JPH08233867A - Bridge detection circuit - Google Patents

Abstract

PURPOSE: To compensate for and improve the linearity of a detection circuit detecting a current in a non-contact manner or a circuit detecting a magnetic change. CONSTITUTION: This detecting circuit is in the constitution of a bridge comprising a semiconductor magnetoresistance element R11 and three reference resistors R12, R13 and R14 to convert a near-by passing current or a magnetic flux change to a voltage signal by the magnetoresistance element. In the detecting circuit, an output of an amplifier circuit 2 for amplifying an output terminal of the bridge and a constant source voltage are negatively fed back by a synchronous addition circuit 3, which are impressed to an input terminal of a power source of the bridge thereby improving the linearity. The source voltage impressed to the synchronous addition circuit 3 is an output of a temperature compensation circuit 4 consisting of a semiconductor element and resistors, so that the temperature is compensated for as well as the linearity. The linearity can thus by compensated for in a wide dynamic range simply by adding the simple addition circuit, achieving high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit technique for compensating for and improving the linearity of a bridge detection circuit for non-contact current detection or a bridge detection circuit for detecting magnetic changes.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 4, a detection circuit for converting a proximity passing current or a change in magnetic flux into a voltage signal by a current detection circuit formed in a bridge by one semiconductor magnetoresistive element and three reference resistors is shown in FIG. , A temperature-compensated voltage is applied between the input terminals, and the output voltage is obtained by the differential amplifier having a constant gain between the output terminals. It does not change linearly.

That is, it is assumed that the resistance of the semiconductor magnetoresistive element to be detected changes from R to R + Δr due to the proximity passing current or the change in magnetic flux. Further, this resistance change Δr has a temperature characteristic of a temperature coefficient β (generally β <0), and if the temperature coefficients of the three reference resistors are minute and negligible, the terminal voltage ΔV becomes

[0004]

[Formula 1] Since this terminal voltage ΔV has a term of Δr in the denominator and numerator, it does not change linearly with respect to the resistance change Δr.

[0005]

For this reason, the conventional structure has a problem that it cannot be used only at a small Δr, or cannot be used linearly at full scale.

Further, in order to cancel the temperature dependence of Δr, V
It is a known technique to give IN a temperature characteristic in the opposite direction to the temperature characteristic of Δr. That is, the input voltage is VSUP and the base-emitter saturation voltage of the transistor Q4 is VB.
E

[0007]

[Formula 2] Than

[0008]

[Formula 3] Therefore, even if Δr decreases with respect to temperature due to the negative characteristic, V
Since BE has a negative characteristic with respect to temperature, VIN increases and Δr
Although the temperature dependence of can be canceled out, its effect is limited because the denominator and the numerator have a term of Δr.

The present invention is intended to solve the above-mentioned problems, and its object is to provide Δr possessed by the above-mentioned prior art.
Solves the problem that the linearity is maintained only in a very small range, or the limit of the dynamic range is therefor and the limit of temperature compensation, and the output voltage of the bridge is linear with respect to the resistance change of the semiconductor magnetic resistance element to be detected. The present invention provides a device that can be changed dynamically.

[0010]

In order to achieve the above-mentioned object, the present invention comprises a semiconductor magnetoresistive element and a reference resistance in a bridge, and the magnetoresistive element converts a proximity passing current or a magnetic flux change into a voltage signal. In the bridge detection circuit to do, an amplifier circuit for amplifying the output voltage of the bridge,
A synchronous adder circuit for inputting the output of the amplifier circuit and a power supply voltage and adding them in synchronization, and a negative feedback of the output of the amplifier circuit by the synchronous adder circuit, and applying it to the power supply input terminal of the bridge And a negative feedback circuit that operates.

Further, the present invention adopts a constitution characterized in that the power supply voltage applied to the synchronous adder circuit comprises an output of a temperature compensating circuit by a semiconductor element and a resistor.

[0012]

According to the present invention, in order to detect a change in the proximity passing current or the magnetic flux as described above, a semiconductor magnetoresistive element and a reference resistor are formed in a bridge, and the magnetoresistive element changes the proximity passing current or the magnetic flux change into a voltage signal. In the bridge detection circuit for converting to, an amplifier circuit that amplifies the output voltage of the bridge, and the output of the amplifier circuit and the power supply voltage are input,
Further, since the synchronous adder circuit for adding in a synchronized manner and the negative feedback circuit for applying the negative feedback of the output of the amplifier circuit to the power source input terminal of the bridge, the output of the bridge is provided. The voltage can be linearly changed with the resistance change of the magnetoresistive element to be detected over the entire dynamic range, and the linearity of the output voltage can be compensated.

Further, according to the present invention, in the bridge detection circuit, the constant power supply voltage applied to the synchronous adder circuit is composed of the output of the temperature compensation circuit by the semiconductor element and the resistor. It can be performed in combination with linearity compensation.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic circuit block diagram showing an embodiment of the bridge detection circuit of the present invention. Further, FIG. 2 is an example of the application circuit of FIG. 3 is a circuit configuration diagram showing an embodiment of the bridge detection circuit of the present invention. The present invention is used as shown in FIG. 2 to detect a proximity current or a change in magnetic flux.

In FIGS. 1 and 3, a proximity current or a magnetic flux change is detected through a resistance change of R11 in a bridge composed of one semiconductor magnetic resistance element R11 to be detected and three reference resistors R12, R13 and R14. .

The voltage applied to the input terminal is VIN, and R11
= R12 = R13 = R14 = R, assuming that the resistance change according to the proximity current and the magnetic flux change of R11 is Δr, the terminal voltage ΔV is

[0018]

[Formula 4] Becomes

Here, the gain (amplification factor) of the amplifier circuit 2 is set to K.
Assuming 1, the detection voltage VOUT is K1 · ΔV. The amplifier circuit 2 is composed of a known measurement differential amplifier, and K1 can be set by a resistance around the operational amplifier. VOUT = K1ΔV ... The output voltage VOUT and the constant voltage V are applied to the synchronous addition circuit 3 of the next stage. Where the addition ratio is

[0020]

[Formula 5] So that the resistors R31, R32, R of the synchronous adder circuit 3
33 is set as R33 / R31 = K2 and R32 = R33.

Then, the output of the synchronous adder circuit 3 is V +
It is K2 · VOUT. With this output as VIN, negative feedback is applied to the input terminal of the bridge.

That is, VIN = V + K2 · VOUT ...
Is established. ,Than

[0023]

[Formula 6] Substituting here,

[0024]

[Formula 7] This can be summarized as {4 · R- (2-K1 · K2) Δr}
VOUT = K1 · Δr · V.

Here, K1 · K2 = 2. That is, when the product of the gain of the amplifier circuit 2 and the magnification K2 of the synchronous addition circuit 3 is set to 2,

[0026]

[Formula 8] Therefore, the output voltage VOUT is an output that is linearly proportional to Δr, that is, the change of the magnetoresistive element to be detected.

If the magnetoresistive element has temperature characteristics, the output voltage is

[0028]

[Formula 9] Here, the temperature compensation circuit

[0029]

[Formula 10] When is applied, the temperature characteristic of Δr and the temperature characteristic of V work in opposite directions, and it is possible to perform temperature compensation.

[0030]

As described above, the present invention provides a bridge detection circuit in which a semiconductor magnetoresistive element and a reference resistance are formed in a bridge, and the magnetoresistive element converts a proximity passing current or a magnetic flux change into a voltage signal. , An amplifier circuit for amplifying the output voltage of the bridge, a synchronous adder circuit for inputting the output of the amplifier circuit and the power supply voltage, and adding them in synchronization, and an output of the amplifier circuit for negative output by the synchronous adder circuit. Since it consists of a negative feedback circuit that adds feedback and applies it to the power supply input terminal of the bridge, it is possible to perform linearity compensation with high versatility by adding a simple additional circuit as compared with the conventional one. It has an excellent effect.

Further, in the bridge detection circuit of the detection circuit, since the constant power supply voltage applied to the synchronous addition circuit is composed of the output of the temperature compensating circuit by the semiconductor element and the resistor, the temperature compensation of the output voltage is linearity compensation. It has an excellent effect that it can be done together.

[Brief description of drawings]

FIG. 1 is a schematic circuit block diagram showing an embodiment of a bridge detection circuit of the present invention.

FIG. 2 is an application circuit example of the bridge detection circuit shown in FIG.

FIG. 3 is a circuit configuration diagram showing an embodiment of a bridge detection circuit of the present invention.

FIG. 4 is a schematic circuit block diagram showing an example of a conventional detection circuit.

[Explanation of symbols]

 1 sensor including semiconductor magnetoresistive element 2 amplifier circuit 3 synchronous addition circuit 4 temperature compensation circuit 5 bridge detection circuit R11 of the present invention, semiconductor magnetoresistive elements R12, R13, R14 reference resistance R31, R32, R33 summing gain setting resistance R41 , R42 Temperature compensation resistor Q4 Temperature compensation transistor element

Claims (2)

[Claims] 1. A bridge detection circuit comprising a semiconductor magnetoresistive element and a reference resistance, wherein the magnetoresistive element converts a proximity passing current or a magnetic flux change into a voltage signal, and an amplifier for amplifying an output voltage of the bridge. Circuit,
A synchronous adder circuit for inputting the output of the amplifier circuit and a power supply voltage and adding them in synchronization, and a negative feedback of the output of the amplifier circuit by the synchronous adder circuit, and applying it to the power supply input terminal of the bridge And a negative feedback circuit for performing the bridge detection circuit. 2. The power supply voltage applied to the synchronous adder circuit is
The bridge detection circuit according to claim 1, wherein the bridge detection circuit comprises an output of a temperature compensation circuit including a semiconductor element and a resistor.