Position detection device
A position detection device includes a first position detector, a second position detector, and a signal generator. The first position detector includes a first magnetic field generation unit, a second magnetic field generation unit, and a first magnetic sensor. The second position detector includes a third magnetic field generation unit, a fourth magnetic field generation unit, and a second magnetic sensor. The positions of the second and fourth magnetic field generation units vary in response to variations in a detection-target position. The signal generator generates a position detection signal, which is the sum of a first detection signal generated by the first magnetic sensor and a second detection signal generated by the second magnetic sensor. Each of the first and second position detectors includes a bias magnetic field generation unit.
1. A magnetic sensor device comprising a first magnetic sensor, a second magnetic sensor, and a signal generator, wherein
the first magnetic sensor is configured to detect, at a first detection position in a first reference plane, a first detection-target magnetic field and to generate a first detection signal that varies in magnitude according to a direction of the first detection-target magnetic field, wherein the first detection-target magnetic field is a magnetic field component parallel to the first reference plane,
the second magnetic sensor is configured to detect, at a second detection position in a second reference plane, a second detection-target magnetic field and to generate a second detection signal that varies in magnitude according to a direction of the second detection-target magnetic field, wherein the second detection-target magnetic field is a magnetic field component parallel to the second reference plane,
the signal generator generates a third detection signal by using the first detection signal and the second detection signal,
the first detection-target magnetic field includes a first magnetic field component and a second magnetic field component,
a strength of the second magnetic field component varies whereas none of a strength of and direction of the first magnetic field component and a direction of the second magnetic field component vary, wherein the first magnetic field component is a component of a first magnetic field at the first detection position, the component of the first magnetic field being parallel to the first reference plane, and the second magnetic field component is a component of a second magnetic field at the first detection position, the component of the second magnetic field being parallel to the first reference plane,
the second detection-target magnetic field includes a third magnetic field component and a fourth magnetic field component,
a strength of the fourth magnetic field component varies whereas none of a strength and direction of the third magnetic field component and a direction of the fourth magnetic field component vary, wherein the third magnetic field component is a component of a third magnetic field at the second detection position, the component of the third magnetic field being parallel to the second reference plane, and the fourth magnetic field component is a component of a fourth magnetic field at the second detection position, the component of the fourth magnetic field being parallel to the second reference plane,
the direction of the third magnetic field component is opposite to the direction of the first magnetic field component,
the direction of the fourth magnetic field component is opposite to the direction of the second magnetic field component, and
a variable range of the first detection signal includes a first reference value, and a variable range of the second detection signal includes a second reference value, wherein the first reference value is an average value of a maximum value and a minimum value of the first detection signal when the direction of the first detection-target magnetic field varies over a range of 360°, and the second reference value is an average value of a maximum value and a minimum value of the second detection signal when the direction of the second detection-target magnetic field varies over the range of 360°.
2. The magnetic sensor device according to claim 1 , wherein
each of the first magnetic sensor and the second magnetic sensor includes at least one magnetoresistive element,
the at least one magnetoresistive element includes a magnetization pinned layer having a magnetization whose direction is fixed, and a free layer having a magnetization whose direction is variable according to the direction of the first or second detection-target magnetic field,
the first reference plane is a plane that contains the direction of the magnetization of the magnetization pinned layer in the first magnetic sensor and the direction of the first detection-target magnetic field,
the direction of the first detection-target magnetic field when the first detection signal is of the first reference value is the same as one of two directions orthogonal to the direction of the magnetization of the magnetization pinned layer in the first magnetic sensor,
the second reference plane is a plane that contains the direction of the magnetization of the magnetization pinned layer in the second magnetic sensor and the direction of the second detection-target magnetic field, and
the direction of the second detection-target magnetic field when the second detection signal is of the second reference value is the same as one of two directions orthogonal to the direction of the magnetization of the magnetization pinned layer in the second magnetic sensor.
3. The magnetic sensor device according to claim 1 , wherein a value in the middle of the variable range of the first detection signal is the first reference value, and a value in the middle of the variable range of the second detection signal is the second reference value.
4. The magnetic sensor device according to claim 1 , further comprising at least one bias magnetic field generation unit for generating a bias magnetic field to be applied to at least one of the first or second magnetic sensor, wherein
the bias magnetic field applied to at least one of the first magnetic sensor or the second magnetic sensor causes the variable range of the first detection signal to include the first reference value and causes the variable range of the second detection signal to include the second reference value.
5. The magnetic sensor device according to claim 4 , wherein the strength of the second magnetic field component and the strength of the fourth magnetic field component corresponding to the same detection-target position are different from each other in absolute value.
6. The magnetic sensor device according to claim 4 , wherein the at least one bias magnetic field generation unit includes a first bias magnetic field generation unit for generating a first bias magnetic field to be applied to the first magnetic sensor, and a second bias magnetic field generation unit for generating a second bias magnetic field to be applied to the second magnetic sensor.
7. The magnetic sensor device according to claim 6 , wherein the first bias magnetic field and the second bias magnetic field are in directions non-parallel to each other.
8. A magnetic sensor device comprising a first magnetic sensor and a second magnetic sensor, wherein
the first magnetic sensor is configured to detect, at a first detection position in a first reference plane, a first detection-target magnetic field and to generate a first detection signal that varies in magnitude according to a direction of the first detection-target magnetic field, wherein the first detection-target magnetic field is a magnetic field component parallel to the first reference plane,
the second magnetic sensor is configured to detect, at a second detection position in a second reference plane, a second detection-target magnetic field and to generate a second detection signal that varies in magnitude according to a direction of the second detection-target magnetic field, wherein the second detection-target magnetic field is a magnetic field component parallel to the second reference plane,
the first detection-target magnetic field includes a first magnetic field component and a second magnetic field component,
a strength of the second magnetic field component varies whereas none of a strength of and direction of the first magnetic field component and a direction of the second magnetic field component vary, wherein the first magnetic field component is a component of a first magnetic field at the first detection position, the component of the first magnetic field being parallel to the first reference plane, and the second magnetic field component is a component of a second magnetic field at the first detection position, the component of the second magnetic field being parallel to the first reference plane,
the second detection-target magnetic field includes a third magnetic field component and a fourth magnetic field component,
a strength of the fourth magnetic field component varies whereas none of a strength and direction of the third magnetic field component and a direction of the fourth magnetic field component vary, wherein the third magnetic field component is a component of a third magnetic field at the second detection position, the component of the third magnetic field being parallel to the second reference plane, and the fourth magnetic field component is a component of a fourth magnetic field at the second detection position, the component of the fourth magnetic field being parallel to the second reference plane
the direction of the third magnetic field component is opposite to the direction of the first magnetic field component,
the direction of the fourth magnetic field component is opposite to the direction of the second magnetic field component, and
a variable range of the first detection signal includes a first reference value, and a variable range of the second detection signal includes a second reference value, wherein the first reference value is an average value of a maximum value and a minimum value of the first detection signal when the direction of the first detection-target magnetic field varies over a range of 360°, and the second reference value is an average value of a maximum value and a minimum value of the second detection signal when the direction of the second detection-target magnetic field varies over the range of 360°.
9. The magnetic sensor device according to claim 8 , wherein
each of the first magnetic sensor and the second magnetic sensor includes at least one magnetoresistive element,
the at least one magnetoresistive element includes a magnetization pinned layer having a magnetization whose direction is fixed, and a free layer having a magnetization whose direction is variable according to the direction of the first or second detection-target magnetic field,
the first reference plane is a plane that contains the direction of the magnetization of the magnetization pinned layer in the first magnetic sensor and the direction of the first detection-target magnetic field,
the direction of the first detection-target magnetic field when the first detection signal is of the first reference value is the same as one of two directions orthogonal to the direction of the magnetization of the magnetization pinned layer in the first magnetic sensor,
the second reference plane is a plane that contains the direction of the magnetization of the magnetization pinned layer in the second magnetic sensor and the direction of the second detection-target magnetic field, and
the direction of the second detection-target magnetic field when the second detection signal is of the second reference value is the same as one of two directions orthogonal to the direction of the magnetization of the magnetization pinned layer in the second magnetic sensor.
10. The magnetic sensor device according to claim 8 , wherein a value in the middle of the variable range of the first detection signal is the first reference value, and a value in the middle of the variable range of the second detection signal is the second reference value.
11. The magnetic sensor device according to claim 8 , further comprising at least one bias magnetic field generation unit for generating a bias magnetic field to be applied to at least one of the first or second magnetic sensor, wherein
the bias magnetic field applied to at least one of the first magnetic sensor or the second magnetic sensor causes the variable range of the first detection signal to include the first reference value and causes the variable range of the second detection signal to include the second reference value.
12. The magnetic sensor device according to claim 11 , wherein the strength of the second magnetic field component and the strength of the fourth magnetic field component corresponding to the same detection-target position are different from each other in absolute value.
13. The magnetic sensor device according to claim 11 , wherein the at least one bias magnetic field generation unit includes a first bias magnetic field generation unit for generating a first bias magnetic field to be applied to the first magnetic sensor, and a second bias magnetic field generation unit for generating a second bias magnetic field to be applied to the second magnetic sensor.
14. The magnetic sensor device according to claim 13 , wherein the first bias magnetic field and the second bias magnetic field are in directions non-parallel to each other.