JPH033403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a voltage-current conversion circuit that converts voltage to current using a differential amplifier, and particularly relates to adjustment of the maximum value of the converted current value.

Conventional technology A voltage-current conversion circuit using a differential amplifier is
As shown in the figure, the emitters of a pair of transistors 2 and 4 are commonly connected, a constant current source 6 is installed on the emitter side, the collector of transistor 2 is connected to the positive potential line, and the transistor 4
A current mirror circuit consisting of transistors 8 and 10 is installed on the collector side of the transistor to take out the output current. A variable voltage source 12 is connected between the base of transistor 2 and the ground line, and a constant reference bias voltage is set between the base of transistor 4 and the ground line by constant voltage source 14. A driving power source is connected between the positive potential line and the ground line, and V _CC is the voltage thereof.

In such a voltage-current conversion circuit, the emitter area of the transistor 2 is set to a times the emitter area of the transistor 4, the constant current given by the constant current source 6 is I _A , and the voltage set by the constant voltage source 14 is
If V _B , then by adjusting the voltage V _I of the variable voltage source 12, the current flowing through the transistors 2 and 4 will be divided according to the difference voltage (V _I - V _B ) between the voltage V _I and the voltage V _B. A current I _O flowing to the transistor 4 side is taken out from the transistor 10.

The relationship between this current I _O and the differential voltage (V _I − V _B ) is
This is given by the relationship shown in FIG.

Problems to be Solved by the Invention In the case of this voltage-current conversion circuit, the upper limit current value for the input voltage is fixed at the constant current value I _A of the constant current source 6, and the upper limit current value is determined by the circuit conditions. Unable to adjust value to arbitrary value.

Therefore, it is an object of the present invention to provide a voltage-current conversion circuit that allows the upper limit of the converted current value to be arbitrarily adjusted and that allows the upper limit current value to be precisely set.

Means for Solving the Problems The present invention provides first and second differential amplifiers whose output currents are adjusted according to input voltage, a variable constant current source whose output currents can be adjusted and a first current mirror circuit that adds the output of the variable constant current source to the output side of the differential amplifier; a current given to the differential amplifier from the first current mirror circuit; and an output current of the first differential amplifier. The second to take out the difference current between
and a third current mirror circuit that outputs a difference current between the current from the second current mirror circuit and the output current of the second differential amplifier.

Operation The first and second differential amplifiers generate a predetermined output current depending on the input voltage. On the other hand, the variable constant current source generates a desired constant current, and this constant current is combined with the output current of the first differential amplifier by the first current mirror circuit, and the difference current is The difference current between the output current of the second differential amplifier and the current from the second current mirror circuit is combined with the output current of the second differential amplifier via the second current mirror circuit.
It is output from the third current mirror circuit.

Therefore, a current corresponding to the input voltage is output from the third current mirror circuit, and the upper limit current value is adjusted to a desired value by the variable current source.

Embodiments Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of the voltage-current conversion circuit of the present invention.

In FIG. 1, this voltage-current conversion circuit includes:
First and second differential amplifiers 20A and 20B are installed. That is, transistors 22,2
4 and constant current source 26 constitute a first differential amplifier 20A, and transistors 28 and 3 constitute a first differential amplifier 20A.
0 and the constant current source 32 constitute a second differential amplifier 20B.

The emitter area of the transistor 22 is set to be a times the emitter area of the transistor 24, and the emitter area of the transistor 28 is also set to be a times the emitter area of the transistor 30.

A variable voltage source 34 is commonly connected to the base of each transistor 22, 28, and a bias voltage V _I of a desired value is set to be adjusted. is connected, and a constant reference bias voltage V _B is set.

The collectors of the transistors 22 and 28 are commonly connected to the positive potential line, and a first current mirror circuit 38 is installed on the collector side of the transistor 28. The first current mirror circuit 38 is made up of transistors 40 and 42, and inverts the constant current flowing through the variable current source 44 to connect the first differential amplifier 20A.
Add to the output side of.

Further, a second current mirror circuit 46 is installed between the collectors of the transistors 24 and 30. This second current mirror circuit 46 is composed of transistors 48 and 50, and transistor 24
The difference current between the current drawn by the transistor 42 and the current supplied from the transistor 42 is inverted and supplied to the collector side of the transistor 30.

And on the collector side of the transistor 30,
A third current mirror circuit 52 is provided to take out the difference current between the current drawn by transistor 30 and the current supplied by transistor 50. This third current mirror circuit 52 is composed of transistors 54 and 56.
The difference current flowing through the transistor 56 is taken out from the collector of the transistor 56.

The operation will be explained based on the above configuration.

The constant current flowing through the constant current sources 26 and 32 is I _A , the constant current flowing through the variable current source 44 is I _B , and the constant currents I _A , I _B
Let the magnitude relationship be I _A ≧ I _B.

It is assumed that current I _A flows through transistors 24 and 30 when voltage V _I =0 is set across transistors 22 and 28 by variable voltage source 34 .

At this time, the current I _B flowing through the variable current source 44 is
The current flows from the transistor 42 to the transistor 24 via the first current mirror circuit 38 and is combined with the current I _A flowing through the transistor 24 . That is, a difference current given by (I _A - I _B ) is generated. If current I _A is smaller than current I _B (I _A <I _B ), transistor 42 is saturated.

The differential current (I _A −I _B ) generated on the collector side of the transistor 24 is supplied to the collector side of the transistor 30 via the second current mirror circuit 46 and is combined with the current I _A flowing through the transistor 30 .

On the collector side of the transistor 30, I _A −(I _A
−I _B ), and this difference current I _A
−(I _A −I _B )=I _B is inverted by the third current mirror circuit 52 and taken out from the emitter of the transistor 56 as an output current I _O.

That is, when the voltage V _I =0, the output current I _O is
I _B , and the maximum value of the output current I _O is the variable current source 4
It is given by the current I _B of 4. Therefore, the values are as shown by a, b, c and d in FIG.
It can be arbitrarily adjusted by a variable current source 44.

Further, when the voltage V _I is increased from 0, an output current I _O corresponding to the voltage (V _I −V _B ) is extracted, which is similar to the conventional voltage-current conversion circuit shown in FIG. That is, this is transistor 2
If the current flowing through the collector of 4.30 is I _C , then
Depending on the value of voltage V _I , in the region I _O ≧ I _B , I _C = I _B , I _C
This is clear from the fact that in the region <I _B , I _O ≧ I _C .

The variable current source 44 may be composed of a transistor 53, a resistor 55, a differential amplifier 58, and a voltage-current converter 45, as shown in FIG. That is, when the control voltage V _C is set to the voltage setting terminal 60 formed at the non-inverting input terminal (+) of the differential amplifier 58, the differential amplifier 58 supplies a current to the transistor 53 according to the control voltage V _C. A current corresponding to the control voltage V _C flows through the transistor 53 . This current causes a voltage drop in the resistor 55, and this voltage drop is fed back to the inverting input terminal (-) of the differential amplifier 58, and a constant current according to the control voltage V _C flows through the transistors 40 and 53.

According to such a voltage-current converter 45, the maximum value of the output current can be adjusted by the voltage applied to the voltage setting terminal 60, and can be accurately set to any value.

FIG. 4 shows an application example of the voltage-current conversion circuit of the present invention, in which parts common to the embodiments shown in FIGS. 1 and 3 are given the same reference numerals.

In this embodiment, the voltage-current conversion circuit of the present invention is used to control the gain of an amplifier, and the voltage applied to the voltage setting terminal 60 becomes the operating current of the amplifier 62 after being converted to a current. , an amplification gain can be set in the amplifier 62 according to the voltage applied to the voltage setting terminal 60.

That is, the output of the voltage-current converter 45 is applied to the first current mirror circuit 38 via a current mirror circuit consisting of transistors 64 and 66, and the first differential amplifier 20A is connected to PNP type transistors 23 and 25. and a constant current source 27,
The second differential amplifier 20B is composed of PNP type transistors 29 and 31 and a constant current source 33. The first current mirror circuit 38 has NPN type transistors 41 and 43, and the second current mirror circuit 46 has NPN type transistors 41 and 43.
NPN type transistors 49, 51, and the third current mirror circuit 52 have PNP type transistors 57,
59, and each circuit is composed of transistors of a conductivity type opposite to that of the embodiment.

The variable gain amplifier 62 includes transistors 68, 70, 72, 74, 76, 78, 8
0, 82, a resistor 84, and a voltage source 85. A differential amplifier is configured by the transistors 68 and 70, and when, for example, an audio signal is applied to an input terminal 86 formed in the transistor 68, it is amplified based on an arbitrarily adjusted gain.
The amplified output is output from the output terminal 88 to the outside.

By coupling the voltage-current conversion circuit of the present invention to such a variable gain amplifier,
A desired amplification gain can be arbitrarily and accurately set by voltage, a desired signal amplification can be realized, and the maximum gain can be adjusted and set accurately.

Effects of the Invention As explained above, according to the present invention, the following effects can be obtained.

(1) In voltage-current conversion, the maximum value of the converted current value can be adjusted to a desired value and set accurately.

(2) The maximum value of the converted current value can be easily and accurately adjusted by operating the variable current source regardless of the input voltage, and the variable current source can also be operated by adjusting or subtracting the voltage. can.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the voltage-current conversion circuit of the present invention, FIG. 2 is an explanatory diagram showing its operation,
Fig. 3 is a circuit diagram showing another embodiment of the voltage-current conversion circuit of the present invention, Fig. 4 is a circuit diagram showing an application example of the voltage-current conversion circuit of the invention, and Fig. 5 is a conventional voltage-current conversion circuit. FIG. 6 is an explanatory diagram showing its operation. 20A...first differential amplifier, 20B...second differential amplifier, 38...first current mirror circuit, 44...
Variable current source, 46...Second current mirror circuit, 52
...Third current mirror circuit.

Claims (1)

[Claims] 1. The first stage where the output current is adjusted according to the input voltage.
and a second differential amplifier, a variable constant current source whose output current can be adjusted, and a first current mirror circuit that adds the output of the variable constant current source to the output side of the first differential amplifier. a second current mirror circuit that takes out the difference current between the current given to the differential amplifier from the first current mirror circuit and the output current of the first differential amplifier; A voltage-current conversion circuit comprising: a third current mirror circuit that outputs a difference current from the output current of the second differential amplifier.