Magnetic sensor device and magnetic encoder
A magnetic sensor device includes a magnetic sensor, a die pad, and four leads. The magnetic sensor includes a bridge circuit including a plurality of arms and a plurality of pads electrically connected to the bridge circuit. One of the plurality of arms is provided between one of the plurality of pads and a different one of the plurality of pads in circuit configuration. The magnetic sensor further includes a sub-pad electrically connected between one end and another end of the one arm and also electrically connected to the die pad.
1. A magnetic sensor device comprising:
a magnetic sensor configured to detect a target magnetic field including a magnetic field component in a first direction;
a die pad supporting the magnetic sensor; and
a plurality of leads, wherein
the magnetic sensor includes a bridge circuit including a plurality of arms and a plurality of pads electrically connected to the bridge circuit, the plurality of arms being each constituted of a plurality of magnetic detection elements and configured such that a resistance changes according to change of strength of the magnetic field component,
each of the plurality of arms is configured to have sensitivity to the magnetic field component with strength changing according to a position in the first direction while not having sensitivity to an external magnetic field with strength and a direction being same irrespective of the position in the first direction,
each of the plurality of pads is electrically connected to one corresponding lead among the plurality of leads,
the plurality of pads include a first pad, a second pad, and a third pad,
the plurality of arms include a first arm provided between the first pad and the second pad in circuit configuration and a second arm provided between the second pad and the third pad in circuit configuration, and
the magnetic sensor further includes a first sub-pad electrically connected between one end and another end of the first arm and electrically connected to the die pad.
2. The magnetic sensor device according to claim 1 , wherein
one of the first pad and the third pad constitutes a power supply port of the magnetic sensor,
another one of the first pad and the third pad constitutes a ground port of the magnetic sensor, and
the second pad constitutes a signal port of the magnetic sensor.
3. The magnetic sensor device according to claim 1 , wherein the first sub-pad is not electrically connected to an external circuit in a state where the magnetic sensor device is mounted on a mount.
4. The magnetic sensor device according to claim 1 , wherein no pad is electrically connected between one end and another end of the second arm.
5. The magnetic sensor device according to claim 1 , wherein the magnetic sensor further includes a second sub-pad electrically connected between one end and another end of the second arm.
6. The magnetic sensor device according to claim 5 , wherein the second sub-pad is not electrically connected to the plurality of leads and the die pad.
7. The magnetic sensor device according to claim 1 , wherein
the plurality of pads further includes a fourth pad, and
the plurality of arms further includes a third arm provided between the third pad and the fourth pad in circuit configuration and a fourth arm provided between the first pad and the fourth pad in circuit configuration.
8. The magnetic sensor device according to claim 7 , wherein no pad is electrically connected between one end and another end of the second arm, between one end and another end of the third arm, and between one end and another end of the fourth arm.
9. The magnetic sensor device according to claim 7 , wherein the magnetic sensor further includes a second sub-pad electrically connected between one end and another end of the second arm, a third sub-pad electrically connected between one end and another end of the third arm, and a fourth sub-pad electrically connected between one end and another end of the fourth arm.
10. The magnetic sensor device according to claim 9 , wherein the second sub-pad, the third sub-pad, and the fourth sub-pad are not electrically connected to the plurality of leads and the die pad.
11. The magnetic sensor device according to claim 7 , wherein the number of the plurality of leads is four.
12. The magnetic sensor device according to claim 1 , wherein the plurality of arms are configured such that the resistance of each of the plurality of arms changes in a different phase according to periodic change of the strength of the magnetic field component.
13. The magnetic sensor device according to claim 12 , wherein
each of the plurality of arms includes two resistors connected in series, and
in each of the plurality of arms, the two resistors are configured such that the resistances of the two respective resistors change in a same phase according to periodic change of the strength of the magnetic field component and configured such that the resistances of the two respective resistors change in opposite phases according to periodic change of the strength or the direction of the external magnetic field.
14. The magnetic sensor device according to claim 13 , wherein the first sub-pad is electrically connected to a connection point of the two resistors of the first arm.
15. The magnetic sensor device according to claim 1 , wherein
the plurality of magnetic detection elements are a plurality of magnetoresistive elements, and
each of the plurality of magnetoresistive elements includes a magnetization pinned layer having a first magnetization whose direction is fixed, a free layer having a second magnetization whose direction is variable, and a gap layer arranged between the magnetization pinned layer and the free layer.
16. The magnetic sensor device according to claim 15 , wherein
each of the plurality of arms includes two resistors connected in series,
the first magnetization of the magnetization pinned layer of each of the plurality of magnetoresistive elements in one of the two resistors includes a component in a first magnetization direction, and
the second magnetization of the magnetization pinned layer of each of the plurality of magnetoresistive elements in another of the two resistors includes a component in a second magnetization direction opposite to the first magnetization direction.
17. The magnetic sensor device according to claim 16 , wherein the first sub-pad is electrically connected to a connection point of the two resistors of the first arm.
18. A magnetic encoder comprising:
the magnetic sensor device according to claim 1 ; and
a magnetic field generator configured to generate the target magnetic field, wherein
the magnetic sensor and the magnetic field generator are configured such that the strength of the magnetic field component in a reference position changes when at least one of the magnetic sensor and the magnetic field generator operates.
19. The magnetic encoder according to claim 18 , wherein the magnetic field generator is a magnetic scale including a plurality of pairs of N and S poles alternately arranged in the first direction.
20. The magnetic encoder according to claim 18 , wherein the magnetic field generator is a magnetic scale including a plurality of pairs of N and S poles alternately arranged around a rotation axis.