JPH06152257A - Voltage-current conversion circuit - Google Patents

Abstract

PURPOSE:To reduce an influence of the supply voltage variance or the noise by giving a margin to the supply voltage of a voltage-current conversion circuit. CONSTITUTION:The connector of a transistor TR Q5 is connected to the collector of a TR Q1 for the purpose of reducing the number of stages of TRs. This connection reduces the number of stages of TRs to three, and the voltage required for the use without saturation of TRs is three times as high as a forward voltage VBE of TRs; and therefore, a margin is given to the supply voltage, and an influence of the variance of the supply voltage is reduced. This circuit is robust against the noise because the signal amplitude can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage / current conversion circuit.

[0002]

2. Description of the Related Art A conventional voltage-current conversion circuit will be described with reference to FIG. This voltage-current conversion circuit includes transistors Q1, Q2, Q3 and Q4, and the transistors Q1 and Q2 mutually form a current mirror circuit. The resistor R1 is connected as the emitter resistance of the transistor Q1, and the resistor R2 is connected as the emitter resistance of the transistor Q2. The resistors R1 and R2 are each connected to a power supply. Here, the current mirror has two stages in order to improve the precision of the mirror coefficient. The emitters of the transistors Q3 and Q4 are connected to the collectors of the transistors Q1 and Q2, respectively, to form a current mirror circuit with each other. The collector of the transistor Q5 is connected to the collector of the transistor Q3, and the emitter of the transistor Q5 is Darlington-connected to the base of the transistor Q6.

The input signal is input from the positive terminal of the operational amplifier 10 connected to the terminal 1 and supplied from the output of the operational amplifier 10 to the base of the transistor Q5. Further, the negative feedback is provided from the emitter of the transistor Q6 to the operational amplifier 10.

Therefore, the terminals 1 and 3 have the same potential. The current I3 flowing through the terminal 3 is I3 = resistor R3 connected between the terminal 3 and the ground and the voltage V1 at the terminal 1
A current of V1 / R3 flows.

When the current flowing through the resistor R3 is determined, the same amount of current flows in the transistor Q1, and the current of the transistor Q2 is (R1 /
R2) times the current flows, and this current is taken out from the terminal 4 as an output current. Current I1 flowing through resistors R1 and R2
In order to improve the accuracy of the current ratio of I2 and I2, the current mirror has two stages. Further, on the input side of the current mirror, in order to reduce the influence from the input and improve the accuracy of the current mirror, the Darlington circuit of the transistors Q5 and Q6 is connected to the output side of the transistor Q3 and the transistor Q6 is connected.
The base current of is corrected.

[0006]

In the conventional voltage-current conversion circuit, since four transistors are connected in series between the transistors Q1 to Q6 and the power source to the ground, the forward voltage V _BE of the transistor is four times the forward voltage V _BE . Therefore, a power supply voltage of about 3V is required at a minimum. Considering the signal amplitude and the voltage drop across the resistors R1 and R3, the maximum potential that can be taken by the terminal 3 is 2 V or less when the power supply voltage is 5V. For this reason, the input voltage range is extremely narrowed and the signal voltage at the terminal 1 cannot be made large, so that it is easily affected by noise. In addition, there is a drawback that it does not operate normally when the voltage drops due to fluctuations in the power supply voltage.

[0007]

The voltage-current conversion circuit of the present invention comprises a first current mirror circuit comprising first and second transistors having at least one current output terminal, and the first current. There is a second current mirror circuit composed of third and fourth transistors connected to the output terminal of the first transistor of the mirror circuit, and the output terminal of the first transistor has the output terminal of the operational amplifier as an input. The Darlington circuit composed of the fifth and sixth transistors is connected to the third transistor which is the input of the second current mirror circuit, and the output of the Darlington circuit and the inverting input terminal of the operational amplifier are negatively fed back. And a resistor for converting the voltage of the non-inverting input terminal of the operational amplifier into a current in the output of the Darlington circuit,
A current converting means for supplying as an input electrode to the second transistor, which is an input terminal of the second current mirror circuit, is provided, and a predetermined current is output from an output terminal including a fourth transistor of the second current mirror circuit. The Darlington circuit including the output terminal of the first transistor, the fifth and sixth transistors, and the third transistor, which is the input of the second current mirror circuit, are connected to each other.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A voltage / current conversion circuit according to a first embodiment of the present invention will be described with reference to FIG. The voltage-current conversion circuit of this embodiment includes transistors Q1, Q2, Q3 and Q4.
And the transistors Q1 and Q2 form a current mirror circuit with each other. The resistor R1 is connected as the emitter resistance of the transistor Q1, and the resistor R2 is connected as the emitter resistance of the transistor Q2. The resistors R1 and R2 are then connected to the power supply. Next, the emitters of the transistors Q3 and Q4 are respectively connected to the transistor Q1.
And the collectors of Q2 to form a current mirror circuit. The collector of transistor Q5 is connected to the collector of transistor Q1 and the emitter of transistor Q5 is Darlington connected to the base of transistor Q6. The input signal is input from the positive terminal of the operational amplifier and is connected from the output of the operational amplifier to the base of the transistor Q5. Further, it has a configuration in which a negative feedback is applied from the emitter of the transistor Q6 to the operational amplifier. The current value output from the output terminal 4 of this current mirror circuit is determined by the input voltage and the resistors R3, R1 and R2.

The output of the operational amplifier 10 is the transistor Q5.
Since the negative feedback is connected to the operational amplifier 10 via Q6 and Q6, the terminals 1 and 3 have the same potential. The current I3 flowing through the resistor R3 is I due to the resistor R3 connected between the terminal 3 and the ground and the voltage V1 at the terminal 1.
R3 = V1 / R3 is determined. When the current flowing through the resistor R3 is determined, the current I4 flowing through the terminal 4 is determined by the current mirror.

Since the collector of the transistor Q5, which is connected to the collector of the transistor Q1, and the collector of the transistor Q5, and the emitter of the transistor Q3 of the current mirror circuit are connected in common, the lowest voltage that can be used without saturating the transistor is as compared with the conventional example. Therefore, the forward voltage V _BE of the transistor Q3 is reduced by only the forward voltage V _{BE of} 3 transistors.

Next, the voltage-current conversion of the second embodiment of the present invention will be described with reference to FIG.

The voltage-current conversion circuit of the second embodiment is
It has a first current mirror circuit composed of transistors Q1 and Q2, and the emitters of transistors Q3 and Q4 are connected to the collector of transistor Q1 and the base of transistor Q2, respectively, to form a second current mirror circuit. The output of the transistor Q4 is connected to the terminal 5, and the output of the transistor Q2 is used as the output current. Other than that, the configuration is the same as that of the first embodiment, so detailed description will be omitted.

Since the output of the voltage-current conversion circuit of the second embodiment is only the transistor Q2, the forward voltage V _{BE of the} transistor is one less than that of the conventional one, so that the output voltage range can be widened. .

[0014]

As described above, according to the present invention, when the signal is input from the terminal 1 and the output current is obtained by the current mirror circuit, the precision of the mirror coefficient is very high because the current mirror has two stages. Further, because of the configuration of the transistor Q5 and the second current mirror circuit, three transistors are inserted between the power supply and the ground, so the voltage required for circuit operation is smaller than the conventional one by one forward voltage VBE of the transistor. Therefore, the current mirror circuit becomes about the same as when it has one stage. As a result, the signal voltage range can be widened, and the signal is resistant to noise.
Even if the circuit is configured by changing the polarity of the transistor, it is obvious that the operation has no inconvenience and has the same effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a voltage-current conversion circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a voltage-current conversion circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional voltage-current conversion circuit.

[Explanation of symbols]

 1 to 5 terminals 10 operational amplifiers R1 to R3 resistors Q1 to Q6 transistors

Claims (1)

[Claims] 1. A first current mirror circuit composed of first and second transistors having at least one current output terminal, and an output terminal of the first transistor of the first current mirror circuit. A second current mirror circuit composed of third and fourth transistors, wherein the output terminal of the first transistor is a Darlington circuit composed of fifth and sixth transistors with the output terminal of the operational amplifier as an input. A third transistor which is an input of the second current mirror circuit is connected, the output of the Darlington circuit and the inverting input terminal of the operational amplifier are connected so as to form a negative feedback, and the output of the Darlington circuit is connected. In addition, the second transistor, which is an input terminal of the second current mirror circuit, has a resistor for converting the voltage of the non-inverting input terminal of the operational amplifier into a current. A current converting means for supplying as an input electrode is provided, and a predetermined current is output from an output terminal formed of a fourth transistor of the second current mirror circuit, and an output terminal of the first transistor and the fifth and sixth terminals. A voltage-current conversion circuit characterized in that a Darlington circuit composed of a transistor and a third transistor which is an input of the second current mirror circuit are connected.