JPH02189484A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To enable detection of a magnetic field reciprocating in the same direction by a method wherein a level based on a voltage outputted by a magnetoresistance element part according to the magnetic field is determined by a waveform processing part. CONSTITUTION:A magnetoresistance element part 10 is connected at four nodes in the shape of a bridge so that a resistance value of at least one magnetic resistor 11 is lower than those of other magnetic resistors 12 to 14. When a power supply is added to a power supply terminal 31 of one opposite node thereof, an offset voltage is outputted from an output terminal 32 of the other opposite node. In a waveform processing part 20, a detection level being higher than a level based on this offset voltage is set. When a magnetic field is given, the element part 10 outputs the voltage, and the processing part 20 determines the level based on this voltage and outputs a signal when this level exceeds the detection level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic sensor that is incorporated into a detection device or the like that detects the rotation or position of an object and detects a magnetic field.

[Conventional technology]

As an element for detecting a magnetic field, for example, Japanese Patent Publication No. 54-413
There is an electromagnetic conversion element, that is, a magnetoresistive element, disclosed in Japanese Patent No. 35. This magnetoresistive element is formed by connecting ferromagnetic materials having a continuous folded structure in series at joints. Then, a magnetic signal such as a magnetic field rotating within the plane of this element, which is sufficient to saturate this magnetoresistive element, is generated from, for example, a magnetic recording medium, and the magnetoresistive element is placed at a finite distance from this magnetic recording medium. When placed, the magnetoresistive element outputs a signal from the connection part based on this magnetic signal.

[Problems to be Solved by the Invention] The conventional magnetoresistive element described above requires an external magnetic field sufficient to saturate the element, and also requires rotation within the plane of the element. When these conditions are met, the two formulas % formula % hold true, as disclosed in the aforementioned Japanese Patent Publication No. 54-41335. These two equations show that when a magnetic field H strong enough to saturate magnetize the two ferromagnetic materials A and B connected in series at the junction of the magnetoresistive element is applied at an angle θ, the ferromagnetic material A , B shows the change in each electrical resistance P, , P8. However, P represents the electrical resistance when the ferromagnetic materials A and B are saturated magnetized in a direction perpendicular to the current, and P// similarly represents the electrical resistance when saturated magnetized in parallel to the current.

As shown by these equations, when the above-mentioned magnetic field is applied, the resistance changes so that the sum of the resistance values of the two ferromagnetic materials always remains constant, and it is possible to obtain an approximately sine wave as an output waveform. can. An example of such an output waveform is shown in Figure 6 (
Shown in a).

As shown in FIG. 6(a), this output waveform has a substantially sinusoidal shape with one period πrad as the saturation magnetic field rotates. In addition, in FIG. 6(a), waveform 1
01 is the output voltage when the external magnetic field rotates from Orad to 2πrad, and the waveform 102 is 3π/4r
The figure shows the change in output voltage when the external magnetic field is rotated to ad and then reversely rotated to 5π/4 rad.

However, these conventional magnetoresistive elements cannot be used when there is no saturation magnetic field, or when the magnetic field does not rotate and only a component in one direction reciprocates, that is, when the magnetic field is between 0 rad and π/
It has a drawback that it cannot be used when a component that does not rotate and rotates from 2 rad to π rad to 2 π rad but only in the same direction, for example, a component in the Orad direction repeatedly turns on and off.

Furthermore, if a conventional magnetoresistive element is used to detect a magnetic field in which only components in the same direction reciprocate, a waveform processing circuit (comparator) is required to detect the level of the signal output from the magnetoresistive element. I need. This comparator has a threshold level, such as a hysteresis characteristic, and this threshold level is
Usually, the settings are as shown in FIG. 6(a).

That is, the threshold level 103 is set on the plus side, and the threshold level 104 is set on the minus side. However, in order to detect a magnetic field in which only components in the same direction reciprocate using a conventional magnetoresistive element, as shown in FIG. 6(b),
Both threshold levels 103 and 104 need to be set on the plus side. This is unrealistic, and in practice it is necessary to use an external offset resistor (1M adjustment resistor Rref).
It is necessary to add and adjust an initial offset adjustment circuit with etc.

An object of the present invention is to eliminate such drawbacks by integrating a ferromagnetic magnetoresistive element and a waveform shaping processing circuit into the same chip, and to create a magnetic field that can detect magnetic fields reciprocating in the same direction. The purpose is to provide sensors.

[Problem to be solved by the invention]

The present invention is a magnetic sensor using a magnetoresistive element whose resistance value changes when a magnetic field is applied, in which four magnetoresistive elements having at least one different resistance value are connected in a bridge shape at four connection points so that they are facing each other. When a power supply is applied to a connection point, a magnetoresistive element section outputs an offset voltage from another opposing connection point, and a waveform having a detection level set higher than a level based on the offset voltage from the magnetoresistive element section. and a processing section, when a magnetic field is applied, the magnetoresistive element section outputs a voltage, and the waveform processing section determines a level based on this voltage,
The device is characterized in that a signal is output when this level exceeds the detection level.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG.
The figure is a perspective view after molding of this example. This magnetic sensor includes a magnetoresistive element section 10 and a waveform processing section 20.
It is made up of.

Furthermore, the magnetoresistive element section 10 includes magnetoresistive elements 11 to 14.
The waveform processing unit 20 includes a comparator 21 and resistors 22 and 23.

In the magnetic sensor having such a configuration, the magnetoresistive elements 11 to 14 of the magnetoresistive element section 10 have a magnetoresistive effect in which the resistance value changes due to magnetism. An example of the magnetoresistive element section 10 made up of such magnetoresistive elements 11 to 14 is shown in the plan view of FIG.

As shown in FIG. 3, this magnetoresistive element section 10 is
It is formed by depositing a ferromagnetic metal such as Ni-Fe or Ni-Co on a smooth substrate to form a ferromagnetic thin film, and then patterning it into a predetermined shape. This results in
Four magnetoresistive bodies 11-14 are generated. The hatched portions of these four magnetic resistors 11 to 14 include
A conductor film such as an Au film is formed. As a result, in the magnetoresistive element 12, the resistor parts 12A are arranged in parallel with each other due to the evaporation of the ferromagnetic metal.

Further, each resistor portion 12A is connected in series by a conductor portion 12B having a width e generated by forming the conductor film.

In the magnetic resistor 13, the resistor parts 13A are arranged in parallel, and the longitudinal direction of the resistor parts 13A is substantially perpendicular to the longitudinal direction of the resistor part 12A of the magnetoresistive element 12. Furthermore, conductor portion 13B
As a result, each resistor portion 13A is connected in series.

An end 12D of such a magnetic resistor 12 is connected to an end 13C of the magnetic resistor 13, and the magnetic resistors 12 and 13 are connected in series. At the same time, the ends 12D and 13C of the magnetic resistor 12.13 are connected to the output terminal 18.
It is connected to the. The end 12C of the magnetoresistive element 12 is connected to the power supply terminal 15, and the end 12C of the magnetoresistive element 13 is connected to the power supply terminal 15.
3D is connected to the GND terminal 16.

In the magnetic resistor 14, the resistor portions 14A are arranged in parallel, and the longitudinal direction of the resistor portions 14A is approximately perpendicular to the longitudinal direction of the resistor portion 13A of the magnetic resistor 13. Furthermore, conductor portion 14B
As a result, the resistor portions 14A are connected in series.

In the magnetic resistor 11, the resistor portions 11A are arranged in parallel, and the longitudinal direction of the resistor portions 11A is approximately perpendicular to the longitudinal direction of the resistor portion 14A of the magnetic resistor 14. Furthermore, the conductor portion 11B
is the width e of the conductor portion of the other magnetoresistive elements 12 to 14,
The interval d is set longer.

Each resistor portion 11A is connected in series through the conductor portion 11B.

The end portion 11D of the magnetoresistive member 11 is connected to the end portion 14C of the magnetoresistive member 14, and the magnetoresistive members 11 and 14 are connected in series. At the same time, the ends 11D and 14C of the magnetoresistive elements 11.14 are connected to the output terminal 17. An end 11C of the magnetic resistor 11 is connected to the power terminal 15, and an end 14C of the magnetic resistor 14 is connected to the power terminal 15.
D is connected to the GNDr6 child 16.

The four magnetic resistors 11 to 14 connected in this way are
It has a bridge configuration. These four magnetoresistive elements 1
The power supply terminal 15 of the magnetoresistive element section 10 comprising magnetoresistive elements 1 to 14 is connected to the power supply terminal 31 as shown in FIG.
ND terminal 16 is connected to GND terminal 33. The output terminal 17 of the magnetoresistive element section 10 is connected to the minus (-) terminal of the comparator 21, and the output terminal 18 is connected to the plus (+) terminal of the comparator 21.

The comparator 21 of the waveform processing section 20 has a negative (-)
It performs waveform shaping processing on signals input to the terminal and the positive (+) terminal. That is, the comparator 21 performs processing to obtain the voltage difference between the voltages input to the minus (-) terminal and the plus (+) terminal. The comparator 21 is provided with two threshold levels, and when the potential difference level exceeds the first threshold level, the comparator 21 outputs a high-level signal to the output terminal 32. Also, the level of the potential difference is
When the threshold level is cut, the comparator 21 outputs a low level signal to the output terminal 32.

Note that a feedback resistor 22 is attached between the negative (-) terminal of the comparator 21 and the output terminal 32, and a set resistor 23 is attached between the comparator 21 and the GND terminal 33. There is.

Next, the operation of this embodiment will be explained.

A power source is connected between the power terminal 31 and the GND terminal 33 of the magnetic sensor according to this embodiment. As shown in FIG. 5(b), a disk 41 with a sufficiently large diameter has magnets 42 arranged at positions πrad from each other with the N poles on the outside.
This magnetic sensor is placed near the.

In a state where the magnetic field from the magnet 42 is not applied to the magnetic sensor, that is, in an initial state, the magnetoresistive element section 10 of the magnetic sensor has a structure as shown in FIG. 11B is another magnetoresistive element 1
It is set longer than the conductor parts 2 to 14. Therefore, the resistance value of the magnetoresistive element 11 is lower than the resistance values of the other magnetoresistive elements 12 to 14.

The power supply terminal 15 of such a magnetoresistive element section 10 and GND
When power is applied between the magnetoresistive element section 10 and the terminal 16, the voltage at the output terminal 17 of the magnetoresistive element section 10 becomes higher than the voltage at the output terminal 18. That is, the initial offset voltage is set by adjusting the magnetoresistive element section 10.

These voltages are applied to the comparator 21 of the waveform processing section 20, and the voltage at the minus (-) terminal of the comparator 21 becomes higher than the voltage at the plus (+) terminal.

On the other hand, in the comparator 21, as shown in FIG. 5(a), a first threshold level 203 is set on the plus side, and a second threshold level 203 is set on the minus side.
04 is set. Comparator 21 minus (
Since the voltage at the =) terminal is higher than the voltage at the plus (+) terminal, the level of the voltage difference determined by the processing of the comparator 21 is on the negative side and lower than the second threshold level. Therefore, the comparator 21 outputs a low level signal to the output terminal 32.

Next, by rotating a disk 41 having a sufficiently large diameter as shown in FIG. 5(b) in the direction 43 of the arrow, a magnetic field in the same direction 44 is periodically applied to the magnetic sensor side. In such a state, only when the two magnets 42 arranged in the disk 41 pass through the magnetic sensor, the resistance value of the magnetoresistive element section 1O changes, and the voltage at the positive (+) terminal of the comparator 21 changes. becomes higher than the voltage at the negative (-) terminal. Such a voltage is processed by the comparator 21 to obtain a waveform 202 shown in FIG. 5(a). The waveform 202 is generated when the magnet 42 of the disk 41 passes the magnetic sensor, that is, when Orad and πrad,
The first threshold level 203 is exceeded, otherwise the second threshold level 204 is cut.

Therefore, the comparator 21 outputs a high-level signal to the output terminal 32 when the waveform 204 exceeds the first threshold level 203, that is, when a magnetic field is applied to the magnetic sensor.

In this example, the magnetic field in the direction 44 shown in FIG. 5(b) was detected using the magnetoresistive element shown in FIG. 3. Here, when detecting a magnetic field in a direction perpendicular to direction 44, a magnetoresistive element section shown in FIG. 4 is used. Magnetoresistive element 5L of the magnetoresistive element part shown in FIG.
52, 53, and 54 are respectively π/
The shape has been rotated by 2 rad. In the magnetoresistive element 51, the conductor portion indicated by diagonal lines is set to be longer by the distance d than the conductor portions of the other magnetic resistance elements 52 to 54.

Further, the terminal 55 is a power supply terminal, the terminal 56 is a GND terminal, and the terminals 57 and 58 are output terminals.

In this way, in this embodiment, the initial offset voltage is set by adjusting the magnetoresistive element 11 of the magnetoresistive element section 10. However, if the resistance value of the magnetoresistive element 11 is not adjusted, the waveform at the comparator 21 will be the fifth waveform.
This is represented by a waveform 201 in Figure (a). At this time, a state in which level 204 of the two threshold levels 203204 is cut does not occur, and a switching operation is impossible.

Therefore, in this embodiment, the magnetoresistive element section 1 in the magnetic sensor is
By adjusting the offset voltage of 0 and connecting it to a comparator, it is possible to perform a switching operation that becomes high level (on) only when there is a magnetic field in a certain direction.

Furthermore, according to this embodiment, since the magnetoresistive element part and the comparator circuit part are formed in the same chip, and the magnetoresistive element part is formed after the comparator, the magnetoresistive element part can be adjusted depending on the offset of the comparator, etc. It is now possible to adjust the offset of

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to detect a magnetic field that reciprocates in the same direction.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram showing one embodiment of the present invention, FIG. 2 is a perspective view of the embodiment shown in FIG. 1 after molding, and FIG. 3 is an implementation of the embodiment shown in FIG. FIG. 4 is a plan view showing the shape of the magnetoresistive element section in the example when the orientation of the element of the magnetoresistive element section shown in FIG. 3 is rotated by 90 degrees. , FIG. 5 is a diagram showing the output waveform of the magnetoresistive element section of the embodiment shown in FIG. 1, and FIG. 6 is a diagram showing the output waveform of the conventional electromagnetic transducer element. 10... Resistance element section 11-14 20 21 22, 23 31 32 33 33

Claims (1)

[Claims] (1) A magnetic sensor using a magnetoresistive element whose resistance value changes when a magnetic field is applied, in which four magnetoresistive elements with at least one different resistance value are connected in a bridge shape at four connection points and face each other. A magnetoresistive element section that outputs an offset voltage from another opposing connection point when power is applied to a connection point, and a waveform processing having a detection level set higher than a level based on the offset voltage from the magnetoresistive element section. When a magnetic field is applied, the magnetoresistive element section outputs a voltage, and the waveform processing section determines a level based on this voltage,
A magnetic sensor characterized in that it outputs a signal when this level exceeds the detection level.