JPS6366417A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To reduce a drift in the operating point of a sensor and the temperature dependency of a duty ratio when a detecting signal is converted to a square wave by using a silicon plate as a substrate for providing a magnetoresistance effect element thereon. CONSTITUTION:A silicon plate is used as a substrate for providing a magnetoresistance effect element MR thereon. Thus, a good temperature characteristic sensor wherein heat from the magnetoresistance effect element MR constituting a Joule heat generating source is well radiated, a temperature gradient is gentle and a drift in the operating point of a half bridge due to an external temperature is reduced can be obtained. That is, the thermal conductivity of silicon is 0.36cal.cm/(cm<2>.sec. deg.C) which is larger than that of glass by about two figures. Thus, heat generated from the magnetoresistance effect element MR is radiated by using the silicon plate as the substrate. Accordingly, a temperature rise in the magnetoresistance effect element MR is restrained and the drift in the operating point is reduced. Thus, the temperature dependency of a duty ratio when a detecting signal is converted to a square wave is reduced and temperature characteristics can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic sensor in which a magnetoresistance effect element is provided on a substrate to be used as a magnetic signal detection means of a magnetic rotary encoder that detects the rotation angle of a rotating body. It is related to sensors.

[Summary of the invention]

This invention uses a silicon plate as a substrate of a magnetic sensor in which a magnetoresistive element is provided on the substrate to be used as a magnetic signal detection means of a magnetic rotary encoder that detects the rotation angle of a rotating body. This reduces the accumulation of Joule heat generated by the sensor and stabilizes the drift of the operating point of the magnetic sensor due to fluctuations in external temperature.

[Conventional technology]

A conventional magnetic sensor in which a magnetoresistive element is provided on a substrate, which is used as a magnetic signal detection means of a magnetic rotary encoder, is a film made of a Ni-Co alloy or the like with a thickness of 300 to 2000 A on a glass substrate. The magnetoresistive element is formed by vapor depositing the four layers and processing the four lines into a predetermined shape by font etching.

and 1, for example, FeCrC as shown in FIG.

Multi-pole magnetic poles are magnetized at regular intervals on the outer periphery of a rotating body 1 made of a magnet, etc., and approximately 20 to 20 magnetic poles are attached to the magnetic poles of this rotating body 1.
The magnetoresistive elements MR are placed facing each other with a distance of 0 μm. The size of the substrate of this magnetic sensor is several mm.
It is a corner.

Due to changes in the magnetic field accompanying the rotation of the rotating body 1.

The rotation angle of the rotating body 1 can be detected by utilizing the change in the resistance value of the magnetoresistive element MR.

Such a magnetic sensor generally employs a method in which the magnetoresistive element MR is configured in a half-bridge configuration, and as shown in Fig. 2, the magnetoresistive element MRA, L has a phase difference of 180' from the magnetoresistive element MRA, L. The magnetoresistive elements MRA and R placed at the same position are connected in series to form a half-bridge MRA, and the connection part S is connected to the magnetic signal detection end 5 and the other end is connected to the DC current mV and the ground G.

As a result, as shown in FIG. 3, the magnetoresistive effect element MR
A and L change their resistance as shown in curve fi2, and the resistance of magnetoresistive element MRAIR changes as shown in curve 3, so the resistance value of magnetoresistive element MRA I L is expressed as RL, magnetoresistive element MRA, R. If the resistance value of is RR, then the output of the half bridge is vo=V-RL/(RL+
Curve 4 in FIG. 4 is obtained with RR) as the operating point.

With this half-bridge as the basic configuration, as shown in FIG. 5, the outputs of the half-bridge MRA and the half-bridge MRB placed in close proximity with a phase difference of 90 degrees are input to amplifiers 5 and 6, respectively. For example, two-phase outputs A and B with a phase difference of 90'' can be obtained.

As another method, as shown in FIG. Bridge M
There is also a system in which the outputs of RB1 and a half bridge MRB2 disposed close to each other with a phase difference of 180 degrees are input to a differential amplifier 8 to remove common mode noise.

By making the basic configuration half-bridge as described above, even if the external temperature fluctuates, for example, the resistance value R of the magnetoresistive elements MRA, L and MRA, R in FIG.
Since the temperature coefficients α of L and RR are equal, let the temperature change be ΔT.

The respective resistance values RL' and RR' after the change are as follows.

RL' ==RL (1+α・ΔT) ・・・■RR
'=RR(1+α・ΔT)...■, and the operating point vo should ideally remain unchanged at vo=V-RL/(RL+RR)--■.

[Problem that the invention seeks to solve]

However, in such a conventional magnetic sensor in which a magnetoresistive element is formed on a glass substrate, Joule heat generated by the magnetoresistive element itself tends to accumulate, so in reality, it is generated due to fluctuations in external temperature. operating point v
There was a problem that o fluctuated.

That is, as shown by the curved line in FIG. 7 within the half bridge, the magnetoresistive element MRA1L.

A temperature distribution is generated with MRA and R as heat sources and the midpoint P is the apex, and as shown in FIG. , part of this heat is absorbed by the rotating body 1.

The closer the distance to the rotating body 1, the more this heat is absorbed, so 1
If the distance between the rotating body and the half bridge of the magnetic sensor is inclined, the temperature distribution will become as shown, for example, by curve 10 in FIG. 7, and the symmetry will disappear, and the operating point vo will deviate from the equation 0.

If the external temperature fluctuates without this symmetry.

It is clear that the operating point vo tends to drift due to changes in temperature distribution due to changes in Joule heat generated.

In addition, as shown in FIG. 5 or 6, when multiple sets of adjacent half bridges are formed, the poor temperature distribution of each half bridge overlaps, so the P of each half bridge is
The symmetry of the temperature distribution seen from the point is lost, and even if a rotating body is installed parallel to the half bridge, the operating point VO will move, and the operating point V will drift due to changes in external temperature. Cheap.

Table 1 Table 1 shows an example of measuring the voltage at the operating point vo before and after installing a rotating body in a magnetic sensor configured as shown in FIG. The power supply voltage at this time is DC12V.

As described above, if the operating point drifts, a problem arises in that the duty ratio of the square wave changes depending on the external temperature when it is converted into a square wave with a constant voltage threshold by a comparator in the downstream stage of the amplifier.

FIG. 8 shows the temperature dependence of the duty ratio when a signal detected by a magnetic sensor having the characteristics shown in Table 1 is converted into a square wave.

In Fig. 6, curve 11 shows the duty ratio when a comparator is connected after amplifier 7 to convert it into a square wave, and curve 12 shows the duty ratio when a comparator is connected after amplifier 8 to convert it into a square wave. This is an actual measurement example.

This invention was made to solve the above-mentioned problems with conventional magnetic sensors.It reduces the drift of the operating point and reduces the temperature dependence of the duty ratio when converting the detection signal into a square wave. The purpose is to obtain a magnetic sensor with small magnetic field.

[Means for solving problems]

In order to solve the above-mentioned problems, the magnetic sensor according to the present invention uses a silicon (Si) plate as a substrate on which the magnetoresistive element of the magnetic sensor is provided, so that heat from the magnetoresistive element, which is a source of Joule heat generation, is removed. The purpose of the present invention is to provide a magnetic sensor with good temperature characteristics, which has good dissipation, smoothes the temperature gradient, and reduces the drift of the operating point of a half bridge with respect to external temperature fluctuations.

[For production]

The thermal conductivity of silicon (Si) is 0.36 cal/cm
/(cJ・ssc・'c), which is 0.
002～0.004cal・cm/(cof-see・
It is about two orders of magnitude larger than ℃). Therefore, the heat generated from the magnetoresistive element is radiated by using the silicon plate as the substrate, and is not accumulated in one place. As a result, the temperature rise of the magnetoresistive element is suppressed, and the drift of the operating point is also reduced.

〔Example〕

Examples of the present invention will be described below with reference to tables and drawings.

Table 2 shows an example of measuring the voltage at the operating point VO before and after installing a rotating body in a magnetic sensor according to an embodiment of the present invention.

In the magnetic sensor of this embodiment, an eight-bridge formed by magnetoresistive elements is formed on a silicon substrate of several I square as shown in FIG. The power supply voltage is DC12V.

Table 2 As is clear from this Table 2, heat is radiated sufficiently by the silicon substrate, so even if the rotating body 1 is installed, the operating point vo does not fluctuate much, and the temperature distribution changes due to the heat radiation to the rotating body 5. It can be seen that is small.

FIG. S shows the temperature dependence of the duty ratio when a signal detected using this magnetic sensor is converted into a square wave.

Curve g13 shows the duty ratio when a comparator is connected after the amplifier 7 in Fig. 6 to convert it into a square wave, and curve 14 shows the duty ratio when a comparator is connected after the amplifier 8 to convert it into a square wave. This is an actual measurement example.

Compared to the temperature dependence of the duty ratio shown in FIG. 8 when a detection signal from a conventional magnetic sensor using glass as a substrate is converted into a square wave, the duty ratio shown in FIG. is clearly stable with respect to external temperature.

〔Effect of the invention〕

As explained above, the magnetic sensor according to the present invention has a smaller drift in the operating point due to external temperature fluctuations than conventional magnetic sensors, and the temperature dependence of the duty ratio when the detection signal is converted into a square wave. The temperature characteristics are improved.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing the positional relationship between a magnetic sensor and a rotating body, which are objects of the present invention. FIG. 2 is a diagram showing the basic configuration of a magnetoresistive element. Figure 3 is a waveform diagram showing the operating principle of resistance value change of the magnetoresistive element, Figure 4 is a waveform diagram showing an example of the output signal of the magnetic sensor, and Figure 5 is a waveform diagram showing an example of the output signal of the magnetic sensor.
The figure shows an example of how the output of the magnetic sensor is connected to the amplifier, and FIG. 6 is a diagram showing another example of how the output of the magnetic sensor is connected to the amplifier. FIG. 7 is a diagram showing the temperature gradient within the half bridge. FIG. 8 is a diagram showing the temperature dependence of the duty ratio when a signal detected by a conventional magnetic sensor is converted into a square wave, and FIG. FIG. 3 is a diagram showing the temperature dependence of the duty ratio when converted into a wave. 1... Rotating body M R, M RA HL, M RA 1R... Magnetoresistive element MRA4, MRA2, MRBl,
MRB2...Half bridges 5 to 8 consisting of magnetoresistive elements...Amplifier Fig. 1 Fig. 3 Fig. 4 Rotation angle Fig. 7 Fig. 8 Fig. 9 Outside lth CC>

Claims (1)

[Claims] 1. A magnetic sensor in which a magnetoresistive element used as a magnetic signal detection means of a magnetic rotary encoder is provided on a substrate, wherein the substrate is a silicon plate.