JPH04211503A - Voltage/current conversion circuit - Google Patents

Abstract

PURPOSE:To set arbitrary rate of change for an output current value obtained by the voltage/current conversion. CONSTITUTION:A first differential amplifier 1(a) using first and second transistors 2a and 4a whose emitter areas are changed at a certain ratio and a second differential amplifier using third and fourth transistors 2b and 4b whose emitter areas are changed at the certain ratio similarly are provided. By applying voltage to be converted into current to the base of the first and third transistors, an output current which is the voltage/current conversion output of the first and second differential amplifier having the rate of change for current set depending on the ratio of the emitter area via first and second current mirror circuit 14a and 14b installed corresponding to the first and second differential amplifiers can be taken out.

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 that converts voltage to current at an arbitrary rate of change.

FIG. 5 shows a conventional voltage-to-current conversion circuit composed of a differential amplifier. In this voltage-current conversion circuit, a pair of transistors 2 and 4 with a common emitter and a constant current source 6 constitute a differential amplifier that converts voltage into current. A driving power supply is connected, and Vcc is the power supply voltage. Note that transistors having the same current capacity are used as the transistors 2 and 4.

A voltage source 10 is connected between the base of the transistor 2 and the common line to apply a voltage V1 to be converted into a current, and a bias voltage source 12 is connected between the base of the transistor 4 and the common line. It is connected and voltage V2 is applied.

0004

By the way, in such a voltage-current conversion circuit, if the current flowing through the constant current source 6 is I and the current flowing through the transistor 2 is I1, then the change characteristic of the current I1 with respect to the voltage V1 - V2 is Figure 6
It is given by the curve shown in .

[0005] Here, when V1 - V2 = 0, the current I1 becomes I1 = I/2, and the rate of change of this current value is constant, so its applications are limited, such as controlling the amplification gain of an amplifier. was not suitable.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a voltage-current conversion circuit that can set an arbitrary rate of change in the output current value obtained by voltage-current conversion.

[0007]

[Means for Solving the Problems] That is, in the voltage-current conversion circuit of the present invention, first and second transistors (2a, 4a) whose emitter areas differ by a certain ratio have common emitters, A first constant current source (6a
), a voltage to be converted into a current is applied to the base of the first transistor, and a constant voltage is applied to the base of the second transistor.
a), and the third and fourth transistors (2b, 4b) whose emitter areas differ by a certain ratio have a common emitter, and current is caused to flow through the third and fourth transistors on the emitter side. A second constant current source (6b) is installed, and the voltage to be converted into a current is applied to the base of the third transistor in common with the base of the first transistor, and the voltage to be converted into a current is applied to the base of the fourth transistor. a second differential amplifier (1b) to which a constant voltage is applied; and a fifth transistor (1b) having a common base and collector on the collector side of the first transistor of the first differential amplifier.
26), and a sixth transistor (30) whose base and collector of the fifth transistor are connected in common, and extracts a current corresponding to the current flowing through the first transistor. 1 current mirror circuit (14a), and the third current mirror circuit (14a) of the second differential amplifier.
A seventh transistor (28) having a common base and collector is connected to the collector side of the transistor, and an eighth transistor (32) whose base and collector of this seventh transistor are commonly connected. The present invention is characterized in that it includes a second current mirror circuit (14b) connected to the third transistor to take out a current corresponding to the current flowing through the third transistor.

[0008]

[Operation] When a voltage to be converted into a current is commonly applied to the first and second differential amplifiers configured with first and second transistors or third and fourth transistors with different emitter areas. , a current corresponding to the applied voltage change is obtained in the first and second differential amplifiers by voltage-current conversion. In that case, the output current as a voltage-current conversion output has a rate of change according to the emitter area ratio set for the first and second transistors and the third and fourth transistors that constitute each differential amplifier. and the second differential amplifier, the current obtained in the first differential amplifier is taken out through the first current mirror circuit, and the current obtained in the second differential amplifier is taken out through the second current mirror circuit. It will be done.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a voltage-current conversion circuit according to the present invention. This voltage-current conversion circuit is provided with first and second differential amplifiers 1a and 1b as means for receiving a voltage to be converted into a current and converting it into a current. The differential amplifier 1a includes a differential pair consisting of first and second transistors 2a and 4a having a common emitter, and an operating current flows through the transistors 2a and 4a to the common emitter side of each transistor 2a and 4a. A first constant current source 6a is connected. The differential amplifier 1b also includes a differential pair consisting of third and fourth transistors 2b and 4b, each having a common emitter. A second constant current source 6b that supplies an operating current is connected. Transistors 2a and 2b installed in each differential amplifier 1a and 1b
Suppose that the emitter area of transistors 2a and 4b is S1, and the emitter area of transistors 4a and 4b is S2.The area ratio is set to a constant ratio, that is, S1/S2 = 1/a, and the emitter area of each transistor 2a and 4a is 2b
, 4b are set to be different from each other at a constant ratio a.

Each differential amplifier 1a, 1b has first and second current mirror circuits 1 as current extraction means for extracting the current flowing through each differential amplifier 1a, 1b.
4a and 14b are connected. That is, a fifth transistor 26 having a common base and collector is connected between the positive potential line where the power supply terminal 8 is formed and the collector of the transistor 2a.
A sixth transistor 30 having a common collector and base
is connected to the collector of this transistor 30, and a first
An output terminal 34 is formed on the side of the differential amplifier 1a to take out an output current as a voltage/current output. Furthermore, a seventh transistor 2 having a common base and collector is connected between the positive potential line and the collector of the transistor 2b.
8 is installed, and an eighth transistor 32 whose base is common to the base and collector of this transistor 28 is connected, and the collector of this transistor 32 is connected to the voltage and current output obtained on the second differential amplifier 1b side. An output terminal 36 is formed to take out an output current. Therefore, the transistor 26 and the transistor 30 form the first current mirror circuit 14a, and the transistor 28 and the transistor 3 form the first current mirror circuit 14a.
2 constitute a second current mirror circuit 14b, and the current flowing through the transistor 2a is individually taken out from the output terminal 34 through the current mirror circuit 14a, and the current flowing through the transistor 2b is taken out individually from the output terminal 36 through the current mirror circuit 14b.

With the above configuration, the transistor 2
, 4, the current I1 when V1 ≫ V2 becomes V1 = V2 without changing I1 = I.
The current at can be set arbitrarily.

FIG. 2 shows the change in current I1 with respect to voltage V1-V2 on the differential amplifier 1a side of this voltage-current conversion circuit. When V1 −V2 = 0, the current I1 is I
1 = {1/(1+a)}I, and in this case, by adjusting and setting the emitter area ratio a of the transistors 2a and 4a, the voltage-current conversion rate of the current I1 is given by {1/(
1+a)} can be varied. In FIG. 2, with respect to characteristic A, characteristic B is a case where a is increased, and characteristic C is a case where a is decreased. Therefore, when this voltage-current conversion circuit is constructed from a semiconductor integrated circuit, it is possible to obtain an output current value having a rate of change according to any arbitrary emitter area ratio set for the transistors 2a, 4a or the transistors 2b, 4b. .

In each differential amplifier 1a, 1b, as shown in FIG.
Since the voltage-current conversion characteristic shown in is obtained, if the currents flowing through the constant current sources 6a and 6b are both set to I, and the currents flowing through each transistor 2a and 2b are I1 and I2,
The converted currents I1 and I2 are the voltage V1 - V2. Therefore, in this voltage-current conversion circuit, voltage-current conversion characteristics are obtained by each differential amplifier 1a, 1b, as shown in FIG. In this case, the current value of V1 = V2 is I1 = I2
= {1/(a+1)}I, so the rate of change is given by {1/(a+1)}, and each current I1,
The directions of increase and decrease of I2 are opposite, and a highly accurate symmetrical current output can be obtained. For example, each current I1,
If you install an amplifier whose gain is individually controlled by I2,
The amplification gain when V1 = V2 can be set to any value.

According to this voltage-current conversion circuit,
As the characteristics of the differential amplifiers 1a and 1b, each transistor 2a
, 2b, 4a, and 4b cancel each other out, and there is no effect of temperature change on the voltage-current conversion characteristics, so the temperature characteristics are good, and the power supply voltage range used is wide, and the input impedance is high. It has the advantage that the input voltage can be controlled with positive and negative voltages with respect to the reference voltage (bias voltage).

Next, FIG. 4 shows an amplification gain control circuit using the voltage-current conversion circuit shown in FIG. In the voltage-current conversion circuit of this embodiment, the voltage-current conversion circuit of FIG.
type transistors 2a', 2b', 4a', 4b', 2
6', 28', and 30' constitute first and second differential amplifiers 1a, 1b, and first and second current mirror circuits 14a, 14b, as in the previous embodiment.

In this voltage-current conversion circuit, a differential amplifier 1
The output currents obtained at a and 1b are applied as gain control currents to the first and second amplifiers 40A and 40B. Amplifiers 40A, 40B are transistors 42, 44, 4
The amplified outputs are taken out from output terminals 58A and 58B. Each of the amplifiers 40A and 40B is constituted by a differential amplifier, and a signal to be amplified is inputted to the base of a transistor 42, and a predetermined bias is applied to the base of a transistor 44.

According to this configuration, currents having opposite increasing and decreasing directions are provided as operating currents by varying the voltage V1 from each transistor 26', 28'.
The amplification gain is controlled accordingly, and amplified outputs can be taken out from the output terminals 58A, 58B based on the gain.

[0018]

As explained above, according to the present invention, the rate of change of the output current value as a voltage-current conversion output can be arbitrarily controlled by the emitter area ratio of the transistors constituting the first and second differential amplifiers. The current obtained from each differential amplifier can be taken out using a current mirror circuit installed for each differential amplifier, and the output current can be used for a wide range of purposes such as amplifier control. It is possible to perform high voltage gain control, etc.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a voltage-current conversion circuit of the present invention.

FIG. 2 is a diagram showing voltage-current conversion characteristics of the voltage-current conversion circuit shown in FIG. 1;

FIG. 3 is a diagram showing voltage-current conversion characteristics of the voltage-current conversion circuit shown in FIG. 1;

FIG. 4 is a circuit diagram showing an amplification gain control circuit which is an embodiment of the voltage-current conversion circuit of the present invention.

FIG. 5 is a circuit diagram showing a conventional voltage-current conversion circuit.

6 is a diagram showing voltage-current conversion characteristics of the voltage-current conversion circuit shown in FIG. 5. FIG.

[Explanation of symbols]

1a First differential amplifier 1b Second differential amplifier 2a First transistor 4a Second transistor 2b Third transistor 4b Fourth transistor 6a First constant current source 6b Second constant current source 14a First current mirror circuit 14b Second current mirror circuit 26 Fifth transistor 28 Seventh transistor 30 Sixth transistor 32 Eighth transistor

Claims (1)

[Claims] 1. First and second transistors having emitter areas different by a certain ratio have a common emitter, and a first constant current is caused to flow through the first and second transistors on the emitter side. Install a current source, and
A first differential amplifier, in which a voltage to be converted into a current is applied to the base of the transistor, and a constant voltage is applied to the base of the second transistor; The emitters of the fourth transistors are made common, and a second constant current source is installed on the emitter side of the fourth transistor to supply current to the third and fourth transistors, and the base of the third transistor is connected to the first constant current source. a second differential amplifier to which the voltage to be converted into a current is applied in common to the base of the transistor, and a constant voltage is applied to the base of the fourth transistor; A fifth transistor whose base and collector are commonly connected is connected to the collector side of the transistor, and a sixth transistor whose base and collector of the fifth transistor are commonly connected is connected to the collector side of the first transistor. A first current mirror circuit that extracts a current corresponding to the current flowing through the transistor, and a seventh transistor having a common base and collector are connected to the collector side of the third transistor of the second differential amplifier. and a second current mirror circuit that connects an eighth transistor whose base and collector of the seventh transistor are commonly connected, and extracts a current corresponding to the current flowing through the third transistor. A voltage-current conversion circuit characterized by comprising: