JP3308123B2 - Magnetoresistive sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetoresistive effect (hereinafter abbreviated as "MR") sensor used in a detecting section of a detecting device such as a magnetic linear encoder or a rotary encoder for detecting a position, a rotation speed or the like. It is about.

[0002]

2. Description of the Related Art An MR sensor of this type outputs a signal corresponding to a relative position with respect to a magnetic recording medium which is magnetized in a predetermined pattern, and is independent of the relative speed with respect to the magnetic recording medium. The electric resistance of the MR element constituting the MR sensor changes according to the strength of the magnetic field, and the change becomes a change in the voltage between both ends due to the drive current and is taken out as a detection signal. For this reason, fluctuations in the voltage between both ends due to causes other than the magnetic field,
The so-called offset directly causes a malfunction or a reduction in operation margin. The fluctuation of the offset voltage is due to the temperature fluctuation.

Conventionally, the MR sensor has a three-terminal circuit configuration or a bridge circuit configuration to solve the problem of offset. For this reason, function trimming or the like is performed on the circuit so that the offset voltage becomes 0V. However, an offset voltage is generated due to a temperature distribution generated by an operation current flowing through each MR element during operation of the MR sensor. For the same reason, there has been a problem that the settling time of the offset voltage at power-on is required.

In order to solve this problem, all the MR elements for the A-phase and the B-phase (displaced by 90 degrees from the A-phase) to be obtained in the final stage are all interleaved with each other so that the operating current is reduced. Differences in temperature distribution can be reduced. However, in such a circuit configuration, the MR
It is difficult to provide all the connection terminals on one side of the MR chip on which the sensor circuit pattern is formed, and a three-dimensional pattern configuration is required, which makes it very difficult to manufacture. In particular, when connecting the output terminal of the MR chip to the differential amplifier, it is very difficult to connect the connection terminals to one side of the MR chip in a general connection method such as soldering or wire bonding unless the connection terminals are concentrated on one side.

Conventionally, there has been an MR sensor as shown in FIG. 3 in which all connection terminals are provided on one side of an MR chip. This MR sensor is for detecting a relative position with respect to a magnetic recording medium called a magnetic memory in which N poles and S poles are alternately magnetized at a predetermined pitch λ along one direction as an object to be detected. In order to also detect the direction of relative movement with respect to the memory, it is possible to obtain detection signals of the A phase and the B phase whose phases are shifted from each other by 90 degrees.

In FIG. 3, reference numeral 1 denotes an MR element. In this case, for simplification, it is shown as being composed of one MR element element formed of a linear pattern of ferromagnetic thin film resistors. The MR elements 1 are arranged in eight rows along one direction. In order to distinguish each element by the role related to the output of the A phase and the B phase, the A phase
The B and B phase elements are denoted by reference numerals B1 to B4, and their arrangement is A1 to A4 and B1 to B4 in order from the left.

Two elements adjacent to each other in order from the end of the arrangement of the eight MR elements 1 are connected in series, both ends of the series connection are connected to the power supply terminal Vcc and the ground terminal G, and the midpoint between the elements is connected. Four three-terminal circuits are formed connected to the output terminal 2. In order to distinguish each output led to the four output terminals 2 with respect to the A phase and the B phase,
Symbols A +, A-, B +, B- are given to them.

The outputs A + and A- are input to a differential amplifier 3, and the differential output is output as an A-phase detection signal A. The outputs B + and B- are input to the differential amplifier 4, and the differential output is output as a B-phase detection signal B.

In FIG. 3, MR elements A1 and A2,
A (2n + 1) λ where A3 and A4, B1 and B2, and B3 and B4 are the magnetization pitch (distance between adjacent N pole and S pole) of the above-described magnetic memory, and n is 0 or a positive integer. /
2] They are arranged at positions separated from each other, and when λ is set as one wavelength of the detection waveform and this is made to correspond to 360 degrees of the phase, they are arranged at positions 180 degrees out of phase with each other. Also, M
The R elements A2 and A3, and B2 and B3 are arranged at positions shifted in phase by 180 degrees. The MR elements A4 and B1 are [(n +
[1/4] λ] and at a position where the phase is shifted by 90 degrees.

Then, as shown in FIG. 4, the MR elements A1 to A
4, B1 to B4 form two bridge circuits (differential circuits), so that if the resistance changes of the MR elements A1 and A4, A2 and A3, B1 and B4, and B2 and B3 change equally, no offset voltage is generated. .

[0011]

However, in the case of the arrangement shown in FIG. 3, the corresponding MR in the two bridge circuits is used.
Elements A1 and A4, A2 and A3, B1 and B4, B2 and B3
They are not arranged symmetrically with respect to the geometric center line (center line orthogonal to the arrangement direction of the MR elements) of the entire circuit pattern of the MR sensor.

For this reason, when an operating current is applied to each MR element, the temperature distribution due to the temperature rise due to the operating current differs between the corresponding MR elements, and the resistance balance between the corresponding MR elements is disturbed. And the offset voltage becomes unstable. In the case of this circuit, although not related to the offset, when a deviation between the magnetization pitch of the magnetic memory and the pitch of the MR element pattern occurs as described later, A,
A phase shift of the B phase occurs.

FIG. 5 shows another conventional example. In the case of this conventional example, the arrangement of the eight MR elements 1 itself is the same as that of the conventional example of FIG. 3, but each of the outputs of the four three-terminal circuits is any one of the outputs A +, A-, B + and B-. The arrangement is different, and the arrangement is A +, B +, A-, B- in order from the left. That is, each MR element 1 is
When distinguished by the roles related to the phase and the phase B, the arrangement is A1, A2, B1, B2, A3, A4, B3 in order from the left.
B4.

In this arrangement, the symmetry with respect to the above-mentioned center line approaches the line symmetry as compared with the conventional example of FIG. 3, but the offset due to the temperature distribution still occurs because it is not perfect yet. FIG. 3 also shows the phase difference between the A and B phases due to the mismatch between the pitches of the magnetic memory and the MR element pattern.
Although it is smaller than the example, it is not yet complete.

Here, the phase shift will be described. FIG.
In the above, point c is the electrical center point of the A phase, d is the electrical center point of the B phase, and x1 indicates the distance between cd and d. FIG.
In the graph, point e is the electrical center point of the A phase, f is the electrical center point of the B phase, and x2 indicates the distance between e and f.

For example, a description will be given of a shift when the magnetic memory is made of plastic such as PET, and the magnetic memory is coated with magnetic powder on one side, and the magnetic memory is stretched with a certain tension. . Assuming that the expansion rate of the magnetic memory at this time is α, the phase shifts by x1 * (α−1) / λ * 360 degrees in the case of FIG. In the case of FIG. 5, the phase is x2 * (α-1) / λ * 360 degrees,
Although FIG. 5 is more advantageous by the difference between the lengths of x1 and x2, the phase shift does not become zero. For this reason, it is desirable that the value of the distance x between the electrical center points of the A phase and the B phase eventually becomes 0.

The present invention has been made in view of the above circumstances, and in this type of MR sensor, it is possible to prevent a change in offset voltage due to a temperature generated by an operating current flowing through the MR element, and to provide a magnetic sensor. A due to the difference between the magnetization pitch of the memory and the pitch of the MR element pattern
It is an object of the present invention to provide a configuration capable of preventing occurrence of a phase error between phase and B-phase outputs.

[0018]

According to the present invention, there is provided, according to the present invention, a relative position with respect to a magnetic recording medium in which N poles and S poles are alternately magnetized at a predetermined pitch λ in one direction. An MR sensor for detecting the one end on the same side sequentially in one direction, where n is 0 or a positive integer.
The interval between the cattle is (2n + 1) λ / 2, (n + ／) λ,
(2n + 1) λ / 2, (2n + 1) λ / 2, (2n +
1) λ / 2, (n + 3/4) λ, and (2n + 1) λ / 2
And eight MR elements arranged in a line at an interval referred to as above. By serially connecting two adjacent elements in order from the end of the arrangement of the eight MR elements, both ends are connected to a power supply and a ground, and the middle between the elements. Four three-terminal circuits whose outputs are taken out from the points are formed, and the outputs of the four three-terminal circuits are sequentially arranged from one side in the order of arrangement of the circuits into A +, B +, B−, A−.
The differential output of A + and A− and the differential output of B + and B− are each configured to obtain two-phase detection signals that are 90 ° out of phase with each other.

[0019]

SUMMARY OF] According to such a configuration, output of the MR sensor force A
In the MR elements corresponding to two three-terminal circuits for obtaining + and A−, and the MR elements corresponding to two three-terminal circuits for obtaining outputs B + and B− ,
Distribution of temperature generated by operating current flowing in each
There will be the same like, it is possible to prevent the occurrence of the offset voltage due to the temperature.

Further, the error of the phase difference between the two phases does not occur even when the pitch deviation of the magnetization pitch and the MR element pattern of magnetic recording medium has occurred.

[0021]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2 of the conventional example shown in FIG.
5 that are common or equivalent to those in FIG. 5 are denoted by the same reference numerals, and a description of the common parts will be omitted.

First, before describing the MR sensor of this embodiment, a magnetic memory to be detected by the MR sensor will be described. As the magnetic memory, for example, a magnetic material obtained by mixing a magnetic powder of Ba ferrite with a binder of a copolymer of vinyl acetate and vinyl acetate with a thickness of 10 μm on a PET base material is used. In addition, Fe-Cr-
A metal magnetic body such as Co may be used. For example, in the case of a linear encoder for a printer, the magnetic memory is 36
N-pole and S-pole alternately correspond to the recording density of 0 DPI.
It is magnetized at a pitch of 0.6 μm. This value is the above-described magnetization pitch (the distance between the NS poles) λ.

Next, the MR sensor of this embodiment will be described with reference to FIGS. FIG. 1 shows an MR like FIG. 3 and FIG.
The circuit configuration of the MR sensor is shown by simplifying the element pattern. FIG. 2 shows an MR chip formed on a substrate of an MR chip.
4 shows an actual circuit pattern of the sensor.

As shown in FIG. 1, in the MR sensor of this embodiment, eight MR elements 1 are arranged in a line as in the conventional example, and two adjacent elements are connected in series from the end of the array. As a result, four three-terminal circuits are formed, both ends of which are connected to the power supply terminal Vcc and the ground terminal G, and the midpoint between the elements is connected to each of the output terminals 2, thereby forming the two bridge circuits of FIG. And the arrangement of each of the outputs of the three-terminal circuit as one of the outputs A +, A-, B +, and B- is different. That is, the outputs of the three-terminal circuit are arranged in the order of A +, B +, B-, and A- from left to right. Arrangement is A from the left
1, A2, B1, B2, B3, B4, A3, and A4.

In addition, the arrangement interval of the MR elements is different from the conventional example, and n is 0 or a positive integer, as shown in FIG.
(2n + 1) λ / in the rightward order from the leftmost MR element A1
2, (n + ／) λ, (2n + 1) λ / 2, (2n +
1) λ / 2, (2n + 1) λ / 2, (n + 3/4) λ,
They are arranged at an interval of (2n + 1) λ / 2.

Then, as shown in FIG. 1, the outputs A +, A-
Is input to the + and-input terminals of the differential amplifier 3, and the differential output is output as the A-phase detection signal A. The outputs B + and B- are input to the differential amplifier 4, and the differential output is output as a B-phase detection signal B whose phase is shifted from the A-phase by 90 degrees.

In FIG. 1, offset adjustment in the differential amplifiers 3 and 4 is performed by variable resistors 5 and 6.

Next, the details of the pattern of the actual MR sensor shown in FIG. 2 will be described.

The substrate 7 of the MR chip shown in FIG. 2 is formed of glass, ceramics, or a thermally oxidized Si wafer. Permalloy is vapor-deposited on the substrate 7 to a thickness of about 500 angstroms, and is composed of eight MR elements 1 shown by photolithography. All connection terminals (output terminal 2, power supply terminal Vcc, ground terminal G) are on one side of the chip. To form a circuit pattern of the MR sensor. Here, n included in the equation indicating the arrangement interval of each MR element is 0 or a positive integer as described above, but the smaller the value of n, the smaller the size of the entire MR chip. It is desirable to select an optimal value of n in consideration of the size of the MR chip, the accuracy of the photolithography, and the like.

In FIG. 2, each MR element 1 has a linear MR element element 8 made of a ferromagnetic thin film resistor.
Are arranged in parallel at an interval λ, and are connected in series in a zigzag manner. The number of the elements 8 is not limited to seven, and is determined by how much the electric resistance value is determined by the width and the length L of the element. It is desirable that the electric resistance is increased so that the heat generation due to the operating current is suppressed and the consumption current value is decreased by increasing the electric resistance value. However, this has a problem that the number of elements increases and the pattern shape becomes large. Therefore, it is necessary to select an optimal value. Since the width and length of the element affect the characteristics as an encoder, it cannot be easily changed in a direction in which the electric resistance value increases, and there is an optimum value naturally. The interval between the elements 8 is not limited to λ,
May be set to mλ as an arbitrary positive integer.

[0031]

According to the MR sensor of this embodiment as described above,
For example, two 3's constituting each of the bridge circuits of FIG.
The corresponding MR elements A1, A4, A2 of the terminal circuits
A3, B1 and B4, B2 and the temperature distribution becomes similar generated by the operating current flowing through the respectively to what B3,
The offset voltage in the bridge circuit of FIG.
Even if it is not, it does not change and becomes stable.

Further, A, is an error of the phase difference between the B phase does not occur even when the pitch deviation of the magnetization pitch λ and the MR element pattern of magnetic memory occurs.

Next, referring to FIGS. 6 and 7, the effect of the present embodiment relating to the offset voltage will be described in detail. FIGS. 6 and 7 show the power supply voltage V under different temperature environments for the MR sensor of the conventional example and the MR sensor of this embodiment, respectively.
9 is a graph showing a relationship between cc and an offset voltage before entering the differential amplifiers 3 and 4.

Originally, if only the power supply voltage changes, the offset voltage before entering the differential amplifier shows a proportional relationship with the power supply voltage even if it is not zero. When this is not a proportional relationship, it is because an offset voltage is generated due to the difference in various temperature balances. If it is proportional, the offset voltage of the final output by the differential amplifiers 3 and 4 is adjusted for any power supply voltage Vcc by adjusting the variable resistors 5 and 6 at the predetermined power supply voltage Vcc value in FIG. It can be set to 0.

In this regard, in the conventional example, as shown in FIG. 6, the relationship between the power supply voltage Vcc and the offset voltage before the differential amplifier loses linearity under different temperature environments 1 and 2, and the predetermined power supply voltage Vcc Offset voltage by value (final output)
Becomes zero at other power supply voltages Vcc. In contrast, in the present embodiment, as shown in FIG. 7, the offset voltage before the differential amplifier shows a linear change with respect to the power supply voltage Vcc, and is found to be proportional to the power supply voltage Vcc.
As a result, in this embodiment, the power supply voltage dependency of the offset voltage of the final output can be reduced, and the offset voltage of the final output can be set to zero.

Further, according to the MR sensor of this embodiment,
All connection terminals can be put out on one side of the MR chip,
Connection to a differential amplifier can be easily performed, and the size of the MR chip can be reduced.

Note that the arrangement of the MR elements shown in FIGS. 1 and 2 is reversed, and the arrangement intervals are (2n + 1) λ / 2, (n + ／) λ,
(2n + 1) λ / 2, (2n + 1) λ / 2, (2n +
1) λ / 2, (n + 3/4) λ, (2n + 1) λ / 2, and the output arrangement of each three-terminal circuit is A +, B in order from the right.
+, B- and A- may be used.

[0039]

As is apparent from the above description, according to the present invention, the relative position with respect to the magnetic recording medium in which the N pole and the S pole are alternately magnetized at a predetermined pitch λ in one direction is detected. The distance between one end on the same side in order along one direction, where n is 0 or a positive integer
There (2n + 1) λ / 2 , (n + 1/4) λ, (2n +
1) λ / 2, (2n + 1) λ / 2, (2n + 1) λ /
2, (n + 3/4 ) λ, (2n + 1) λ / 2 has eight MR elements arranged in a line at intervals of, said eight M
By connecting two adjacent elements in series from the end of the array of R elements in series, four three-terminal circuits are formed in which both ends are connected to a power supply and a ground and an output is taken out from a middle point between the elements. A +, B +, B−, and A− are respectively assigned to the outputs of the terminal circuits in this order from one side in the arrangement order of the circuits.
The differential output of A + and A- and the differential output of B + and B- are configured to obtain two-phase detection signals having a phase shift of 90 degrees from each other. In addition to preventing the occurrence of an offset voltage due to the changing temperature, the magnetization pitch of the magnetic recording medium and the MR
An excellent effect that an error in the phase difference between the two phases does not occur even when a pitch shift of the element pattern occurs.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit configuration of an embodiment of an MR sensor according to the present invention.

FIG. 2 is a plan view showing a circuit pattern of the MR sensor according to the embodiment.

FIG. 3 is a circuit diagram showing a circuit configuration of a conventional MR sensor.

FIG. 4 shows an MR sensor comprising two MR elements.
FIG. 3 is a circuit diagram showing two bridge circuits.

FIG. 5 is a circuit diagram showing a circuit configuration of another conventional MR sensor.

FIG. 6 is a graph showing a relationship between a power supply voltage and an offset voltage in a conventional MR sensor.

FIG. 7 is a graph showing a relationship between a power supply voltage and an offset voltage in the MR sensor of the example.

[Explanation of symbols]

 1, A1 to A4, B1 to B4 MR element 2 Output terminal 3, 4 Differential amplifier 5, 6 Variable resistor 7 MR chip substrate 8 MR element element G Ground terminal Vcc power supply terminal

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shuzo Yasuhiko 1248 Shimokagemori, Chichibu City, Saitama Prefecture Canon Electronics Co., Ltd. (56) References JP-A-59-105503 (JP, A) JP-A-2-2 272782 (JP, A) JP-A-62-247213 (JP, A) JP-A-1-212313 (JP, A) JP-A 1-212312 (JP, A) JP-A-4-270917 (JP, A) JP-A-2-210218 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 43/08 G01D 5/245 G01R 33/09 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A magnetoresistive sensor for detecting a relative position with respect to a magnetic recording medium in which N and S poles are alternately magnetized at a predetermined pitch λ along one direction, wherein n is 0 or positive. As an integer in the same order in one direction
Side ends are (2n + 1) λ / 2, (n + 1)
/ 4) λ, (2n + 1) λ / 2, (2n + 1) λ / 2,
(2n + 1) λ / 2, (n + 3/4) λ, (2n + 1)
It has eight magneto-resistive elements arranged in a line at an interval of λ / 2, and the two elements adjacent to each other are connected in series from the end of the arrangement of the eight magneto-resistive elements. Are connected to each other and the output is taken out from the middle point between the elements. Four-terminal circuits are formed, and the outputs of the four three-terminal circuits are A +, B +, B-, and A + in order from one side in the arrangement order of the circuits. A magneto-resistive device characterized in that the differential output of A + and A- and the differential output of B + and B- provide two-phase detection signals having a phase shift of 90 degrees from each other. Effect sensor. 2. The magneto-resistance effect element comprises a plurality of linear magneto-resistance effect element elements formed of a ferromagnetic thin film resistor arranged in parallel at an interval of mλ (m is a positive integer),
The magnetoresistive sensor according to claim 1, wherein the magnetoresistance effect sensor is configured to be connected in series in a zigzag manner.