Electricity: measuring and testing – Magnetic – Displacement
Utility Patent
1997-07-17
2001-01-02
Strecker, Gerard (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207120, C324S207250, C324S252000
Utility Patent
active
06169396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sensing device for detecting a change in an applied magnetic field, and more particularly, to a sensing device which is particularly suitable for detecting the information about the rotation of, for example, an internal combustion engine.
2. Description of the Related Art
A magnetoresistance (MR) element is widely used to detect a magnetic field. This device changes in resistance in response to the direction of a magnetic field applied to a thin film of a ferromagnetic material (such as Ni—Fe, Ni—Co) with respect to the direction of a current flowing through the thin ferromagnetic film. However, the output level of the MR device is not high enough to achieve high-accuracy detection. To solve this problem, a magnetic field sensing device using a giant magnetoresistance (GMR) element capable of providing a high-level output signal has recently been proposed.
The GMR element has a multilayer structure consisting of alternating magnetic layers and non-magnetic layers each having a thickness in the range from a few Å to a few tens of Å. Such a multilayer structure is known as the superlattice structure, and a specific example is disclosed in a paper entitled “Magnetoresistance effect of superlattice” published in the Journal of Magnetics Society of Japan, Vol. 15, No.51991, pp.813-821. Specific structures includes (Fe/Cr)n, (permalloy/Cu/Co/Cu)n, (Co/Cu)n, etc. These superlattice structures exhibit much greater magnetoresistance effect (change in magnetoresistance) than conventional MR devices. In these GMR elements with superlattice structure, the magnetoresistance effect depends only on the relative jangle between magnetization of adjacent magnetic layers, and therefore the change in resistance does not depend on the direction of the external magnetic field applied with respect to the direction of current (this property is referred to as “in-plane magnetic field sensitivity).
Taking the above advantage, it has been proposed to construct a magnetic field sensing device with GMR elements in which a magnetic field sensing plane for detecting the change in the magnetic field is formed substantially with GMR elements, wherein electrodes are formed so that the respective GMR elements are connected in such a manner as to form a bridge circuit, to which a voltage Vcc and ground are applied. The change in resistance of the GMR elements is converted into a change in voltage via the bridge circuit, thereby detecting the change in the magnetic field applied to the GMR elements. In the GMR element, it is possible to have hysteresis in the characteristic of resistance versus applied magnetic field by optimizing the film thicknesses of the magnetic and non-magnetic layers within the range from a few Å to a few tens of Å.
However, in a sensing device constructed with a GMR bridge circuit, the above-described hysteresis varies from element to element due to the variations in response characteristics, or the overall temperature coefficient, among GMR elements constituting the bridge circuit. As a result, an imbalance occurs between the resistance change of GMR elements located on a pair of opposite sides of the bridge and the resistance change of GMR elements located on the other pair of opposite sides. This makes it difficult to obtain a high-accuracy signal in detection. One known technique to solve the above problem is to construct a magnetic field sensing device by positioning GMR elements so that there is a deviation between the center of the magnetic field sensing plane of the GMR elements and a magnet thereby ensuring that the sensing device operates at an operating point where a greater hysteresis occurs.
FIG. 9
is a schematic diagram illustrating such a sensing device, wherein its side view and plan view are shown in FIGS.
9
a
and
9
b
, respectively. This sensing device includes: a rotating shaft
1
; a rotary magnetic material member
2
serving as magnetic field variation inducing means having at least one protruding or recessed portion and being adapted to rotate in synchronization with the rotation of the rotating shaft
1
; a GMR element
3
disposed at a location a predetermined distance apart from the rotary magnetic material member
2
; and a magnet
4
serving as magnetic field generating means for supplying a magnetic field to the GMR element
3
, wherein the GMR element
3
includes a magnetoresistance pattern
3
a
serving as a magnetic field sensing pattern formed on a thin film plane (magnetic field sensing plane). Furthermore, as shown in
FIG. 9B
, the GMR element
3
is disposed so that the center of the magnetic field sensing plane of the GMR element
3
is shifted by a predetermined amount L from the center of the magnet
4
, for example, in a direction opposite to the rotation direction of the rotary magnetic material member
2
. In this structure, the magnetic field applied to the sensing plane of the GMR element
3
changes in response to the rotation of the rotary magnetic material member
2
, and a corresponding change occurs in the resistance of the magnetoresistance pattern
3
a.
FIG. 10
is a block diagram illustrating the construction of the sensing device using the GMR elements having the property of hysteresis. This sensing device includes: a Wheatstone bridge circuit
11
including GMR elements disposed a predetermined distance apart from the rotary magnetic material member
2
so that a magnetic field is applied from a magnet
4
to the GMR elements; a differential amplifier
12
for amplifying the output signal of the Wheatstone bridge circuit
11
; a comparator
13
for comparing the output of the differential amplifier
12
with a reference value and outputting either a “0” signal or a “1” signal depending on the comparison result; a waveform shaping circuit
14
for shaping the waveform of the output of the comparator
13
and supplying a “0” or “1” signal having sharply rising and falling edges to the output terminal
15
; and a temperature compensation circuit
20
for correcting the reference value (threshold value) associated with the comparator
13
in accordance with the temperature coefficients of the GMR elements.
FIG. 11
is a circuit diagram illustrating a specific example of the circuit shown in FIG.
10
. The Wheatstone bridge circuit
11
includes GMR elements
10
A,
10
B,
10
C, and
10
D disposed on the respective branches of the bridge, wherein one end of the GMR element
10
A and one end of the GMR element
10
C are connected in common to a power supply terminal Vcc via a node
16
, one end of the GMR element
10
B and one end of the GMR element
10
D are connected in common to ground via a node
17
, the other end of the GMR element
10
A and the other end of the GMR element
10
B are connected to a node
18
, and the other end of the GMR element
10
C and the other end of the GMR element
10
D are connected to a node
19
. Although in a practical device the GMR elements
10
A,
10
B,
10
C, and
10
D are formed in a separate fashion in the magnetoresistance pattern
3
a
of the GMR element
3
, these GMR elements
10
A,
10
B,
10
C, and
10
D are generically represented by the GMR element
3
in FIG.
9
.
The node
18
of the Wheatstone bridge circuit
11
is connected, via a resistor, to the inverting input of an amplifier
12
a
constituting a differential amplifier
12
. The node
19
is connected, via a resistor, to the non-inverting input of the amplifier
12
a
. The output of the amplifier
12
a
is connected to the inverting input of a comparator
13
via a resistor. The non-inverting input of the comparator
13
is connected to a voltage divider serving as a reference power supply, wherein the non-inverting input of the comparator
13
is also connected via a resistor to the output of the comparator
13
. The output of the comparator
13
is connected to the base of a transistor
14
a
of a waveform shaping circuit
14
. The collector of the transistor
14
a
is connected to an output terminal
15
and also
Shinjo Izuru
Yokotani Masahiro
Mitsubishi Denki & Kabushiki Kaisha
Strecker Gerard
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Sensing device for detecting change in an applied magnetic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensing device for detecting change in an applied magnetic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensing device for detecting change in an applied magnetic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457819