JPH0432969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic detection device that can be used as a rotary encoder or a linear encoder.

For example, a magnetic signal recorded in the form of a magnetization pattern with equally spaced bit lengths on a disk or cylinder having a magnetic recording medium attached to a rotating shaft is transferred to a ferromagnetic magnetoresistive element (hereinafter abbreviated as MR element).
A so-called rotary encoder is known that detects the rotation angle of a rotating shaft by reading it with a magnetic sensor having a rotary shaft. However, in a conventional rotary encoder, when a disk or cylinder having a magnetic recording medium is attached to the output shaft of the motor and the rotation angle of the output shaft is detected by reading this with a magnetic sensor,
Since a considerably large magnetic field leaks to the outside from the excitation permanent magnet and armature of the motor, the S/N ratio of the detection output of the magnetic sensor deteriorates due to the influence of this external magnetic field, resulting in malfunction. In order to solve such problems, for example, Japanese Patent Laid-Open No. 54-162556 discloses a disk having a magnetic recording medium attached to the output shaft of a motor, a magnetic sensor placed opposite the disk, and the magnetic sensor. An angle detector has been proposed in which the drive circuit and signal processing circuit are magnetically shielded by surrounding them with a high permeability magnetic material. However, there are drawbacks such as the fact that it is extremely difficult to completely magnetically shield the angle detector from the leakage magnetic field from the motor. In addition, in order to eliminate the influence of the external magnetic field, another magnetic sensor detects only the external magnetic field, and this detection signal and the output signal of the magnetic sensor that detects the magnetic recording medium are electrically calculated. It may be possible to compensate for the effects, but in this case, the magneto-resistance characteristics of the MR elements that make up the magnetic sensor are not perfectly proportional, so if the operating point shifts, the output signal will be distorted, making it difficult to achieve high precision. There is a problem that cannot be detected.

Furthermore, in Japanese Patent Application No. 57-36644, the present inventor provided two magnetic sensors, detected a noise magnetic field with one magnetic sensor, and used the detection output to generate a magnetic field that canceled out the noise magnetic field with the other magnetic sensor. Although a magnetic detector has been proposed that can detect only a signal magnetic field by generating it, it cannot be applied to cases where only a noise magnetic field cannot be detected.

For example, it is possible to use a magnetic detector to control the drive and rotation angle of a direct drive motor, but in this case,
In order to perform drive control, it is necessary to detect the rotor magnetic field, and to perform rotation angle control, it is necessary to detect a magnetization pattern provided on the outer periphery of the rotor. In this case, since the rotor magnetic field and the magnetic field due to the magnetization pattern are applied to the magnetic detector in a superimposed manner, the conventional magnetic detector cannot perform accurate drive control or rotation angle control.

Furthermore, although magnetic sensors using magnetoresistive elements have extremely high sensitivity, they become saturated with a relatively small magnetic field, so if a noise magnetic field is large, for example, they will become saturated and no detection output can be obtained. .

On the other hand, as a magnetic sensor equipped with a magnetoresistive element, two layers of magnetoresistive elements are provided above and below with an insulating film in between, and magnetic bias is applied to each other. −37205
It is described in the No. 3 publication, etc., and is publicly known. For example, in the magnetic sensor described in Japanese Patent Publication No. 53-37204, two layers of magnetoresistive elements are stacked one above the other, and the magnetic field generated by the drive current flowing through one magnetoresistive element applies a bias magnetic field to the other magnetoresistive element. Hereinafter, this will be referred to as the primary bias method. In addition, in the magnetic sensor described in Japanese Patent Publication No. 53-37205, a magnetic field generated by a drive current flowing through one magnetoresistive element is applied to the other magnetoresistive element, and the magnetization in the other magnetoresistive element is changed. The component produces a reverse magnetic field, and this reverse magnetic field is applied to one of the magnetoresistive elements as a bias magnetic field, and this is hereinafter referred to as a secondary bias method.

FIG. 1 is a circuit diagram of the magnetic detector described in the above-mentioned Japanese Patent Publication No. 53-37204. First and second magnetoresistive elements MR1 and MR2 stacked one above the other with an insulating film in between are connected in parallel between a constant current source S and the ground potential, and the constant current source S and magnetoresistive elements MR1 and MR2 voltage appearing at the connection point with
The difference between V ₁ and V ₂ is determined using a differential amplifier DA.

Such a mutual magnetic bias type magnetic detector is constructed, for example, by sequentially depositing a first magnetoresistive film, an insulating film, and a second magnetoresistive film on an insulating substrate. In order to obtain an output, it is necessary that the first and second magnetoresistive films have the same magnetic properties. A method for manufacturing such a magnetic detector includes depositing a first magnetoresistive film and an electrode film on a substrate, patterning them by photo-etching, etc., and then depositing an insulating film.
A generally considered method is to further deposit and pattern a second magnetoresistive film and an electrode film thereon. However, in such a manufacturing method, since the first and second magnetoresistive elements are formed from different magnetoresistive films, it is difficult for them to have the same film thickness, specific resistance, temperature coefficient of resistance, etc., and the disadvantage is that the magnetic properties are not uniform. There is. Furthermore, since the first and second magnetoresistive elements are formed by patterning in separate steps, their dimensional accuracy is poor and they do not have the same dimensions, resulting in a disadvantage that differences appear in their magnetic properties. Therefore, an unbalanced voltage, which is an output voltage in the absence of a magnetic field, is generated and this drifts depending on the temperature, so there is a drawback that accurate magnetic detection cannot be performed.

The purpose of the present invention is to be able to accurately detect two superimposed magnetic fields without being influenced by each other,
In particular, it is possible to detect a signal magnetic field on which a noise magnetic field is superimposed without being affected by the noise magnetic field.
The present invention aims to provide a magnetic detector that can obtain an output signal with a high S/N ratio.

Another object of the present invention is to provide a magnetic detector which has a large dynamic range and can perform accurate detection without saturation even when an input magnetic field is applied.

Still another object of the present invention is to provide a magnetic detector that can suppress the occurrence of unbalanced voltage due to variations in resistance temperature coefficient, film thickness, shape factor, etc., and can perform more accurate detection. be.

The magnetic detector of the present invention includes at least two layers of magnetoresistive elements each stacked with an insulating film in between,
At least two sets of magnetic sensors in which these magnetoresistive elements are magnetically biased in opposite directions are arranged so as to have a phase difference of approximately 180° with respect to the magnetization pattern that generates the first magnetic field. The magnetic sensor is characterized in that the obtained signal is supplied to a magnetic field generating means provided in the other magnetic sensor to selectively detect one or both of the first and second magnetic fields superimposed on each other. It is something to do.

In a preferred embodiment of the present invention, both magnetic sensors are provided with magnetic field generating means, and the output of one magnetic sensor is also supplied to the magnetic field generating means provided on the other magnetic sensor. Try to expand the range equivalently.

The magnetic field generating means used in the magnetic detector of the present invention is
It can be constructed extremely simply by using a conductive layer laminated on the magnetoresistive element with an insulating layer interposed therebetween.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a diagrammatic perspective view showing the configuration of an example of a magnetic sensor used in the magnetic detector of the present invention, and the upper insulating layer and the conductive layer for generating the magnetic field are omitted for clarity. There is. In this example, four magnetoresistive elements Ra ₁ , Ra ₂ , Rb ₁ , and Rb ₂ are provided, and the elements Ra ₁ and Rb ₁ and Ra ₂ and Rb ₂ are formed by patterning the same magnetoresistive film, respectively. Elements Ra ₁ and Ra ₂ and Rb ₁ and Rb ₂ are stacked one above the other with an insulating layer INS in between. These elements are formed side by side on an insulating substrate S.

As shown in FIG. 3, a conductor is connected to the magnetoresistive element via a through hole formed in an insulating layer. That is, the magnetoresistive element Ra ₂ on the substrate S has insulating layers INS ₁ and INS ₂ and the magnetoresistive element Ra 2 on the substrate S.
The conductor C ₁ is connected to the magnetoresistive element Ra ₁ through a through hole formed in the insulating layer INS 2, and the conductor C ₂ is connected to the magnetoresistive element Ra ₁ through a through hole formed in the insulating layer INS ₂ . Further, on the insulating layer _INS2 , a conductive film La is deposited which acts as a magnetic field generating means, which will be described later.

The magnetoresistive elements Ra ₁ , Ra ₂ , Rb ₁ and
Rb ₂ is connected as shown in FIG. That is,
One ends of magnetoresistive elements Ra ₁ and Rb ₁ are commonly connected to the positive terminal of power supply E, and the other end of element Ra ₁ is connected to element Ra _2.
The other end of element Rb ₁ is connected to one end of element Rb ₂ , and the other ends of elements Ra ₂ and Rb ₂ are connected to the power supply E.
Commonly connected to the negative terminal of Current therefore flows through the magnetoresistive elements Ra ₁ , Ra ₂ , Rb ₁ , Rb ₂ in the direction indicated by the arrows in FIG. 4, with the result that these elements are magnetically biased toward each other. In this example, since the secondary bias effect is large, each element is magnetically biased as shown in FIG. In other words, the element
A magnetic bias +Hb directed upward from the bottom of the page is applied to Ra ₁ and Rb ₁ , and a magnetic bias -Hb directed downward from the top of the page is applied to the elements Ra ₂ and Rb ₂ .

Because of this magnetic bias, magnetoresistive elements
The operating characteristics of Ra ₁ , Rb ₁ and Ra ₂ , Rb ₂ are shown in Figure 5A.
It becomes symmetrical as shown in . That is, curve A shows the operating characteristics of elements Ra ₁ and Rb ₁ , and when an input magnetic field indicated by I is applied, a resistance change as shown by curve R _A is obtained, and curve B shows the operating characteristics of elements Ra ₂ and Rb _2.
The resistance value changes as shown by the curve R _B for an input magnetic field of 1. Therefore, the voltage V _T appearing at terminals Ta and Tb in FIG. 4 becomes as shown in FIG. 5. Magnetoresistive elements have high sensitivity, but the magnetic field range in which an output voltage proportional to the input magnetic field can be obtained, that is, the range in which they operate linearly +
H _L to −H _L are relatively narrow, and when the input magnetic field exceeds ±H _L , the output is no longer linear and accurate detection cannot be performed.

In the present invention, as shown in FIG. 6, conductive films La and Lb functioning as magnetic field generating means are laminated with an insulating layer interposed in each magnetic sensor constructed as described above. Element Ra ₁ of one magnetic sensor and
At the connection point with Ra ₂ , Ta is connected to the negative input terminal of a differential amplifier DEFa having a large gain, and the reference power supply Ea is connected to the positive input terminal. Connect the output terminal of this differential amplifier DEFa to one end of the conductive layer La,
The other end of this conductive layer is connected to one end of conductive layer Lb,
The other end of this conductive layer is grounded. The connection point Tb between elements Rb ₁ and Rb ₂ of the other magnetic sensor is connected to a differential amplifier.
Connect to the page side input terminal of DEFb, and connect the reference power supply Eb to the positive side input terminal. Reference power supply Ea and Eb
The voltage value of is selected such that the output voltages of the differential amplifiers DEFa and DEFb are zero when no magnetic field acts on the magnetic sensors Ua and Ub.

In the present invention, the substrates S of the magnetic sensors Ua and Ub configured as described above are tilted by an angle θ with respect to a direction perpendicular to the displacement direction D of the recording medium M on which a magnetization pattern is recorded, as shown in FIG. let This inclination angle θ is determined by two sets of magnetoresistive elements Ra ₁ ,
It is assumed that Ra ₂ , Rb ₁ , and Rb ₂ have a phase difference of approximately 180° with respect to the period of the magnetization pattern.

With this configuration, one magnetic sensor Ua
The magnetic field due to the magnetization pattern applied to the magnetoresistive elements Ra ₁ and Ra ₂ of the other magnetic sensor Ub and the magnetic field due to the magnetization pattern applied to the magnetoresistive elements Rb ₁ and Rb ₂ of the other magnetic sensor Ub are always in opposite directions. On the other hand,
Generally, the noise magnetic field will be applied to the magnetoresistive elements of both magnetic sensors in the same direction. Therefore, as shown in FIG.
For example, the signal magnetic field due to the magnetization pattern + H _S
and the noise magnetic field +H _N are applied in a superimposed manner, and the signal magnetic field -H _S due to the magnetization pattern and the noise magnetic field +H _N are applied in a superimposed manner to the other magnetic sensor Ub. Therefore, in one magnetic sensor Ua, an output voltage proportional to the input magnetic field (H _S +H _N ) is obtained from the differential amplifier DEFa, and this output voltage causes the series-connected conductive layers La and
A current flows through Lb, thereby generating a magnetic field of -(H _S +H _N ) in the angular magnetic sensor. Therefore,
The net magnetic field applied to the other magnetic sensor Ub is
(−H _S +H _N )−(H _S +H _N )=−2H _S , and the noise magnetic field H _N is canceled out and removed. Therefore, the noise component is removed and only the signal component due to the magnetization pattern is output from the differential amplifier DEFb, which increases the selectivity between the signal magnetic field and the noise magnetic field, resulting in an output signal with a high S/N ratio. As a result, the accuracy of detecting the amount of displacement is significantly increased.

Furthermore, in this example, one of the magnetic sensors
Ua is also provided with a conductive layer La that acts as a magnetic field generating means, and a current proportional to the output voltage of the differential amplifier DEFa flows through this conductive layer La, so that the magnetoresistive elements Ra ₁ , Ra ₂ of this magnetic sensor Ua The magnetic field applied to is significantly smaller than the input magnetic field (H _S +H _N ), and the dynamic range is equivalently significantly wider.

That is, in FIG. 5B, the input magnetic field (H _S
+H _N ) is larger than H _L , the magnetic field actually applied to the magnetoresistive elements Ra ₁ and Ra ₂ is the conductive layer L _a
These elements operate in a linear range, allowing for accurate detection, since they are canceled by the oppositely directed magnetic fields generated by H L and are smaller than H _L . Therefore, the noise magnetic field is quite large.
It becomes possible to effectively detect the small signal magnetic field H _S superimposed on H _N. In this way, the net magnetic field applied to the magnetoresistive elements Ra ₁ and Ra ₂ of the magnetic sensor Ua becomes smaller, so the differential amplifier DEFa
The gain is increased so that an output voltage proportional to the input magnetic field (H _S +H _N ) can be obtained.

FIG. 8 shows another embodiment of the magnetic detector of the present invention, in which three magnetic sensors Ua, Ub and Uc are formed on a substrate S. Each magnetic sensor Ua, Ub, Uc has two layers of magnetoresistive elements Ra ₁ , Ra ₂ ; Rb ₁ , Rb ₂ ; Rc ₁ , Rc ₂ as in the previous example.
and conductive layers La, Lb, and Lc are provided. These elements are connected as shown in FIG. That is, the first
The second magnetic sensors Ua and Ub are connected in the same manner as in the previous example, and the other end of the conductive layer Lb is connected to the conductive layer Lb.
The conductive layer Lc is connected to the other end of the conductive layer Lc, and one end of the conductive layer Lc is grounded. Therefore, the conductive layer Lc includes another conductive layer La.
And current will flow in the opposite direction to Lb. As shown in FIG. 8, the substrate S is arranged obliquely with respect to the direction perpendicular to the displacement direction D of the recording medium M on which the magnetization pattern is recorded, and the magnetic sensor Ua and the magnetic sensors Ub and Uc are arranged in the magnetization pattern. They are made to have a phase difference of 180° from each other. Therefore, the first magnetic field H ₁ caused by the magnetization pattern
are applied in opposite phases to the magnetic sensor Ua and the magnetic sensors Ub and Uc. On the other hand, the second
The magnetic field H ₂ is applied to all magnetic sensors in the same phase.

Here, as shown in FIG. 10, the first magnetic field _H1 shown by the broken line _H1 and the second magnetic field _H2 shown by the broken line _H2 are superimposed as shown by the solid line _H1 + _H2 . shall be. As explained in the example, the magnetic sensor Ua
The output voltage of the high gain differential amplifier DEFa connected to is proportional to the input magnetic field H ₁ +H ₂ , and a current corresponding to this voltage flows through the conductive layers Lb and Lc. Therefore _, in the magnetic sensor _Ub , a magnetic field _{-H 1} +H ₂ - ₍ H ₁ +H ₂ )=−2H ₁ is applied to the magnetoresistive elements Rb ₁ and Rb ₂ , and an output voltage V _H1 proportional to the first magnetic field H ₁ is obtained from the differential amplifier DEFb.

On the other hand, in the magnetic sensor Uc, the current flowing through the conductive layer Lc is opposite to that in the magnetic sensor Ub, so
A net magnetic field - _{H 1} + H ₂ + (H ₁ + H ₂ ) = 2H ₂ will be applied to the magnetoresistive elements Rc ₁ and Rc ₂ , and a second magnetic field proportional to H ₂ will be applied from the differential amplifier DEFc. An output voltage V _H2 will be obtained. In this way, in this example, the first and second magnetic fields H ₁ and H ₂ that are superimposed on each other can be completely separated and detected.

In the embodiment described above, three magnetic sensors were provided to separate and detect the first and second magnetic fields, but even in the embodiment with two magnetic sensors as shown in FIG. It is also possible to separate and detect the magnetic field. That is, as shown in FIG. 11, by determining the difference between the output of the differential amplifier DEFa and the output of the differential amplifier DEFb by the third differential amplifier DEFd, the first magnetic field H ₁ and the second magnetic field H The output voltages V _H1 and V _H2 , each proportional to ₂ , can be detected separately. In this case, the differential amplifier
In order to equalize the gain and polarity of both inputs to DEFd, it is preferable to connect an inverting amplifier AMP between differential amplifiers DEFb and DEFd.

The present invention is not limited to the embodiments described above, but can be modified in many ways. For example, in the embodiments described above, the magnetic sensor is arranged so that the magnetoresistive element is perpendicular to the recording medium on which the magnetization pattern is recorded, but it can also be arranged so that it is parallel to the recording medium. Furthermore, in the embodiment described above, in order to arrange the magnetic sensor so as to have a phase difference of approximately 180° with respect to the magnetization pattern,
Although the substrate on which the magnetic sensor is provided is tilted with respect to the direction perpendicular to the displacement direction, the magnetic sensor may also be disposed offset parallel to the displacement direction. Further, in the above-described embodiment, each magnetic sensor is provided with two magnetoresistive elements, but four magnetoresistive elements may be provided and these may be bridge-connected.

In this case, the reference voltage can be omitted and the influence of drift can also be eliminated. In the above-described embodiment, the magnetoresistive elements of each magnetic sensor were magnetically biased in opposite directions by the secondary mutual bias effect, but it is also possible to magnetically bias the magnetoresistive elements by the primary mutual bias effect, provide a conductive layer, and conduct current. It is also possible to create a magnetic bias by flowing .

Next, an embodiment will be described in which magnetic sensors each having four magnetoresistive elements are arranged shifted in parallel to the displacement direction. 12A and 12B show the arrangement relationship between the magnetic sensor and the magnetization pattern. In the example shown in FIG. 12A, the two-layer magnetoresistive elements Ra ₁ , Ra ₂ ; Rb ₁ , Rb ₂ ; Rc ₁ , Rc ₂ ;
Magnetic sensors Ua, Ub, Uc and Ud comprising Rd ₁ and Rd ₂ are sequentially moved by 180° with respect to the magnetization pattern in the arrangement direction of the magnetization pattern recorded on the recording medium M, that is, in the displacement direction D of the recording medium M. Arrange them parallel to each other. Furthermore, in the embodiment shown in FIG. 12B,
Two-layer magnetoresistive elements Ra ₁ , Ra ₂ and
A magnetic sensor Ub includes magnetic sensors Ua and Uc including Rc ₁ and Rc _{2 shifted in a direction perpendicular to the displacement direction, and also includes two layers of magnetoresistive elements Rb 1 and} Rb ₂ and Rd ₁ and Rd ₂ , respectively. and Ud are arranged to be shifted in a direction perpendicular to the displacement direction, and further, magnetic sensors Ua, Uc and magnetic sensors Ub, Ud are arranged to be shifted by 180° parallel to the displacement direction with respect to the magnetization pattern.

FIG. 13 shows the method of connecting the magnetoresistive element and the conductive layer. H ₁ + H ₂ is applied as an external magnetic field to the magnetic sensors Ua and Uc, and -H ₁ + H ₂ is applied to the magnetic sensors Ub and Ud. is being applied.

Therefore, if magnetic sensors Ua and Uc are bridge-connected, H ₁ +
An output voltage proportional to H ₂ is obtained, and a current proportional to this voltage is applied to the conductive layers La, Lb, Lc connected in series.
and flows to Ld. Therefore, the magnetic sensor Ub
and Ud has a net magnetic field −H ₁ +H ₂ −(H ₁ +H ₂ )
= -2H ₁ is applied, so -2H ₁ is applied from the differential amplifier DEFb that bridge-connects these magnetic sensors.
This results in an output voltage V _H1 proportional to .
In this example, the magnetoresistive elements are bridge-connected, so
Since unbalanced voltages due to differences in film thickness, temperature resistance coefficient, shape coefficient, etc. of the magnetoresistive elements are canceled out, accurate detection without temperature drift or offset can be performed.

As explained above, according to the present invention, the first and second magnetic fields superimposed on each other can be detected separately, so that, for example, a signal magnetic field superimposed on a noise magnetic field can be detected without being affected by the noise magnetic field. It is possible to perform extremely accurate detection. Furthermore, since the dynamic range can be expanded, even large input magnetic fields can be detected accurately.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a magnetic detector using a conventional magnetoresistive element, FIG. 2 is a perspective view showing the configuration of an example of the magnetic detector of the present invention, and FIG. 3 is a sectional view thereof. FIG. 4 is a diagram showing the wiring method of the magnetoresistive element, FIG. 5 A and B are graphs showing its operating characteristics, FIG. 6 is a circuit diagram showing the overall wiring method, and FIG. 8 is a plan view showing the arrangement relationship between the magnetic detector and the magnetization pattern;
The figure is a diagram showing the configuration of another embodiment of the magnetic detector of the present invention, FIG. 9 is a circuit diagram showing the overall wiring method, and FIG. 10 is a diagram showing the input magnetic field in order to explain its operation. FIG. 11 is a circuit diagram showing the overall wiring method of yet another embodiment of the magnetic detector of the present invention, and FIGS. 12A and B are waveform diagrams in which the magnetic sensor is shifted in parallel to the arrangement direction of the magnetization pattern. FIG. 13 is a diagram showing two embodiments of the arranged magnetic detector of the present invention, and FIG. 13 is a circuit diagram showing the overall wiring method. S...Substrate, Ra ₁ , Ra ₂ , Rb ₁ , Rb ₂ , Rc ₁ ,
Rc ₂ , Rd ₁ , Rd ₂ ... Magnetoresistive element, INS, INS ₁ ,
INS ₂ ...Insulating layer, La, Lb, Lc, Ld...Conductive layer,
E...Power supply, Ea, Eb, Ec...Reference power supply, M...
Recording medium, Ua, Ub, Uc, Ud...magnetic sensor,
DEFa, DEFb, DEFc, DEFd...Differential amplifier.

Claims (1)

[Claims] 1. At least 2 layers each laminated with an insulating film in between.
at least two sets of magnetic sensors each comprising a layer of magnetoresistive elements, the magnetoresistive elements magnetically biased in opposite directions, such that the magnetization pattern has a phase difference of approximately 180° with respect to the magnetization pattern producing the first magnetic field. and supplying a signal obtained from one magnetic sensor to a magnetic field generating means provided in the other magnetic sensor to selectively detect one or both of the first and second magnetic fields superimposed on each other. A magnetic detector characterized by being configured as follows. 2. The magnetic detector according to claim 1, configured to increase the range of detectable magnetic field strength by supplying the signal obtained from one of the magnetic sensors to the magnetic field generating means provided in the other magnetic sensor. A magnetic detector characterized by: