JP3257491B2 - Voltage-current conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage-current converter, and more particularly, to a voltage-current converter having bipolar input / output and a wide input voltage range.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional voltage-current conversion circuit, wherein CM4 and CM5 are current mirror circuits, Q1 to Q1.
Q3 is a transistor constituting the current mirror circuit CM5, 1 is a voltage input terminal, 2 is a current mirror circuit CM4
, An input terminal 3, a current output terminal, Q4 a voltage matching transistor between the current mirror circuits CM4 and CM5, Q5
Is a startup transistor and R1 is a resistor.
The ratio between the input current and the output current of the current mirror circuit CM4 is 1: 2.

The operation of this conventional example will be described. The startup transistor Q4 is inactive during normal operation. The current flowing through the resistor R1 is equal to the collector currents of the three transistors Q1, Q2, and Q3 of the current mirror circuit CM5. The current mirror circuit CM4 also equalizes the collector current of the transistor Q4. Accordingly, the collector-emitter voltages of the transistors Q1 and Q4 become equal, and the input voltage VIN applied to the input terminal 1 is
And the voltage VR applied to both ends of the resistor R1 becomes equal.

Accordingly, if the resistance value of the resistor R1 is R1 and the output current is IO, IO = VIN / R1 is established, and voltage-current conversion is performed.

[0005]

However, in such a conventional circuit configuration, when a bipolar voltage-to-current conversion circuit is formed, in addition to the circuit of FIG. 5, the polarity of the transistor is reversed with the same configuration. It is necessary to prepare one circuit. That is, the number of elements is twice as large as that of the circuit of FIG.
Since the number of transistors of each of the current mirror circuits CM4 and CM5 is three, the total number of transistors is 16
And two resistors are required, and the number of elements increases.

In the conventional circuit configuration, the input voltage range is a value obtained by subtracting the range of the output terminal of the current mirror circuit CM4 and the collector-emitter voltage of the transistor Q4 from the power supply voltage VCC (VCC-0. 9V), and there is a problem that the input voltage range is narrow.

An object of the present invention is to make it possible to cope with bipolar input / output with a circuit configuration having a small number of elements and to widen an input voltage range.

[0008]

The voltage-current conversion circuit according to the present invention comprises an input terminal of a first current mirror circuit formed by a PNP transistor and an input terminal of a second current mirror circuit formed by an NPN transistor. Are connected via a first and a second resistor connected in series, and the other end of a third resistor having one end connected to a connection point of these resistors is used as an input terminal;
The point at which the output terminals of the first and second current mirror circuits are connected to each other is defined as an output terminal, and the resistance values of the first, second, and third resistors are R1, R2, and R3, respectively. Assuming that the power supply voltage is VCC and the power supply voltage of the second current mirror circuit is VDD, R1 = R2 = R and R3 = aR (a
Is an arbitrary coefficient), VDD = −VCC, the voltage of the input terminal is VIN, and the output current of the output terminal is IOUT. If IOUT = − (2 / (2a + 1)) VIN / R Is performed.

The first current mirror circuit has two PNPs.
The transistor and the second current mirror circuit are two NPs
It can be composed of N transistors.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a voltage-current conversion circuit according to the present invention. This voltage-current conversion circuit includes an input terminal of a first current mirror circuit CM1 composed of two PNP transistors Q1 and Q2, and two NPN transistors Q2.
First and second resistors R1 and R2 connected in series with the input terminal of a second current mirror circuit CM2 constituted by Q4;
The other end of a third resistor R3 having one end connected to a connection point M between the resistors R1 and R2 is used as an input terminal 4, and the output terminals of the first and second current mirror circuits CM1 and CM2. The point N at which they are connected is referred to as an output terminal 5.

The operation of the voltage / current conversion circuit will be described. Now, it is assumed that the transistors Q1, Q2 and Q3, Q4 differ only in polarity but have exactly the same characteristics, and the current amplification factor is infinite. The resistance values of the resistors R1, R2, and R3 are R1, R2, and R3, respectively, and the power supply voltage is VDD = -V.
CC.

R1 = R2 = R R3 = aR (a is an arbitrary coefficient) In the case of (1), if the voltage of the input terminal 4 is VIN and the output current of the output terminal 5 is IOUT, IOUT = − ( 2 / (2a + 1)) VIN / R (2) holds, and voltage-current conversion is performed. This is derived as follows.

The currents flowing through the resistors R1, R2, R3 are represented as Ir1, Ir2, Ir3, respectively. When VIN is open, the voltage Vm at the connection point M between the resistors R1 and R2 is zero. That is, if VIN = 0, Ir3 = 0. Ir1 and Ir2 at this time are represented by If.

Considering the inflow / outflow current at the point M, even if the voltage of VIN is applied to the input terminal 4 and Vm changes, Ir1
+ Ir3 = Ir2 always holds. At this time, the changes in the current flowing through the resistors R1 and R2 are -Vm / R1 and Vm, respectively.
/ R2,

If − (− Vm / R1) + (VIN−Vm) / R3 = If + (Vm / R2) (3)

From the above equations (1) and (3), If-(-Vm / R) + (VIN-Vm) / aR = If + (Vm / R) (4)

When this equation (4) is solved for Vm, Vm = VIN / (2a + 1) (5)

From the point M, the current mirror circuits CM1 and CM
The current values Ir1 and Ir2 supplied to M2 are completely equal to the current values supplied to the N points from the current mirror circuits CM1 and CM2. Therefore, the current Ir3 flowing through the resistor R3 is -I
OUT, and the following relationship holds:

IOUT = Ir3 = − (VIN−Vm) / aR (6) By substituting equation (5) of equation (6), equation (2) is given.

FIG. 2 shows the same power supply voltage (VCC = 2.5 V, VDD = -2.5 V) for the voltage-current conversion circuit according to the present invention shown in FIG. 1 and the conventional voltage-current conversion circuit shown in FIG.
5 is a graph comparing the voltage-current conversion characteristics at V). In FIG. 1, R1 = R2 = 2 × R3 = 10 KΩ, and in FIG.
= 10 KΩ, and the voltage-current conversion coefficients were made equal. However, although the polarity of IOUT with respect to VIN is opposite between the present invention and the conventional example, it does not affect the essential characteristic comparison.

In FIG. 2, the input / output linearity is broken in the region of VCC-0.9V <VIN in the conventional voltage-current converter, but in the voltage-current converter according to the present invention, VDD <V
Input / output linearity is maintained in the entire range of IN <VCC.

In the example shown in FIG. 1, the current mirror circuits CM1 and CM2 each include two transistors Q1 and Q2.
2 and Q3.Q4, but as shown in FIGS. 3 and 4, three transistors Q1, Q2.
A three-transistor type or a Wilson type based on 3.Q4.Q6 has the same effect as described above.

[0024]

As apparent from the above description, according to the present invention, it is possible to cope with bipolar input / output with a circuit configuration having a small number of elements. In addition, when all signals in the power supply voltage range are input, the bias point inside the circuit can be set so that the current mirror circuit operates normally, so that the input voltage range can be widened and the voltage and current for all input signals in that range Conversion can be performed.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of an example of a voltage-current conversion circuit according to the present invention.

FIG. 2 is a graph comparing the voltage-current conversion characteristics of the voltage-current conversion circuit of FIG. 1 and a conventional voltage-current conversion circuit.

FIG. 3 is an electric circuit diagram of another example of the present invention in which a current mirror circuit is configured by three transistors.

FIG. 4 is an electric circuit diagram of a modified example of FIG.

FIG. 5 is an electric circuit diagram of a conventional voltage-current conversion circuit.

[Explanation of symbols]

 4 Input terminal 5 Output terminal R1, R2, R3 Resistance Q1, Q2, Q3, Q4, Q5, Q6 Transistor CM1, CM2 Current mirror circuit M, N Connection point

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 1/42-1/56 H03F 3/20-3/32 H03F 3/34-3/36 H03F 3/42-3 / 44 H03F 3/50-3/52

Claims (2)

(57) [Claims] An input terminal of a first current mirror circuit composed of a PNP transistor and an input terminal of a second current mirror circuit composed of an NPN transistor are connected in series with a first and a second resistor. And the other end of the third resistor having one end connected to the connection point of these resistors is set as an input terminal, and the point connecting the output ends of the first and second current mirror circuits is set as an output terminal. , R1, R2, R3 as the resistance values of the first, second, and third resistors, VCC as the power supply voltage of the first current mirror circuit, and VDD as the power supply voltage of the second current mirror circuit. = R and R3
= AR (a is an arbitrary coefficient), VDD = -VCC, the input terminal voltage is VIN, and the output current of the output terminal is IOUT. IOUT =-(2 / (2a + 1)) VIN / R A voltage-to-current conversion circuit, wherein the voltage-to-current conversion is performed by: 2. The voltage-current conversion circuit according to claim 1, wherein each of the first current mirror circuit and the second current mirror circuit comprises two transistors.