Title: Magnetic switch capable of instantaneous switching of an output signal and magnetic sensor
Abstract: A magnetic switch using magnetoresistive elements having respective free layers whose magnetization directions are varied by an external magnetic field. The magnetic switch also has a first magnet and a second magnet that produce respective magnetic fields that serve as the external magnetic field and are different from each other in strength and opposite to each other in direction, and a magnetic shield member whose relative position with respect to the first magnet and the second magnet varies. The magnetic shield member moves between a first position with which both of the magnetic fields of the first magnet and the second magnet act on the magnetoresistive elements to magnetize their free layers in a first direction and a second position with which only one of the magnetic fields of the first magnet and the second magnet acts on the magnetoresistive elements to magnetize their free layers in a second direction that is opposite to the first direction.
Patent Number: 6,900,713 Issued on 05/31/2005 to Kasashima, et al.
| Inventors:
|
Kasashima; Masao (Miyagi-ken, JP);
Tokunaga; Ichiro (Miyagi-ken, JP);
Okumura; Hirofumi (Miyagi-ken, JP);
Kikuchi; Seiji (Miyagi-ken, JP)
|
| Assignee:
|
Alps Electric Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
215735 |
| Filed:
|
August 9, 2002 |
Foreign Application Priority Data
| Aug 13, 2001[JP] | 2001-245487 |
| Current U.S. Class: |
335/207; 335/205 |
| Intern'l Class: |
H01H 009/00 |
| Field of Search: |
335/202-207,215
|
References Cited [Referenced By]
U.S. Patent Documents
| 3680026 | Jul., 1972 | Masuda et al.
| |
| 3768095 | Oct., 1973 | Lins et al.
| |
| 4868530 | Sep., 1989 | Ahs.
| |
| 5554964 | Sep., 1996 | Jansseune.
| |
| 5596272 | Jan., 1997 | Busch.
| |
| 5745978 | May., 1998 | Aboaf et al.
| |
| 5960523 | Oct., 1999 | Husby et al.
| |
| 6054226 | Apr., 2000 | Takeda et al.
| |
| 6060969 | May., 2000 | Hufgard et al.
| |
| Foreign Patent Documents |
| 2000/-011827 | Jan., 2000 | JP.
| |
Primary Examiner: Donovan; Lincoln
Assistant Examiner: Rojas; Bernard
Attorney, Agent or Firm: Beyer, Weaver & Thomas LLP
Claims
1. A magnetic switch which performs switching using a magnetoresistive element
having a free layer whose direction of magnetization is changed by an external
magnetic field, the magnetic switch comprising:
a first magnet;
a second magnet for producing a magnetic field that is stronger than and opposite
in direction to a magnetic field produced by the first magnet; and
a magnetic shield member movably disposed between the first magnet and the second
magnet,
wherein the magnetoresistive element is disposed adjacent to the first magnet,
and the second magnet is disposed at a longer distance from the magnetoresistive
element than the first magnet,
wherein a switching signal for a switch operation is output by operating the
magnetoresistive element to determine the direction of magnetization of the free
layer by the direction of the magnetic field of the second magnet when the magnetic
shield member is not placed between the first magnet and the second magnet, and
by operating the magnetoresistive element to determine the direction of magnetization
of the free layer by the direction of the magnetic field of the first magnet when
the magnetic shield member is placed between the first magnet and the second magnet.
2. The magnetic switch according to claim 1, characterized in:
that the magnetoresistive elements are two magnetoresistive elements that further
have respective fixed layers whose magnetization directions are fixed and that
are combined together in such a manner that the magnetization directions of the
fixed layers are opposite to each other; and
that the two magnetoresistive elements are connected to each other in series
and incorporated in a bridge circuit.
3. The magnetic switch according to claim 1, characterized in:
that the magnetoresistive elements are two magnetoresistive elements that further
have respective fixed layers whose magnetization directions are fixed and that
are combined together in such a manner that the magnetization directions of the
fixed layers are opposite to each other; and
that the two magnetoresistive elements are connected to each other in series
and constitute a voltage dividing circuit.
4. A magnetic sensor which detects a member to be detected by using a magnetoresistive
element having a free layer whose direction of magnetization is changed by an external
magnetic field, the magnetic sensor comprising:
a first magnet;
a second magnet for producing a magnetic field that is stronger than and opposite
in direction to a magnetic field produced by the first magnet; and
a magnetic shield member movably disposed between the first magnet and the second
magnet,
wherein the magnetoresistive element is disposed adjacent to the first magnet,
and the second magnet is disposed at a longer distance from the magnetoresistive
element than the first magnet,
wherein a detection signal indicating detection of the member to be detected
is output by operating the magnetoresistive element to determine the direction
of magnetization of the free layer by the direction of the magnetic field of the
second magnet when the magnetic shield member is not placed between the first magnet
and the second magnet, and by operating the magnetoresistive element to determine
the direction of magnetization of the free layer by the direction of the magnetic
field of the first magnet when the magnetic shield member is placed between the
first magnet and the second magnet.
5. The magnetic sensor according to claim 4, characterized in:
that the magnetoresistive elements are two magnetoresistive elements that further
have respective fixed layers whose magnetization directions are fixed and that
are combined together in such a manner that the magnetization directions of the
fixed layers are opposite to each other; and
that the two magnetoresistive elements are connected to each other in series
and incorporated in a bridge circuit.
6. The magnetic sensor according to claim 4, characterized in:
that the magnetoresistive elements are two magnetoresistive elements that further
have respective fixed layers whose magnetization directions are fixed and that
are combined together in such a manner that the magnetization directions of the
fixed layers are opposite to each other; and
that the two magnetoresistive elements are connected to each other in series
and constitute a voltage dividing circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic switch and a magnetic sensor.
2. Description of the Related Art
A non-contact type magnetic switch using a magnetoresistive element are known.
In this conventional non-contact type magnetic switch, a permanent magnet is disposed
in the vicinity of a magnetoresistive element that exhibits the magnetoresistance
effect and a magnetic field of the permanent magnet acts on the magnetoresistive
element. Further, a shield plate for shielding the magnetoresistive element from
the magnetic field of the permanent magnet is movably disposed between the magnetoresistive
element and the permanent magnet.
The magnetoresistive element basically has a lamination structure that is composed
of a free layer (free magnetic layer), a non-magnetic layer, a fixed layer (pinned
magnetic layer), and an exchange bias layer (antiferromagnetic layer).
A bias magnetic field of the exchange bias layer acts on the fixed layer, whereby
the fixed layer is magnetized and the magnetization direction is fixed to a particular
direction. On the other hand, the magnetization direction of the free layer is
varied by an external magnetic field.
In the above conventional non-contact type magnetic switch using a magnetoresistive
element, the permanent magnet is used as a magnet for applying an external magnetic
field to the free layer. The magnetization direction of the free layer is varied
to a desired direction, that is, rotated with respect to the magnetization direction
of the fixed layer, by the permanent magnet.
The magnetic shield plate for interrupting the magnetic field of the permanent
magnet to act on the magnetoresistive element is inserted between or retreated
from between the magnetoresistive element and the permanent magnet, whereby the
strength of the magnetic field acting on the magnetoresistive element is varied
and the magnitude of its resistance is thereby varied. A switch operation is performed
based on an output signal that reflects a resistance variation of the magnetoresistive element.
However, in the conventional non-contact type switch, since the resistance
of the magnetoresistive element varies in accordance with the strength of a magnetic
field, that is, insertion or retreat of the shield plate, the resistance of the
magnetoresistive element varies gradually as the shield plate approaches (goes
into) the space between the magnetoresistive element and the permanent magnet or
goes away (retreats) from the space. That is, the output signal of the magnetoresistive
element (i.e., the resistance) varies slowly at the time of switching.
Therefore, the conventional non-contact type magnetic switch using a magnetoresistive
element is not suitable for switch operations for, for example, instantaneous on/off
switching and instantaneous detection of a movement of a member to be detected.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a magnetic switch and a magnetic
sensor in which an output signal of magnetoresistive elements is switched instantaneously
by changing the resistances of magnetoresistive elements instantaneously in accordance
with the direction of a magnetic field.
The present inventors have invented a magnetic switch and a magnetic sensor in
which the magnetization directions of the fixed layers of at least two magnetoresistive
elements are set opposed to each other and the free layers of the respective magnetoresistive
elements are magnetized by two magnets and that switches an output signal instantaneously
through rapid resistance variations of the magnetoresistive elements even with
a configuration that the strength of a magnetic field varies gradually.
That is, to attain the above object, the invention provides a magnetic switch
which performs switching of a switch using magnetoresistive elements having respective
free layers whose magnetization directions are varied by an external magnetic field,
characterized in that magnetic fields of a first magnet and a second magnet that
are different from each other in strength and opposite to each other in direction
are caused to selectively act, as an external field, on the magnetoresistive elements
in response to a switching manipulation on the switch, whereupon the magnetoresistive
elements produce a switching signal for a switch operation.
As one embodiment of the above magnetic switch, the invention provides a magnetic
switch using magnetoresistive elements having respective free layers whose magnetization
directions are varied by an external magnetic field, comprising a first magnet
and a second magnet that produce respective magnetic fields that serve as the external
magnetic field and are different from each other in strength and opposite to each
other in direction; and a magnetic shield member whose relative position with respect
to the first and second magnets is varied, wherein the magnetic shield member moves
between a first position with which both of the magnetic fields of the first and
second magnets act on the magnetoresistive elements to magnetize their free layers
in a first direction and a second position with which only one of the magnetic
fields of the first and second magnets acts on the magnetoresistive elements to
magnetize their free layers in a second direction that is opposite to the first direction.
In this case, the magnetic field of the first magnet may be stronger than that
of the second magnet, and the magnetization directions of the free layers may be
determined by a direction of the magnetic field of the first magnet when the magnetic
shield member is located at the first position and by a direction of the magnetic
field of the second magnet when the magnetic shield member is located at the second position.
The invention can be implemented as not only the magnetic switch but also a magnetic
sensor. The invention provides a magnetic sensor which detects a member to be detected
using magnetoresistive elements having respective free layers whose magnetization
directions are varied by an external magnetic field, characterized in that magnetic
fields of a first magnet and a second magnet that are different from each other
in strength and opposite to each other in direction are caused to selectively act,
as an external field, on the magnetoresistive elements in accordance with a movement
of the member to be detected, whereupon the magnetoresistive elements produce a
detection signal indicating detection of the member to be detected.
As one embodiment of the above magnetic sensor, the invention provides a magnetic
sensor which detects a member to be detected having a magnetic shield function
by using magnetoresistive elements having respective free layers whose magnetization
directions are varied by an external magnetic field, comprising a first magnet
and a second magnet that produce respective magnetic fields that serve as the external
magnetic field and are different from each other in strength and opposite to each
other in direction, wherein a relative position of the member to be detected with
respect to the first and second magnets varies; and wherein a first state in which
both of the magnetic fields of the first and second magnets act on the magnetoresistive
elements and a second state in which only one of the magnetic fields of the first
and second magnets acts on the magnetoresistive elements are established as the
relative position of the member to be detected with respect to the first and second
magnets varies, whereby the member to be detected is detected.
In this case, the magnetic field of the first magnet may be stronger than that
of the second magnet, and the magnetization directions of the free layers may be
determined by a direction of the magnetic field of the first magnet when the member
to be detected is in the first state and by a direction of the magnetic field of
the second magnet when the member to be detected is in the second state.
The magnetoresistive elements that are used in the above magnetic switch or magnetic
sensor may be two magnetoresistive elements that further have respective fixed
layers whose magnetization directions are fixed and that are combined together
in such a manner that the magnetization directions of the fixed layers are opposite
to each other, and the two magnetoresistive elements may be connected to each other
in series and incorporated in a bridge circuit or a voltage dividing circuit. A
detection result of the magnetoresistive elements is output.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a magnetic switch according to an embodiment of the
invention and shows a state that a magnetic shield member is retreated from the
space between magnetoresistive elements and a first permanent magnet;
FIG. 2 is a front view of the magnetic switch according to the embodiment of
the invention and shows a state that the magnetic shield member is inserted in
the space between the magnetoresistive elements and the first permanent magnet;
FIG. 3 is a side view of the magnetic switch according to the embodiment of
the invention and shows how the magnetic shield member enters and retreats from
the space between the magnetoresistive elements and the first permanent magnet;
FIG. 4 is a perspective view of the magnetic switch according to the embodiment
of the invention and shows how the magnetic shield member enters and retreats from
the space between the magnetoresistive elements and the first permanent magnet;
FIG. 5 is a sectional view showing an exemplary magnetoresistive element used
in the magnetic switch according to the embodiment of the invention;
FIGS. 6A and 6B show magnetization directions of the magnetoresistive elements
used in the magnetic switch according to the embodiment of the invention;
FIG. 7 is a circuit diagram of a circuit in which the magnetoresistive elements
used in the magnetic switch according to the embodiment of the invention are incorporated
in a bridge circuit;
FIGS. 8A-8C show output signal waveforms at respective points of the bridge
circuit; and
FIG. 9 is a circuit diagram of a circuit in which the magnetoresistive elements
used in the magnetic switch according to the embodiment of the invention are incorporated
in a voltage dividing circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be hereinafter described with
reference to the accompanying drawings.
As shown in FIGS. 1,
2, and
4, a holder
1 of a magnetic
switch
has an inverted gate shape in which a pair of arms
3 and
4 are provided
at both ends of a base
2 so as to extend parallel with and be opposed to
each other. The one arm
3 is provided with magnetoresistive elements
5
and a second permanent magnet (hereinafter referred to as "second magnet")
6,
and the other arm
4 is provided with a first permanent magnet (hereinafter
referred to as "first magnet")
7.
The magnetoresistive elements
5 are provided in a hermetic structure by
using an IC package or resin sealing and mounted on a board
8. And the magnetoresistive
elements
5 are attached to the inner surface of the arm
3 via the
board
8.
The second magnet
6 is attached to the arm
3 at a magnetic field
acting position where to magnetize free layers
5d (see FIG. 5) of
the magnetoresistive elements
5. The magnetic field acting position is set
at such a position that magnetic field lines
6a of the second magnet
6 act on the free layers
5d of the magnetoresistive elements
5 and hence the magnetic field (external magnetic field) of the second magnet
6 can magnetize the free layers
5d of the magnetoresistive
elements
5. Although the second magnet
6 shown in FIGS. 1,
2,
and
4 is separate from the magnetoresistive elements
5, it may be
integrated with the magnetoresistive elements
5.
The first magnet
7 is attached to the arm
4 in such a manner that
the first magnet
7 is located at such a position (magnetic field acting
position) that its magnetic field (external magnetic field) can act on and magnetize
the free layers
5d of the magnetoresistive elements
5, and
that magnetic field lines (the direction of the magnetic field)
7a of
the first magnet
7 are parallel with and opposite in direction to the magnetic
field lines (the direction of the magnetic field)
6a of the second
magnet
6 (180° is formed). The first magnet
7 is a magnet that
produces a magnetic field that is stronger by hundreds of gausses than that produced
by the second magnet
6.
Next, the magnetoresistive elements
5 that are used in the magnetic
switch will be described in a specific manner with reference to FIG.
5.
This exemplary structure is of a case that the second magnet
6 is provided
separately from the magnetoresistive elements
5. Each magnetoresistive element
5 has a basic configuration in which an exchange bias layer (antiferromagnetic
layer)
5a, a fixed layer (pinned magnetic layer)
5b,
a non-magnetic layer
5c, and a free layer (free magnetic layer)
5d
are laminated, and is a kind of GMR (giant magnetoresistive) element that utilizes
the giant magnetoresistance effect.
For the magnetoresistive element
5 to exhibit a giant magnetoresistance
effect, an α-Fe
2O
3 layer, an NiFe layer, a Cu layer,
and an NiFe layer, for example, are employed as the exchange bias layer
5a,
the fixed layer
5b, the non-magnetic layer
5c, and
the free layer
5d, respectively. However, the invention is not limited
to such a case and any materials can be employed as long as they allow the magnetoresistive
element
5 to exhibit a giant magnetoresistance effect. Further, the structure
of the magnetoresistive element
5 is not limited to the above lamination
structure as long as it exhibits a giant magnetoresistance effect.
The fixed layer
5b of the magnetoresistive element
5 shown
in FIG. 5 is magnetized by the exchange bias layer
5a and its magnetization
direction is fixed (pinned) in a particular direction by the exchange bias layer
5a. The magnetization direction of the free layer
5d with
respect to that of the fixed layer
5b is varied by the magnetic fields
of the magnets
6 and
7 (external magnetic field). Terminal layers
9 are joined to both sides of the magnetoresistive element
5. A variation
in the resistance between the two terminal layers
9 is output, the variation
depending on the direction of magnetization, caused by an external magnetic field,
of the free layer
5d with respect to the fixed magnetization direction
of the fixed layer
5b.
The fixed layers
5b of the magnetoresistive elements
5 are
magnetized in such a manner that their magnetization direction is fixed to a particular
direction. The first magnet
7 is a magnet that produces a magnetic field
that is stronger than that produced by the second magnet
6. And the free
layers
5d of the magnetoresistive elements
5 are magnetized
by the first magnet
7 and the second magnet
6 in opposite directions
(180° is formed). In this embodiment, the free layers
5d are
magnetized by the second magnet
6 in the same direction as and in the opposite
direction (180° is formed) to the magnetization directions of the fixed layers
5b, respectively.
The magnetic switch further has a magnetic shield member
10 made of a
ferromagnetic material whose relative position with respect to the first magnet
7 and the second magnet
6 is changed. The magnetic shield member
10 is moved between a first position with which both of the magnetic fields
of the first magnet
7 and the second magnet
6 are allowed to act
on the magnetoresistive elements
5 to magnetize their free layers
5d
in a first direction and a second position with which one of the magnetic fields
of the first magnet
7 and the second magnet
6 is allowed to act on
the magnetoresistive elements
5 to magnetize their free layers
5d
in a second direction that is opposite to the first direction.
In the example of FIGS. 1-4, the magnetic shield member
10 is provided
so as to be able to enter and retreat from the space between the first magnet
7
and the magnetoresistive elements
5 by going between the paired arms
3
and
4 that are parallel with each other. In this embodiment, the plate-like
magnetic shield member
10 is caused to enter or retreat from the space between
the first magnet
7 and the magnetoresistive elements
5 by making
a linear movement that is perpendicular to the line connecting the first magnet
7 and the magnetoresistive elements
5 while being guided by a guide
(not shown). Alternatively, a fan-shaped magnetic shield member
10 may be
caused to enter or retreat from the space between the first magnet
7 and
the magnetoresistive elements
5 by making a rotational movement in a plane
that is perpendicular to the line connecting the first magnet
7 and the
magnetoresistive elements
5.
In this embodiment, the first position is a position to which the magnetic shield
member
10 retreats from between the first magnet
7 and the magnetoresistive
elements
5. On the other hand, the second position is a position where the
magnetic shield member
10 resides when having entered the space between
the first magnet
7 and the magnetoresistive elements
5.
When the magnetic shield member
10 has been moved to the second position
by a driving means (not shown), the magnetic shield member
10 makes the
magnetic field lines
7a go away from the free layers
5d
of the magnetoresistive elements
5 to shield those from the magnetic
field of the first magnet
7 and allows only the magnetic field of the second
magnet
6 to act as external magnetic field on the magnetoresistive elements
5. Therefore, only the magnetic field of the second magnet
6 that
is weaker than that of the first magnet
7 acts, as an external magnetic
field, on the free layers
5d of the magnetoresistive elements
5.
On the other hand, when the magnetic shield member
10 has been moved to
the first position, both of the magnetic fields of the first magnet
7 and
the second magnet
6 act on the magnetoresistive elements
5 as external
magnetic fields. The magnetic field of the first magnet
7 is stronger than
that of the second magnet
6 and the first magnet
7 and the second
magnet
6 have the functions of magnetizing the free layers
5d
of the magnetoresistive elements
5 in opposite directions (180°
is formed). Therefore, the magnetic field of the second magnet
6 is canceled
out by that of the first magnet
7 and the magnetic field of the first magnet
7 dominantly acts on the free layers
5d of the magnetoresistive
elements
5, whereby the magnetization direction of the free layers
5d
of the magnetoresistive elements
5 is reversed so as to become opposite
to the direction of magnetization that has been caused by the second magnet
6
(180° is formed)
The resistances of the magnetoresistive elements
5 vary as the magnetization
direction of the free layers
5d of the magnetoresistive elements
5 is reversed depending on which of the magnetic fields of the first magnet
7 and the second magnet
6 acts (dominantly). When the magnetization
direction of the free layers
5d is reversed, the fixed layers
5b
of the magnetoresistive element
5 are magnetized in opposite directions
(180° is formed). Therefore, resistance variations occur instantaneously.
In this embodiment, at least two magnetoresistive elements
5 shown in
FIG.
5 are used and the resistances of the magnetoresistive elements
5 that vary
instantaneously in accordance with the magnetic field direction are output as an
output signal. The two magnetoresistive elements
5 are formed on the board
8 so as to be arranged in the lateral direction as shown in FIG.
6A.
Alternatively, they are formed on the board
8 so as to be arranged in the
longitudinal direction as shown in FIG.
6B.
The magnetization directions H
2 of the fixed layers
5b of
the two magnetoresistive elements
5 that are formed on the board
8
are opposite to each other (180° is formed), and the magnetization directions
H
1 of the free layers
5d are equalized by the second magnet
6. In the examples of FIGS. 6A and 6B, the magnetization direction H
1
of the free layer
5d of one magnetoresistive element (GMR
1)
is opposite (180° is formed) to that of the magnetization direction H
2
of its fixed layer
5b. The magnetization direction H
1 of the
free layer
5d of the other magnetoresistive element (GMR
2)
is the same as the magnetization direction H
2 of its fixed layer
5b.
A description will be made with reference to FIG. 7 with a notation that terminal
layers at both ends of each magnetoresistive element
5 are denoted by
9a
and
9b and the respective magnetoresistive elements are denoted
by GMR
1 and GMR
2. The two magnetoresistive elements GMR
1 and
GMR
2 are connected to each other in series by connecting the terminal layer
9a of the magnetoresistive element GMR
2 to the terminal layer
9b of the magnetoresistive element GMR
1.
A bridge circuit shown in FIG. 7 is formed in such a manner that the two magnetoresistive
elements GMR
1 and GMR
2 are used in the two respective sides and two
fixed resistors
11 and
12 are used in the remaining two sides, respectively.
More specifically, the terminal layer
9a of the magnetoresistive
element GMR
1 is connected to a terminal
11a of the fixed resistor
11, and their connecting point A
1 is connected to a terminal Vdd
of a voltage source. The terminal layer
9b of the magnetoresistive
element GMR
2 is connected to a terminal
12b of the fixed resistor
12, and their connecting point A
2 is connected to a ground terminal
of the voltage source. The two fixed resistors
11 and
12 may be replaced
by two magnetoresistive elements.
The terminal layer
9b of the magnetoresistive element GMR
1
is connected to the terminal layer
9a of the magnetoresistive element
GMR
2, and their connecting point B
1 is connected to one input terminal
of a comparator
13 via a fixed resistor R
1. The terminal
11b
of the fixed resistor
11 is connected to the terminal
12a
of the fixed resistor
12, and their connecting point B
2 is connected
to the other input terminal of the comparator
13 via a fixed resistor R
2.
A feedback fixed resistor R
3 is provided between the one input terminal
and the output terminal of the comparator
13. The terminal Vdd of the voltage
source is connected to the other input terminal of the comparator
13 via
a variable resistor R
4 and a fixed resistor R
5.
The output terminal of the comparator
13 is connected to one input terminal
of a comparator
14. A terminal Vφc of another voltage source is connected
to the other input terminal of the comparator
14 via a voltage dividing
resistor R
6 and a fixed resistor R
7, whereby the voltage of the other
input terminal of the comparator
14 is set at a reference voltage Ref. In
this embodiment, the reference voltage Ref is set at 2.5 V. A feedback fixed resistor
R
8 is provided between the one other input terminal and the output terminal
of the comparator
14.
The operation of the magnetic switch will be described below with an assumption
that the state that the magnetic shield member
10 has entered the space
between the magnetoresistive elements GMR
1 and GMR
2 (
5) and
the first magnet
7 (see FIG. 2) corresponds to switch on and the state that
the magnetic shield member
10 has retreated from between the magnetoresistive
elements GMR
1 and GMR
2 (
5) and the first magnet
7 (see
FIG. 1) corresponds to switch off. It is also assumed that the magnetization directions
of the fixed layers
5b and the free layers
5d of the
two respective magnetoresistive elements GMR
1 and GMR
2 have the relationship
shown in FIG.
6A.
In the case of switch off, the magnetic shield member
10 retreats from
between the magnetoresistive elements GMR
1 and GMR
2 and the first
magnet
7 as shown in FIG.
1 and hence the magnetic field of the first
magnet
7 acts on the magnetoresistive elements GMR
1 and GMR
2.
In this case, since the magnetic field of the first magnet
7 is stronger
than that of the second magnet
6, the magnetization direction of the free
layers of the magnetoresistive elements GMR
1 and GMR
2 becomes the
same as the direction of the magnetic field lines
7a of the first
magnet
7. Therefore, the magnetization direction of the free layer of the
magnetoresistive element GMR
1 becomes the same as that of its fixed layer
and the magnetization direction of the free layer of the magnetoresistive element
GMR
2 becomes opposite to that of its fixed layer (180° is formed).
The resistance R
GMR2 of the magnetoresistive element GMR
2 becomes
greater than the resistance R
GMR1 of the magnetoresistive element GMR
1
(R
GMR1<R
GMR2). As shown in FIG. 8A, the voltage at the
connecting point B
1 of the two magnetoresistive elements GMR
1 and
GMR
2 becomes higher than 2.5 V.
In the case of switch on, the magnetic shield member
10 enters the space
between the magnetoresistive elements GMR
1 and GMR
2 and the first
magnet
7 as shown in FIG. 2, and hence the magnetoresistive elements GMR
1
and GMR
2 are shielded from the magnetic field of the first magnet
7
and only the magnetic field of the second magnet
6 acts on the magnetoresistive
elements GMR
1 and GMR
2. In this case, the magnetization direction
of the free layers of the magnetoresistive elements GMR
1 and GMR
2
becomes the same as the direction of the magnetic field lines
6a of
the second magnet
6. Therefore, the magnetization direction of the free
layer of the magnetoresistive element GMR
1 becomes opposite to that of its
fixed layer (180° is formed) and the magnetization direction of the free layer
of the magnetoresistive element GMR
2 becomes the same as that of its fixed
layer. The resistance R
GMR1 of the magnetoresistive element GMR
1
becomes greater than the resistance R
GMR2 of the magnetoresistive element
GMR
2 (R
GMR2<R
GMR1). As shown in FIG. 8A, the
voltage at the connecting point B
1 of the two magnetoresistive elements
GMR
1 and GMR
2 becomes lower than 2.5 V.
As shown in FIG. 8B, an amplified voltage of the voltage at the connecting point
B
1 appears at the output of the comparator
13. The amplified voltage
is compared with the reference voltage Ref for the comparator
14. As shown
in FIG. 8C, at the output of the comparator
14, an output signal of 5 V
appears in the case of switch off and an output signal of 0 V appears in the case
of switch on. In this manner, resistance variations of the magnetoresistive elements
GMR
1 and GMR
2 are output as a voltage variation.
In the magnetic switch according to this embodiment, the magnetic fields of the
first magnet
7 and the second magnet
6 that are different from each
other in strength and opposite to each other in direction are caused to selectively
operation, as an external magnetic field, on the magnetoresistive elements
5
in response to a switching manipulation on the switch, whereupon the magnetoresistive
elements
5 produce a switching signal for a switch operation. The switch
is switched based on the switching signal. By moving the magnetic shield member
10, the direction of the magnetic field to act on the magnetoresistive elements
5 (i.e., the direction in which to magnetize the free layers of the magnetoresistive
elements
5) can be changed between opposite directions (180° is formed).
Therefore, even with the configuration in which the strength of the magnetic field
varies slowly, the resistances of the magnetoresistive elements
5 can be
changed rapidly. A switch operation can be performed quickly based on such rapid
resistance variations.
Since the at least two magnetoresistive elements GMR
1 and GMR
2
that are connected to each other in series are incorporated in the bridge circuit
as shown in FIG. 7, the switch can be switched accurately and reliably without
being influenced by noise as caused by an external noise magnetic field, an environmental
magnetic field, or the like.
Although in FIG. 7 the at least two magnetoresistive elements GMR
1
and GMR
2 that are connected to each other in series are incorporated in
the bridge circuit, the invention is not limited to such a case. As shown in FIG.
9, magnetoresistive elements GMR
1 and GMR
2 that are connected to
each other in series may be incorporated in a voltage dividing circuit.
To incorporate magnetoresistive elements GMR
1 and GMR
2 that are
connected to each other in series in a voltage dividing circuit, a terminal Vdd
of a voltage source is connected to the terminal layer
9a of the
magnetoresistive element GMR
1 and a ground terminal of the voltage source
is connected to the terminal layer
9b of the magnetoresistive element
GMR
2. The terminal layer
9b of the magnetoresistive element
GMR
1 is connected to the terminal layer
9a of the magnetoresistive
element GMR
2, and their connecting point B
1 is connected to one input
terminal of a comparator
13 via a fixed resistor R
1. The other part
of the configuration that relates to the comparators
13 and
14 is
the same as shown in FIG.
7.
In the case of switch off, the magnetic shield member
10 retreats from
between the magnetoresistive elements GMR
1 and GMR
2 and the first
magnet
7 as shown in FIG.
1 and hence the magnetic field of the first
magnet
7 acts on the magnetoresistive elements GMR
1 and GMR
2.
In this case, since the magnetic field of the first magnet
7 is stronger
than that of the second magnet
6, the magnetization direction of the free
layers of the magnetoresistive elements GMR
1 and GMR
2 becomes the
same as the direction of the magnetic field lines
7a of the first
magnet
7. Therefore, the magnetization direction of the free layer of the
magnetoresistive element GMR
1 becomes the same as that of its fixed layer
and the magnetization direction of the free layer of the magnetoresistive element
GMR
2 becomes opposite to that of its fixed layer (180° is formed).
The resistance R
GMR2 of the magnetoresistive element GMR
2 becomes
greater than the resistance R
GMR1 of the magnetoresistive element GMR
1
(R
GMR1<R
GMR2) As shown in FIG. 8A, the voltage at the
connecting point B
1 of the two magnetoresistive elements GMR
1 and
GMR
2 becomes higher than 2.5 V.
In the case of switch on, the magnetic shield member
10 enters the space
between the magnetoresistive elements GMR
1 and GMR
2 and the first
magnet
7 as shown in FIG. 2, and hence the magnetoresistive elements GMR
1
and GMR
2 are shielded from the magnetic field of the first magnet
7
and only the magnetic field of the second magnet
6 acts on the magnetcresistive
elements GMR
1 and GMR
2. In this case, the magnetization direction
of the free layers of the magnetoresistive elements GMR
1 and GMR
2
becomes the same as the direction of the magnetic field lines
6a of
the second magnet
6. Therefore, the magnetization direction of the free
layer of the magnetoresistive element GMR
1 becomes opposite to that of its
fixed layer (180° is formed) and the magnetization direction of the free layer
of the magnetoresistive element GMR
2 becomes the same as that of its fixed
layer. The resistance R
GMR1 of the magnetoresistive element GMR
1
becomes greater than the resistance R
GMR2 of the magnetoresistive element
GMR
2 (R
GMR2<R
GMR1). As shown in FIG. 8A, the
voltage at the connecting point B
1 of the two magnetoresistive elements
GMR
1 and GMR
2 becomes lower than 2.5 V.
As shown in FIG. 8B, an amplified voltage of the voltage at the connecting point
B
1 appears at the output of the comparator
13. The amplified voltage
is compared with the reference voltage Ref for the comparator
14. As shown
in FIG. 8C, at the output of the comparator
14, an output signal of 5 V
appears in the case of switch off and an output signal of 0 V appears in the case
of switch on. In this manner, resistance variations of the magnetoresistive elements
GMR
1 and GMR
2 are output as a voltage variation.
With the magnetic switch according to this embodiment, since the magnetoresistive
elements that are connected to each other in series constitute the voltage dividing
circuit, the configuration of the circuit for picking up resistance variations
of the magnetoresistive elements as a voltage variation can be simplified.
Whether to use the above voltage dividing circuit or bridge circuit may be
determined in accordance with the subject of the switch operation.
Although the above description is directed to the case that the magnetic
switch is formed, the invention is not limited to such a case. A magnetic sensor
can be constructed that uses magnetoresistive elements having respective free layers
whose magnetization directions are varied by an external magnetic field, and that
detects a member to be detected having a magnetic shield function.
This magnetic sensor is different from the magnetic switch in that the magnetic
shield member
10 of the magnetic switch is used as a member to be detected
having a magnetic shield function and that the member (
10) to be detected
is detected. The configuration of the magnetic sensor is the same as the magnetic
switch in the other points.
The member (
10) to be detected moves in such a manner that its relative
position with respect to the first magnet
7 and the second magnet
6
varies. As the relative position of the member (
10) to be detected varies
with respect to the first magnet
7 and the second magnet
6, there
occur a first state in which both of the magnetic fields (external magnetic fields)
of the first magnet
7 and the second magnet
6 act on the magnetoresistive
elements
5 and a second state in which only one of the magnetic fields (external
magnetic fields) of the first magnet
7 and the second magnet
6 acts
on the magnetoresistive elements
5, whereby the member (
10) to be
detected is detected.
A state that the magnetic shield member
10 has retreated from between
the
first magnet
7 and, the magnetoresistive elements
5 is employed as
the first state. On the other hand, a state that the magnetic shield
10
has entered the space between the first magnet
7 and the magnetoresistive
elements
5. In the second state, the member (
10) to be detected shields
the magnetoresistive elements
5 from the magnetic field of the first magnet
7 that is stronger than that of the second magnet
6 and hence only
the magnetic field of the second magnet
6 acts on the magnetoresistive elements
5 as an external magnetic field.
In this magnetic sensor, the magnetic fields of the first magnet
7 and
the second magnet
6 that are different from each other in strength and opposite
to each other in direction are caused to selectively act, as an external field,
on the magnetoresistive elements
5 in accordance with a movement of the
member (
10) to be detected. The magnetoresistive elements
5 outputs
a detection signal indicating detection of the member (
10) to be detected,
based on which the member (
10) to be detected is detected. As the member
(
10) to be detected moves, the direction of the magnetic field to act on
the magnetoresistive elements
5 (i.e., the direction in which to magnetize
the free layers of the magnetoresistive elements
5) can be changed between
opposite directions (180° is formed). Therefore, even with the configuration
in which the strength of the magnetic field varies slowly, the resistances of the
magnetoresistive elements
5 can be changed rapidly. The member (
10)
to be detected can be detected quickly based on such rapid resistance variations.
As described above, according to the invention, the magnetic fields of the first
magnet and the second magnet that are different from each other in strength and
opposite to each other in direction are caused to selectively act, as an external
field, on the magnetoresistive elements. The magnetoresistive elements produces
an output signal that correspond to rapid resistance variations, based on which
a switch operation or detection of the member to be detected can be performed quickly.
*
