JP2013200303A - Magnetic sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor device with improved voltage utilization rate.SOLUTION: A magnetic sensor device includes a bias magnet 10 which generates a bias magnetic field of known magnitude in a direction perpendicular to a magnetic field under measurement. A circuit unit 20 outputs a voltage signal, which is proportional to sine of an angle between a direction of a composite magnetic field of the magnetic field under measurement and the bias magnetic field and the direction of the magnetic field under measurement, and amplifies the voltage signal with gain proportional to an inverse of resistance that is proportional to cosine of the angle to output an amplified signal which is proportional to tangent of the angle between the direction of the composite magnetic field of the magnetic field under measurement and the bias magnetic field and the direction of the magnetic field under measurement.

Description

  The present invention relates to a magnetic sensor device that detects the strength of a magnetic field.

  A giant magnetoresistive element (GMR element) can perform detection with relatively high accuracy with respect to the direction of the magnetic field, but has lower detection accuracy than the direction with respect to the strength of the magnetic field. In order to obtain a circuit for detecting the strength of the magnetic field using such a GMR element, a GMR element in which the magnetization direction of the fixed layer is arranged in the direction of the magnetic field to be measured, and a direction orthogonal to the direction of the magnetic field to be measured A magnetic field having a known magnitude (bias magnetic field) is applied to the GMR element having the magnetization direction of the fixed layer arranged in a direction perpendicular to the direction of the magnetic field to be measured.

  Then, the cosine value of the angle θ formed by the direction of the sum of the bias magnetic field and the measurement target magnetic field with respect to the measurement target magnetic field and the sine value are obtained from each GMR element and converted into a digital value at each predetermined sampling timing. Convert. Next, a calculation for dividing the sine value of the digital value obtained here by the cosine value is performed by an arithmetic unit to obtain a tangent value. This tangent value is nothing but the strength of the magnetic field to be measured divided by the strength of the bias magnetic field, so that the strength of the magnetic field to be measured is obtained.

German Patent Application Publication No. 10113131

  However, the division by the arithmetic unit is only obtained at every predetermined sampling timing, and does not become a continuous output value.

  On the other hand, according to the technique disclosed in Patent Document 1, in the circuit shown in FIG. 5, the output of the sensor bridge 4 that outputs a voltage signal proportional to the cosine value of the angle θ formed above and the reference voltage Vref (12). The operational amplifier circuit obtained as described above controls the input voltage V of the sensor bridge 4 (proportional to the reciprocal of the cosine value of the angle θ formed above) so that the output of the sensor bridge 4 becomes equal to the reference voltage. This controlled input voltage V also outputs a voltage signal proportional to the sine value of the angle θ formed above (the sensor bridge 5 (the GMR element included in the sensor bridge 4 is perpendicular to the magnetization direction of the fixed layer). It is also supplied to a sensor bridge including a GMR element.

  Therefore, the output of the sensor bridge 5 outputs a voltage signal obtained by multiplying the input voltage V proportional to the reciprocal of the cosine value of the formed angle θ by the sine value of the formed angle θ. A signal proportional to the tangent of the angle θ is obtained.

  However, the circuit of Patent Document 1 has a problem that the voltage utilization factor is low because the output of the sensor bridge 5 operates in the range of the input voltage V.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a magnetic sensor device capable of improving the voltage utilization rate.

  The present invention for solving the problems of the above-described conventional example is a magnetic sensor device, which includes a bias magnet that generates a bias magnetic field of a known magnitude in a direction orthogonal to the magnetic field to be measured, and the magnetic field to be measured. A voltage signal output means for outputting a voltage signal proportional to a sine of an angle formed by a combined magnetic field with a bias magnetic field with respect to the direction of the magnetic field to be measured, and a combined magnetic field of the magnetic field to be measured and the bias magnetic field is the measurement A resistance means exhibiting a resistance value proportional to the cosine of the angle formed with respect to the direction of the target magnetic field, and a voltage signal output from the voltage signal output means is amplified with a gain proportional to the reciprocal of the resistance value exhibited by the resistance means. And a variable gain amplifier that outputs a signal that is proportional to the tangent of the angle formed with respect to the direction of the magnetic field to be measured. . In another aspect of the present invention, a coil that generates a bias magnetic field of a known magnitude in a direction orthogonal to the measurement target magnetic field, and a combined magnetic field of the measurement target magnetic field and the bias magnetic field are included in the measurement target magnetic field. A voltage signal output means for outputting a voltage signal proportional to the sine of the angle formed with respect to the direction, and a combined magnetic field of the measurement target magnetic field and the bias magnetic field is proportional to the cosine of the angle formed with respect to the direction of the measurement target magnetic field The resistance means exhibiting the resistance value and the voltage signal output from the voltage signal output means are amplified with a gain proportional to the reciprocal of the resistance value exhibited by the resistance means, and the combined magnetic field of the measurement target magnetic field and the bias magnetic field Includes a variable gain amplifier that outputs a signal proportional to the tangent of the angle formed with respect to the direction of the magnetic field to be measured.

  Here, the voltage signal output means may include a giant magnetoresistive element or a Hall element.

  According to the present invention, since the voltage signal output means is not limited in input voltage by the output of the bridge, the range of the power supply voltage can be used effectively and the voltage utilization rate can be improved.

It is a schematic diagram showing the example in the case of utilizing the magnetic sensor apparatus which concerns on embodiment of this invention as a current sensor. It is a schematic diagram showing the example in the case of utilizing the magnetic sensor apparatus which concerns on embodiment of this invention as a magnetic encoder. It is a schematic circuit diagram showing an example of the circuit part of the magnetic sensor apparatus which concerns on embodiment of this invention. It is a schematic circuit diagram showing another example of the circuit part of the magnetic sensor apparatus which concerns on embodiment of this invention. It is a schematic circuit diagram showing another example of the circuit part of the magnetic sensor apparatus which concerns on embodiment of this invention. It is a schematic circuit diagram showing another example of the circuit part of the magnetic sensor apparatus which concerns on embodiment of this invention. It is a schematic circuit diagram showing another example of the circuit part of the magnetic sensor apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the example of the pattern of the circuit part of the magnetic sensor apparatus which concerns on embodiment of this invention. It is a top view showing the example of a pattern of the plane coil as a bias magnetic field application means of the magnetic sensor apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the example of arrangement | positioning of the GMR element group superimposed on the planar coil of the magnetic sensor apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the structural example of the GMR element group superimposed on the planar coil of the magnetic sensor apparatus which concerns on embodiment of this invention.

  Embodiments of the present invention will be described with reference to the drawings. An example of the magnetic sensor device 1 according to the embodiment of the present invention is used as a current sensor as illustrated in FIG. 1 or a magnetic encoder 2 as illustrated in FIG.

In the use as the current sensor shown in FIG. 1, the magnetic sensor device 1 is arranged at a position away from the conducting wire 40 through which the current to be measured flows by a predetermined distance. The direction of the magnetic field (the direction of the magnetic lines applied to the detection unit that detects the magnetic field created by the bias magnet 10 itself) coincides with the direction of the current I flowing through the conductor 40 (the positive direction of the Hx axis). A bias magnet 10 and a circuit unit 20 are disposed. Here, the circuit unit 20 includes a first GMR element group 11 and a first operational amplifier 12 as voltage signal output means, a second GMR element group 13 as a resistance means, and a second operational amplifier which is a variable gain amplifier. 14 and a reference potential supply unit 15. Note that a bypass capacitor or the like for reducing the influence of noise is appropriately inserted and is not shown here (the same applies to the following drawings). For example, the bypass capacitor is inserted between at least one of the power supply potential terminal and the common potential GND terminal. The capacitance of the capacitor in this case may be selected according to the noise level.
In FIG. 3 described later, the detection unit corresponds to the GMR elements 11a and 11b and the GMR elements 13a and 13b. In the example illustrated in FIG. 5, the detection unit corresponds to the GMR elements 11a, 11b, 11c, and 11d and the GMR elements 13a and 13b.

  In addition, the magnetic encoder 2 shown in FIG. 2 uses an annular magnet scale 30 that is magnetized in the rotational direction (circumferential direction) of the rotating body to be measured and whose magnetization direction is periodically changed by π. And on the outer periphery of this magnet scale 30, the two magnetic sensor apparatuses 1 respectively arranged substantially equidistant from this magnet scale 30 are included. Each of the bias magnets 10 of the magnetic sensor device 1 is arranged so that the direction of the magnetic lines of force coincides with the width direction of the magnet scale 30. In the example of the magnetic encoder 2 in FIG. 2, the magnetic lines of force of the bias magnets 10 of the two magnetic sensor devices 1 may be arranged to face in the same direction. In FIG. 2, except for the lead-line arrow attached to the reference numeral, the other arrows indicate the magnet scale magnetization direction or the bias magnet 10 magnetization direction.

  In these examples, as shown in FIG. 3, the first GMR element group 11 includes GMR elements 11a and 11b whose fixed layers are magnetized in the direction of the magnetic field to be measured (Hy direction). Note that the magnetization directions of the fixed layers of the GMR element 11a and the GMR element 11b differ by an angle π. FIG. 3 is a schematic circuit diagram showing an example (an example of a bipolar power supply) of the circuit unit 20 of the magnetic sensor device 1 according to the present embodiment.

  Here, the GMR elements 11a and 11b are connected in series between the positive side + Vc of the power supply potential and the negative side −Vc of the power supply potential. Further, at a point where these GMR elements 11a and 11b are connected to each other (this potential is hereinafter referred to as Vy, and this point is referred to as point Vy), the non-inverting input terminal of the first operational amplifier 12 is connected to the resistor R7. Connected through.

  The second GMR element group 13 includes GMR elements 13a and 13b whose fixed layer is magnetized in a direction orthogonal to the magnetic field to be measured (the direction of the magnetic field by the bias magnet 10). The magnetization directions of the fixed layers of the GMR element 13a and the GMR element 13b are also different by an angle π. Here, one end of the GMR element 13a is connected to the non-inverting input terminal of the first operational amplifier 12 via the resistor R8, and this one end is connected to the common potential GND. The other end is connected to one end of the GMR element 13 b and the inverting input terminal of the second operational amplifier 14. The other end side of the GMR element 13 b is connected to the output terminal of the second operational amplifier 14. The output terminal of the second operational amplifier 14 is connected to the non-inverting input terminal of the second operational amplifier 14 via the resistor R6, and the output potential Vo of the output terminal of the second operational amplifier 14 remains unchanged. The output potential of the circuit unit 20 (that is, the output potential of the current sensor 1 or the magnetic encoder 2) Vo is obtained. A continuous output value can be obtained from the output terminal of the second operational amplifier 14.

  The reference potential supply unit 15 is formed by connecting two resistors R11 and R12 having substantially the same resistance value in series between the positive electrode + Vc and the negative electrode −Vc of the power supply potential. The point where the resistors R11 and R12 are connected to each other is therefore the midpoint potential of the power supply potential. In one example of the present embodiment, this midpoint potential is the reference potential Vref (the midpoint potential is “0” because it is a bipolar power supply).

  In the example of the circuit unit 20, the GMR elements 11 a and 11 b constituting the first GMR element group 11 and the two resistors R 11 and R 12 of the reference potential supply unit 15 are formed from the first operational amplifier 12. A bridge circuit is formed. Therefore, these two resistors R11 and R12 may be formed using a film made of the same material as that of the GMR element. However, it is preferable to use a resistor whose magnetoresistance change rate is sufficiently low or a resistor whose electric resistance does not change. As a result, it is possible to obtain an effect of compensating for the characteristics of the GMR element that changes with temperature.

  The reference potential Vref is connected to the inverting input terminal of the first operational amplifier 12 via the resistor R9. The output terminal of the first operational amplifier 12 is connected to the inverting input terminal of the first operational amplifier 12 via the resistor R10. The potential of the output terminal of the first operational amplifier 12 is hereinafter referred to as Vi. The output terminal of the first operational amplifier 12 is connected to the non-inverting input terminal of the second operational amplifier 14 via a resistor R5. The non-inverting input terminal of the first operational amplifier 12 is also connected to the common potential GND through the resistor R8.

The circuit unit 20 of the magnetic sensor device 1 according to the present embodiment has the above configuration and operates as follows. The resistance values R1 and R2 of the GMR elements 11a and 11b are obtained by using the angle θ between the magnetization direction of any one of the fixed layers and the external magnetic field,
R1 = Rm−r · sin θ,
R2 = Rm + r · sin θ,
It is written. Rm corresponds to the electric resistance value of the GMR element when the fixed layer magnetization direction and the free layer magnetization direction are orthogonal to each other in the GMR element. The sign of sin θ is different between the GMR elements 11a and 11b because the magnetization directions of the fixed layers are different from each other by an angle π.

On the other hand, the resistance value R4 of the GMR element 13a and the resistance value R3 of the GMR element 13b are obtained by using the angle θ between the magnetization direction of any one of the fixed layers and the external magnetic field,
R3 = Rm−r · cos θ,
R4 = Rm + r · cos θ,
It is written. Rm corresponds to the electrical resistance value of the GMR element when the fixed layer magnetization direction and the free layer magnetization direction are orthogonal to each other in the GMR element. The reason why the sign of cos θ differs between the GMR elements 13a and 13b is that the magnetization directions of the fixed layers differ from each other by an angle π.

として、

と表される。一方、参照電位Ｖrefは既に述べたように「０」であるから、第１のオペアンプ１２の非反転入力の電位Ｖ＋と、反転入力の電位Ｖ−とはそれぞれ次の（１），（２）式で表されるものとなる：

The midpoint potential Vy generated by the GMR elements 11a and 11b is a current i

As

It is expressed. On the other hand, since the reference potential Vref is “0” as described above, the non-inverting input potential V + and the inverting input potential V− of the first operational amplifier 12 are the following (1) and (2), respectively. Would be represented by an expression:

と書ける。しかしながらここではＶrefは０であるので、結局Ｖiは、

と書くことができる。 Since these are virtual shorts, V + = V−. Here, Vi is the output potential of the first operational amplifier 12, and when the resistors R7 and R9 have the same resistance value Rj and the resistors R8 and R10 have the same resistance value Rk,

Can be written. However, Vref is 0 here, so Vi is

Can be written.

  As described above, in this embodiment, the power supply potential supplied to the voltage signal output means maintains a constant potential and is not limited by other circuits. Therefore, the width of the output voltage signal is conventionally limited. It is larger than that.

と書かれる。これらはバーチャルショートとなるから、Ｖ＋＝Ｖ−であり、従って、

となる。 On the other hand, the gain of the second operational amplifier 14 is variably controlled by the resistance values of the GMR elements 13 a and 13 b included in the second GMR element group 13. That is, the non-inverting input potential V + and the inverting input potential V− of the second operational amplifier 14 are respectively

It is written. Since these are virtual shorts, V + = V−, and therefore

It becomes.

であり、Ｖiは（３）式で与えられる通りである。ここで抵抗器Ｒ５とＲ６とがともに抵抗値Ｒａの抵抗であるようにすれば、

となるので、（３）式を用いて、第２のオペアンプ１４の出力電位Ｖｏ、すなわち回路部２０の出力電位Ｖｏが、

となって、角θの正接に比例する信号が出力されることとなる。 Where Vo is the output potential of the second operational amplifier 14,

And Vi is as given by equation (3). Here, if both resistors R5 and R6 are resistors having a resistance value Ra,

Therefore, using equation (3), the output potential Vo of the second operational amplifier 14, that is, the output potential Vo of the circuit unit 20 is

Thus, a signal proportional to the tangent of the angle θ is output.

なので、この回路部２０の出力はそのまま、この比に比例する値となっている。 The tangent of this angle θ is nothing but the ratio of the “magnetic field strength Hx” that the bias magnetic field exerts on the detection unit as it is and the “magnetic field strength Hy” that the measurement object exerts on the detection unit. That means

Therefore, the output of the circuit unit 20 is a value proportional to this ratio as it is.

  In the examples so far, the example using the bipolar power supply has been described, but the present embodiment is not limited to this.

  FIG. 4 is a schematic circuit diagram illustrating a configuration example of the circuit unit 20 using a single power source. As illustrated in FIG. 4, an example of the circuit unit 20 with a single power supply includes a first GMR element group 11 and a first operational amplifier 12 as voltage signal output means, and a second GMR element group as resistance means. 13, a second operational amplifier 14 that is a variable gain amplifier, and a reference potential supply unit 15 ′. In addition, the same code | symbol is attached | subjected about what becomes the same structure as the case of the bipolar power supply demonstrated previously, and detailed description is abbreviate | omitted.

  In this example, the GMR element 11a and the GMR element 11b of the first GMR element group 11 are connected in series between the power supply potential + Vc and the common potential GND. A connection point (middle point) between the GMR element 11 a and the GMR element 11 b is connected to a non-inverting input terminal of the first operational amplifier 12. The output terminal of the first operational amplifier 12 is connected to the inverting input terminal of the first operational amplifier 12 through the resistor R8, and is connected to the non-inverting input terminal of the second operational amplifier 14 through the resistor R5. Is done.

  An inverting input terminal of the second operational amplifier 14 is connected to a connection point (middle point) between the GMR element 13 a and the GMR element 13 b in the second GMR element group 13. Further, the terminal on the side different from the connection point of the GMR element 13a is connected to the output terminal of the reference potential supply unit 15 ', and is connected to the inverting input terminal of the first operational amplifier 12 through the resistor R7. Yes.

  The output terminal of the second operational amplifier 14 is connected to the output terminal of the circuit unit 20 as it is, and is connected to the non-inverting input terminal of the second operational amplifier 14 via the resistor R6. Further, the output terminal of the second operational amplifier 14 is also connected to a terminal on the side different from the connection point of the GMR element 13 b of the second GMR element group 13.

  The reference potential supply unit 15 ′ includes two resistors R 9 and R 10 (that is, R 9 = R 10) having substantially the same resistance value, and a third operational amplifier 16. The resistors R9 and R10 are connected in series between the power supply potential + Vc and the common potential GND. A non-inverting input terminal of the third operational amplifier 16 is connected to a point connecting these resistors R9 and R10. Further, the output terminal of the third operational amplifier 16 serves as the output terminal of the reference potential supply unit 15 ′ and is also connected to the inverting input terminal of the third operational amplifier 16.

Also in this example, the resistance values R1 and R2 of the GMR elements 11a and 11b are obtained by using the angle θ between the magnetization direction of any one of the fixed layers and the external magnetic field,
R1 = Rm−r · sin θ,
R2 = Rm + r · sin θ,
It is written. The reason why the sign of sin θ differs between the GMR elements 11a and 11b is that the magnetization directions of the fixed layers differ from each other by an angle π.

Further, the resistance value R4 of the GMR element 13a and the resistance value R3 of the GMR element 13b are obtained by using the angle θ formed by the magnetization direction of any one of the fixed layers and the external magnetic field,
R3 = Rm−r · cos θ,
R4 = Rm + r · cos θ,
It is written. The reason why the sign of cos θ differs between the GMR elements 13a and 13b is that the magnetization directions of the fixed layers differ from each other by an angle π. Here, R5 = R6, R9 = R10, R7 = R9 = Rj, and R8 = R10 = Rk.

となる。この（４）式によると、単電源の場合の出力電位は、Ｖｃ／２だけオフセットしているが、角θの正接に比例する項が含まれるので、その出力から、測定対象が検出部に印加する「磁場の強さ」が求められる。つまり、電流センサ１として用いるのであれば、検知の対象である電流量がここで求めた「磁場の強さ」に比例するので、適宜比例定数を定めて（例えば実験による）、電流量を得ることができる。この「磁場の強さ」は、単位をエルステッド(Ｏe)或いはアンペア毎メートル(Ａ／ｍ)とするものである。 In this example, as a result of calculation, the potential Vo of the output terminal of the circuit unit 20 is

It becomes. According to this equation (4), the output potential in the case of a single power supply is offset by Vc / 2, but includes a term proportional to the tangent of the angle θ. “Magnetic field strength” to be applied is required. That is, if the current sensor 1 is used, the amount of current to be detected is proportional to the “magnetic field strength” obtained here, so that a proportional constant is appropriately determined (for example, by experiment) to obtain the amount of current. be able to. This "magnetic field strength" is in units of Oersted (Oe) or ampere per meter (A / m).

  If it is used as the magnetic encoder 2, “magnetic field strength” proportional to the magnetic flux density distribution in the rotational direction of the magnet scale 30 can be detected at two different locations from the configuration of FIG. 2. The amount of rotation of the magnetic scale 30 can be obtained by observing the change of the “magnetic field strength” (a widely known method can be adopted as a specific method for this purpose, so a detailed description thereof is omitted here). .

  Furthermore, in another example of the present invention, the first GMR element group has a full bridge configuration, and the voltage signal output means is realized by using the first GMR element group and an instrumentation amplifier. is there. As shown in FIG. 5, the configuration example of the circuit unit 20 according to this example includes a first GMR element group 11 ′ and instrumentation amplifier 17 as voltage signal output means, and a second GMR as resistance means. It includes an element group 13, an operational amplifier 14 'that is a variable gain amplifier, and a reference potential supply unit 15'. In addition, the same code | symbol is attached | subjected about what becomes the same structure as the thing in the circuit part 20 demonstrated previously, and detailed description is abbreviate | omitted.

  The first GMR element group 11 'in this example includes four GMR elements 11 including GMR elements 11a to 11d. Here, GMR elements 11a and 11b are connected in series between power supply potential + Vc and common potential GND. The GMR elements 11c and 11d are further connected in series between the power supply potential + Vc and the common potential GND. The GMR element 11a connected to the power supply potential Vc side and the GMR element 11d connected to the common potential GND side are arranged in one direction parallel to the direction (Hy direction) of the magnetic field applied to the detection unit by the measurement object. The fixed layer is magnetized. The GMR element 11c connected to the power supply potential + Vc side and the GMR element 11b connected to the common potential GND side are different from the GMR elements 11a and 11d by an angle π (the other direction parallel to Hy). The fixed layer is magnetized. The GMR elements 11a and 11d are R1, and the GMR elements 11b and 11c are R2.

  The instrumentation amplifier 17 includes three operational amplifiers 17a to 17c and resistors R7 to R13. Since the instrumentation amplifier 17 is widely known, explanation of its operation and the like is omitted, but the reference potential terminal Vx side is connected to the output terminal of the reference potential supply unit 15 ′ via the resistor R11. Is connected to the output terminal out of the instrumentation amplifier 17 via the resistor R5.

  The second GMR element group 13 includes GMR elements 13a and 13b in which the fixed layer is magnetized in a direction orthogonal to the magnetic field applied to the detection unit by the measurement target (the direction of the magnetic field by the bias magnet 10). The magnetization directions of the fixed layers of the GMR element 13a and the GMR element 13b are also different by an angle π. Here, one end of the GMR element 13a is connected to the output terminal of the reference potential supply unit 15 '. The other end side of the GMR element 13a is connected to one end side of the GMR element 13b. Further, the other end of the GMR element 13b is connected to the output terminal of the operational amplifier 14 '. The inverting input terminal of the operational amplifier 14 'is connected to these connection points (connection point between the other end side of the GMR element 13a and one end side of the GMR element 13b, that is, a midpoint).

  Furthermore, the output terminal of the operational amplifier 14 'is connected to the output terminal of the circuit unit 20, and is also connected to the non-inverting input terminal of the operational amplifier 14' via the resistor R6.

となる。
なお図５のＧＭＲ素子１１ｃ、１１ｄを、図３記載のＲ１１、Ｒ１２のような固定の抵抗器で置き換える場合、回路部２０の出力電位Ｖｏは（５）式の分子の「２ｎ」を「ｎ」に変更したものとなる。 In this circuit unit 20, the resistance values of the resistors R14 and R15, the resistance values of the resistors R5 and R6, the resistance values of the resistors R10 and R12, and the resistance values of the resistors R11 and R13 are substantially equal to each other. To be equal to In the following description, the resistance values of the resistors R10 and R12 are denoted as Rj, and the resistance values of the resistors R11 and R13 are denoted as Rk. When the resistance values of the resistors R7 and R9 are substantially equal to each other and the value is written as n × R8 (n is a natural number) using the resistance value R8 of the resistor R8, the output of the circuit unit 20 The potential Vo is

It becomes.
When the GMR elements 11c and 11d in FIG. 5 are replaced with fixed resistors such as R11 and R12 shown in FIG. 3, the output potential Vo of the circuit unit 20 is “n” in the numerator of equation (5). It will be changed to.

  That is, the output of the circuit unit 20 is also offset by Vc / 2, but a term proportional to the tangent of the angle θ is included, and therefore, the strength of the magnetic field applied to the detection unit by the measurement object is determined from the output. H is required.

となる。
なお図６の回路部では、Ｒ５＝Ｒ６、Ｒ１４＝Ｒ１５、Ｒ７＝Ｒ１０、Ｒ８＝Ｒ９とする。 Note that the instrumentation amplifier is not limited to that illustrated in FIG. 5, but may be a simple instrumentation amplifier 17 ′ as illustrated in FIG. 6, for example. FIG. 6 is a schematic circuit diagram illustrating an example of the circuit unit 20 employing a simple instrumentation amplifier. In the example of FIG. 6, the terminals Vx and out correspond to the terminals Vx and out of the instrumentation amplifier 17 of FIG. In the circuit unit 20 employing the instrumentation amplifier 17 'according to the example of FIG.

It becomes.
In the circuit portion of FIG. 6, R5 = R6, R14 = R15, R7 = R10, and R8 = R9.

  Further, in the above description, the voltage signal output means includes the first GMR element group 11 and an amplifier different from the final stage variable gain amplifier, but the present embodiment is not limited to this. . FIG. 7 shows an example of the circuit unit 20 in which the voltage signal output means is replaced with a simpler one in the example of the single power source illustrated in FIG.

  The circuit unit 20 illustrated in FIG. 7 includes a first GMR element group 11 as a voltage signal output unit, a second GMR element group 13 ″ as a resistance unit, an operational amplifier 14 ″ as a variable gain amplifier, and a reference potential. And a supply unit 15. In this case as well, the same components as those already described are denoted by the same reference numerals and detailed description thereof is omitted.

  In the example of FIG. 7, the first GMR element group 11 includes GMR elements 11 a and 11 b in which the fixed layer is magnetized in the direction of the magnetic field (Hy direction) applied to the detection unit by the measurement target. Note that the magnetization directions of the fixed layers of the GMR element 11a and the GMR element 11b differ by an angle π.

  Here, the GMR elements 11a and 11b are connected in series between the positive side + Vc of the power supply potential and the common potential GND. Further, a non-inverting input terminal of the operational amplifier 14 ″ is connected to a point (potential Vy) connecting these GMR elements 11a and 11b via a resistor R5.

  Further, the second GMR element group 13 ″ includes GMR elements 13 ″ a and 13 ′ whose fixed layers are magnetized in a direction orthogonal to the magnetic field applied to the detection unit by the measurement target (the direction of the magnetic field by the bias magnet 10). ″ B is included. The magnetization directions of the fixed layers of the GMR element 13 ″ a and the GMR element 13 ″ b are also different by an angle π. Here, one end side of the GMR element 13 ″ a is connected to the reference potential supply unit 15. Connected to the output terminal. The other end is connected to one end of the GMR element 13 ″ b and the inverting input terminal of the operational amplifier 14 ″. The other end of the GMR element 13 ″ b is connected to the output terminal of the operational amplifier 14 ″ via a resistor R9. The output terminal of the operational amplifier 14 ″ is connected to the non-inverting input terminal of the operational amplifier 14 ″ via a resistor R6. The output potential Vo of the output terminal of the operational amplifier 14 ″ becomes the output potential Vo of the circuit unit 20.

  The reference potential supply unit 15 is formed by connecting resistors R7 and R8 in series between the positive side + Vc of the power supply potential and the common potential GND. A connection point (middle point) between the resistors R7 and R8 serves as an output terminal of the reference potential supply unit 15. It is assumed that the resistance values of the resistors R7 and R8 are substantially equal to each other, and this resistance value is substantially equal to 2 × R9 using the resistance value R9 of the resistor R9. These two resistors R7 and R8 may also be formed using a film made of the same material as the GMR element. However, it is preferable to use a resistor whose magnetoresistance change rate is sufficiently low or a resistor whose electric resistance does not change. As a result, it is possible to obtain an effect of compensating for the characteristics of the GMR element that changes with temperature. This resistor R9 is added in order to balance this component in consideration of the fact that a half of the resistance component of the resistor R7 is evaluated together with Rm on the input side of the operational amplifier 14 ″.

となる。この回路部２０によっても、その出力はＶｃ／２だけオフセットしているが、角θの正接に比例する項が含まれるので、その出力から、測定対象が検出部に印加する磁場の強さが求められる。 Here, Rm is the electric resistance value of each GMR element 11a, 11b, 13 ″ a and 13 ″ b when the fixed layer magnetization direction and the free layer magnetization direction are orthogonal in the GMR element. It is equivalent. At this time, it is assumed that the resistance values of the resistors R5 and R6 are substantially equal and these values are sufficiently larger than Rm. That is, it is assumed that R5 = R6 >> Rm. Then, the output potential Vo of the circuit unit 20 is

It becomes. Although the output of the circuit unit 20 is also offset by Vc / 2, since a term proportional to the tangent of the angle θ is included, the strength of the magnetic field applied to the detection unit by the measurement object is determined from the output. Desired.

  FIG. 8A shows a substrate on which a GMR element is arranged when the first GMR element group which is a voltage signal output means forms a half bridge (including a case where a resistor and a GMR element form a full bridge). It is the schematic which showed the example of the pattern of (sensor substrate). In FIG. 8A, the magnetization direction of the fixed layer of each GMR element is indicated by an arrow on the GMR element. In addition, the magnetic field direction Hy applied to the sensor substrate by the measurement target and the magnetic field direction (not shown in FIG. 8) applied to the sensor substrate by the bias magnet 10 (not shown in FIG. 8) orthogonal to the magnetic field direction Hy in the plane of the sensor substrate. Hx axis direction) is also indicated by arrows.

  As illustrated in FIG. 8A, the fixed layers of the GMR elements 11a and 11b included in the first GMR element group 11 are magnetized in parallel with the direction Hy of the magnetic field to be measured. The magnetization directions of the fixed layers differ from each other by an angle π. On the other hand, the fixed layers of the GMR elements 13a and 13b included in the second GMR element group 13 are magnetized in parallel to the direction Hx of the magnetic field generated by the bias magnet 10, and the magnetization direction of the fixed layer of each element is They differ from each other by an angle π. Terminals on both ends of each GMR element 11a, 11b, 13a, 13b are drawn out and connected to other circuit elements of the circuit unit 20. The circuit element may be disposed on another substrate or may be disposed on the sensor substrate.

  FIG. 8B is a schematic diagram showing an example of the pattern of the substrate (sensor substrate) on which the GMR elements are arranged when the first GMR element group as the voltage signal output means constitutes a full bridge.

  As illustrated in FIG. 8B, the fixed layers of the GMR elements 11 ′ to 11 ′ d included in the first GMR element group 11 ′ are magnetic fields applied to the sensor substrate (detection unit thereof) by the measurement target. The magnetization directions of the pinned layers of the GMR elements 11′a and 11′b are different from each other by an angle π, and the magnetization directions of the pinned layers of the GMR elements 11′a and 11′d are magnetized in parallel. Are the same, and the magnetization directions of the fixed layers of the GMR elements 11'c and 11'd differ from each other by an angle π. On the other hand, the fixed layers of the GMR elements 13a and 13b included in the second GMR element group 13 are magnetized in parallel to the direction Hx of the magnetic field generated by the bias magnet 10, and the magnetization direction of the fixed layer of each element is They differ from each other by an angle π. Terminals on both ends of each GMR element 11′a to 11′d, 13a, 13b are drawn out to the outside and connected to other circuit elements of the circuit unit 20. The circuit element may be disposed on another substrate or may be disposed on the sensor substrate.

  Furthermore, in the examples so far, the first GMR element group 11 may be replaced with a Hall element. In the case of replacing with a Hall element, the power supply potential + Vc is connected to the input terminal In +, and In− is connected to −Vc or the common potential GND. Furthermore, since the output terminals Out + and Out− are respectively differential outputs, they may be connected to, for example, the non-inverting input terminal and the inverting input terminal of the first operational amplifier 12 respectively.

  As described above, according to the present embodiment, the bias magnet 10 that generates a bias magnetic field of a known magnitude is arranged in a direction orthogonal to the measurement target magnetic field. The GMR element group 11 outputs a voltage signal proportional to the sine (sin θ) of the angle θ formed by the combined magnetic field of the bias magnetic field and the magnetic field to be measured with respect to the direction of the magnetic field to be measured. This voltage signal may be amplified as appropriate.

  On the other hand, the GMR element 11 includes the GMR element 13 in which the fixed layer is magnetized in a direction rotated by π / 2 with respect to the magnetization direction of the fixed layer of the GMR element 11 included in the GMR element group 11. Using the two GMR element groups 13, a resistance having a resistance value proportional to the cosine (cos θ) of the angle θ formed by the combined magnetic field of the measurement target magnetic field and the bias magnetic field with respect to the direction of the measurement target magnetic field is obtained.

  Then, using a variable gain amplifier, the voltage signal (proportional to sin θ) by the first GMR element group 11 as voltage signal output means is converted into the reciprocal (1 / cos θ) of the resistance value by the second GMR element group 13. Amplification is performed with a proportional gain to output a signal proportional to the tangent (sin θ / cos θ) of the angle θ formed by the combined magnetic field of the measurement target magnetic field and the bias magnetic field with respect to the direction of the measurement target magnetic field.

  Similarly, when a Hall element is used in place of the first GMR element group (11a, 11b, etc. in FIG. 4), the magnetic sensing direction of the Hall element and the GMR elements 13 included in the second GMR element group 13 are also the same. The magnetization direction of the fixed layer may be different from the magnetization direction by π / 2.

  In the above description, the bias magnet 10 of the magnetic sensor device 1 is a permanent magnet. However, the present embodiment is not limited to this. In the magnetic sensor device 1 according to the example of the present embodiment, at least the first GMR element group 11 (or GMR element group 11 ′) as the voltage signal output means and the second GMR element group 13 as the resistance means. Is formed on the sensor substrate as illustrated in FIGS. 8A and 8B, for example.

  In this example, a thin planar coil 50 is arranged in a plane parallel to the surface of the sensor substrate illustrated in FIG. 8, and current is supplied to the planar coil 50 so that the planar coil 50 has a known size. It functions as a bias magnetic field applying means for generating a bias magnetic field.

  FIG. 9 is a plan view according to an example of the planar coil 50. As illustrated in FIG. 9, the planar coil 50 functioning as a bias magnetic field applying unit has a conductive wire parallel to the direction of the current I (Hx direction) flowing through the conductive wire 40 and a direction parallel to the surface of the sensor substrate. Conductive wires parallel to a direction (Hy direction) orthogonal to Hx are alternately connected to form a spiral shape. In the present embodiment, the portion of the conductive wire parallel to the Hy direction in the planar coil 50 is disposed above the sensor substrate with a predetermined distance (for example, 1 to 5 μm). Such an arrangement can be realized by a thin film process.

  In an example of this embodiment, a power source + Vc is connected to the inner peripheral end of the planar coil 50, and the outer peripheral end is connected to a common potential (GND). That is, the current Ib flows through the planar coil 50 from the inner circumference side to the outer circumference side. Thereby, in the part of the conducting wire parallel to the Hy direction in the planar coil 50, the magnetic field in the Hx direction (direction of the current I to be measured) or the direction opposite to the current I to be measured (the negative direction of the Hx axis) is generated. It is formed. In the example of FIG. 9, if a portion P represented by a broken line is a portion to be superimposed on the sensor substrate, a magnetic field in a direction opposite to the current I to be measured (negative direction of the Hx axis) is present at the lower portion of this portion. Is formed.

  Therefore, in this example of the present embodiment, for example, a circuit similar to that shown in FIG. 3 is used. That is, the GMR elements 11a and 11b are connected in series between the positive side + Vc of the power supply potential and the negative side −Vc of the power supply potential. Further, at a point where these GMR elements 11a and 11b are connected to each other (this potential is hereinafter referred to as Vy, and this point is referred to as point Vy), the non-inverting input terminal of the first operational amplifier 12 is connected to the resistor R7. Connected through.

  The second GMR element group 13 has a fixed layer that is parallel or antiparallel to a direction orthogonal to the magnetic field to be measured (the direction of the magnetic field formed by the planar coil 50 at a location where the circuit unit 20 is located). It includes magnetized GMR elements 13a and 13b. The magnetization directions of the fixed layers of the GMR element 13a and the GMR element 13b are also different by an angle π. Here, one end side of the GMR element 13b is connected to the common potential GND. The other end is connected to one end of the GMR element 13 a and the inverting input terminal of the second operational amplifier 14. The other end side of the GMR element 13 a is connected to the output terminal of the second operational amplifier 14. The output terminal of the second operational amplifier 14 is connected to the non-inverting input terminal of the second operational amplifier 14 via the resistor R6, and the output potential Vo of the output terminal of the second operational amplifier 14 remains unchanged. The output potential of the circuit unit 20 (that is, the output potential of the current sensor 1 or the magnetic encoder 2) Vo is obtained.

  The reference potential supply unit 15 is formed by connecting two resistors R11 and R12 having substantially the same resistance value in series between the positive electrode + Vc and the negative electrode −Vc of the power supply potential. The point where the resistors R11 and R12 are connected to each other is therefore the midpoint potential of the power supply potential. In one example of the present embodiment, this midpoint potential is the reference potential Vref (the midpoint potential is “0” because it is a bipolar power supply).

  In the example of the circuit unit 20, the GMR elements 11 a and 11 b constituting the first GMR element group 11 and the two resistors R 11 and R 12 of the reference potential supply unit 15 are formed from the first operational amplifier 12. A bridge circuit is formed. Therefore, these two resistors R11 and R12 may be formed using a film made of the same material as that of the GMR element. However, it is preferable to use a resistor whose magnetoresistance change rate is sufficiently low or a resistor whose electric resistance does not change. As a result, it is possible to obtain an effect of compensating for the characteristics of the GMR element that changes with temperature.

The reference potential Vref is connected to the inverting input terminal of the first operational amplifier 12 via the resistor R9. The output terminal of the first operational amplifier 12 is connected to the inverting input terminal of the first operational amplifier 12 via the resistor R10. The potential of the output terminal of the first operational amplifier 12 is hereinafter referred to as Vi. The output terminal of the first operational amplifier 12 is connected to the inverting input terminal of the second operational amplifier 14 via a resistor R5. The non-inverting input terminal of the first operational amplifier 12 is also connected to the common potential GND through the resistor R8.
Also in this example of the present embodiment, the planar coil 50 functions as a bias magnetic field applying unit and operates in the same manner as the example using a permanent magnet. In this example, the planar coil can be formed by a thin film process.

  Further, each GMR element included in the GMR element group 11 (or GMR element group 11 ′) is disposed in a substantially constant bias magnetic field in the Hx-axis direction, and each GMR element included in the GMR element group 13 is also included in the GMR element group 13. The GMR elements need only be arranged in a substantially constant bias magnetic field in the Hx-axis direction, and the direction of the bias magnetic field at the place where each of the GMR element group 11 and the GMR element group 13 is arranged. May be in opposite directions (one is the positive direction of the Hx axis and the other is the negative direction of the Hx axis).

  Therefore, in the conductor pattern of the planar coil 50 illustrated in FIG. 10, the current is negative in the Hy axis direction (opposite to the Hy axis arrow) in the range (P, Q) in which the conductors are arranged in parallel to the Hy axis direction. The GMR element group 11 (or GMR element group 11 ') is arranged at a position overlapping the side (range P) toward the direction of (), and the current is directed in the positive direction of the Hy axis (the direction of the arrow on the Hy axis). The GMR element group 13 may be arranged at a position overlapping the side (range Q). For the sake of explanation, FIG. 10 also shows a GMR element group that passes through the conductive wire pattern of the planar coil 50 and is positioned below the conductive wire pattern. Even in the case illustrated in FIG. 10, the circuit unit 20 can use the same one as already described, but the GMR element 13 a has a pinned layer magnetized in the negative direction of the Hx axis, In the GMR element 13b, the fixed layer is magnetized in the positive direction of the Hx axis. With this arrangement, the size of the planar coil 50 can be made equal to the size of the pattern of the circuit unit 20.

  In this case, as illustrated in FIGS. 11A and 11B, the GMR element groups 11, 11 ′, and 13 include a pair of linear GMR elements in which the magnetization directions of the fixed layers are different from each other by an angle π. They are arranged in parallel, and one end is connected to each other with a conducting wire, and the pad is drawn out. Further, a pad is connected to the other end side of each GMR element, and the GMR element groups 11, 11 'and 13 are formed in a substantially square shape. The magnetization direction of the fixed layer may be the direction of the current flowing through the GMR element, or may be the direction orthogonal to the direction of the current. Further, the GMR element groups 11, 11 ′, 13 according to another example include a GMR element in which the fixed layer is magnetized in the direction of the current flowing through the GMR element, and a GMR in which the fixed layer is magnetized in the direction orthogonal to the direction of the current. An element may be used to form a substantially L shape as illustrated in FIG. In these drawings, the arrow superimposed on the GMR element represents the magnetization direction of the fixed layer.

  As an example of the measurement result by the magnetic sensor device 1 of the present embodiment including the circuit unit 20 shown in FIG. 3, the applied magnetic field as a measurement target from the outside is about −4000 A / m (−50 Oe) to +4000 A / m. The output potential Vo of the circuit unit 20 was measured while changing it to (50 Oe).

  As a result, the output potential Vo changed in proportion to the strength of the magnetic field to be measured in a range from about −2500 A / m (−30 Oe) to +2500 A / m (30 Oe). Thus, it has been found that the output potential Vo can output a signal proportional to the strength of the magnetic field to be measured within a range where the output of the operational amplifier is not saturated.

DESCRIPTION OF SYMBOLS 1 Magnetic sensor apparatus, 2 Magnetic encoder, 10 Bias magnet, 11, 11 '1st GMR element group, 12 1st operational amplifier, 13, 13 "2nd GMR element group, 14 2nd operational amplifier, 14' , 14 "operational amplifier, 15, 15 'reference potential supply section, 16 third operational amplifier, 17, 17' instrumentation amplifier, 20 circuit section, 30 magnet scale, 40 conductor, 50 planar coil.

Claims (4)

A bias magnet that generates a bias magnetic field of a known magnitude in a direction perpendicular to the magnetic field to be measured;
A voltage signal output means for outputting a voltage signal proportional to the sine of an angle formed by the combined magnetic field of the measurement target magnetic field and the bias magnetic field with respect to the direction of the measurement target magnetic field;
A resistance means that exhibits a resistance value proportional to a cosine of an angle formed by the combined magnetic field of the measurement target magnetic field and the bias magnetic field with respect to the direction of the measurement target magnetic field;
The voltage signal output from the voltage signal output means is amplified with a gain proportional to the reciprocal of the resistance value exhibited by the resistance means, and the combined magnetic field of the measurement target magnetic field and the bias magnetic field is in the direction of the measurement target magnetic field. A variable gain amplifier that outputs a signal proportional to the tangent of the angle to the
A magnetic sensor device. The magnetic sensor device according to claim 1,
A magnetic sensor device in which the voltage signal output means includes a giant magnetoresistive element or a Hall element. A coil that generates a bias magnetic field of a known magnitude in a direction orthogonal to the magnetic field to be measured;
A voltage signal output means for outputting a voltage signal proportional to the sine of an angle formed by the combined magnetic field of the measurement target magnetic field and the bias magnetic field with respect to the direction of the measurement target magnetic field;
A resistance means that exhibits a resistance value proportional to a cosine of an angle formed by the combined magnetic field of the measurement target magnetic field and the bias magnetic field with respect to the direction of the measurement target magnetic field;
The voltage signal output from the voltage signal output means is amplified with a gain proportional to the reciprocal of the resistance value exhibited by the resistance means, and the combined magnetic field of the measurement target magnetic field and the bias magnetic field is in the direction of the measurement target magnetic field. A variable gain amplifier that outputs a signal proportional to the tangent of the angle to the
A magnetic sensor device. The magnetic sensor device according to claim 3,
At least the voltage signal output means and the resistance means are formed on the sensor substrate,
The coil is arranged in a plane parallel to the surface of the sensor substrate, and supplies a current to the coil to generate a bias magnetic field of the known magnitude.

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