JPH0353562B2 - - Google Patents

Description

[Detailed description of the invention]

B. Industrial Application Field In this case, the present invention relates to a magnetic field detection element using a ferromagnetic magnetoresistive element used in a device for detecting the rotation direction and rotation speed of a rotating magnetic field. B. Prior Art A magnetic field detection element using an anisotropic ferromagnetic magnetoresistive element suitable for detecting the direction of a magnetic field is known from Japanese Patent Publication No. 57-5067. As shown in FIG. 1, this magnetic field detection element 1 consists of two ferromagnetic magnetoresistive elements A and B having zigzag current paths formed as films on one substrate and connected in series. , the main current paths A' and B' of the two current paths are arranged so as to be substantially perpendicular to each other, and an output terminal 4 is provided at the connection point of both magnetoresistive elements A and B, and the other end of both magnetoresistive elements Current supply terminals 2 and 3 are respectively provided on the sides, and the respective resistance values of both magnetoresistive elements change according to a change in the direction of the magnetic field component substantially parallel to the surface of the substrate, and the resistance value of each of the magnetoresistive elements changes due to this change. It is a magnetoelectric transducer configured to detect a change in voltage at an output terminal, and is connected to a bridge circuit together with resistors 5 and 6 as shown in FIG. 2 to generate a DC voltage between current supply terminals 2 and 3. It is used by applying . Then, depending on the rotation angle of the magnetic field component, a sinusoidal output voltage change is produced at the output terminal 4, as shown in FIG. 3, with two cycles of one rotation (360 degrees) of the magnetic field component. 7 is an operational amplifier (OP amplifier) which amplifies and shapes the sine wave signal output from the output terminal 4 into a rectangular wave. The number of rotations of the magnetic field component can be detected by counting the output pulses of the operational amplifier 7. To detect the direction of rotation, as shown in FIG. 5, magnetoresistive elements C and D, whose main current paths are arranged at right angles to each other and are connected in series, are connected to the magnetoresistive elements A and B. Arranged at a 45° angle,
As shown in FIG. 6, a bridge circuit is constructed with resistors 9 and 10, and the output signal is amplified and shaped into a rectangular wave by an operational amplifier 11. This rectangular wave output is 45 degrees with the rectangular wave output of the operational amplifier 7. This can be done by taking advantage of the phase (angle) shift. Specifically, it is possible to detect the rotational direction by connecting a detection circuit for determining the rotational direction of the magnetic field to the output terminals of the operational amplifiers 7 and 11. The circuit known in the publication can be used. C. Purpose of the invention Magnetic field detection elements that detect the rotational direction and rotation speed of a magnet generally have a narrow and limited range where a strong magnetic field exists, so their area needs to be reduced; In order to achieve this, it is necessary that the width of the main current path be greater than a certain level, and there is a limit to the ability to reduce the size of the element by reducing this width and thereby reducing the area. In the conventional element as shown in Fig. 5, four magnetoresistive elements A, B, C, and D are used as a magnetic field detection element for detecting the rotational direction and rotation speed of a magnetic field, so the area of one magnetoresistive element is Limited to 1/4 of the total. Therefore, if the area of the entire element is set to a certain size, the area of one magnetoresistive element will be limited to 1/4 of the above-mentioned certain area, and the resistance value per element will also be below a certain value, including the above-mentioned reasons. limited to.
Also, since elements A and B, C and D are connected in series, and A, B and C and D are connected in parallel, the electrical resistance of the entire element is the same as the resistance of each element, and the direction of rotation can be detected. The detection element shown in FIG. 5 has the disadvantage that it consumes twice as much current as the detection element 1 shown in FIG. 1, which does not require rotational direction detection, if the area per element is the same. In view of the above, it is an object of the present invention to propose a novel magnetic field detection element that can be used in a rotational direction detection device and has a large electric resistance value throughout the detection element and consumes little current. D. Structure and Embodiments of the Invention In order to achieve the above object, the magnetic field detection element of the present invention is provided on a single substrate with approximately equal electrical resistance values, as shown in the embodiment of FIG. First, second, and third ferromagnetic magnetoresistive elements A, B, and C are connected in series, and current paths of these magnetoresistive elements, that is, first, second, and third ferromagnetic magnetoresistive elements A, B, and C are connected in series. each current path extends in a substantially zigzag shape, and main current paths A' and B' of the first and second current paths respectively form an angle of approximately 72° with respect to each other;
The main current paths B' and C' of the second and third current paths are arranged at an angle of approximately 72 degrees to each other, and the connection point between the first and second magnetoresistive elements A and B. A first output terminal 12 is provided at the connection point between the second and third magnetoresistive elements B and C.
An output terminal 13 is provided, and current supply terminals 2 and 3 are provided at both ends of the first, second, and third magnetoresistive elements connected in series, and current supply terminals 2 and 3 are provided at both ends of the first, second, and third magnetoresistive elements connected in series, and current supply terminals 2 and 3 are provided at both ends of the first, second, and third magnetoresistive elements connected in series. The device is configured to detect changes in voltage occurring at the first and second output terminals as the magnetic field component rotates. FIG. 8 is a diagram illustrating the angles that the main current paths A', B', and C' make with each other, and the angles that they make are allowed to be in the range of about 69° to 74°. In general, the electrical resistance ρ of a ferromagnetic magnetoresistive element
(θ) is maximum when the current and magnetization direction are parallel, and minimum when they are orthogonal, and is expressed by the following formula (Voigt−
Thomson's equation). ρ (θ) = ρ⊥ sin ² θ + ρ ₁₁ cos ² θ ...(1) where ρ is the angle between the current and the magnetization direction, ρ⊥ is the resistance value when θ = 90°, and ρ ₁₁ is θ = 0 This is the resistance value at °. Also, since there is a relationship of ρ ₁₁ > ρ⊥, ρ ₁₁
If −ρ⊥△ρ, equation (1) can be transformed to ρ(θ)ρ ₀ +△ρ/2cos2θ ……(2). Note that ρ ₀ (ρ⊥＋ρ ₁₁ )/2
It is. Now, in order to analyze the magnetic field detection element of this invention, we will calculate the angle formed by three ferromagnetic magnetoresistive elements A, B, and C, which have approximately the same electrical resistance value, by element B and A.
The angle between elements B and C is generalized as α and the angle between elements B and C as -α (see FIG. 12). Resistance value of element B ρ _B (θ)
In the same way as formula (2) was derived from formula (1), ρ _B (θ) = ρ _B ⊥ sin ² θ + ρ _B11 cos ₂ θ ρ ₀ +△ρ/2cos2θ ...(3) Element A Since the angles of and C are shifted from element B by α and -α, similarly, ρ _A (θ) = ρ ₀ +△ρ/2cos2 (θ-α) ...(4) ρ _C (θ) =ρ ₀ +△ρ/2cos2(θ+α)...(5). Note that ρ ₀ ρ _A1 +ρ _A11 /2ρ _B1 +ρ _B11 /2 ρ _C1 +ρ _C11 /2. Therefore, the resistance value R when elements A, B, and C are connected in series is R=ρ _A (θ) + ρ _B (θ) + ρ _C (θ) = 3ρ ₀ +△ρ/2 (1+2cos2α) cos2 (θ)... …(6) becomes. Therefore, there is a DC voltage V _D at current supply terminals 2 and 3.
, the voltage at the first output terminal 12 V ₁ (θ)
is V ₁ (θ)={ρ _B (θ) + ρ _C (θ)}V ₀ /R=V ₀ −ρ
₀ +△ρ/2cos(2θ−2α)/3ρ ₀ +△ρ/2(1+2c
os2α) cos2θ……(6′). Moreover, the voltage V ₂ (θ) of the second output terminal 13 is V ₂ (θ)=ρ _C (θ)・V ₀ /R=ρ ₀ +△ρ/2cos(2
θ+2α)/3ρ ₀ +△ρ/2(1+2cos2α)cos2θV ₀ …
…(7) becomes. Now if α=72°, V ₁ (θ), V ₂ (θ)
is V ₁ (θ)=V ₀ −ρ ₀ +△ρ/2cos(2
θ−144゜)/3ρ ₀ −0.31△ρcos2θV ₀ …(8) V ₂ (θ)=ρ ₀ +△ρ/2cos(2θ+1
44゜)/3ρ ₀ −0.31△ρcos2θ……(9). Since △ρ is usually about 2 to 5% of ρ ₀ , from equation (8), voltage V ₁ (θ) is a sinusoidal voltage that increases and decreases up and down around 2/3V ₀ , and from equation (9) Than
It can be seen that V ₂ (θ) becomes a sinusoidal voltage that increases and decreases up and down with 1/3 V ₀ as the center. The respective changes from the center △V ₁ (θ) and △V ₂ (θ) are △V ₁ (θ) = V ₁ (θ) - 2/3V ₀ = -△ρ/2 {cos
(2θ−144°) +0.2cos2θ}/3ρ ₀ −0.31△ρcos2θV
₀ ...(10) △V ₂ (θ) = V ₂ (θ) - 1/3V ₀ = △ρ/2 {cos (2
θ＋144゜）＋0.2cos2θ｝／3ρ ₀ −0.31△ρcos2θV ₀ …
…(11) becomes. In this invention, θ when △V ₁ (θ) becomes 0
It is necessary that the phase of the value of θ and the value of θ at which ΔV ₂ (θ) becomes 0 is approximately 45°. To find this in general, you can solve the following simultaneous equations from equations (6') and (7) (-π2α, 2θπ). V ₁ (θ) - 2/3V ₀ = 0 ... (12) V ₂ (θ - 45°) - 1/3V ₀ = 0 ... (13) Omitting the counting procedure and showing the conclusion, the solution is As α±71.57°±72°, the phase of V ₁ (θ) and V ₂ (θ) at α=±72°

[Table] When the angle α is in the range of 69° to 74°, the phase difference between V ₁ (θ) and V ₂ (θ) is approximately within the range of 40° to 50°. Therefore, as shown in FIGS. 7 and 8, ferromagnetic resistance effect elements A, B, and C are arranged offset by 72 degrees, and a DC voltage is applied to both ends 2 and 3 of their series connection.
When multiplied by V ₀ , the output signals of output terminals 12 and 13 for changes in angle θ become as shown in Fig. 9,
The voltage fluctuations are sinusoidal waves with a phase shift of 45° from each other. Therefore, the element 1 shown in FIG. 7 is connected to resistors 14 to 17 and operational amplifiers 18 and 19 as shown in FIG. After shaping, the first and second outputs obtained at the output terminals 20 and 21 of the operational amplifiers 18 and 19, respectively, become rectangular waves having a phase shift of approximately 45° from each other, as shown in FIG. Become. These two rectangular wave signals are
The direction of rotation of the magnetic field can be determined by inputting it to a detection circuit known in the publication. Further, the number of rotations can be determined by counting output pulses as in the conventional case. E. Effect of the invention In this invention, three magnetoresistive effect elements A,
Since B and C are connected in series, the electrical resistance of the entire element (that is, the magnetic field detection element) is three times the resistance value of each magnetoresistive element. Moreover, if the area of the magnetic field detection element 1 is the same as that of the conventional one shown in FIG. 3
Since it can be doubled, if the width of the main current path is set to be the same as the conventional one, the length will be approximately 4/3 times, and the resistance per magnetoresistive element will be 4/3 times that of the conventional product. . Therefore, the electrical resistance of the magnetic field detection element 1 can be increased four times that of the conventional product (FIG. 5), and the current consumption can be reduced accordingly. In addition, it is easily possible to increase the overall combined resistance by changing the arrangement of the four elements A, B, C, and D in Figure 5 as shown in Figure 13 and connecting the four elements in series. . The series resistance value in this case is the same as in the case of the present invention, but the total amplitude W of the fluctuation of the output voltages V ₁ (θ) and V ₂ (θ) is W = 1/4・△ρ/ρ・V ₀ , and the total amplitude W0.28·Δρ/ρ ₀ V ₀ in the case of this invention has the effect of obtaining a larger value. Furthermore, in the case where four elements are connected in series as shown in Fig. 13, the center values of V ₀ (θ) and V ₂ (θ) are 3/4V ₀ and 1/4V ₀ , respectively, but in this invention, /
3V ₀ and 1/3V ₀ , which is a value closer to 1/2V ₀ . Considering that the possible input voltage range of operational amplifiers that increase or decrease the output voltages V ₁ (θ) and V ₂ (θ) is around 1/2 V ₀ in most cases, this invention is more advantageous. It is.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the outline of a conventional magnetic field detection element, Figure 2 is an electric circuit diagram using the element in Figure 1, and Figure 3 is for explaining the output voltage obtained with the element in Figure 2. 4 is a diagram for comparing and explaining the output of the operational amplifier 7 in FIG. 2 and the output of the element 1, FIG. 5 is a diagram showing another example of the conventional magnetic field detection element, and FIG. 7 is a diagram showing an embodiment of the present invention. FIG. 8 is a diagram explaining the angular relationship of the main current path of the one shown in FIG. 7. Figure 9 is a diagram explaining the output voltage of the one in Figure 7, Figure 10 is an electric circuit using the magnetic field detection element of Figure 7, Figure 11 is a diagram showing the output voltage of Figure 10, and Figure 12. 13 is an explanatory diagram for explaining the principle of the present invention, and FIG. 13 is a diagram showing a magnetic field detection element that is a modification of the conventional example shown in FIG. 5. 1... Magnetic field detection element, 2, 3... Current supply terminal, 12... First output terminal, 13... Second output terminal, A, B, C... Ferromagnetic magnetoresistive element,
A′, B′, C′…Main current path.

Claims (1)

[Claims] 1. First, second, and third ferromagnetic magnetoresistive elements A, B, and C having substantially equal electrical resistance values provided on one substrate are connected in series,
The current paths of these magnetoresistive elements, that is, the first, second and third current paths, respectively extend in a substantially zigzag shape, and the main current paths A' and B' of the first and second current paths are connected to each other. are at an angle of approximately 72° to each other, and the main current paths of the second and third current paths
B' and C' are arranged at an angle of approximately 72 degrees to each other, and a first output terminal 12 is provided at a connection point between the first and second magnetoresistive elements A and B,
A second output terminal 13 is provided at the connection point between the second and third magnetoresistive elements B and C, and the second output terminal 13 is provided at both ends of the first, second, and third magnetoresistive elements connected in series. are provided with current supply terminals 2 and 3, respectively, and are configured to detect changes in voltage occurring at the first and second output terminals as the magnetic field component rotates substantially parallel to the surface of the substrate. Magnetic field detection element.