JP2000019235A - Mi sensor excellent in temperature characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetism-impedance(MI) sensor which is excellent in temperature characteristic. SOLUTION: In the MI sensor, when a constant-current circuit and a peak- hold circuit are fed back by using an operational amplifier (OP) 7, the temperature characteristics of both circuits are enhanced. The temperature characteristic is at 1%/F.S. or lower in the temperature range of -40 to 85 deg.C. In addition, when the OP 7 whose performance as a unity gain bandwidth is at 100 MHz or higher is used, the MI sensor of high sensitivity is obtainable. In addition, when the upper limit of a resistance value used in the constant-current circuit is set at 500 Ω, it is possible to suppress the attenuation of a signal at a high frequency in the constant-current circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic-impedance sensor (hereinafter referred to as MI sensor).

[0002]

2. Description of the Related Art Small dimensions comparable to those of a Hall element or an MR element are possible, and the magnetic field detection sensitivity is one of the Hall element and the MR element.
An MI sensor using a magnetic-impedance (MI) effect, in which the impedance of an amorphous wire, which is a detection object of the sensor, greatly changes due to an external magnetic field, has been proposed as a sensor that is at least 00 times the same as a fluxgate sensor. Yes. As for the MI effect, the higher the frequency, the greater the change in impedance. Therefore, it is desirable to measure the frequency as high as possible, preferably using a pulse. Figure 1 shows a block diagram of an electronic circuit that measures impedance using pulses. In the electronic circuit, a sharp pulse with a time width of several ns is oscillated by an oscillation circuit, and the pulse current is supplied to an amorphous wire as a detection object through a constant current circuit. The peak value of the output obtained at this time corresponds to the external magnetic field. The signal is converted to DC by a peak hold circuit and amplified by an amplifier circuit. In the conventional circuit, an MI sensor with a large impedance change and excellent sensitivity could be constructed to handle a sharp pulse with a time width of several n to several tens of seconds, but the temperature compensation of the circuit was not sufficient. In particular, the temperature compensation of the constant current circuit and the peak hold circuit was not sufficient. This is because the temperature characteristics of the digital element 1 of the constant current circuit shown in FIG. 10 and the SBD2 (Schottky barrier diode) element of the peak hold circuit shown in FIG. 12 are poor. For this reason, the temperature characteristics of the entire circuit are degraded. In fact, when investigating the temperature characteristics, there was a problem that it became 50% / FS under the condition of -40 to 85 ° C. Therefore, it was difficult to apply it to automobiles. The present invention provides an MI sensor in which the temperature characteristics of the entire circuit are improved by compensating the temperature of the constant current circuit and the peak hold circuit.

[0003]

In the MI sensor, feedback is applied to a constant current circuit and a peak hold circuit using an operational amplifier (hereinafter, referred to as OP). It is desirable that the unity gain bandwidth of the OP has a performance of 100 MHz or more. In a constant current circuit, the upper limit of the resistance used in the circuit is preferably set to 500Ω.

According to the present invention, temperature compensation is performed by applying feedback to the constant current circuit and the peak hold circuit using the OP. As shown in Fig. 2, the constant current circuit
Two OPs 7 and 11 were used, and a feedback circuit using two OPs 12 and 13 was used as a peak hold circuit as shown in FIG. The operation of the constant current circuit is briefly described. By applying feedback at OP7 so that the voltage drop of the resistor 10 becomes equal to the inverted input voltage, the output current becomes a constant current. At this time, the voltage generated in the amorphous wire is simultaneously divided by the resistor 9 and the resistor 8 and positive feedback is applied. Therefore, the efficiency is reduced by the current flowing therethrough. Therefore, a current is prevented from flowing through the resistors 9 and 8 by inserting a voltage follower circuit into the voltage dividing circuit using OP11.
In fact, as shown in FIG. 4, the temperature characteristic 17 of the conventional circuit is 100% / FS and the temperature characteristic 18 of the circuit of the present invention is 1% / FS at -40 to 85.degree. The operation of the peak hold circuit is briefly described. The voltage charged in the capacitor 15 through the SBD 14 is measured. The resistor 16 is inserted and discharged for continuous measurement. O
By giving feedback in P12, SBD14
The aim is to improve the temperature characteristics of. Further, by attaching a voltage follower using OP13, electrical isolation from a subsequent-stage amplifier circuit is achieved. In fact, as shown in FIG. 5, the temperature characteristic 19 of the conventional circuit under the condition of -40 to 85 ° C. is 50%.
The temperature characteristic 20 of the circuit of the present invention is extremely improved to 1% / FS compared to / FS. More preferably, an OP having a unity gain bandwidth of 100 MHz or more is used.
Actually, the MI effect is a phenomenon in which the high-frequency impedance is changed by an external magnetic field, and the change in the impedance is small at a low frequency. In this case, the circuit of the present invention performs feedback using the OP, so that the high frequency impedance cannot be measured if the frequency characteristic of the OP is poor. In fact, as shown in FIG. 6, when examining the influence of the unity gain bandwidth, which is a typical frequency characteristic of the OP, on the MI characteristic, it can be seen that the MI characteristic deteriorates extremely below 100 MHz. Therefore, it is desirable that the unity gain bandwidth of the OP be 100 MHz or more. Furthermore, in a constant current circuit, the signal is attenuated when the resistance of the circuit is large because the signal has a high frequency. In fact, when investigating the effect of the resistance value on the output of the circuit as shown in Fig. 7, when the resistance exceeds 500Ω, the signal is reduced to about half and the signal is attenuated rapidly. Therefore, it is desirable that the resistance of the constant current circuit be 500Ω or less.

The present invention will be described below in detail based on embodiments. FIG. 8 shows an embodiment of the circuit of the MI sensor according to the present invention. The constant current circuit used two OPs with unity gain of 1.3 GHz to feed back the pulse signal. Also, the value of the resistor should be
100Ω. The peak hold circuit has a unity gain of 1.3GHz to feed back the pulse signal.
Were used. As a comparative example, a conventionally proposed circuit was subjected to a test as shown in FIG. -40 ℃
As a result of investigating the temperature characteristics in the temperature range from to 85 ° C., as shown in FIG.
For 50% / FS, the MI sensor of the present invention has a temperature characteristic of 22%.
Is 1% / FS.

[0004]

As described above, according to the present invention, an MI sensor having excellent temperature characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an MI sensor.

FIG. 2 shows a constant current circuit according to the present invention.

FIG. 3 shows a peak hold circuit of the product of the present invention.

FIG. 4 is a diagram showing temperature characteristics of a constant current circuit.

FIG. 5 is a diagram showing temperature characteristics of a peak hold circuit.

FIG. 6 is a diagram showing the effect of unity gain on output.

FIG. 7 is a diagram showing the effect of resistance on output.

FIG. 8 is a circuit diagram of the product of the present invention.

FIG. 9 is a diagram showing temperature characteristics of the product of the present invention.

FIG. 10 is a constant current circuit diagram of a conventional MI sensor.

FIG. 11 is a peak hold circuit diagram of a conventional MI sensor.

FIG. 12 is a circuit diagram of a conventional product.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 digital element 2 SBD 3 capacitor 4 resistor 5 resistor 6 resistor 7 OP 8 resistor 9 resistor 10 resistor 11 OP 12 OP 13 OP 14 SBD 15 capacitor 16 resistor 17 Graph of conventional circuit 18 Graph of present invention 19 Graph of conventional circuit 20 Graph of the present invention 21 Graph of the conventional circuit 22 Graph of the present invention

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshinori Mohri 3F term of 3911, Shimada Kuroishi, Tenpaku-cho, Tempaku-ku, Nagoya 2F017 AB05 AD42 AD53 AD55 AD69

Claims (3)

[Claims] In an MI sensor, an operational amplifier (hereinafter referred to as OP) is provided in a constant current circuit and a peak hold circuit.
The MI sensor has a temperature characteristic of 1% / FS or less in the temperature range of -40 ° C to 85 ° C. 2. The MI sensor according to claim 1, wherein the OP has a performance with a unity gain bandwidth of 100 MHz or more. 3. The MI sensor according to claim 2, wherein the upper limit of the resistance value of the constant current circuit is 500Ω.