JP2596391B2 - Magnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic reluctance (M
The present invention relates to a magnetic sensor that detects the position and rotation of an object using an R) element (hereinafter, referred to as an MR element).

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional magnetic sensor (integrated magnetic sensor) using an MR element. FIG.
FIG. 4 is a diagram showing an arrangement of the MR elements shown in FIG. 3 on a semiconductor wafer.

In FIGS. 3 and 4, reference numeral 110 denotes a power source,
111 is an operational amplifier circuit, 112 is a semiconductor integrated circuit, 11
Reference numerals 3 to 116 denote MR resistors, and 117 denotes a semiconductor wafer.
The circuit of the conventional magnetic sensor shown in FIG. 3 has the following configuration.

A bridge circuit is formed by each of the MR resistors 113 to 116, and a power supply 110 is connected to the bridge circuit. The feedback-side line of the bridge circuit including the MR resistors 113 to 116 is grounded. The operational amplifier circuit 111 is a circuit for detecting a midpoint potential difference in the bridge circuit composed of the MR resistors 113 to 116. The minus terminal is connected to a line connecting the MR resistor 113 and the MR resistor 115, and the plus terminal is connected to the MR resistor 115. It is connected to a line connecting the resistor 114 and the MR resistor 116.

[0005] As shown in FIG. 4, each of the MR resistors 113 to 116 is provided on an operational amplifier circuit 111 on a semiconductor wafer 117.
And the like, and is formed integrally with the semiconductor integrated circuit 112 having a folded structure.
The pattern of each of the MR resistors 113 to 116 is such that the length direction of the pattern of the MR resistor is the MR resistor 113 and the MR resistor 11.
6, the MR resistor 114 and the MR resistor 115 are in the same direction, and the MR resistors 113 and 116 and the MR resistor 1
The directions of 14 and 115 are orthogonal. In each of the MR resistors 113 to 116 thus configured, the MR resistor 113
When a magnetic field in a direction perpendicular to the pattern length direction of the MR resistor (or MR resistor 116) is applied, the resistance values of the MR resistors 114 and 115 are constant and the MR resistors 113 and 115 are fixed.
When only the resistance value of the resistance 116 decreases and a magnetic field in the parallel direction is applied, on the contrary, the MR resistances 113 and 116
Is constant, and only the resistance values of the MR resistors 114 and 115 decrease.

Hereinafter, the operation of the conventional magnetic sensor configured as described above will be described.

When a magnetic field is externally applied (an object approaches), the MR resistor 113 and the MR resistor 1 of the MR resistors 113 to 116 provided on the semiconductor wafer 117 are provided.
16, or the resistance value of any one pair of the MR resistor 114 and the MR resistor 115 decreases (which resistance value changes is determined by the direction of the magnetic field). Then, FIG.
In the circuit shown in (1), a difference occurs in the midpoint potential of the bridge circuit of the MR resistor detected by the operational amplifier 111, and the intermediate potential difference is amplified by the operational amplifier 111 and output. The position of the object is detected based on the midpoint potential difference of the bridge circuit of the MR resistor output from the operational amplifier circuit 111.

The magnetic sensor described above is widely used for detecting a flow rate of a water heater or the like, detecting a vehicle speed, and detecting a position of a cylinder or the like.

[0009]

In the conventional magnetic sensor shown in FIG. 3, since the feedback line of the bridge circuit composed of four MR resistors is grounded, the current consumption is large in the value of the MR resistors. Dependent. Therefore, in order to suppress this current consumption, it is necessary to increase the value of the MR resistor. However, since a ferromagnetic thin film is generally used for an MR resistor formed on a semiconductor wafer, it is difficult to increase the resistivity (sheet resistance) itself. Conventionally, the MR resistor has a folded structure as shown in FIG. In this case, the current path is lengthened to increase the value of the MR resistance. As described above, in the conventional magnetic sensor in which the current path is lengthened by using the MR resistor formed on the semiconductor wafer as a folded structure pattern, if a pattern having a long current path is formed, the chip area becomes large, and the cost is reduced. There is a problem that it becomes difficult to plan.

Further, in the conventional magnetic sensor having a large area in which the folded pattern is formed as described above, if even one of the folded patterns of the MR resistor is broken, a failure occurs, resulting in low reliability. There is a point.

The present invention has been made in view of the above problems, and has as its object to provide a magnetic sensor having a small chip area and excellent reliability.

[0012]

The magnetic sensor of the present invention comprises:
First to third resistors connected in parallel to an output line of a power supply, and first and second transistors connected on the collector side to the power supply via the first and second resistors, respectively. A current mirror circuit, a third transistor having a base side and a collector side connected to the power supply via the second and third resistors, respectively, and supplying a base current to the first and second transistors; First and second magnetoresistive elements inserted into lines on the emitter side of the first and second transistors and having directionality in detecting a magnetic field, respectively; the potential on the collector side of the first transistor and the second And an operational amplifier circuit for detecting a difference between the potential of the transistor on the collector side and the first and second resistors having the same resistance value. The first and second magnetoresistive elements are arranged so that the magnetic field detection directions are orthogonal to each other, and the operational amplifier circuit is generated by a change in the resistance value of the first and second magnetoresistive elements. It is characterized by outputting a potential difference.

In this case, the resistance values of the first and second resistors are set to values larger than the resistance values of the first and second magnetoresistive elements, and the current consumption of the magnetic sensor is reduced by the first and second resistance values. It may be determined by the resistance value of the resistor.

Further, the first to third transistors are M
It may be constituted by an OS field transistor.

[0015]

In the magnetic sensor of the present invention configured as described above, since the resistance values of the first and second resistors are set to the same value, the circuit of the magnetic sensor operates as a current mirror circuit. Therefore, in the magnetic sensor of the present invention, when no magnetic field is applied, the resistance values of the first and second magneto-resistive elements have the same value, so that the potential on the collector side of the first transistor and the second transistor Does not differ from the potential on the collector side. On the other hand, when a magnetic field is applied, the resistance value of one of the first and second magnetoresistive elements decreases.
A potential difference occurs between the potential on the collector side of the second transistor and the potential on the collector side of the second transistor. The position of the object is detected based on the potential difference generated by applying the electric field.

The current consumption of the magnetic sensor of the present invention is determined by the first and second resistors and the resistance of the first and second magnetoresistive elements. In the present invention, since the resistance values of the first and second resistors are set to values larger than those of the first and second magnetoresistive elements, the current consumption is determined by the resistance values of the first and second resistors. It is determined. Therefore, it is not necessary to set the resistance value of the MR resistor to a large value in order to reduce the current consumption unlike the related art, and it is possible to set the resistance values of the first and second magnetic resistance elements to a small value.

In the magnetic sensor according to the present invention, the supply of the base current to the first and second transistors constituting the current mirror circuit is performed by the third resistor and the third resistor from the power supply.
Therefore, even if the resistance values of the first and second resistors are increased, the current flowing through the first and second magnetoresistive elements does not extremely decrease.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a magnetic sensor according to one embodiment of the present invention.

In FIG. 1, reference numerals 1 and 2 denote an MR resistor and 3 to 5
Is a semiconductor resistor, 6 to 8 are transistors, 9 is an operational amplifier circuit, and 10 is a power supply.

Each of the semiconductor resistors 3 to 5 is connected in parallel to the output line of the power supply 10 whose feedback line is grounded. The collector of the transistor 6 is connected to the semiconductor resistor 3, the collector of the transistor 7 is connected to the semiconductor resistor 4, Collectors are connected to the semiconductor resistors 5 respectively. The base of the transistor 6 is connected to the base of the transistor 7, and the connection line is connected to the emitter of the transistor 8. The base of the transistor 8 is connected to a line connecting the collector of the transistor 6 and the semiconductor resistor 3. In this circuit, the transistor 8 supplies the base current of the transistors 6,7.

The MR resistor 1 is connected to the emitter of the transistor 6, and the MR resistor 2 is connected to the emitter of the transistor 7. The MR resistor 1 and the MR resistor 2 are connected, and the connection line is grounded.

The operational amplifier circuit 9 has a minus terminal connected to a line connecting the collector of the transistor 6 and the semiconductor resistor 3, and a plus terminal connected to a line connecting the collector of the transistor 7 and the semiconductor resistor 4. . In the operational amplifier circuit 9, a potential difference between a line connecting the collector of the transistor 6 and the semiconductor resistor 3 and a line connecting the collector of the transistor 7 and the semiconductor resistor 4 is obtained, and the potential difference is amplified. Is output. In the figure, the connection point of the minus terminal of the operational amplifier circuit 9 is indicated by A, and the connection point of the plus terminal is indicated by B.

Here, the pattern of the MR resistors 1 and 2 formed on the semiconductor wafer will be described.

FIG. 2 is a diagram showing an example of the pattern of the MR resistors 1 and 2 in the circuit shown in FIG.

The MR resistors 1 and 2 are formed integrally with the semiconductor integrated circuit 12 on the semiconductor wafer 11 and have a folded pattern. The pattern of each of the MR resistors 1 and 2 corresponds to the pattern width direction of the MR resistor 1 and M
The pattern width direction of the R resistor 2 is formed to be orthogonal to each other, and is arranged in a hook shape along the side of the semiconductor wafer 11. In this embodiment, the number of turns of the pattern of the MR resistors 1 and 2 is small, and the area thereof is small.

Each of the MR resistors 1, 2 constructed as described above
Then, when a magnetic field in a direction perpendicular to the pattern length direction of the MR resistor 1 is applied, the resistance value of the MR resistor 2 is constant and the resistance value of the MR resistor 1 decreases, and conversely, Is applied, the resistance value of the MR resistor 1 is constant and the resistance value of the MR resistor 2 decreases.

Next, the operation of the magnetic sensor of the present embodiment configured as described above will be described.

In the circuit shown in FIG.
If the current flowing through the collector of the transistor 7 is Ic1 and the current flowing through the collector of the transistor 7 is Ic2, each collector current Ic
1, Ic2 satisfies the following relational expression.

Ic1 = Is × exp (q ÷ (kTVBE1)) (1) Ic2 = Is × exp (q ÷ (kTVBE2)) (2) (Ic1 × R3) + VBE1 = (Ic2 × R4) + VBE2 (3) From equations (1) to (3), Ic1 × R3 + kT ÷ (q × ln (Ic1 ÷ Is)) − Ic2 × R4-kT ÷ (q × ln (Ic2 ÷ Is)) = 0 (4) . Here, ls is the collector saturation current, q is the electron charge, and k is the Boltzmann constant.

At this time, if the values of the MR resistor 1 and the MR resistor 2 are equal, the circuit shown in FIG. 1 has a current mirror circuit configuration, the collector current Ic1 and the collector current Ic2 become equal, and the point A in the circuit is obtained. Is also equal to the potential at point B.

As described above, in this embodiment, the resistance values of the MR resistors 1 and 2 are set to the same value, and the state where the potential at the point A and the potential at the point B in the circuit are equal is set as the reference state. Have been.

When a magnetic field is applied from the outside (an object approaches), each MR provided on the semiconductor wafer 11 is
The resistance value of one of the resistances 1 and 2 decreases (which resistance value changes depends on the direction of the magnetic field).
Then, in the circuit shown in FIG. 1, a difference occurs between the potential at the point A and the potential at the point B detected by the operational amplifier circuit 9, and the potential difference is amplified by the operational amplifier circuit 9 and output.

The output signal from the operational amplifier circuit 9 reflects the position of an object in a magnetic field applied from the outside, that is, the position of the object. Therefore, in the magnetic sensor of this embodiment, the position of the object is detected based on the output signal from the operational amplifier circuit 9.

Next, the relationship between the current consumption and the resistance value in the magnetic sensor of this embodiment will be described.

The current consumption of the magnetic sensor of this embodiment is determined by the resistance values of the semiconductor resistors 3 and 4 and the MR resistors 1 and 2. Therefore, if the resistance values of the semiconductor resistors 3 and 4 are set large, the current consumption can be suppressed even if the MR resistors 1 and 2 are set small.

The semiconductor resistors 3 and 4 are diffusion resistors or polysilicon resistors, and are formed on the semiconductor wafer 11 by an ion implantation method or the like. Therefore, the sheet resistance can be freely controlled, and a large resistance value can be easily obtained with a small area. In the circuit shown in FIG. 1, since the base current of the transistors 6 and 7 is supplied from the power supply 10 via the semiconductor resistor 5 and the transistor 8, even if the resistance of the semiconductor resistors 3 and 4 is large, the MR The current flowing through the resistors 1 and 2 does not become extremely small. Therefore, even if the resistance values of the semiconductor resistors 3 and 4 are increased, the potential difference detected by the operational amplifier circuit 9 is not affected.

Further, since the size of the area of the MR resistor pattern does not affect the potential difference detected by the operational amplifier circuit 9, the area of the MR resistor pattern can be set to be sufficiently small.

As described above, in this embodiment, by setting the resistance values of the semiconductor resistors 3 and 4 to a large value, M
The degree of freedom in setting the resistance value of the R resistor increases, and the pattern of the MR resistor is set to a small area as shown in FIG.

In the magnetic sensor of this embodiment described above, the semiconductor integrated circuit and the transistor have been described as being bipolar. However, the present invention is not limited to this. For example, a MOS integrated circuit and a MOS electric field transistor may be used. You may comprise. In this case, the MR resistance is MOS
Connected to the source side of the electric field transistor.

[0041]

Since the present invention is configured as described above, it has the following effects.

According to the first and second aspects, since the current consumption is determined by the magnitude of the resistance values of the first and second resistors, the resistance value of the magnetoresistive element is set at the time of design. This has the effect of increasing the degree of freedom. Further, since the resistance value of the magnetoresistive element can be reduced, the printed pattern area of the magnetoresistive element can be reduced, and a low-cost, highly reliable magnetic sensor can be provided. .

According to the third aspect of the present invention, the MOS
Since it is constituted by the integrated circuit and the MOS electric field transistor, there is an effect that the current consumption is further reduced.

Further, since the output signal can be directly processed by the external processing unit, there is no need to provide a level conversion circuit, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetic sensor according to one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a pattern of MR resistors 1 and 2 in the circuit shown in FIG.

FIG. 3 is a circuit diagram of a conventional magnetic sensor using an MR element.

FIG. 4 is a diagram showing an arrangement of the MR elements shown in FIG. 3 on a semiconductor wafer.

[Explanation of symbols]

 1, 2 MR resistor 3, 4, 5 Semiconductor element 6, 7, 8 Transistor 9 Operational amplifier circuit 10 Power supply

Claims (3)

(57) [Claims] A first resistor connected in parallel to an output line of the power supply; a first resistor connected to the power supply via a first resistor and a second resistor connected to the power supply via the first resistor. A current mirror circuit including a transistor, a third side configured to supply a base current to the first and second transistors, wherein a base side and a collector side are connected to the power supply via the second and third resistors, respectively. A transistor; first and second magnetoresistive elements each having a directionality in detecting a magnetic field, respectively inserted into emitter-side lines of the first and second transistors; and a collector on the collector side of the first transistor. An operational amplifier circuit for detecting a difference between a potential and a potential on the collector side of the second transistor, wherein the first and second resistors are resistors Are set to the same value, the first and second magnetoresistive elements are arranged so that the directions of detecting the magnetic fields are orthogonal to each other, and the operational amplifier circuit is configured to control the resistance of the first and second magnetoresistive elements. A magnetic sensor for outputting a potential difference caused by a change in a value. 2. The magnetic sensor according to claim 1, wherein the resistance values of the first and second resistors are set to values larger than the resistance values of the first and second magnetic resistance elements, and the consumption of the magnetic sensor is increased. A magnetic sensor, wherein a current is determined by resistance values of the first and second resistors. 3. The magnetic sensor according to claim 1, wherein the first to third transistors are constituted by MOS field-effect transistors.