JPH05273320A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To suppress the output variation of magnetic resistance elements caused by the temperature characteristics of their resistance values. CONSTITUTION:A constant-current circuit 2 and comparator 3 which compares voltages generated by magnetic resistance elements R1-R4 with each other are mounted on a chip together with a magnetic resistance element circuit 1 composed of the elements R1-R4. The circuit 2 is provided with resistors 4 and 5 and connected in series between the circuit 1 and GND. Even when the resistance values of the elements R1-R4 vary due to temperature, a fixed current can be secured by the action of the circuit 2. In addition, the initial fluctuation of the elements R1-R4 can be suppressed by adjusting the resistors 4 and 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor in which a ferromagnetic magnetoresistive element and a waveform processing circuit are integrated on the same chip.

[0002]

2. Description of the Related Art Conventionally, a magnetic sensor having a magnetoresistive element is incorporated in a detection device or the like used for rotation detection or object position detection.

FIG. 3 is a cutaway perspective view of a conventional magnetic sensor. As shown in FIG. 3, the conventional magnetic sensor has a magnetoresistive element circuit 1 and a signal processing circuit 9 mounted on a substrate 12 and connected to a terminal 11 by a bonding wire 10. Moreover, it is constructed by covering the whole with the package 13. The terminal 11 represents a power supply (+ VCC) terminal, a GND terminal, and a sensor output terminal.

FIG. 4 is a pattern diagram of the magnetoresistive element circuit shown in FIG. As shown in FIG. 4, the conventional magnetic sensor has magnetoresistive elements R1, R2, R3 having a continuous folding structure at a position separated from the magnetic recording medium by a finite distance and made of Ni-Fe, Ni-Co or the like. , R4 are connected in series. The respective connection portions of these magnetic resistance elements R1 to R4 are used as a power supply terminal A1, magnetic resistance element circuit output terminals A2, A3 and GND terminal A4.

FIG. 5 is a circuit diagram of the magnetic sensor shown in FIG. As shown in FIG. 5, this magnetic sensor circuit includes a magnetoresistive element circuit 1 including the above-described magnetoresistive elements R1 to R4.
And a comparator 3 for inputting and comparing signals from the element circuit terminals A2 and A3, and resistors 7 and 8. In this way, by amplifying and comparing the potential difference between the outputs A2 and A3 terminals of the magnetoresistive element circuit 1, the polarity of the magnetic field is determined to be ON / OFF, and the number of pulses proportional to the amount of movement of the DUT is output. can do. Therefore, such a magnetic sensor is applied to speed detection and position detection by counting the number of pulses using a counter.

[0006]

In the above-mentioned conventional magnetic sensor, the temperature characteristic of the resistance value of the magnetoresistive element has an influence. That is, the resistance value of the magnetoresistive element is + 0.3% / ° C.
Although it has a positive temperature coefficient of a certain degree, the temperature characteristic of the amount of change in resistance value due to application of a unit magnetic field is sufficiently smaller than the temperature coefficient. Circuit output A in FIG.
The potential difference ΔE generated between 2 and A3 is as follows when the input impedance of the comparator is infinite and the resistance value change due to the magnetic field of the magnetoresistive element is represented by ΔR.

ΔE = (R4 + ΔR4) I1−R3 · I2 Here, the path currents I1 and I2 are I1 = VCC / (R1
+ R4 + ΔR4) and I2 = VCC / (R2 + ΔR2)
+ R3).

Assuming that R1 at VCC = 10V and 0 ° C.
˜R4 = 20 KΩ, ΔR = 200 Ω, ΔE≈50 mV at 0 ° C. (R1 to R4 = 20 KΩ) ΔE≈40 mV at 80 ° C. (R1 to R4 = 24.8)
KΩ), and ΔE is reduced by about 20%. This decrease in ΔE causes a decrease in the sensitivity of the magnetic sensor and a hysteresis variation of the output signal with respect to the magnetic field. Therefore, the conventional magnetic sensor has a drawback that a decrease in ΔE causes a malfunction of a processing circuit such as a counter connected to the next stage. Further, in the conventional magnetic sensor, it is difficult to finely adjust the resistance value once the magnetoresistive element is patterned,
There is a drawback in that variations in resistance and variations in bias points caused by variations in manufacturing conditions such as exposure, development, and etching cannot be absorbed, which hinders improvement of the yield rate.

An object of the present invention is to provide a magnetic sensor capable of compensating for the characteristic variation of the magnetoresistive element and improving the yield rate.

[0010]

The magnetic sensor of the present invention comprises:
A magnetoresistive element circuit comprising a plurality of magnetoresistive elements formed by depositing a ferromagnetic alloy thin film on a substrate and patterning it into a specific shape; and a transistor and a resistor, which are connected in series to the magnetoresistive element circuit. Constant current circuit,
And a comparator for amplifying and comparing the voltage signal generated by the magnetoresistive element.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit diagram of a magnetic sensor showing an embodiment of the present invention. As shown in FIG. 1, this embodiment is similar to the conventional example of FIG. 4 described above, in which magnetoresistive elements (hereinafter referred to as MR elements) R1, R2, R3, and R4 are patterned in the same shape and arranged in a skewed manner. Magnetoresistive element circuit 1
A constant current circuit 2 connected in series with the circuit 1 and GND; a comparator 3 for inputting and amplifying the A2 and A3 outputs of the magnetoresistive element circuit 1 for comparison; and resistors 7 and 8. is doing. The MR element circuit 1 has a characteristic that when the magnetic fields of the same polarity are applied, the MR elements R1 and R3 arranged in a skewed manner produce the same resistance value fluctuations. Also,
Since the MR elements R2 and R4 are patterned in the direction perpendicular to the MR elements R1 and R3, the MR elements R1 and R4 are
When the resistance of No. 3 changes, the resistance values of the MR elements R2 and R4 do not change. Due to this characteristic, M including the MR elements R1 to R4
A potential difference occurs between the outputs A2 and A3 of the R element circuit 1. On the other hand, the constant current circuit 2 is composed of resistors 4 and 5 and a resistor 6 and transistors Q1 and Q2, and has MR elements R1 to R4.
And a monolithic circuit on the same substrate. The constant current circuit 2 keeps the collector current I3 of the transistor Q2 constant, so that even if the resistance values of the MR elements R1, R2, R3, and R4 change due to temperature changes, the current flowing through the MR elements R1 to R4. The value of (I1 + I2) does not change. Further, the MR elements R1 and R4 and the MR elements R2 and R
Since 3 has a symmetrical shape, if I1 + I2 = constant,
I1 = I2 = constant relationship holds.

Here, the MR due to the addition of the unit magnetic field
Since the change in resistance ΔR of the elements R1 to R4 with temperature is extremely small, if it is not changed, the potential difference ΔE between the outputs A2 and A3 of the MR element is as follows.

ΔE = (R4 + ΔR4) I1−R3 · I2 (at normal temperature) ΔE = (R4 + α4 + ΔR4) I1− (R3 + α3) ·
I2 (when temperature changes) Note that α3 and α4 are the temperature changes of the MR element.

At this time, the temperature change is equally applied to the MR elements R3 and R4, and if the MR elements have the same size and shape, then R3 = R4, α3 = α4.

Next, temperature fluctuations of the constant current circuit 2 will be calculated for 0 ° C. and 80 ° C. Here, the MR elements R1 to R
4 is I3, the base / emitter voltage of transistors Q1 and Q2 is VBE, and the collector cutoff current is ICB.
O and the current amplification factor are hFE, and it is assumed that the respective constants change with temperature as shown in Table 1.

[0016]

[Table 1]

When the current is obtained from the above values, I at 0 ° C.
3 = 0.909 (mA), and I3 = 0.09 at 80 ° C.
It becomes 923 (mA). Therefore, the current value changes by about 1.5%. However, if the temperature coefficient of the resistance change due to the magnetoresistive effect is ignored, the potential difference ΔE between the A2 and A3 outputs is ΔE.
The temperature fluctuation of is in agreement with the temperature characteristic of the current I3 of the constant current circuit 2. Therefore, the temperature variation of the potential difference ΔE between 0 ° C. and 80 ° C. is about + 1.8%, and Δ of the above-described conventional example configuration.
Even if the fluctuation of E is -20%, the characteristic is improved 10 times or more.

FIG. 2 is a circuit diagram of a magnetic sensor showing another embodiment of the present invention. As shown in FIG. 2, in this embodiment, the resistors 4 and 5 in the constant current circuit 2 are replaced with the trimming resistors 4a and 5.
It is replaced with a. Others are the same as those in the above-described embodiment. In this embodiment, the MR elements R1, R2, R3,
The currents I1 and I2 flowing through R4 are adjustable. The adjustment method is as follows. A magnetic field having a specified value is applied to the MR elements R1 to R4, and the potential difference Δ generated between the outputs A2 and A3 at this time.
E is measured, and resistors 4, 5 are set so that ΔE is within the standard.
To trim. Thereby, the initial variation of the magnetic sensor can be corrected.

[0019]

As described above, the magnetic sensor of the present invention has the effect of compensating for characteristic variations due to the temperature coefficient of the MR element by connecting a constant current circuit in series with the MR element. Further, when the trimming resistor is provided in the constant current circuit, it becomes possible to absorb the initial variation of the resistance value of the MR element, and the characteristic can be stabilized.
There is an effect that the non-defective rate can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a magnetic sensor showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a magnetic sensor showing another embodiment of the present invention.

FIG. 3 is a cutaway perspective view of a conventional magnetic sensor.

FIG. 4 is a pattern diagram of the magnetoresistive element circuit in FIG.

5 is a circuit diagram of the magnetic sensor shown in FIG.

[Explanation of symbols]

 1 Magnetoresistive element circuit 2 Constant current circuit 3 Comparator 4-8 Resistance 4a, 5a Trimming resistance R1-R4 Magnetoresistive element Q1, Q2 Transistor

Claims (1)

[Claims] 1. A magnetoresistive element circuit comprising a plurality of magnetoresistive elements formed by depositing a ferromagnetic alloy thin film on a substrate and patterning it into a specific shape, and a magnetoresistive element circuit comprising a transistor and a resistor. A magnetic sensor, comprising: a constant current circuit connected in series with the above; and a comparator for amplifying and comparing a voltage signal generated by the magnetoresistive element.