined by the amount of deviation of the measured potential value from the ideal value. A method for defining the normal range will be described in detail later.

  According to the present embodiment, the determination operation detects a failure of the bridge circuit 14 in a state in which one to three of the first to fourth resistors R11 to R14 of the bridge circuit 14 have failed. be able to. This will be described in detail below.

  When only the first resistor R11 out of the first to fourth resistors R11 to R14 fails, the potentials of the first and second contacts J11 and J12 are out of the normal range. When only the second resistor R12 fails, the potentials of the second and third contacts J12 and J13 are out of the normal range. When only the third resistor R13 fails, the potentials of the third and fourth contacts J13 and J14 are out of the normal range. When only the fourth resistor R14 fails, the potentials of the fourth and first contacts J14 and J11 are out of the normal range.

  When only the first and second resistors R11 and R12 fail, the potentials of the first and third contacts J11 and J13 are out of the normal range. When only the first and third resistors R11 and R13 fail, the potentials of the first to fourth contacts J11 to J14 are out of the normal range. When only the first and fourth resistors R11 and R14 fail, the potentials of the second and fourth contacts J12 and J14 are out of the normal range, respectively. When only the second and third resistors R12 and R13 fail, the potentials of the second and fourth contacts J12 and J14 are out of the normal range, respectively. When only the second and fourth resistors R12 and R14 fail, the potentials of the first to fourth contacts J11 to J14 are out of the normal range. When only the third and fourth resistors R13 and R14 fail, the potentials of the first and third contacts J11 and J13 are out of the normal range, respectively.

  When the three resistors R12 to R14 other than the first resistor R11 fail, the potentials of the first and second contacts J11 and J12 are out of the normal range. When the three resistors R11, R13, R14 other than the second resistor R12 fail, the potentials of the second and third contacts J12, J13 are out of the normal range. When three resistors R11, R12, R14 other than the third resistor R13 fail, the potentials of the third and fourth contacts J13, J14 are out of the normal range. When the three resistors R11 to R13 other than the fourth resistor R14 fail, the potentials of the fourth and first contacts J14 and J11 are out of the normal range.

  The failure of the first to fourth resistors R11 to R14 includes, for example, a failure due to a short circuit of the MR element 50 and a failure due to disconnection of the lower electrode 42 and the upper electrode 43. In any case, the potentials of the first to fourth contacts J11 to J14 are out of the normal range as described above.

  So far, the example in the case of inspecting the bridge circuit 14 has been described. When the inspection is performed on the bridge circuit 24, the first to fourth contacts J11 to J14 of the bridge circuit 14 are replaced with the first to fourth contacts J21 to J24 of the bridge circuit 24, and the first The measurement operation, the second measurement operation, and the determination operation are executed. According to the present embodiment, one to three resistors among the first to fourth resistors R21 to R24 of the bridge circuit 24 are determined by a determination operation, as in the case of detecting a failure of the bridge circuit 14. It is possible to detect a failure of the bridge circuit 24 in the form of failure.

  As described above, in the present embodiment, the control device 74 performs the first measurement operation (step S101), the second measurement operation (step S102), and the determination operation (steps S103, S104, S105). Execute. The failure detection method according to the present embodiment includes a first measurement procedure corresponding to the first measurement operation, a second measurement procedure corresponding to the second measurement operation, and a determination procedure corresponding to the determination operation. I have.

  According to the failure detection method and the failure detection apparatus 70 according to the present embodiment, it is possible to detect a failure of the bridge circuit in a mode in which the potentials of the two output contacts do not change. Hereinafter, this will be described by taking as an example a case where a failure of the bridge circuit 14 is detected. As described above, in the bridge circuit 14, the second and fourth contacts J12 and J14 are two output contacts.

  First, with reference to FIGS. 12 and 13, the failure of the bridge circuit 14 in a mode in which the potentials of the two output contacts (second and fourth contacts J12 and J14) do not change will be described. FIG. 12 is an explanatory diagram showing a connection relationship between the voltage source 71 and the potential measuring device 72 and the contacts J11 to J14 of the bridge circuit 14 in the first measurement operation and measurement procedure in the flowchart shown in FIG. FIG. 13 is an explanatory diagram showing a connection relationship between the voltage source 71 and the potential measuring device 72 and the contacts J11 to J14 of the bridge circuit 14 in the second measurement operation and measurement procedure in the flowchart shown in FIG.

  As one aspect in which the potentials of the two output contacts do not change, as shown in FIG. 12, the same number of one or more MR elements 50 in the third resistor R13 and the fourth resistor R14. Is short-circuited, and the resistance values of the third and fourth resistors R13 and R14 are each shifted from the desired value by the same value. 12 and 13, the third and fourth resistors R13 and R14 that have failed as described above are hatched. In this aspect, the potential of the fourth contact J14 is the same as when the resistance values of the third and fourth resistors R13 and R14 are both desired values. Therefore, in this aspect, as shown in FIG. 12, the failure of the bridge circuit 14 cannot be detected by monitoring the potentials of the two output contacts (second and fourth contacts J12 and J14). .

  On the other hand, in the present embodiment, not only the potentials of the second and fourth contacts J12 and J14 corresponding to the two output contacts are measured by the first measurement operation and the measurement procedure shown in FIG. By applying the voltage between the second contact J12 and the fourth contact J14 by the second measurement operation and measurement procedure shown in FIG. 13, the potentials of the first and third contacts J11 and J13 are also changed. taking measurement. As shown in FIG. 13, when the resistance values of the third and fourth resistors R13 and R14 are shifted from the desired values by the same value, the first measured by the second measurement operation and the measurement procedure. The potentials of the third contacts J11 and J13 are out of the normal range. Therefore, according to the present embodiment, the resistance values of the third and fourth resistors R13, R14 are respectively determined by the determination operation (steps S103, S104, S105) and the determination procedure in the flowchart shown in FIG. It is also possible to detect a failure of the bridge circuit 14 in a mode that is shifted from the desired value by the same value.

  As an aspect in which the potentials of the two output contacts do not change, in addition to the above example, the same number of one or more MR elements 50 are short-circuited in the first resistor R11 and the second resistor R12. Thus, there is a mode in which the resistance values of the first and second resistors R11 and R12 are each shifted from the desired value by the same value. In this aspect, the potential of the second contact J12 is the same as when the resistance values of the first and second resistors R11 and R12 are both desired values. According to the present embodiment, it is possible to detect a failure of the bridge circuit 14 of this aspect.

  Next, taking the bridge circuit 14 as an example, a method for defining the normal range used in the determination operation and determination procedure in the present embodiment will be described. In this example, the first to fourth resistors R11 to R14 of the bridge circuit 14 each include 50 MR elements 50 connected in series. Further, it is assumed that all MR elements 50 included in the bridge circuit 14 have no variation in resistance value due to failure, and the resistance value is 100Ω. As a failure mode of the resistors R11 to R14, a mode in which one of the 50 MR elements 50 included in one resistor is short-circuited is considered. In the first measurement operation, a voltage of 5V is applied between the first contact J11 and the third contact J13 so that the potential of the first contact J11 is 5V and the potential of the third contact J13 is 0V. Apply. In the second measurement operation and measurement procedure, the second contact J12 and the fourth contact J14 are arranged so that the potential of the second contact J12 is 5V and the potential of the fourth contact J14 is 0V. A voltage of 5V is applied.

  If there is no failure in any of the resistors R11 to R14, the potential of the second contact J12 and the potential of the fourth contact J14 measured by the first measurement operation and the measurement procedure, and the second measurement operation In addition, the potential of the first contact J11 and the potential of the third contact J13 measured by the measurement procedure are both 2.5V, which is an ideal value.

  When only the first resistor R11 out of the first to fourth resistors R11 to R14 fails, the potentials of the first and second contacts J11 and J12 are each 25.3 mV from the ideal value. To increase. When only the second resistor R12 fails, the potential of the second contact J12 decreases by 25.3 mV from the ideal value, and the potential of the third contact J13 increases by 25.3 mV from the ideal value. . When only the third resistor R13 fails, the potentials of the third and fourth contacts J13 and J14 are each reduced by 25.3 mV from the ideal value. When only the fourth resistor R14 fails, the potential of the fourth contact J14 increases by 25.3 mV from the ideal value, and the potential of the first contact J11 decreases by 25.3 mV from the ideal value. .

  When only the first and second resistors R11 and R12 fail, the potentials of the first and third contacts J11 and J13 increase by 25.3 mV from their ideal values, respectively. When only the first and third resistors R11 and R13 fail, the potentials of the first and second contacts J11 and J12 are increased by 25.3 mV from the ideal values, respectively. The potentials of the contacts J13 and J14 are each reduced by 25.3 mV from the ideal value. When only the first and fourth resistors R11 and R14 fail, the potentials of the second and fourth contacts J12 and J14 increase by 25.3 mV from their ideal values, respectively. When only the second and third resistors R12 and R13 fail, the potentials of the second and fourth contacts J12 and J14 are each reduced by 25.3 mV from the ideal value. When only the second and fourth resistors R12 and R14 fail, the potentials of the first and second contacts J11 and J12 decrease by 25.3 mV from the ideal value, respectively, and the third and fourth The potentials of the contacts J13 and J14 are each increased by 25.3 mV from the ideal value. When only the third and fourth resistors R13 and R14 fail, the potentials of the first and third contacts J11 and J13 are decreased from the ideal value by 25.3 mV, respectively.

  In addition, when the three resistors R12 to R14 other than the first resistor R11 fail, the potentials of the first and second contacts J11 and J12 are each reduced by 25.3 mV from the ideal value. When three resistors R11, R13, and R14 other than the second resistor R12 fail, the potential of the second contact J12 increases by 25.3 mV from the ideal value, and the potential of the third contact J13. Decreases by 25.3 mV from the ideal value. When three resistors R11, R12, and R14 other than the third resistor R13 fail, the potentials of the third and fourth contacts J13 and J14 increase by 25.3 mV from their ideal values, respectively. When the three resistors R11 to R13 other than the fourth resistor R14 fail, the potential of the fourth contact J14 decreases by 25.3 mV from the ideal value, and the potential of the first contact J11 is ideal. Increase by 25.3 mV from the value.

  Thus, when one to three of the first to fourth resistors R11 to R14 of the bridge circuit 14 fail, at least one of the first to fourth contacts J11 to J14. One potential fluctuates (increases or decreases) by 25.3 mV from the ideal value.

  Here, the amount of fluctuation from the ideal value of the potential of the first to fourth contacts J11 to J14 is defined as the offset amount of each potential. When the potential of the first to fourth contacts J11 to J14 increases from the ideal value, the offset amount is a positive value, and when the potential of the first to fourth contacts J11 to J14 decreases from the ideal value. The offset amount is a negative value.

  The normal range of the potential of the first to fourth contacts J11 to J14 is such that the absolute value of the offset amount of the potential of the first to fourth contacts J11 to J14 is the first to fourth resistors R11 to R14. What is necessary is just to prescribe | regulate as the range smaller than the absolute value of the amount of offsets of the electric potential of the 1st thru | or 4th contact J11-J14 when one to three resistors of this.

  Specifically, in the above example, two numerical values TH1 and TH2 that are larger than 0 and smaller than 25.3 are determined, and the normal range of the potentials of the first to fourth contacts J11 to J14 is an ideal value (2. 5V) may be defined as a range from a potential lower by −TH1 (mV) to a potential higher by an ideal value (2.5V) by TH2 (mV). The numerical values TH1 and TH2 may be equal or different.

  Up to this point, the description has been made on the assumption that all MR elements 50 included in the bridge circuit 14 have no variation in resistance value not caused by a failure. Variations in value can occur. Therefore, with reference to FIG. 14, a method for defining the normal range of the potentials of the first to fourth contacts J11 to J14 in consideration of variations in the resistance value of the MR element 50 not caused by a failure will be described below. . In the following description, the preconditions other than the variation in the resistance value of the MR element 50 are the same as those in the above example.

  FIG. 14 is a histogram showing an example of the distribution of potentials measured by the first or second measurement operation in the flowchart shown in FIG. In FIG. 14, the horizontal axis indicates the offset amount defined as described above, and the vertical axis indicates the frequency. When there is a variation in the resistance value of the MR element 50 not caused by a failure, the offset amount of the potential of the first to fourth contacts J11 to J14 in the bridge circuit 14 that is not broken is distributed around 0 mV. Hereinafter, such a distribution is referred to as a normal distribution. In FIG. 14, a distribution having a peak when the offset amount is 0 mV and having an offset amount within a range of −12 mV to 9 mV represents a normal distribution.

  On the other hand, when one to three of the first to fourth resistors R11 to R14 of the bridge circuit 14 fail, at least one of the first to fourth contacts J11 to J14. The potential offset amount is −25.3 mV or 25.3 mV unless the variation in the resistance value of the MR element 50 due to failure is taken into consideration. When there is a variation in the resistance value of the MR element 50 not due to a failure, the offset amount of the potential of at least one of the first to fourth contacts J11 to J14 is about −25.3 mV, 25 Distributed around 3 mV. Hereinafter, the offset amount distribution near −25.3 mV is referred to as a first distribution at the time of failure, and the offset amount distribution near 25.3 mV is referred to as a second distribution at the time of failure. FIG. 14 shows a first distribution at the time of failure existing in the range of −27 mV to −21 mV, and a second distribution at the time of failure existing in the range of 18 mV to 30 mV. For ease of understanding, the frequencies in the first and second distributions at the time of failure shown in FIG. 14 are the first and second distributions at the time of failure that occur in the actual manufacturing process of the bridge circuit 14. There are more than the frequency.

  Normally, as shown in FIG. 14, the first and second distributions at the time of failure do not overlap with the distributions at the normal time. Therefore, in consideration of variations in the resistance value of the MR element 50 not caused by a failure, the value of -TH1 (mV) is set to a value between the first distribution at the time of failure and the distribution at the time of normal. , TH2 (mV) may be set to a value between the distribution at normal time and the second distribution at failure. The normal range of the potentials of the first to fourth contacts J11 to J14 is a range where the offset amount is -TH1 (mV) to TH2 (mV). In the example shown in FIG. 14, the value of -TH1 (mV) is set to -16.5 mV, the value of TH2 (mV) is set to 16.5 mV, and the potentials of the first to fourth contacts J11 to J14 are set. Is defined as a range in which the offset amount is −16.5 mV to 16.5 mV.

  In addition, this invention is not limited to the said embodiment, A various change is possible. For example, the failure detection method and apparatus of the present invention can be applied to all bridge circuits including first to fourth resistors that are not limited to the first to fourth magnetic detection elements. The failure detection method and apparatus of the present invention can also be applied to detection of a failure in a bridge circuit including first to fourth resistors having reactances in addition to resistors. In this case, the voltage applied between the first contact and the third contact and the voltage applied between the second contact and the fourth contact may each be an alternating voltage.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic sensor, 2 ... Magnet, 10 ... 1st detection part, 20 ... 2nd detection part, 14, 24 ... Bridge circuit, 30 ... Operation part, 50 ... MR element, 70 ... Failure detection apparatus, 71 ... Voltage source 72 ... Potential measuring device 73 ... Switching device 74 ... Control device

Claims (10)

First to fourth contacts and first to fourth resistors, both ends of the first resistor being connected to the first contact and the second contact, respectively, both ends of the second resistor Are respectively connected to the second contact and the third contact, both ends of the third resistor are respectively connected to the third contact and the fourth contact, and both ends of the fourth resistor are respectively connected to the fourth contact. And a fault detection method for the bridge circuit connected to the first contact,
A first measurement procedure in which a voltage is applied between the first contact and the third contact to measure a potential of the second contact and a potential of the fourth contact;
A second measurement procedure for applying a voltage between the second contact and the fourth contact to measure the potential of the first contact and the potential of the third contact;
When the potentials of the first to fourth contacts measured by the first and second measurement procedures are all within the normal range, the bridge circuit is determined to be normal, and otherwise And a determination procedure for determining that the bridge circuit is in failure.   The bridge circuit failure detection method according to claim 1, wherein each of the first to fourth resistors is a magnetic detection element whose resistance value changes in accordance with an external magnetic field.   The bridge circuit failure detection method according to claim 2, wherein the magnetic detection element includes a plurality of magnetoresistive elements connected in series.   Each of the plurality of magnetoresistive elements includes a magnetization fixed layer having a fixed magnetization direction, a free layer whose magnetization changes according to the external magnetic field, and a nonmagnetic layer disposed between the magnetization fixed layer and the free layer. The fault detection method for a bridge circuit according to claim 3, further comprising: a layer.   The bridge circuit failure detection method according to claim 4, wherein the nonmagnetic layer is a tunnel barrier layer. First to fourth contacts and first to fourth resistors, both ends of the first resistor being connected to the first contact and the second contact, respectively, both ends of the second resistor Are respectively connected to the second contact and the third contact, both ends of the third resistor are respectively connected to the third contact and the fourth contact, and both ends of the fourth resistor are respectively connected to the fourth contact. And a fault detection device for a bridge circuit connected to the first contact,
A voltage source for generating a voltage;
An electric potential measuring device for measuring electric potential;
A switching device for switching a connection relationship between the voltage source and the potential measuring device and the first to fourth contacts;
A controller that controls the switching device and determines whether the bridge circuit is faulty,
The controller is
The switching device is controlled to connect the voltage source to the first and third contacts, and the potential measuring device is connected to the second and fourth contacts, and the voltage source supplies the first contact. A first measuring operation in which a voltage is applied between the first contact and the third contact, and the potential measurement device measures the potential of the second contact and the potential of the fourth contact;
The switching device is controlled to connect the voltage source to the second and fourth contacts, and the potential measuring device is connected to the first and third contacts, and the voltage source supplies the second contact. A second measuring operation in which a voltage is applied between the first contact and the fourth contact, and the potential measuring device measures the potential of the first contact and the potential of the third contact;
When the potentials of the first to fourth contacts measured by the first and second measurement operations are all within the normal range, the bridge circuit is determined to be normal, and otherwise Performs a determination operation for determining that the bridge circuit is faulty.   The bridge circuit failure detection device according to claim 6, wherein each of the first to fourth resistors is a magnetic detection element whose resistance value changes according to an external magnetic field.   8. The failure detection apparatus for a bridge circuit according to claim 7, wherein the magnetic detection element includes a plurality of magnetoresistive elements connected in series.   Each of the plurality of magnetoresistive elements includes a magnetization fixed layer having a fixed magnetization direction, a free layer whose magnetization changes according to the external magnetic field, and a nonmagnetic layer disposed between the magnetization fixed layer and the free layer. 9. The fault detection device for a bridge circuit according to claim 8, further comprising a layer.   The bridge circuit failure detection device according to claim 9, wherein the nonmagnetic layer is a tunnel barrier layer.

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