JP3515248B2 - Differential magnetic resistance circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a differential magnetoresistive circuit used as a magnetic detector.

[0002]

2. Description of the Related Art As a magnetic detection circuit for detecting a change in magnetic field, a differential magnetic resistance circuit (half bridge circuit) as shown in FIG. 2 is known. This differential magnetoresistive circuit 11
Is a device in which two magnetoresistive elements 12 and 13 made of semiconductor are connected in series, and a terminal 1 to which a reference voltage is applied.
4 and 15, and this reference voltage to the magnetoresistive elements 12 and 1.
The output terminal 16 outputs the midpoint voltage divided by 3.

Here, the magnetoresistive elements 12 and 13 are elements that change their resistance values according to the strength of the magnetic field. For example, those disclosed in Japanese Patent Publication No. 50-21229 are known.

Now, such a differential magnetoresistive circuit 11
However, if, for example, the ferromagnetic substance 17 and the non-magnetic substance 18 as shown in FIG. 3 are placed close to an array in which they are periodically arranged, the magnetoresistive elements 12 and 13 are arranged in accordance with their positions. The surrounding magnetic fields change differently, and accordingly, the resistance values of the magnetoresistive elements 12 and 13 also change differently. Therefore, a change in the relative position of the differential magnetoresistive circuit 11 and the ferromagnetic body 17 and the nonmagnetic body 18 is detected as a change in the midpoint voltage obtained according to the ratio of the resistance values of the magnetoresistive elements 12 and 13. It will be.

However, such a differential magnetoresistive circuit 11
In many cases, the temperature coefficient of resistance of the magnetoresistive elements 12 and 13 has a slight difference due to a slight difference in characteristics of the materials of these elements and a slight difference in the structure of these elements. In such a case, the temperature difference around the differential magnetoresistive circuit 11 may cause a difference in the temperature coefficient of resistance 2
The resistance values of the individual magnetoresistive elements 12 and 13 change at different ratios even though the surrounding magnetic field is unchanged. As a result, the midpoint voltage obtained from the output terminal 16 also changes, which hinders accurate detection of magnetic field changes.

Therefore, the differential magnetic resistance circuit 21 shown in FIG.
In the above, in one magnetic resistance element 22, by connecting in parallel a resistor 27 having a resistance temperature coefficient significantly smaller than those of the magnetic resistance elements 22 and 23 and having an appropriate resistance value, two magnetic resistance elements The temperature drift of the output voltage due to the difference in the characteristics of 22 and 23 is compensated.

[0007]

However, when the temperature compensating resistor 27 is connected in this manner, the output voltage (offset voltage) of the differential magnetoresistive circuit 21 in the initial state in which the magnetic field does not exist is equal to that of the resistor. The offset voltage will change from the set offset voltage when 27 is not connected.

Further, when there are a plurality of differential magnetoresistive circuits 21, the resistance value α of the resistor 27 is set to a different value for each differential magnetoresistive circuit 21. The fluctuations of the offset voltage due to the resistors 27 in the magnetoresistive circuit 21 are not the same, and eventually the output voltage of each differential magnetoresistive circuit 21 under the same condition varies.

The present invention focuses on such problems,
An object of the present invention is to provide a differential magnetoresistive circuit that outputs a preset common output voltage under the same magnetic field in a plurality of differential magnetoresistive circuits that are compensated for temperature drift.

[0010]

According to a first aspect of the present invention, in a differential magnetoresistive circuit in which two magnetoresistive elements are connected in series and a midpoint voltage thereof is used as an output voltage, these magnetoresistive elements are A first resistor having a remarkably small temperature coefficient of resistance is connected in parallel to one of the magnetoresistive elements, and a second resistor having a remarkably small temperature coefficient of resistance as compared with these magnetoresistive elements is connected to the second resistor. One magnetoresistive element is connected in series to each of the magnetoresistive elements, and the magnetoresistive element is
A circuit comprising a child, the first resistor and the second resistor
The temperature coefficient of resistance of the path and the resistance of the other magnetoresistive element.
Make the coercive temperature coefficient approximately equal and supplement the midpoint voltage.
To correct .

According to a second aspect of the present invention, the second resistor is connected in series to the side of the magnetoresistive element in which the first resistor is connected in parallel with respect to the midpoint of the two magnetoresistive elements. The resistance value β of the second resistor is β = {(a ₁ + α) b ₁ − (a ₁ b ₁ + b ₁ α + αa
₁ ) χ} / (a ₁ + α) χ is set. Here, a ₁ is a resistance value of the magnetoresistive element in which the first resistors are connected in parallel at a predetermined temperature t ₁ in a predetermined magnetic field, and b ₁ is a predetermined value in the predetermined magnetic field. the resistance of the other magnetoresistive element at a temperature t _1, alpha is the resistance of the first resistor, KaiV an offset voltage V ₀ with respect to the reference voltage V _{C C} chi is applied to the differential magnetoresistive circuit _{C C} And the value is χ.

In a third aspect of the invention, the second resistor is connected in series on the side opposite to the magnetoresistive element in which the first resistor is connected in parallel with respect to the midpoint of the two magnetoresistive elements. , The resistance value β of this second resistor is β = {(a ₁ + α) b ₁ − (a ₁ b ₁ + b ₁ α + αa
₁ ) χ} / (a ₁ + α) (χ-1)}. Here, a ₁ is a resistance value of the magnetoresistive element in which the first resistors are connected in parallel at a predetermined temperature t ₁ in a predetermined magnetic field, and b ₁ is a predetermined value in the predetermined magnetic field. the resistance of the other magnetoresistive element at a temperature t _1, alpha is the resistance of the first resistor, KaiV an offset voltage V ₀ with respect to the reference voltage V _{C C} chi is applied to the differential magnetoresistive circuit _{C C} And the value is χ.

[0013]

According to the first aspect of the invention, the temperature drift of the output voltage is compensated by the first and second resistors, and at the same time, the difference is produced by the second resistor connected in series to the differential magnetoresistive circuit. The offset voltage of the dynamic magnetic resistance circuit is set arbitrarily, and the output voltage is set to a common arbitrary value for the plurality of differential magnetic resistance circuits.

In the second aspect of the invention, the second resistor connected in series with the side of the magnetoresistive element in which the first resistor of the differential magnetoresistive circuit is connected in parallel with respect to the set offset voltage. Since the resistance value of is properly set, an appropriate preset offset voltage and output voltage common to a plurality of differential magnetoresistive circuits are output.

According to the third aspect of the invention, with respect to the set offset voltage, the second resistive element is connected in series on the opposite side of the magnetoresistive element in which the first resistive element of the differential magnetoresistive circuit is connected in parallel.
Since the resistance value of the resistor is appropriately set, a preset appropriate offset voltage and output voltage common to the plurality of differential magnetoresistive circuits are output.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

[0017] Here, the differential magnetoresistive circuit 1, as in the conventional example, the magnetoresistive element 2 and 3 are connected in series and dividing the reference voltage V _{C C} applied between the terminals 4 and 5 min The midpoint voltage is taken out from the output terminal 6.

The magnetoresistive elements 2 and 3 are elements that change their resistance values depending on the strength of the magnetic field.
It is composed of a semiconductor having a high electron mobility such as nSb (indium antimony).

Further, in the present invention, the first resistor 7 is provided in parallel with the magnetoresistive element 2, and the magnetoresistive element 2,
The second resistor 8 is connected in series with the third resistor 3, respectively. Here, the resistors 7 and 8 are resistors having a resistance temperature coefficient that is so small as to be negligible with respect to the resistance temperature coefficients of the magnetoresistive elements 2 and 3 which are semiconductors. Etc. are used.

Regarding the resistance values of the resistors 7 and 8, the temperature coefficient of resistance of the circuit including the magnetoresistive element 2 and the resistors 7 and 8 is approximately equal to the temperature coefficient of resistance of the magnetoresistive element 3. To be chosen. Specifically, it is as follows.

That is, first, the predetermined temperatures t ₁ and t ₂ appropriately selected according to the usage of the differential magnetoresistive circuit 1.
, The resistance value a of the magnetoresistive element 2 in the same magnetic field is
₁ and a ₂ and the resistance values b ₁ and b ₂ of the magnetoresistive element 3 are measured. Here, the temperature t _1, as the t _2, for example if the differential magnetoresistive circuit 1 was also used in high temperature t ₂ in addition to the normal temperature t _1, these temperatures t _1, t ₂
Is selected.

Next, assuming that the resistance values α and β of the resistors 7 and 8 do not change with respect to the temperature change, the differential magnetoresistive circuit 1 at the temperature t ₁ and the temperature t ₂ in the same magnetic field. The resistance values α and β are determined so that the output voltages of the same are the same. That is, the resistance values α and β are determined such that the midpoint voltage between the parallel circuit including the magnetoresistive element 2 and the resistor 7 and the magnetoresistive element 3 becomes equal at both temperatures.

Where (midpoint voltage at t ₁ ) = V _{C C} b ₁ / {b ₁ + a ₁ α / (a ₁ + α) + β} (1), and (midpoint voltage at t ₂ ). = V _{C C} b ₂ / {b ₂ + a ₂ α / (a ₂ + α) + β} (2) Therefore, by equating the right side of these equations (1) and (2), The resistance values α and β to be obtained are obtained.

Thus, for example, for the temperatures t ₁ and t _{2 at} which the differential magnetoresistive circuit 1 is actually used, the resistor 7,
By properly determining the resistance values α and β of 8, the resistance temperature coefficient of the circuit including the magnetoresistive element 2 and the resistors 7 and 8 and the resistance temperature coefficient of the magnetoresistive element 3 are almost equal to each other in the normal operating temperature range. Since the resistance value between the terminals 4 and 6 and the resistance value between the terminals 5 and 6 change at substantially the same rate, the output voltage fluctuation caused by the resistance fluctuation due to temperature change is canceled out. The fluctuation of the output voltage is suppressed.

On the other hand, if the output voltage (offset voltage) V ₀ in the initial state where no magnetic field exists is χ V _{C C} ,
The offset voltage V ₀ is determined arbitrarily by enumeration and χV _{C C} a right side of the right side or (2) of the above formula (1). That is, b ₁ / {b ₁ + a ₁ α / (a ₁ + α) + β} = χ (3), where the resistance value β of the resistor 8 is β = {(a ₁ + α) b _1- ( a ₁ b ₁ + b ₁ α + αa ₁ ) χ} / (a ₁ + α) χ (4)

In the present embodiment, as shown in FIG. 1, the resistor 8 is a magnetoresistive element in which the resistor 2 is connected in parallel rather than the output terminal 6 at the midpoint of the magnetoresistive elements 2 and 3. Two
Side, that is, connected in series to the terminal 4 side, but conversely, the resistor 8 is provided on the side opposite to the magnetoresistive element 2, that is, on the magnetoresistive element 3 and terminal 5 side with respect to the output terminal 6. Other embodiments in which they are connected in series are also possible. The resistance value β of the resistor 8 in this case is β = {(a ₁ + α) b ₁ − (a ₁ b ₁ + b ₁ α + αa ₁ ) χ} / {(a ₁ + α) (χ−1)} ... ( 5) becomes. As described above, the location where the resistor 8 is connected in series to the differential magnetoresistive circuit 1 can be arbitrarily selected according to the resistance values α, β and χ of the resistors 7 and 8.

In the present invention, the offset voltage V ₀ can thus be set to an arbitrary value common to the plurality of differential magnetoresistive circuits 1. For example, the V ₀ V _{C C}
If it is desired to set / 2, it is sufficient to set χ = 0.5 in the equation (4) or the equation (5), and V ₀ = in all differential magnetoresistive circuits 1 in which β is set in this way. V _{C C} /
It becomes 2.

The resistance values α and β of the resistors 7 and 8 are set separately for each differential magnetoresistive circuit 1, and each differential magnetoresistive circuit 1 is set. On the other hand, appropriate resistance values α and β are set.

Next, the operation will be described.

The differential magnetoresistive circuit 1 of the present invention is, for example,
In the same manner as described in the description of the conventional example, the position of the differential magnetoresistive circuit 1 changes in the environment in which the surrounding magnetic field changes periodically depending on the position. Is detected as a fluctuation of. Here, between the terminals 4 and 5 is given a constant reference voltage V _{C C,}
The output voltage of the differential magnetoresistive circuit 1 is the reference voltage V
The value of the midpoint voltage obtained by dividing _{C C} by the parallel circuit including the magnetoresistive element 2 and the resistor 7, the magnetoresistive element 3 and the resistor 8 is taken out.

At this time, if the magnetic fields around the magnetoresistive elements 2 and 3 change differently due to, for example, changes in the position of the differential magnetoresistive circuit 1, these magnetoresistive elements 2 and 3 are changed.
The resistance value of γ also shows different changes corresponding to different variations of this magnetic field. As a result, these magnetoresistive elements 2, 3
The reference voltage V _{C C} dividing the resulting output voltage varies by, detected as changes in the position of the differential magnetoresistive circuit 1 corresponds to a change in the ambient magnetic field of the differential magnetoresistive circuit 1 To be done.

When the ambient temperature changes during use of the differential magnetoresistive circuit 1, the magnetoresistive elements 2 and 3 change their resistance values according to the temperature coefficient of resistance peculiar to each element. Since the resistance temperature coefficients of the magnetoresistive elements 2 and 3 are not necessarily equal, the resistance values of these magnetoresistive elements 2 and 3 change at different rates.

However, in the present invention, since the resistors 7 and 8 having appropriate values are connected to the magnetoresistive element 2, the change rate of the resistance value of the magnetoresistive element 3 is equal to that of the magnetoresistive element 2. The resistance values of the circuits of the bodies 7 and 8 are approximated to each other, and the resistance values of the magnetoresistive element 3 and this circuit change at almost the same rate with respect to temperature changes. The parts due to will cancel each other out. Therefore, the output voltage output as the ratio of these resistance values does not change depending on the temperature change.

Further, in the present invention, the differential magnetoresistive circuit 1
Since a resistor 8 having an appropriate resistance value β is connected in series with, is selected arbitrarily regardless of the presence of the temperature compensating resistor 7 which differs depending on each differential magnetoresistive circuit 1. An offset voltage V ₀ = χV _{C C} common to the plurality of differential magnetoresistive circuits 1 can be set according to χ.

Further, even when the magnetic field state is detected by the differential magnetoresistive circuit 1, the offset voltage V
_{Since 0} is common, all differential magnetoresistive circuits 1 output a common output voltage in response to similar magnetic field changes. On the other hand, it can be configured to output an appropriate output voltage set in advance.

As described above, the present invention is effective as a means for reducing the temperature drift of the output of the differential magnetoresistive circuit 1, especially when it is used at a high temperature, and at the same time, the offset voltage of the differential magnetoresistive circuit 1 is reduced. It can be set arbitrarily, and the plurality of differential magnetoresistive circuits 1 can be set to output the same output voltage with respect to the same magnetic field change. There is an advantage that the offset voltage need not be adjusted when the circuit 1 is incorporated in various machines.

[0037]

According to the first aspect of the present invention, the temperature drift of the output voltage is compensated by the first and second resistors connected in parallel and in series, and at the same time, it is connected in series to the differential magnetoresistive circuit. With the second resistor, the offset voltage of the differential magnetoresistive circuit can be arbitrarily set, and the output voltage can be set to a common arbitrary value for the plurality of differential magnetoresistive circuits.

In the second invention, the second resistor connected in series to the side of the magnetoresistive element in which the first resistor of the differential magnetoresistive circuit is connected in parallel with respect to the set offset voltage. Since the resistance value of is properly set, a preset proper offset voltage and output voltage common to a plurality of differential magnetoresistive circuits can be output.

According to the third aspect of the invention, with respect to the set offset voltage, the magnetic resistance element in which the first resistor of the differential magnetoresistive circuit is connected in parallel is connected to the second side connected in series on the opposite side.
Since the resistance value of the resistor is appropriately set, a preset appropriate offset voltage and output voltage common to the plurality of differential magnetoresistive circuits are output.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram showing a circuit configuration of a conventional example.

FIG. 3 is an explanatory diagram showing a usage situation of a conventional example.

FIG. 4 is a configuration diagram showing a circuit configuration of another conventional example.

[Explanation of symbols]

1 Differential magnetoresistive circuit 2 Magnetoresistive element 3 Magnetoresistive element 7 resistor 8 resistor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-317637 (JP, A) JP-A-6-207974 (JP, A) Fukuihei 6-2116 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G01R 33/02-33/10 G01D 5/12-5/252 G01B ⁷ /00-7/34

Claims (3)

(57) [Claims] 1. A differential magnetoresistive circuit in which two magnetoresistive elements are connected in series and a midpoint voltage thereof is used as an output voltage.
A first resistor having a remarkably small resistance temperature coefficient as compared with these magnetoresistive elements is connected in parallel to one of the magnetoresistive elements, and a first resistance body having a remarkably small resistance temperature coefficient as compared with these magnetoresistive elements. Two resistors are connected in series to the two magnetoresistive elements, and the
The one magnetoresistive element, the first resistor and the second resistor
The temperature coefficient of resistance of the circuit consisting of
A differential magnetoresistive circuit characterized in that the temperature coefficient of resistance of the magnetoresistive element is made substantially equal and the midpoint voltage is corrected. 2. The second resistor is connected in series to the side of the magnetoresistive element in which the first resistor is connected in parallel with respect to the midpoint of the two magnetoresistive elements, and the second resistor is connected in series. The resistance value β of the resistor is β = {(a ₁ + α) b ₁ − (a ₁ b ₁ + b ₁ α + αa
₁ ) χ} / (a ₁ + α) χ (where a ₁ is the resistance value of the magnetoresistive element in which the first resistor is connected in parallel at a predetermined temperature t ₁ in a predetermined magnetic field, b ₁ Is the resistance value of the other magnetoresistive element at a predetermined temperature t ₁ in a predetermined magnetic field, α is the resistance value of the first resistor, and χ is the reference voltage V _{C C} applied to the differential magnetoresistive circuit. 2. The differential magnetoresistive circuit according to claim 1, wherein the offset voltage V ₀ is set so as to satisfy a value χ) when the offset voltage V ₀ is defined as χV _{C C.} 3. The second resistor is connected in series on the side opposite to the magnetoresistive element in which the first resistor is connected in parallel with respect to the midpoint of the two magnetoresistive elements, and the second resistor is connected in series. The resistance value β of the resistor is β = {(a ₁ + α) b ₁ − (a ₁ b ₁ + b ₁ α + αa
₁ ) χ} / (a ₁ + α) (χ-1)} (where a ₁ is the magnetoresistive element of the _one in which the first resistors are connected in parallel at a predetermined temperature t ₁ in a predetermined magnetic field) A resistance value, b ₁ is a resistance value of the other magnetoresistive element at a predetermined temperature t ₁ in a predetermined magnetic field, α is a resistance value of the second resistor, and χ is a reference voltage applied to the differential magnetoresistive circuit. differential magnetoresistive circuit according to claim 1, characterized in that setting the offset voltage V ₀ with respect to V _{C C} so as to satisfy the values chi) when determined as χV _{C C.}