JP3396092B2 - Magnetic detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic detector using a magnetoresistive element, and more particularly to obtaining a stable output with respect to changes in ambient temperature and changes with time. The present invention relates to a magnetic detection device capable of performing the following. 2. Description of the Related Art At present, a magnetic detector using a magnetoresistive element applies a predetermined DC bias magnetic field from a 45 ° direction to a magnetoresistive element pattern of the magnetoresistive element.
The magnetic quantity and the magnetic polarity are detected based on the magnitude and polarity of the output with reference to the output of the magnetoresistive element at the time of the bias magnetic field. FIG. 5 is a principle diagram showing a magnetic detection operation of a conventional magnetic detection device using a magnetoresistive element. The principle will be described with reference to FIG.
And the output of the magnetoresistive element at that time is V1. When the external magnetic field H2sinωt is applied in the above state, the magnetic field applied to the magnetoresistive element is (H1 + H2sinωt).
And the output of the magnetoresistive element at the time of the magnetic field (H1 + H2) is V
If it is set to 2, the output Vout ′ of the magnetoresistive element is expressed by the following equation. Vout ′ = V1 + (V2−V1) sinωt (1) Therefore, the magnetic detection device is based on the output V1 of the magnetoresistive element in the initial state (0 external magnetic field). , The magnitude and polarity of the external magnetic field can be determined from the second term (V2−V1) sin ωt in Expression (1). FIG. 6 is a diagram showing an example of an amplifier circuit for amplifying the output of a magnetoresistive element of a conventional magnetism detecting device using a magnetoresistive element. Normally, the magnetic field applied from the outside is not limited to an AC magnetic field, but also includes a DC magnetic field (earth magnetism belongs to a DC magnetic field). Therefore, it is necessary for the magnetic detection device to have a DC response, and it is necessary to DC-amplify Vout ′ represented by Expression (1). The output of the magnetoresistive element is usually a very small value, and is normally amplified by a differential amplifier circuit using an IC as shown in FIG. In the example shown in FIG. 6, the output of a magnetoresistive element is amplified by a differential amplifier circuit using an integrated circuit IC1 ', and a variable resistor V
The offset voltage (output when the external magnetic field is 0) of the amplifier circuit is set by R1 'and VR2', and the amplification degree is set by the variable resistor VR3 '. The magnetoresistive elements have resistance temperature characteristics, and as a result, the magnetoresistive element offset output voltage (the magnetoresistive element output voltage when the bias magnetic field is zero). Changes with temperature. In addition, the offset output voltage of the magnetoresistive element also changes due to a change with time. This change is given by the equation (1)
In the above, if the amount of change in the offset output voltage of the magnetoresistive element is ΔV, which contributes to both the outputs V1 and V2 of the magnetoresistive element, the output Vout ′ of the magnetoresistive element is expressed by the following equation. Vout ′ = (V1 + △ V) + ｛(V2 + △ V) − (V1 + △ V)｝ sinωt = (V1 + △ V) + (V2−V1) sinωt (2) As is clear from equation (2), an error occurs in the reference voltage at an external magnetic field of 0 of the magnetic detection device, and the error is amplified due to the configuration of the amplifier circuit (DC response is required). Has the disadvantage that the offset output error appears. Further, the temperature change and the change with time of the magnetoresistive element offset output voltage cannot be corrected because the change polarity can be both positive and negative. According to the present invention, a temperature change of the magnetic detecting device is provided.
It is another object of the present invention to provide a magnetic detection device that is safe against changes in the surrounding environment by removing error factors due to changes with time. According to the present invention, there is provided a magnetoresistive element including four magnetoresistors, a bias coil for applying a predetermined bias magnetic field to the magnetoresistive element, and a magnetoresistive element. A magnetic detection device comprising an amplifier for amplifying an output from an element, wherein two AC rectangular wave voltages having mutually opposite homologous levels are applied to the bias coil. According to the present invention, there is also provided a magnetic detecting device wherein the amplifier is constituted by an amplifier circuit including at least a high-pass filter. Further, the present invention is the magnetic detection device, wherein the amplifier includes two synchronous detection circuits for synchronously detecting an output signal from the amplification circuit at a cycle of the AC voltage. . Further, the present invention is the magnetic detection device, wherein the amplifier includes a function for detecting a difference between output signals of the two synchronous detection circuits. That is,
Akira is a magnetoresistive element composed of four magnetoresistors,
Applying a predetermined bias magnetic field to the magnetoresistive element
Bias coil and the output from the magnetoresistive element.
Amplifier, and the bias coils
A magnet that applies two alternating square-wave voltages at the inverse homology level
Air detector, wherein the amplifier comprises at least a hyper
And an output from the amplification circuit.
Two signals for synchronous detection of the signal at the cycle of the AC voltage
A synchronous detection circuit, and output signals of the two synchronous detection circuits.
And a calculator for calculating the difference
Is a magnetic detection device. The output voltage of the magnetoresistive element is amplified by an amplifier circuit including a high-pass filter, and the amplifier circuit detects two synchronization signals by two synchronous detection circuits to determine a difference between the two synchronization signals. Accordingly, it is possible to relatively easily remove a temperature drift and a change with time of the offset output voltage of the magnetic detection device, and to provide a magnetic detection device that is stable against changes in the surrounding environment. Embodiments of the present invention will be described below with reference to the drawings. The magnetoresistive element used in the magnetic detector of the present invention is connected in series and in a square shape so that four magnetoresistive patterns are orthogonal to each other, and has two bias voltage applying terminals and two output terminals. The bias coil has four terminals, and is configured to apply a predetermined DC bias magnetic field from a 45 ° direction to the pattern of the magnetic resistance. FIG. 1 is a principle diagram showing the magnetic detection operation of the magnetic detection device when the external magnetic field is zero. When two AC rectangular wave voltages at the reverse homology level are applied between the two terminals of the bias coil, an AC rectangular wave bias magnetic field having a positive / negative magnetic field amount H1 is applied to the magnetoresistive element. As shown in FIG. 1, the output voltage characteristic of the magnetoresistive element with respect to the magnetic field is symmetric with respect to the magnetoresistive element output voltage Vout axis.
The same value is obtained as the output voltage of the magnetoresistive element when the positive and negative magnetic fields are the same. Therefore, the AC rectangular wave bias magnetic field is + H1
When the output of the magnetoresistive element is Vout1 and the output of the magnetoresistive element when the AC rectangular wave bias magnetic field is −H1 is Vout2, the output voltage of the magnetoresistive element in FIG. In both cases, an output voltage V1 of the magnetoresistive element corresponding to the bias magnetic field H1 is obtained. Vout1 = V1 (AC rectangular wave bias magnetic field + H1) (3) Vout2 = V1 (AC rectangular wave bias magnetic field-H1) (4) At this time, the magnitude and polarity of the external magnetic field are
It is represented by equation (5). Vout3 = Vout1-Vout2 (5) Therefore, in the case of FIG. 1 (in the case of no external magnetic field)
Vout3 is as follows: Vout3 = 0... (6) Vout3 is as follows: Vout3 = (V1 + ΔV) − (V1 + ΔV) (7) As is clear from equations (6) and (7), Vout3 in the state of no external magnetic field is an output irrelevant to a change in the external environment. FIG. 2 is a principle diagram showing a magnetic detection operation of the magnetic detection device of the present invention when an external magnetic field H2 is applied. When the external magnetic field H2 is applied to the state of FIG. 1, the amount of the magnetic field applied to the magnetoresistive element changes,
The magnetic field applied to the magnetoresistive element when the AC rectangular bias magnetic field is + H is (H1 + H2), and the magnetic field applied to the magnetoresistive element when the AC rectangular bias magnetic field is −H is (−H1 + H2). Assuming that the output voltage of the magnetoresistive element at the time of the magnetic field (H1 + H2) is V2 and the output voltage of the magnetoresistive element at the time of the magnetic field (−H1 + H2) is V3, Vout1 and Vout2 are represented by the following equations. Vout1 = V1 + (V2-V1) (8) Vout2 = V1 + (V3-V1) (9) That is, when the magnetic field is (H1 + H2), and At the time of the magnetic field (-H1 + H2), the output of the magnetoresistive element changes in accordance with the amount of magnetism around V1 (output voltage of the magnetoresistive element when the external magnetic field is 0). Since the magnitude and polarity of the external magnetic field are expressed by the following equation (5), Vout shown in FIG.
3 is as follows: Vout3 = V2−V3 (10) Further, due to a change in the external environment, V2 → V
Vout when changing from 2 + ΔV, V3 → V3 + ΔV
3 is as follows: Vout3 = (V2 + ΔV) − (V3 + ΔV) = V2−V3 (11) As is clear from equations (10) and (11), Vout3 at the time of the external magnetic field H2 is an output irrelevant to a change in the external environment. Therefore, always Vout3
, It is possible to perform magnetic detection without being affected by an external environmental change such as a temperature change or a temporal change. FIG. 3 is a diagram showing an embodiment of a magnetoresistive element output amplifying circuit of a magnetic detection device according to the present invention. The magnetoresistive element output is a differential DC amplifier composed of resistors R1 and R2 and an integrated circuit IC1. The first-stage amplification is performed by a circuit, and a high-pass filter including a capacitor C1 and a resistor R3 connected to an output terminal of the integrated circuit IC1 removes a DC amplification voltage component such as a temperature change or a change with time of the integrated circuit IC1 offset voltage and the magnetoresistive element offset voltage. Removed, adjusting resistor VR3, resistor R
4. A two-stage amplifier circuit for amplifying with an in-phase amplifier circuit composed of an integrated circuit IC2. If the cut-off frequency of the high-pass filter composed of the capacitor C1 and the resistor R3 is set to be considerably smaller than the frequency of the AC rectangular wave bias magnetic field, the amplifier output becomes a rectangular wave output, and the output of the magnetoresistive element can be amplified. Becomes VR1 and VR2 are adjustment resistors for arbitrarily setting the offset voltage of the circuit.
Is an adjusting resistor for arbitrarily setting the amplification degree of the magnetoresistive element output amplifier circuit. FIG. 4 is a block diagram of circuit functions from the magnetoresistive element to the output of the magnetic detector. Two AC rectangular wave voltages (A wave, B wave) applied to the bias coil
90) phase (A)
A wave 90 ° phase modulator 4 and a B wave 270 ° phase modulator 5 that output signals at the time of 270 ° phase (B wave) and 270 ° (B wave). Calculator 8 which performs a synchronous detection with a signal from the modulator by an A-wave 90 ° phase-locked detector 6 and a B-wave 270 ° phase-locked detector 7 to calculate a difference between two synchronous detection output signals.
Through which the output of the magnetic detection device 9 can be obtained. Although the block function of FIG. 4 may be performed only by circuit processing, the number of components can be reduced by combining a microcomputer, and the size can be reduced. As described above, it is possible to relatively easily remove the temperature drift and the change with time of the offset output voltage of the magnetic detection device, and to provide a stable magnetic detection device with respect to a change in the surrounding environment. It became possible to provide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a principle diagram showing a magnetic detection operation when an external magnetic field of a magnetic detection device of the present invention is zero. FIG. 2 is a principle diagram showing a magnetic detection operation of the magnetic detection device of the present invention when an external magnetic field H2 is applied. FIG. 3 is a diagram showing an example of an output voltage amplifying circuit at the output of a magnetoresistive element of the magnetic detection device according to the present invention based on the principle shown in FIGS. FIG. 4 is a block diagram of a circuit function according to the present invention from the magnetoresistive element to the output of the magnetic detector. FIG. 5 is a principle diagram showing a magnetic detection operation of a conventional magnetic detection device using a magnetoresistive element. FIG. 6 is a diagram showing an example of an output amplifier circuit of a magnetoresistive element of a conventional magnetic detection device using a magnetoresistive element. [Description of Signs] 1 (A wave, B wave, two) AC rectangular wave voltage 2 Magnetoresistive element 3 Amplifying circuit 4 (A wave 90 ° phase) modulator 5 (B wave 270 ° phase) modulator 6 (A Wave 90 ° phase) synchronous detector 7 (B wave 270 ° phase) synchronous detector 8 arithmetic unit 9 magnetic detector C1 capacitor H1 (bias) magnetic field (amount) H2 external magnetic field IC1, IC2, IC1 ′ integrated circuits R1, R2 , R3, R4, R1 ', R2', R3 '
Resistance V1, V2, V3 Magnetoresistive element output Vcc Offset voltage VR1, VR2, VR1 ', VR2'VR3' Variable resistance (adjustment resistance)

Claims (1)

(57) [Claim 1] A magneto-resistive element composed of four magneto-resistors, a bias coil for applying a predetermined bias magnetic field to the magneto-resistive element, and a magneto-resistive element. output Ri Do from an amplifier for amplifying the, a magnetic detection device for applying two AC rectangular wave voltage is reversed homologous level with each other in the bias coil, the amplifier is less when
Amplifying circuit including a high-pass filter and the amplifying circuit
These output signals are synchronously detected at the cycle of the AC voltage.
Output of the two synchronous detection circuits;
A magnetic detection device, comprising: a calculator for calculating a difference between force signals .