JPH11122056A - Offset compensating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ovoid the effects of variations in source voltage, even at a low source voltage time by inputting the output of a reference voltage generation which is connected between a positive and a negative power source to a 1st differential amplifier and inputting its output to the positive and negative of a 2nd differential amplifier. SOLUTION: An anode of a Zener diode 3 for reference voltage generation is connected to the plus input of a 1st differential amplifier 1 and a cathode is connected to the negative input to obtain and input a stable reference voltage free of the effects of variations of power sources Vcc and Vee as the output voltage of the differential amplifier 1 to attenuating circuits 6 and 7, whose outputs are inputted to adding circuits 8 and 9. The power source voltage variation effects can be avoided by adjusting the attenuation quantities of the attenuating circuits 6 and 7, so that the offset voltage generated when there is no cross-linking magnetic flux to a Hall element 5 is canceled. The anode and the cathode of the Zener diode 3 are passed through a constant-current circuit 10 to input a constant current to a terminal 11 of the H all element 5 and the power source Vee to a terminal 13, and this is driven with the constant current to stabilize temperature characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to offset compensation of a sensing circuit using a hall element, an operational amplifier and the like.

[0002]

2. Description of the Related Art A current sensor has been developed in which a coil is wound around a core and a magnetic flux proportional to a current flowing through the coil is generated inside the core, the magnetic flux is detected by a Hall element, and the signal is converted into a voltage. ing. The Hall element used therein has an offset voltage which is generated even if the magnetic flux which is the input is zero due to manufacturing variations. Conventionally, in order to compensate for this offset voltage, as shown in FIG. 3, Zener diodes 21 and 22 are used as reference voltage generators, the voltage is adjusted by a variable resistor 23, and the output is added via an adder circuit 8. Input to the differential amplifier to compensate.

[0003]

In recent years, the use of current sensors has expanded, and there is a demand for a low power supply voltage of ± 5 V when using them. In response to such a demand, a conventional offset compensation circuit using a Zener diode as a reference voltage generator has a problem that a large fluctuation in offset voltage due to a fluctuation in power supply voltage remains. This essential problem arises from the fact that the stability is degraded when the Zener diode itself has a low voltage.

[0004]

The present invention has the following circuit to solve these problems. An offset characterized in that the output of a reference voltage generator connected between a positive and a negative power supply is input to a first differential amplifier, and the output is input to a plus and a minus of a second differential amplifier. Compensation circuit.

[0005]

The reference voltage generator connected between the positive and negative power supplies generates a voltage fluctuation of an in-phase component with respect to the power supply voltage fluctuation. This is input to the first differential amplifier. Then, only the voltage of the reference voltage generator, which is not affected by the power supply voltage fluctuation, is generated from the output due to the common mode signal rejection ratio of the differential amplifier.
The offset voltage can be compensated from positive to negative by changing the ratio of the positive and negative inputs of the second differential amplifier.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a current sensor using an offset compensation circuit according to the present invention. 1 is a first differential amplifier 2 is a second differential amplifier 3 is a Zener diode for generating a reference voltage 4 is a resistor 5 Hall elements 6 and 7 are attenuation circuits 8 and 9 are addition circuits 10 are constant current circuits. Vcc is a positive power supply, and Vee is a negative power supply.

As shown in FIG. 1, the cathode of the Zener diode 3 is connected to Vcc, the anode of the Zener diode 3 is connected to a terminal having a resistor 4, and the other end of the resistor 4 is connected to Ve.
e. Assuming that Vcc = + 5V and Vee = -5V, there is a voltage of 10V, so that 5.1V having good characteristics can be used for the Zener diode 3.

The anode of the Zener diode 3 is connected to the positive input of the differential amplifier 1, and the cathode of the Zener diode 3 is connected to the negative input of the differential amplifier 1. Therefore,
The output voltage of the differential amplifier 1 generates a stable reference voltage which is not affected by fluctuations of the power supplies Vcc and Vee. This is input to attenuation circuits 6 and 7, and the respective outputs are input to adders 8 and 9. Here, if the attenuation of the attenuation circuits 6 and 7 is adjusted so as to cancel the offset voltage generated when the flux linkage to the Hall element is zero, an offset adjustment circuit that is not affected by the power supply voltage can be realized.

On the other hand, the anode and cathode of the Zener diode 3 are also connected to a constant current circuit 10 to generate a current based on the input voltage. The output of the constant current circuit is connected to the input terminal 11 of the Hall element 5, and the input terminal 13 on the opposite side is connected to Vee, so that the Hall element 5 is driven with a constant current. This is generally performed in order to stabilize the temperature characteristic of the sensitivity of the Hall element when driven by a constant current.

As described above, when the Hall element is driven at a constant current and the magnetic flux is linked to the Hall element, the Hall voltage Vh is changed to the output terminal 1 of the Hall element 5 by the so-called Hall effect.
Occurs between 2 and 14. If this is input to the second differential amplifier and amplified, a voltage proportional to the magnetic flux linked to the Hall element can be obtained. By utilizing this, a magnetic flux proportional to the current flowing through the coil by winding the coil around the core is generated inside the core, and the magnetic flux is detected by a Hall element, whereby a current sensor can be configured.

FIG. 2 shows an actual circuit diagram. FIG. 4 shows the power supply voltage fluctuation characteristic of the offset voltage realized by this circuit.
Shown in If the power supply voltage fluctuation characteristic is within about ± 30 mV, it is sufficient for practical use, and FIG. 4 shows that this is satisfied. It should be noted that the present invention contributes to a reduction in production cost because only one zener diode is required as a reference voltage source as compared with the related art.

[0012]

As described above in detail, according to the present invention, even at a low power supply voltage, the offset voltage can be adjusted without being affected by the power supply voltage fluctuation.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing a power supply voltage fluctuation characteristic of an offset voltage according to the embodiment of the present invention.

FIG. 3 shows a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st differential amplifier 2 2nd differential amplifier 3 Zener diode for reference voltage generation 4 Resistance 5 Hall element 6, 7 Attenuation circuit 8, 9 Addition circuit 10 Constant current circuit

[Procedure amendment]

[Submission date] January 29, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing a power supply voltage fluctuation characteristic of an offset voltage according to the embodiment of the present invention.

FIG. 4 shows a conventional example.

[Description of Signs] 1 First differential amplifier 2 Second differential amplifier 3 Zener diode for generating reference voltage 4 Resistor 5 Hall element 6, 7 Attenuation circuit 8, 9 Addition circuit 10 Constant current circuit 11, 13 Hall Element input terminals 12, 14 Hall element output terminals

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

[Correction contents]

FIG. 2

Claims (3)

[Claims] An output of a reference voltage generator connected between a positive power supply and a negative power supply is input to a first differential amplifier, and the output is input to plus and minus of a second differential amplifier. An offset compensation circuit characterized in that: 2. An offset compensation circuit, wherein a zener diode is used for the reference voltage generator according to claim 1. 3. An output of the reference voltage generator according to claim 1 is input to a constant current circuit, an output of which is connected to an input of a Hall element, and an output of the Hall element is input to the second differential amplifier. And an output compensating circuit for obtaining a voltage whose output is proportional to the magnetic flux linked to the Hall element.