JPH05326986A - Sensor output stabilization circuit - Google Patents

Abstract

(57) [Summary] (Modified) [Object] The present invention provides a sensor output stabilizing circuit that prevents the occurrence of an error in the detection voltage due to the variation in the resistance value of the detection element and enables accurate measurement. The purpose is to do. [Structure] A detection element 2 having a bridge structure and having a resistance value that changes according to a detected physical quantity is connected between an output terminal 6 of a non-inverting amplifier 1 and a negative side input terminal 7, and a negative side input terminal 7 has a sensing resistor 3 In the sensor output circuit that is grounded via the sensor output circuit that outputs a detection voltage from the middle of the bridge of the detection element 2, the sensing resistor 3 is formed on the same substrate by the same process as the detection element 2.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improvements in sensor output circuits. In particular, the present invention relates to an improvement for the purpose of providing a sensor output stabilizing circuit that prevents an error in the detection voltage due to variations in the resistance value of the detection element and enables accurate measurement.

[0002]

2. Description of the Related Art A conventional sensor output circuit will be described below with reference to the drawings. FIG. 7 is a configuration diagram of a sensor output circuit according to a conventional technique.

In FIG. 7, reference numeral 1 is a non-inverting amplifier, and 4 is a detection element connected between the output terminal 6 and the negative input terminal 7 of the non-inverting amplifier 1, for example, a ferromagnetic thin film magnetoresistive element. Is. The detecting element 4 has a bridge structure, and the resistors 41 and 43 on the opposite sides of the bridge and the resistors 42 and 44 on the other opposite sides have magnetic field characteristics of opposite polarities (positive or negative). .. Reference numeral 5 is a sensing resistor connected between the negative input terminal 7 of the non-inverting amplifier 1 and the ground. Reference numeral 8 is a plus side input terminal of the non-inverting amplifier 1. Reference numeral 9 is a detection terminal for outputting the voltage between the intermediate points of the bridge as a detection voltage V ₂ .

Next, the operation of the above sensor output circuit will be described. This circuit is a constant current circuit in which a constant current is output from the non-inverting amplifier 1 regardless of the resistance value of the detection element 4, and the constant output current value is the resistance value of the sensing resistor 5 with respect to the input voltage V _1. It is the value divided by. Placing the detection element 4 in the magnetic field to be measured, the resistance of each side of the bridge of the detection element 4 changes its resistance value based on the positive or negative magnetic field characteristic of the detection voltage V _2, the detection element Four
Is detected as a value obtained by multiplying the difference between the resistance value of the resistor 41 and the resistance value of the resistor 42 by 1/2 of the constant output current. By the way, the sensing resistor 5 is an external resistor, and changes in the resistance value with respect to temperature can be ignored, but changes in the resistance value with respect to the temperature of the detection element 4 cannot be ignored, so the temperature characteristics of the detection element 4 can be ignored. Voltage V to compensate for
₁ is used to exclude that the detection voltage is affected by temperature changes.

[0005]

However, in the sensor output circuit according to the prior art, there is a variation in the resistance value due to the process of the detection element, which causes a variation in the detection voltage, resulting in an error in the detection voltage. There is a drawback that it causes.

An object of the present invention is to eliminate this drawback, and to provide a sensor output stabilizing circuit which prevents the occurrence of an error in the detection voltage due to the variation in the resistance value of the detection voltage and enables an accurate measurement. To provide.

[0007]

The above object can be achieved by any of the following means. The first means is to connect a detection element (2), which has a bridge configuration and has a resistance value that changes according to a detected physical quantity, between the output terminal (6) and the negative side input terminal (7) of the non-inverting amplifier (1). The negative input terminal (7) is grounded via a sensing resistor (3), and the sensing output circuit outputs a detection voltage from the middle of the bridge of the detection element (2). The resistor (3) is a sensor output stabilizing circuit formed on the same substrate by the same process as that of the detection element (2).

In the above structure, the effect is remarkable when the detecting element (2) is a ferromagnetic thin film magnetoresistive element. Further, in the above configuration, the sensing resistor (3) has elements having positive and negative magnetic field characteristics connected in series, and when the resistance change due to the magnetic field is canceled, the measurement accuracy is further improved.

The second means is the first transistor.
(Q₁Constant current circuit for supplying a constant current to
(S₁) And the first transistor (Q₁) More
First transistor with large amount and base
(Q₁) A second transistor connected to the base of
(Q₂) In the same constant current as the first constant current circuit
A second constant current circuit (S₂) And the first constant
Current circuit (S₁) And the second constant current circuit (S₂)When
Constant current control circuit (S₃)When,
The first transistor (Q₁) Emitter and above
Second transistor (Q₂) Connected with the emitter
Sensing resistor (3) and the first transistor
(Q₁) Is connected to the base, and the emitter is
The first transistor (Q ₁) Connected to the emitter
The collector is a detection element whose resistance changes with the detected physical quantity.
Third transistor connected to power supply via (2)
(Q₃) And the terminal voltage of the detection element (2)
Therefore, the sensing resistance (3) is used as the detection voltage.
The same process as the above-mentioned detection element (2)
It is a sensor output stabilizing circuit formed on a substrate.

A third means includes a reference voltage bandgap reference voltage generating circuit (S ₄₎ is output is applied to the base of the transistor (Q _4), the collector of the transistor (Q ₄₎ the resistance value is detected It is connected to a power source through a detection element (2) that changes in a physical quantity, and the emitter is grounded through a sensing resistor (3). The terminal voltage of the detection element (2) serves as a detection voltage. The sensing resistor (3) is a sensor output stabilizing circuit formed on the same substrate by the same process as that of the detection element (2).

[0011]

In the sensor output stabilizing circuit according to the present invention, since the detection element and the sensing resistor are formed on the same substrate by the same process, variations in the resistance value due to the process are different between the detection element and the sensing resistor. They are the same, and therefore the ratio of the resistance value of the detection element to the resistance value of the sensing resistor is the same. Therefore, even if there is a variation in the resistance value due to the process of the detection element, the detection voltage can be kept constant and accurate measurement can be performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sensor output stabilizing circuit according to a third embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a sensor output stabilizing circuit according to a first embodiment (corresponding to claims 1, 2, and 3). Referring to FIG. 1, reference numeral 1 is a non-inverting amplifier, and 2 is a detection element such as a ferromagnetic thin film magnetoresistive element connected between the output terminal 6 and the negative side input terminal 7 of the non-inverting amplifier 1. The detecting element 2 has a bridge structure, and the resistances 21 and 23 on opposite sides of the bridge and the resistances 22 and 24 on other opposite sides have magnetic field characteristics of opposite polarities (positive or negative). .. Reference numeral 3 is a sensing resistor connected between the negative input terminal 7 of the non-inverting amplifier 1 and the ground. The sensing resistor 3 has a series connection of a positive resistance and a negative resistance whose resistance value changes due to a magnetic field, and eliminates the influence of the magnetic field. The detection element 2 and the sensing resistor 3 are formed on the same substrate (shown by a chain line in the figure) by the same process. Reference numeral 8 is a plus side input terminal of the non-inverting amplifier 1. Reference numeral 9 denotes the voltage between the midpoints of the bridge and the detection voltage V ₂
It is a detection terminal that outputs as.

FIG. 2 shows a detection element 2 formed on the same substrate.
3 is a configuration diagram of a sensing resistor 3 and FIG. See Fig. 2. In the figure, 31 and 32 are resistors whose resistance values change due to a magnetic field and whose polarities are opposite to each other (positive or negative).
32 constitutes the sensing resistor 3. The description of the other symbols is the same as in the case of FIG.

Next, the operation of the sensor output stabilizing circuit according to this embodiment will be described. This circuit is a constant current circuit in which a constant current is output from the non-inverting amplifier 1 regardless of the resistance value of the detection element 2, and the constant output current value is the resistance value of the sensing resistor 3 with respect to the input voltage V _1. It is the value obtained by dividing. When the detecting element 2 is placed in the magnetic field to be measured, the resistance 21 and the resistance 22 of the detecting element 2 have magnetic field characteristics of opposite polarities (positive or negative), so that the detection is performed according to the strength of the measured magnetic field. The voltage V ₂ is detected. The value of the detection voltage V _{2 is} a value obtained by multiplying the difference between the resistance value of the resistor 21 and the resistance value of the resistor 22 by ½ of the constant output current of the non-inverting amplifier 1.

By the way, since the temperature characteristic of the output voltage of the detection element 2 is -0.05% / ° C and the temperature characteristic of the sensing resistor is 0.3% / ° C, the temperature characteristic is 0.35% / ° C.
An input voltage V ₁ of ° C is applied to prevent the detection voltage V ₂ from being affected by temperature changes.

Since the detection element 2 and the sensing resistor 3 are formed on the same substrate by the same process, the variations in the resistance value due to the process are almost the same between the detection element 2 and the sensing resistor 3, and the detection element is almost the same. The variation in the ratio between the resistance value of No. 2 and the resistance value of the sensing resistor 3 can be set to ± 1% or less. Since the detection voltage V ₂ is proportional to the ratio of the resistance value of the detection element 2 and the resistance value of the sensing resistor 3, the variation of the detection voltage V ₂ can be set to ± 1% or less. In the prior art, the variation in the resistance value due to the process of the detection element is ± 25%, while the sensing resistance having a constant resistance value is used, the resistance value of the detection element and the resistance value of the sensing resistance are therefore used. The variation of the ratio is ± 25%, and the variation of the detection voltage is also ± 25%. Therefore, by using the sensor output stabilizing circuit according to the present invention, it is possible to perform remarkably accurate measurement as compared with the prior art.

It is also possible to provide a trimming portion in the sensing resistor 3 to enable fine adjustment of the resistance value and to adjust the output voltage V ₂ .

3 and 4 are block diagrams of a sensor output stabilizing circuit according to the second embodiment (corresponding to claim 4). 3 and 4, the present embodiment is a sensor output stabilizing circuit configured by using a monolithic circuit without using the non-inverting amplifier in the first embodiment.

In the figure, Q ₁ is a first transistor, and Q ₂ is a _second transistor having a larger capacity than the first transistor Q ₁ . S ₁ is a first constant current circuit for supplying a constant current to the first transistor Q ₁ , and S ₂ is a second constant current circuit for supplying a constant current to the second transistor Q _2. is there. S ₃ is a constant current circuit that controls the constant currents of the first constant current circuit and the second constant current circuit. Q ₃ is the third transistor. The base of the third transistor Q ₃ is mutually connected to the bases of the first and second transistors Q ₂ and Q ₃ described above, and the emitter of the _third transistor Q ₃ is the first transistor Q ₁ Connected to the emitter.
Reference numeral 2 denotes a detection element connected between the collector of the third transistor Q ₃ and the power supply, and the resistance value of the detection element 2 changes depending on the detected physical quantity. Then, the terminal voltage of the detection element ₂ is output as the detection voltage V ₂ . Reference numeral 3 denotes a sensing resistor connected between the emitter of the first transistor Q _{1 and} the emitter of the second transistor Q ₂ . Further, Q is a transistor and R is a resistor.

Next, the operation of the circuit of this embodiment will be described. A current proportional to the current generated by dividing the voltage generated at the connection point 10 in the figure by the resistance value of the sensing resistor 3 flows through the detection element 2. Therefore, the detection voltage V ₂ generated at the terminal of the detection element 2 is proportional to the ratio of the resistance value of the detection element 2 and the resistance value of the sensing resistor 3. The voltage generated at the connection point 10 has a temperature characteristic of 0.35% / ° C, and the sensing resistor 3 has a temperature characteristic of 0.3% / ° C, so that the current flowing through the sensing resistor 3 is 0. It has a temperature characteristic of 0.05% / ° C. Therefore, the collector current of the transistor Q ₃ has a temperature characteristic of 0.05% / ° C. on the other hand,
Since the temperature characteristic of the resistance of the detection element 2 is −0.05% / ° C., the detection voltage V ₂ is not affected by the temperature change. Further, since the detection element 2 and the sensing resistor 3 are formed on the same substrate by the same process, the detection element 2 and the sensing resistor 3 may be different in the resistance value due to the process.
And are almost the same, and the ratio of these two resistance values is almost constant. Therefore, the variation of the detection voltage is ± 1%
The following is extremely small and accurate measurement is possible.

5 and 6 are block diagrams of a sensor output stabilizing circuit according to a third embodiment (corresponding to claim 5). 5 and 6, the present embodiment is also a sensor output stabilizing circuit configured by using a monolithic circuit without using the non-inverting amplifier in the first embodiment.

In the figure, S ₄ is a band gap type reference voltage generating circuit. Band gap is absolute zero (-
(273.18 ° C.), which is the voltage peculiar to the substance at 1.273 V in the case of silicon. This voltage has a negative temperature coefficient (about -2.5 mV / ° C) and becomes about 0.7 V at room temperature. The bandgap type reference voltage generating circuit is a circuit which generates a constant voltage of 1.24 V by adding a circuit having a temperature coefficient of +2.5 mV / ° C. to the voltage of about 0.7 V. Q ₄ is a transistor to which a reference voltage generated by the band gap type reference voltage generating circuit S ₄ is applied as a base. Reference numeral 2 is a detection element whose resistance value changes according to the detected physical quantity, and 3 is a sensing resistance. Also, Q
Is a transistor, R is a resistor, and C is a capacitor.

Next, the operation of the circuit of this embodiment will be explained.
Reveal The connection point 11 in the figure has a bandgap reference
The voltage generated by the voltage appears. This voltage depends on the temperature
It is a constant 1.24V which does not change. So the tiger
Register Q_FourThe voltage generated at the emitter of 1.24 ×
(1 + R₂₀₂/ R₂₀₁) And changes with temperature
Absent. However, in general, the base
The voltage generated between the two terminals is -2 mV / ° C.
It is constant and does not vary. Therefore, the transistor Q
_FourEmitter voltage has a constant slope with temperature
Therefore, the above resistance value R₂₀₁Or R
₂₀₂Is selected appropriately, the temperature characteristics of the sensing resistor 3
Can be largely compensated. As a result, Senshin
The current flowing through the resistor 3 can be made almost constant.
It On the other hand, the temperature coefficient of resistance of the detection element 2 is extremely small.
Therefore, the detection voltage V which is a voltage drop in the detection element 2
₂Is almost unaffected by temperature. In addition, the detection voltage V₂Is
In the ratio of the resistance value of the sensing element 2 and the resistance value of the sensing resistor 3,
Since it is proportional, the detection element 2 and the sensing resistor 3 are the same
In this embodiment, which is formed on the same substrate by a process
Therefore, the detection voltage V ₂Variation due to
It can be ± 1% or less.

[0025]

As described below, in the sensor output stabilizing circuit according to the present invention, since the detection element and the sensing resistor are formed on the same substrate in the same process, variations in the resistance value due to the process are different from those of the detection element. It is almost the same as the sensing resistance. Since the detection voltage is proportional to the ratio between the resistance value of the detection element and the sensing resistance value, the variation in the detection voltage due to the process can be reduced to ± 1% or less, which is significantly higher than the variation in the detection voltage of ± 25% in the conventional technique. Few.

Therefore, the present invention prevents the occurrence of an error in the detection voltage due to the variation in the resistance value of the detection element,
A sensor output stabilizing circuit that enables accurate measurement can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a sensor output stabilizing circuit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a detection element and a sensing resistor of the sensor output stabilizing circuit according to the present invention.

FIG. 3 is a configuration diagram of a sensor output stabilizing circuit according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a sensor output stabilizing circuit according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a sensor output stabilizing circuit according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a sensor output stabilizing circuit according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram of a sensor output circuit according to a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 non-inverting amplifier 2 detection element (present invention) 3 sensing resistance (present invention) 4 detection element (prior art) 5 sensing resistance (prior art) 6 output terminal of non-inverting amplifier 7 negative input terminal of non-inverting amplifier 8 non Positive side input terminal of inverting amplifier 9 Detection terminal 10/11 Connection point S ₁ First constant current circuit S ₂ Second constant current circuit S ₃ Constant current control circuit S ₄ Bandgap type reference voltage generation circuit Q ₁・ Q ₂・ Q ₃・ Q ₄ transistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Naruse Tani Narisei 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Michiko Endo 1015, Kamedota, Nakahara-ku, Kawasaki, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Katsuya Shimizu, 2-1,844, Kozoji-cho, Kasugai-shi, Aichi, Fujitsu Limited

Claims (5)

[Claims] 1. A detection element (2), which has a bridge structure and whose resistance value changes with a detected physical quantity, is connected between an output terminal (6) and a negative side input terminal (7) of a non-inverting amplifier (1). The negative input terminal (7) is grounded via a sensing resistor (3), and in the sensor output circuit that outputs a detection voltage from the middle of the bridge of the detection element (2), the sensing resistor (3) Is a sensor output stabilizing circuit, which is formed on the same substrate by the same process as that of the detection element (2). 2. The sensor output stabilizing circuit according to claim 1, wherein the detection element (2) is composed of a ferromagnetic thin film magnetoresistive element. 3. The sensor output stabilization according to claim 2, wherein the sensing resistor (3) is formed by connecting elements having positive and negative magnetic field characteristics in series, and resistance change due to a magnetic field is canceled. circuit. 4. A first constant current circuit for energizing a constant current to the first transistor _{(Q 1) (S 1)} , said first transistor (Q ₁₎ from a large capacity, base first A second constant current circuit (S ₂ ) for supplying the same constant current as the first constant current circuit to a _second transistor (Q ₂ ) connected to the base of the transistor (Q ₁ ) of
A constant current control circuit (S ₃ ) for controlling a constant current in the first constant current circuit (S ₁ ) and the second constant current circuit (S ₂ ), and a first transistor (Q ₁ ) A base is connected to a sensing resistor (3) connected between an emitter and the emitter of the _second transistor (Q ₂ ) and a base of the first transistor (Q ₁ ), and the emitter is the first transistor (Q ₁ ). A third transistor (Q ₃ ) which is connected to the emitter of the transistor (Q ₁ ) and the collector of which is connected to the power source through the detection element (2) whose resistance value changes according to the detected physical quantity; A sensor output stabilizing circuit, wherein the terminal voltage of (2) is used as a detection voltage, and the sensing resistor (3) is formed on the same substrate by the same process as the detection element (2). 5. A bandgap reference voltage generating circuit (S
₄ ) The reference voltage output by the transistor (Q ₄ ) is applied to the base of the transistor (Q ₄ ), and the collector of the transistor (Q ₄ ) is connected to the power source via the detection element (2) whose resistance value changes according to the detected physical quantity, and the emitter Is grounded through a sensing resistor (3), and the terminal voltage of the detection element (2) serves as a detection voltage. The sensing resistor (3) has the same process as the detection element (2) on the same substrate. A sensor output stabilizing circuit, characterized in that