Rotation angle detector

1. A rotation angle detector comprising:

a rotator;

a first detecting rotator rotative in combination with the rotator;

a first magnet attached in a center of the first detecting rotator;

a first anisotropic magnetoresistive element including:

a first Wheatstone bridge and a second Wheatstone bridge each composed of four magnetoresistive elements connected to each other in a rectangular shape and disposed so as to face the first magnet, the second Wheatstone bridge being at an inclination of 45 degrees with respect to the first Wheatstone bridge, the first Wheatstone bridge including a first ground terminal, a first power supply terminal, a first positive output terminal, and a first negative output terminal; and the second Wheatstone bridge including a second ground terminal, a second power supply terminal, a second positive output terminal, and a second negative output terminal;

an amplifier connected to the first anisotropic magnetoresistive element, the amplifier being configured to differentially amplify an output signal from the first anisotropic magnetoresistive element; and

a controller connected to the amplifier, wherein

one of the first positive output terminal and the first negative output terminal is a first output terminal,

the controller connects the first output terminal to a ground so as to detect a presence or absence of a short circuit between the first positive output terminal and the first negative output terminal, and when there is no short circuit, the controller releases connection from the first output terminal to the ground, thereby detecting a rotation angle of the rotator based on a signal outputted from the amplifier in accordance with the output signal of the first anisotropic magnetoresistive element.

2. The rotation angle detector according to claim 1 , further comprising:

a first rectifier element electrically connected to the first output terminal; and

a switching portion connected to the first rectifier element at a forward direction thereof, wherein

the controller detects the presence or absence of the short circuit between the first positive output terminal and the first negative output terminal by switching the switching portion so as to connect the first output terminal to the ground.

3. The rotation angle detector according to claim 2 , further comprising:

a second rectifier element disposed between the switching portion and a second output terminal and connected to the switching portion at a forward direction thereof, the second output terminal being one of a second positive output terminal and a second negative output terminal, the second positive output terminal and the second negative output terminal being opposite in polarity to the first output terminal, wherein

the controller connects the first output terminal and the second output terminal to the ground, thereby detecting a presence or absence of a short circuit between output terminals of the amplifier.

4. The rotation angle detector according to claim 1 , further comprising:

a second detecting rotator rotative in combination with one of the rotator and the first detecting rotator, the second detecting rotator being configured to rotate at a different speed from the first detecting rotator;

a second magnet attached in a center of the second detecting rotator;

a second anisotropic magnetoresistive element including:

a third Wheatstone bridge and a fourth Wheatstone bridge each composed of four magnetoresistive elements connected to each other in a rectangular shape and disposed so as to face the second magnet, the fourth Wheatstone bridge being at an inclination of 45 degrees with respect to the third Wheatstone bridge, wherein

the amplifier is further connected to the second anisotropic magnetoresistive element, and differentially amplifies an output signal of the second anisotropic magnetoresistive element; and

the controller detects a rotation angle of the rotator based on a signal outputted from the amplifier in accordance with the output signal of the first anisotropic magnetoresistive element and the output signal of the second anisotropic magnetoresistive element.

5. The rotation angle detector according to claim 4 , wherein

the third Wheatstone bridge includes a third ground terminal, a third power supply terminal, a third positive output terminal, and a third negative output terminal; the fourth Wheatstone bridge includes a fourth ground terminal, a fourth power supply terminal, a fourth positive output terminal, and a fourth negative output terminal;

one of the third positive output terminal and the third negative output terminal is a third output terminal; and

the controller detects a presence or absence of a short circuit between the third positive output terminal and the third negative output terminal by connecting the third output terminal to the ground; and when there is no short circuit, the controller releases connection from the first output terminal to the ground and connection from the third output terminal to the ground, thereby detecting the rotation angle of the rotator based on the signal outputted from the amplifier in accordance with the output signal of the first anisotropic magnetoresistive element and the output signal of the second anisotropic magnetoresistive element.

6. A rotation angle detector comprising:

a rotator;

a first detecting rotator rotative in combination with the rotator;

a first magnet attached in a center of the first detecting rotator;

a first anisotropic magnetoresistive element including:

a first Wheatstone bridge and a second Wheatstone bridge each composed of four magnetoresistive elements connected to each other in a rectangular shape and disposed so as to face the first magnet, the second Wheatstone bridge being at an inclination of 45 degrees with respect to the first Wheatstone bridge, the first Wheatstone bridge including a first ground terminal, a first power supply terminal, a first positive output terminal, and a first negative output terminal; and the second Wheatstone bridge including a second ground terminal, a second power supply terminal, a second positive output terminal, and a second negative output terminal;

an amplifier connected to the first anisotropic magnetoresistive element, the amplifier being configured to differentially amplify an output signal of the first anisotropic magnetoresistive element;

a controller connected to the amplifier;

a resistor electrically connected between the first ground terminal and a ground; and

a switching portion parallel with the resistor, wherein

the controller switches the switching portion so as to switch the first ground terminal from a state of being connected to the ground directly to a state of being connected to the ground via the resistor, thereby detecting a presence or absence of a short circuit between at least one of:

a) the first positive output terminal and the second positive output terminal,

b) the first positive output terminal and the second negative output terminal,

c) the first negative output terminal and the second positive output terminal, and

d) the first negative output terminal and the second negative output terminal, and

when there is no short circuit, the controller switches the switching portion in such a manner that the first ground terminal is connected to the ground directly, thereby detecting a rotation angle of the rotator based on a signal outputted from the amplifier in accordance with the output signal of the first anisotropic magnetoresistive element.

7. The rotation angle detector according to claim 6 , further comprising:

a second detecting rotator rotative in combination with one of the rotator and the first detecting rotator, the second detecting rotator being configured to rotate at a different speed from the first detecting rotator;

a second magnet attached in a center of the second detecting rotator;

a second anisotropic magnetoresistive element including:

a third Wheatstone bridge and a fourth Wheatstone bridge each composed of four magnetoresistive elements connected to each other in a rectangular shape and disposed so as to face the second magnet, the fourth Wheatstone bridge being at an inclination of 45 degrees with respect to the third Wheatstone bridge, wherein

the amplifier is further connected to the second anisotropic magnetoresistive element, and differentially amplifies an output signal of the second anisotropic magnetoresistive element; and

the controller detects a rotation angle of the rotator based on a signal outputted from the amplifier in accordance with the output signal of the first anisotropic magnetoresistive element and the output signal of the second anisotropic magnetoresistive element.

8. The rotation angle detector according to claim 7 , wherein the third Wheatstone bridge includes a third ground terminal, a third power supply terminal, a third positive output terminal, and a third negative output terminal; the fourth Wheatstone bridge includes a fourth ground terminal, a fourth power supply terminal, a fourth positive output terminal, and a fourth negative output terminal;

the third ground terminal is electrically connected to a ground via the resistor;

the controller switches the switching portion so as to switch the third ground terminal from a state of being connected to the ground directly to a state of being connected to the ground via the resistor, thereby detecting a presence or absence of a short circuit at least one of between the third positive output terminal and the fourth positive output terminal, between the third positive output terminal and the fourth negative output terminal, between the third negative output terminal and the fourth positive output terminal, and between the third negative output terminal and the fourth negative output terminal, and when there is no short circuit, the controller switches the switching portion in such a manner that the first ground terminal and the third ground terminal are connected to the ground directly, thereby detecting a rotation angle of the rotator based on the signal outputted from the amplifier in accordance with the output signal of the first anisotropic magnetoresistive element and the output signal of the second anisotropic magnetoresistive element.