JPS5924469B2 - Voltage-current conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage-to-current conversion circuit whose input voltage-to-output current conversion characteristic is determined according to an exponential function of a control voltage applied to a control input terminal.

FIG. 1 shows -flI of a conventional voltage-current conversion circuit.

The circuit shown in this figure is composed of a voltage-current conversion circuit 1 and a current-voltage conversion circuit 2, and includes an input voltage v1 applied to an input terminal 3 and a collector current 1 of a transistor 4.
2 is determined according to an exponential function of the control input voltage v2 applied to the control input terminal 5.

That is, in the circuit shown in FIG. 1, input terminal 3 is connected to the inverting input terminal of operational amplifier 80 and the collector of transistor 1 via resistor 6 (value R1), the base of transistor 10 is grounded, and the emitter of transistor 1 is connected to is connected to the output terminal of operational amplifier 8 and the emitter of transistor 4.

The control input terminal 5 is connected to the base of the transistor 40, the collector of the transistor 4 is connected to the inverting input terminal of the operational amplifier 90, and a resistor 10 (value R2) is inserted between the inverting input terminal and the output terminal of the operational amplifier 90. , and the output terminal of the operational amplifier 9 is connected to the output terminal 11.

Therefore, in the circuit with the above configuration, the transistor γ
The collector current 11 of and the collector current 12 of transistor 4 are such that the base-emitter voltage of transistor 1 is Vbl, and the base-emitter voltage of transistor 4 is Vbl.
If b2 is assumed, it can be obtained from the following formula from the properties of the PN junction of the transistor.

However, in this equation (1), (Is: ) reverse saturation current q of the base-emitter junction of the transistors 4 and 1: electron charge: Borsomann's constant.

By transforming this equation (1), the following equation is obtained.

In this equation (2), 11. 12) ■If it is s, then “°・“Klog”・” (3) V b 2 medium Kto g 12 The following formula is obtained.

Further, the control input voltage v2 applied to the control input terminal 5 is V2vb -vb . . .
・・・・・・・・・・・・ (4) 2 2
It is 1.

Therefore, by substituting the above equation (3) into this equation (4), the following relationship is obtained.

On the other hand, due to the nature of an operational amplifier, the following relationship holds between the input voltage v1 applied to the input terminal 3 and the collector current 11 of the transistor γ.

Therefore, by substituting this equation (6) into the above equation (5) and transforming it, the following equation is obtained.

This equation (7) shows the conversion characteristic between the input voltage v1 and the output current 12 of the voltage-current conversion circuit 10 shown in FIG.
It is determined according to the exponential function of

Further, the mutual conductance gm of the voltage-current conversion circuit 1 is expressed as follows from the above equation (7), and this mutual conductance gm is also determined according to the exponential function of the control voltage v2.

Furthermore, when determining the gain of the entire circuit shown in Fig. 1, if the output voltage obtained at the output terminal 11 is v3, then from the properties of the operational amplifier, we get...・・・・・・・・・・・・
... (9) The following relationship holds true: V2R2・12.

If we substitute the above equation (7) into this equation (9), we get The following formula is obtained.

From this equation (10), the gain AV of the circuit shown in FIG. It is required as.

Incidentally, in the circuit shown in FIG. 1, the operational amplifier 8 has many unstable elements such as phase rotation, and has the disadvantage that a predetermined attenuation characteristic cannot be obtained at a specific frequency even if v2 is made small.

In addition, the circuit shown in Fig. 1 requires an operational amplifier in its configuration, which increases the cost.
This method has the disadvantage that it can only be applied when is positive.

In view of the above drawbacks, this invention realizes a voltage-to-current conversion circuit with a simple and inexpensive configuration that has good frequency characteristics and can be applied to both positive and negative input voltages. connected to the first common terminal via the resistor and connected to the second common terminal via the second resistor;
A positive power supply terminal is connected to the first common terminal via a first constant current source, and a negative power supply terminal is connected to the second common terminal via a second constant current source. The emitters of a PNP) transistor and a second PNP) transistor are each connected to the first common terminal, while the emitters of a first NPN) transistor and a second ONPN) transistor are each connected to the second common terminal. , the first PNP)
base and collector of transistor, said first NPN
) the base of the second PNP) transistor and the collector of the second NPN) transistor are each grounded, the collectors of the second PNP) transistor and the first ONPN) transistor are each connected to an output terminal, and the second PNP transistor and the second ONPN), the bases of the transistors are connected to respective control input terminals.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, in which the input terminal 15 is connected to the first common terminal 1γ via a resistor 16 (value Ra) (first resistor). The positive power supply terminal 20 is connected to the first common terminal 17 via the first constant current source 21. Further, the negative power supply terminal 22 is connected to the second common terminal 19 via the second constant current source 23.

The first common terminal 1γ is further connected to the emitters of a transistor 24 (first PNP transistor) and a transistor 25 (second PNP transistor), respectively;
The second common terminal 19 further includes a transistor 26 (first ONPN transistor).

They are respectively connected to the emitters of transistors 21 (second NPN transistors).

The base and collector of transistor 240, the base of transistor 26, and the collector of transistor 21 are each grounded, the collectors of transistors 25 and 26 are each connected to output terminal 28, and transistors 25 and 27
The bases of each are connected to a control input terminal 29.

The above constitutes the voltage-current conversion circuit 30, the output terminal 28 of which is connected to the inverting input terminal of the operational amplifier 310.

A resistor 3 is connected between the inverting input terminal and the output terminal of the operational amplifier 310.
2 (value Rb) is inserted, the non-inverting input terminal is grounded, and the output terminal is connected to the terminal 33.

The operational amplifier 31 and the resistor 32 constitute a current-voltage conversion circuit 34.

Thus, in the circuit configured as described above, the emitter current of the transistor 25 is 11 al, the emitter current of the transistor 24 is I2 B, the emitter current of the transistor 27 is il b, the emitter current of the transistor 26 is i2b, and the control input terminal 29 is The control pressure to be applied is V
.

Then, from the properties of the PN junction of the transistor, A relationship is established.

Note that K in this equation (12) is exactly the same as K in the above equation (2), and the process of deriving this equation (12) is almost the same as the process of deriving the above equation (5), so the description is omitted. do.

Transforming the above equation (12), we get The following formula is obtained.

Further, the currents of the first and second constant current sources 21 and 23 are respectively I1, and the input voltage applied to the input terminal 15 is vi.
, ) If the base-emitter voltages of the run rasters 24 to 21 are respectively vb, the following relationship holds true.

However, in this equation (14), it is assumed that vD and vb.

When this formula (I4) is transformed, the following formula is obtained.

If we substitute this equation 05) into the above equation U, we get The following formula is obtained.

If this equation (16) is transformed, the following equation can be obtained.

On the other hand, the output current i of the output terminal 28.

is i02i1a i2b...
...(18) Therefore, by substituting the above equation (17) into this equation (18) and rearranging, the following is obtained.

Further, if the mutual conductance of the voltage-current conversion circuit 30 is gm, then the above equation 1'19) can be obtained.

That is, the above α9), (20i equation is the equation showing the conversion characteristics of the voltage-current conversion circuit 30 shown in FIG. 2, and 0
9) As can be seen from the equation, the output current i of the voltage-current conversion circuit 30.

is proportional to the input voltage vi, and its proportionality constant has an exponential characteristic with the control voltage vc as a parameter.

Next, the output current io of the voltage-current conversion circuit 30 is
The gain AV□ of the entire circuit shown in FIG. 2 when converted into voltage by the current-voltage conversion circuit 34 is calculated.

The output voltage obtained at terminal 33 is V. Then, from the properties of operational amplifiers, vo anygRb ・・・・・・・・・・・・・・・
・・・・・・・・・・・・ (21).

By substituting equation (09) into equation (21) and dividing by the input voltage vi, the gain AVI of the entire circuit shown in FIG. 2 can be obtained as follows.

FIG. 3 shows a specific circuit example of the circuit shown in FIG. 2, and in this figure, parts corresponding to those in FIG. 2 are given the same reference numerals.

As explained above, according to this invention, two PNPs
) A transistor and two NPN) transistors constitute a voltage-to-current conversion circuit, so it can be applied to both positive and negative input voltages, and unstable elements such as phase rotation can be eliminated, resulting in improved frequency characteristics. A good voltage-current conversion circuit can be obtained with a simple and inexpensive configuration.

Therefore, the present invention is suitable for wide use in voltage controlled amplifiers, voltage controlled oscillators, voltage controlled inductors, voltage controlled capacitors, and the like.

Further, the voltage-current conversion circuit according to the present invention is basically a variable gm circuit, that is, a variable resistor (voltage control resistor).
Therefore, it can be widely applied to parts where conventional sliding type variable resistors are used.

When used as a variable resistor, (1) it has good durability because there are no sliding parts, and (2) it can eliminate sliding noise.

■Giang error (deviation in characteristics between elements) in interlocking variable resistors, which was conventionally about 10%, can be minimized. ■Since the mounting location is arbitrary, it is possible to connect without extending the signal cord. , it is possible to improve the S/N ratio, and other advantages can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing →1 of a conventional voltage-current conversion circuit, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG.
The figure shows a specific circuit example of the embodiment shown in FIG. 15...Input terminal, 16...First resistor (resistance), 17...First common terminal, 18.
...Second resistance (resistance), 19...Second
Common terminal, 20...Positive power supply terminal, 21...
...First constant current source, 22...Negative power supply terminal,
23... Second constant current source, 24... First PNP) transistor (transistor), 25...
...Second PNP transistor (transistor), 2
6...First NPN) transistor (transistor), 2γ... Second NPN) transistor (transistor), 28... Output terminal, 29... Surface control input Terminal, 30...Voltage-current conversion circuit.

Claims (1)

[Claims] 1 The input terminal is connected to the first common terminal via the first resistor, and the second common terminal is connected via the second resistor, and the positive power supply terminal is connected via the first constant current source. connected to the first common terminal, while connecting a negative power terminal to the second common terminal via a second constant current source,
) transistor and a second P, NP) transistor are connected to the first common terminal, while the emitters of the second P, NP) transistor are connected to the first common terminal;
The emitters of an NPN transistor and a second NPN transistor are each connected to the second common terminal;
the base and collector of the PNP transistor of the first ONPN); the base of the transistor of the first ONPN; the base of the second NPN transistor;
The collectors of the transistors are each grounded, and the second PNP
and the collectors of the first ONPN transistor and the first ONPN transistor are connected to the output terminals of the second ONPN transistor and the second ONPN transistor.
A voltage-current conversion circuit comprising a base of a transistor and a base of the second NPN transistor connected to a control input terminal.