JP2000337920A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor with new constitution capable of adjusting the offset of a sensor output which is caused by assembling deviation. SOLUTION: Magnetic resistance elements 3, 4 are arranged on a substrate 2. A bias magnet 9 is arranged behind the substrate 2. The elements 3, 4 are positioned in a bias magnetic field of the magnet 9. The change of direction of the bias magnetic field which is caused by the motion of an object to be detected is detected with the elements 3, 4. Electrodes 20 to 23, 30 to 33 for correction are arranged independently of electrodes 5, 6, 7, 8 for obtaining a sensing signal to the elements 3, 4 on the substrate 2. Currents are supplied to the elements 3, 4 through the electrodes 20 to 23, 30 to 33. By current components formed by the currents, components of the currents flowing in the elements, 3, 4 through the electrodes 5, 6, 7, 8 for obtaining the sensing signal are corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor magnetic sensor, and more particularly to a magnetic sensor using a magnetoresistive element, and more particularly to a technique for adjusting an offset of a sensor output.

[0002]

2. Description of the Related Art Hitherto, a gear proximity type rotation sensor using a magnetoresistive element has been known (Japanese Patent Laid-Open No. 3-1959).
No. 70 gazette). This sensor, as shown in FIG.
Magnetoresistive elements 51 and 52 are deposited on a substrate 50, and the substrate 50 is vertically mounted on a magnetized surface 53 a of a bias magnet 53. This substrate 50 is made of a magnetic material
4, and generates a bias magnetic field from the bias magnet 53 toward the gear 54. Then, a change in the bias magnetic field (a change in the direction of the magnetic vector B) with the rotation of the gear 54 is detected as a resistance change. That is, each time one tooth 55 of the gear 54 passes in front of the substrate 50, the direction of the magnetic vector B changes, and the magnetic vector B is extracted as an electric signal.

However, originally, the teeth 55 of the gear 54 (the peaks /
As the direction of the magnetic vector B changes due to (valley), the voltage at the midpoint α of the elements 51 and 52 changes,
Is used to obtain a binarized signal by comparison with the reference voltage Vref. However, an error may occur in the relative positional relationship between the elements 51 and 52 and the bias magnet 53 (when the binary signal is attached to the substrate 50 or the bias magnet 53). If the bias magnet 53 has a magnetizing variation, an offset occurs in the potential at the midpoint α, and the signal waveform SG1 in FIG. 12 should be originally obtained as the signal waveform SG2 in FIG. It may not be possible to quantify.

For this reason, as a countermeasure against offset of the output of the magnetoresistive element caused by a magnet assembly displacement or a magnet magnetization variation, complicated circuits such as an automatic midpoint correction circuit using CMOS and a peak / bottom hold circuit are used. The scheme was used to allow for offset.

However, this method requires a CMOS chip for a processing circuit in addition to the bipolar chip.
There is a problem that miniaturization is difficult.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic sensor capable of adjusting an offset of a sensor output due to a displacement or the like with a novel structure.

[0007]

According to the first aspect of the present invention, a correction electrode is disposed separately from an electrode for obtaining a sensing signal for a magnetoresistive element on a substrate, and a magnetic field is passed through the correction electrode. A current is caused to flow through the resistance element, and a current component formed by this is used to correct a current component flowing through the electrode for obtaining the sensing signal to the magnetoresistance element.

According to this structure, a current flows through the magnetoresistive element through a correction electrode different from an electrode for obtaining a sensing signal with respect to the magnetoresistive element on the substrate. The current component flowing to the magnetoresistive element through the electrode for obtaining the sensing signal is corrected.

In this way, an error occurs in the relative positional relationship between the element and the bias magnet (the substrate or the bias magnet is displaced in the assembly), and the sensor output caused by the bias magnet having a variation in magnetization. Offset can be adjusted.

Here, as described in claim 2, two magneto-resistive elements are connected in series, and a midpoint voltage between the two elements when a predetermined voltage is applied to the series circuit is used as a monitor signal. This is practically preferable.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. This magnetic sensor is used as a vehicle-mounted rotation sensor, and specifically used as a cam angle sensor, a crank angle sensor, a vehicle speed sensor, a rotation sensor incorporated in an automatic transmission, a wheel speed sensor, and the like. It is.

FIG. 1 is a plan view of a magnetic rotation sensor according to this embodiment. A substrate 2 is disposed inside the sensor housing 1, and magnetoresistive elements (hereinafter, referred to as MR elements) 3 and 4 are disposed on the substrate 2. Examples of the material of the MR elements 3 and 4 include a Ni—Co system and a Ni—Fe system, which are deposited on the substrate 2 by an evaporation method and patterned. Each of the MR elements 3 and 4 has a rectangular shape.
However, electrodes 7 and 8 are formed at the center of both ends of the MR element 4. The electrode 5 of the MR element 3 is grounded, and the electrode 6 of the MR element 3 and the electrode 7 of the MR element 4 are electrically connected. The electrode 8 of the MR element 4 is connected to a power supply 16.

Thus, the MR elements 3 and 4 are connected to the power supply 1
6 and a ground (GND) are connected in series, and a voltage at a midpoint α between the two MR elements 3 and 4 when a predetermined voltage Vr is applied to the series circuit is extracted as a sensing signal. It is.

On the other hand, behind the substrate 2, a bias magnet 9 is arranged apart from the substrate 2. The bias magnet 9 has an N-pole surface 10 magnetized to an N-pole and an S-pole surface 11 magnetized to an S-pole, and the N-pole surface 10 faces the substrate 2 side. Then, the MR at the N pole face 10 of the bias magnet 9
A magnetic field (magnetic vector Bbias) directed to the elements 3 and 4 is formed. The MR elements 3 and 4 are located in a bias magnetic field generated by the bias magnet 9.

As shown in FIG. 2, the sensor housing 1 is provided to face a gear 12 made of a magnetic material. More specifically, the MR elements 3 and 4 are
3 and at a predetermined interval. This gear 12
Is fixed to a rotating shaft (e.g., a crankshaft of an engine) and rotates in synchronization with rotation of the crankshaft and the like accompanying driving of the engine.

The direction of the bias magnetic field (magnetic vector) Bbias changes due to the passage of the teeth 13 (peaks and valleys) accompanying the rotation of the gear 12 to be detected. When the direction of the bias magnetic field Bbias changes, the resistance values of the MR elements 3 and 4 also change. As a result, the voltage at the midpoint α also changes.

In FIG. 2, the voltage at the midpoint α is amplified by an operational amplifier 14, compared with a reference voltage Vref by a comparator 15, and a binary signal is transmitted from the comparator 15 based on the magnitude relationship. You. The cycle of the binarized signal corresponds to the rotation speed of the gear 12. Therefore, the rotation speed of the gear 12 is obtained from the cycle of the binary signal. Specifically, the rotation speed of the gear 12 is obtained by measuring the period of the binarized signal (pulse signal) or counting the number of pulses per predetermined time. In this way, the MR elements 3 and 4 can detect a change in the direction of the bias magnetic field due to the movement of the detection target.

Here, originally, when the direction of the magnetic vector Bbias changes due to the passage of the teeth 13 (peaks and valleys) of the gear 12, the voltage at the middle point α changes and the rotation speed can be detected. However, if the assembly of the bias magnet 9 is displaced, or if the magnetization of the bias magnet 9 varies, the voltage at the midpoint α does not become 1/2 of the power supply voltage Vr, but deviates from Vr / 2. Would. Thus, the midpoint α
Is offset from the predetermined value Vr / 2,
There is a possibility that binarization cannot be performed in the comparator 15 at the subsequent stage.

Therefore, in the present embodiment, as shown in FIG. 1, the correction electrodes 20, 2 are provided separately from the electrodes 5, 6 for obtaining a sensing signal for the MR element 3 on the substrate 2.
1, 2 and 23 are arranged, and correction electrodes 30, 31, 32 and 33 are arranged separately from the electrodes 7 and 8 for obtaining a sensing signal for the MR element 4. More specifically, the electrodes 2 are located at the four corners of the rectangular MR element 3.
Electrodes 30, 31, 32, and 33 are formed at four corners of the MR element 4 having a rectangular shape.

This correcting electrode (electrodes 20, 2 in FIG. 1)
1, 30, 31), the current flows through the MR elements 3, 4, and the electrodes 5, 6, 7, 8 for obtaining the sensing signal with the current component formed by the current.
4 is corrected. In FIG. 1, the electrode 21 of the MR element 3 and the electrode 3 of the MR element 4
0 is electrically connected, and the electrode 20 of the MR element 3 and the electrode 31 of the MR element 4 are electrically connected via the power supply 35.

More specifically, when the magnetic vector Bbias applied to the MR elements 3 and 4 is displaced due to a displacement of the bias magnet 9 or the like, the electrodes 20 and 21 located at the diagonal positions of the rectangular MR elements 3 and 4 are used. , 30 and 31, the vector (main current vector) Bmein of the current flowing along the element extending direction in the MR elements 3 and 4 of FIG.
Of the MR elements 3 and 4 is corrected. That is, the electrodes 20, 21, 3 in FIG.
The current vector B for adjustment is obtained by applying a current to 0, 31.
By generating adj and obtaining a composite vector Bmein1 with respect to the main current vector Bmein, the characteristics of the MR elements 3 and 4 are apparently inclined by an angle δ.

As described above, the correction electrodes 20, 21, 3
By adjusting the amount of current flowing to the elements 3 and 4 through 0 and 31, the MR elements 3 and 4 can be corrected to an ideal arrangement with respect to the magnetic vector Bbias of the bias magnet 9, and the offset of the midpoint can be reduced. Can be corrected.

Next, the principle and procedure of adjusting the offset will be described. As a basic characteristic of the MR elements 3 and 4, as shown in FIG. 4, the resistance value R of the MR elements 3 and 4 with respect to the angle θ formed between the direction of the current flowing in the MR elements 3 and 4 and the magnetic field direction is R = Rpara · cos ² θ + Rvert · sin ² θ where Rpara is a resistance value when the current direction and the magnetic field direction are parallel, and Rvert is a resistance value when the current direction and the magnetic field direction are perpendicular.

Here, as shown in FIG. 5, if the MR elements 3 and 4 are extended at an angle of 45 ° with respect to the magnetic vector Bbias by the bias magnet 9, the point P in FIG.
1 and P2, the resistance values of the two elements 3 and 4 are equal.
As a result, the midpoint voltage is changed to the MR elements 3, 4 connected in series.
Of the applied voltage Vr.

However, after the bias magnet 9 is assembled, the assembly of the bias magnet 9 may be displaced.
As shown in FIG. 6, the magnetic field applied to the MR element 4 is 45
° and the magnetic field applied to the MR element 3 is also 1
If it is larger than 35 °, the resistance value of the MR element 4 becomes M as shown by points P1 ′ and P2 ′ in FIG.
It becomes smaller than the resistance value of the R element 3. As a result, the midpoint voltage becomes higher than Vr / 2.

Therefore, the deviation (difference) of the midpoint voltage from Vr / 2 is calculated by using the midpoint voltage (more precisely, the output of the operational amplifier 14 in FIG. 2) as a monitor signal at the time of offset adjustment. The amount of adjustment current for obtaining the composite current vector Bmein1 of No. 7 is determined.

More specifically, the angle θ1 with respect to the bias magnetic field (reference line Lbase) in the main current vector Bmein in FIG.
Is larger than 45 °, the adjustment current vector Badj is generated to generate the combined current vector Bme.
in1 is obtained, and the resultant current vector Bmein
1 is the angle θ3 with respect to the bias magnetic field (reference line Lbase)
= 45 ° vector for adjustment
Generate adj.

For example, when the midpoint voltage deviates from Vr / 2 by the potential difference X, the MR elements 3 and 4 are set at 45 °
Is quantified by an angle θx ° with respect to, and in order to correct this, the adjustment current value is determined so that the combined current vector Bmein1 is 45 °, and the correction current value is indicated by a broken line in FIG. As shown by the solid line in FIG. 8, the MR elements 3 and 4 are subjected to MR element angle correction by an angle δ, and a magnetic field in the same direction is applied to the MR elements 3 and 4. In this way,
The apparent patterns of the MR elements 3 and 4 are adjusted.

As described above, the adjusting current value is determined by monitoring the midpoint voltage after the magnet is assembled. Specifically, in the sensor shown in FIG.
External trim terminals 41, 4 that can be trimmed, such as 0
2 is provided. After the MR elements 3 and 4 have been manufactured and the bias magnet 9 has been assembled, the midpoint voltage is measured (determining the amount of deviation) and the adjustment current is determined (trim position of the external terminal is determined). As shown in FIG. 10, when the external trim terminals 41 and 42 are cut along the cut line Lcut, an amount of current corresponding to the cut portion is supplied to the MR elements 3 and 4 through the correction electrodes. In the case of FIG.
The current value becomes a milliamperes by cutting at the cut line Lcut, and the current value becomes b milliampers by cutting at the cut line Lcut of the terminal 42.
The current value becomes (a + b) milliamperes by cutting at the cut lines Lcut of 1,42. The part (adjustment terminal) X ′ on the opposite side of FIG. 9 is used in the same way when the midpoint voltage becomes smaller than Vr / 2. That is, a current is applied to the electrodes 23, 22, 32, and 33 in FIG. 1 and the current value is adjusted.

In FIG. 9, reference numeral 40 denotes a midpoint monitor terminal, that is, a terminal connected to the output terminal of the operational amplifier 14 in FIG. As described above, the present embodiment has the following features. (A) As shown in FIG. 1, the MR elements 3 and 4 on the substrate 2
To obtain sensing signals for the electrodes 5, 6, 7, 8
Separately, the correction electrodes 20 to 23 and 30 to 33 are arranged,
An electric current is supplied to the MR elements 3 and 4 through the correction electrodes 20 to 23 and 30 to 33, and the MR elements 3 and 4 are passed through the electrodes 5, 6, 7, and 8 for obtaining a sensing signal with a current component formed thereby. 4 was corrected. Thus, a pair of electrodes (20 and 21, 30 and 31,
23 and 22, 32 and 33).
By giving angles to the current components flowing through the R elements 3 and 4, the apparent angles of the MR elements 3 and 4 are adjusted, and errors may occur in the relative positional relationship between the elements 3 and 4 and the bias magnet 9. It is possible to adjust the offset of the sensor output caused by (eg, the substrate 2 or the bias magnet 9 is displaced in assembly) or the bias magnet 9 has uneven magnetization. (B) As shown in FIG. 2, two MR elements 3 and 4 are connected in series, and a midpoint voltage between the two elements 3 and 4 when a predetermined voltage is applied to this series circuit (specifically, the Output) is used as a monitor signal when adjusting the offset, which is practically preferable.

[Brief description of the drawings]

FIG. 1 is a plan view of a magnetic rotation sensor according to an embodiment.

FIG. 2 is a diagram showing an electrical configuration of a sensor.

FIG. 3 is a diagram for explaining various vectors.

FIG. 4 is a diagram illustrating a relationship between a resistance value R and an angle θ between a current direction and a magnetic field direction.

FIG. 5 is a diagram for explaining various vectors.

FIG. 6 is a diagram for explaining various vectors.

FIG. 7 is a diagram for explaining various vectors.

FIG. 8 is a diagram for explaining various vectors.

FIG. 9 is a plan view of a sensor.

FIG. 10 is an enlarged view of a part X in FIG. 9;

FIG. 11 is a view showing a magnetic rotation sensor for explaining a conventional technique.

FIG. 12 is a diagram showing a sensor signal waveform.

[Explanation of symbols]

2 ... substrate, 3 ... MR element, 4 ... MR element, 5-8 ... electrode, 9 ... bias magnet, 20-23 ... correction electrode, 30
33 to correction electrode.

Claims (2)

[Claims] 1. A magnetoresistive element is arranged on a substrate, a bias magnet is arranged behind the substrate, and the magnetoresistive element is positioned in a bias magnetic field by the bias magnet.
In a magnetic sensor in which a change in the direction of a bias magnetic field accompanying movement of a detection target is detected by a magnetoresistive element, a correction is performed separately from an electrode for obtaining a sensing signal for the magnetoresistive element on the substrate. An electrode is arranged, a current is caused to flow to the magnetoresistive element through the correction electrode, and a current component formed by this is used to correct the current component flowing to the magnetoresistive element through the electrode for obtaining the sensing signal. A magnetic sensor comprising: 2. The device according to claim 2, wherein the two magnetoresistive elements are connected in series,
2. The magnetic sensor according to claim 1, wherein a midpoint voltage between the two elements when a predetermined voltage is applied to the series circuit is used as a monitor signal.