JPS6024712A - Voltage-current convertor - Google Patents

Abstract

PURPOSE:To prevent influences of temperature change on output current by making a reference voltage generating section and a current supply transistor of a comparator circuit in current-mirror relation. CONSTITUTION:Input voltage Vin is given to the base of a transistor (TR) Q20, and reference voltage Vref is given to the base of a TRQ21. A TRQ26 forms a current-mirror circuit together with a TRQ27 and the collector of TRQ27 is connected to a next step circuit 23. By making R22=R24, R25=R26=R23, output current Iout becomes (R27/2R25.R28)Vin, current that flows in the current supply transistor becomes irrelevant to output current, and output current is not influenced by change of temperature.

Description

[Detailed description of the invention] [Technical field of invention] This invention relates to a voltage-current converter.

[Technical background of the invention]

FIG. 1 shows a conventional voltage-to-current converter, which is incorporated into an integrated circuit. This converter consists of transistor Q1
~Q4, constant current source 11.12°13, resistors R1, R2,
It is composed of R3 and R3.

An input voltage Vin is applied to the base of the transistor Q1. A reference voltage Vre is applied to the base of the transistor Q2.
f is given. Current sources 11, 12, and 13 each have a current of +1. il+i2 is set to flow.

In this circuit, since the transistors Ql and Q2 are always on, the base potentials of the transistors Q3 and Q4 become Vin-Vj and Vref-Vj, respectively. The input voltage Vin is converted into a current, and the converted current is applied to the collector of the transistor Q3 and input to the next stage circuit 14 which requires this current (Iout).

Here, the current Iout has different r values under the following conditions.

(1) When Vin≦Vref −2R3X i2, I
out=O...■ (2) Vref-2R3Xi2(Vin(Vref+
When 2R3Xi2, (,3) Vref + 2R3X When i2≦vin, Iout == 2 It shows Iout.

In the circuit of FIG. 1, the next stage circuit 14 which requires an output current Iout is connected to the collector of transistor Q3. Unfortunately, the next-stage circuit 14 and its lower voltage circuits cannot all be used.

Therefore, in order to lower the voltage, transistors Q5, Q6, Q7, Q8 and resistors R4 to
By adding a current mirror circuit composed of R7, it is possible to lower the voltage. However, since the current in this case has the characteristics shown in FIG. 2, the current at the collector of transistor Q3 is transmitted. However, ■(
When the sensitivity (slope of the characteristic line in Fig. 2) determined by R3 is small, the input voltage Vi
As nff: increases, the base voltage of transistor Q3 also increases. -1, the collector current of transistor Q3 also increases, so the base voltage of transistor Q5 decreases.

Therefore, if the difference between the base voltage of the transistor Q3 and the base voltage of the transistor Q5 is small and the voltage is lowered, a drawback arises in that a wide dynamic range cannot be achieved.

Therefore, a voltage-current converter shown in FIG. 4 can be considered as a voltage-current converter that can widen the dynamic range even when the voltage is lowered. The converter shown in FIG. 4 uses pnp transistors Q9 and QIO' in the comparator circuit section. Two portions corresponding to the circuits in FIGS. 1 and 3 are given the same reference numerals and their explanations will be omitted. For this converter, the output current is applied to the collector of transistor QIO and to the collector of transistor Qll.

The current flows into the next stage circuit 14 via a current mirror circuit including QI2 and resistors R11 and R12. In this circuit, the base potential of transistor QIO is held constant, so even if the input voltage Vin' is increased,
The difference between the base voltage of IO and the base voltage of transistor Qll, that is, the dynamic range can be widened. Here, when the output current Iout f is calculated, it is obtained from equation (2). If the current source 12 depends on Vcc-nVj, the output current Iout also depends on Vcc-nVj from equation (2). Therefore, this circuit has a problem in that a stable output current Iout cannot be obtained when the temperature changes.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a voltage-current converter that is suitable for reducing voltage, has a wide dynamic range, and obtains a stable output current even with temperature changes. With the goal.

[Summary of the invention]

In this invention, in order to achieve the above object, first and second
A third transistor is used to supply current to the differential amplifier, and a fourth transistor is used to supply current to the differential amplifier.
A current mirror circuit is configured together with the transistor, and a potential having a constant relationship with the potential on the collector side of the fourth transistor is applied as a reference voltage to the pace of the second transistor; It gives input voltage to the pace of.

[Embodiments of the invention]

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

In FIG. 5, transistors Q20, Q2] are constructed symmetrically, each having a collector connected to a power supply terminal 21, and an emitter connected to a ground terminal 22 via resistors R20 and R21'Th, respectively. The input voltage Vin 4 is seen in the pace of transistor Q20, and the transistor Q
The reference voltage Vref is applied to the base 2 of 21.

That is the emitter of transistors Q20 and Q21.

The pnp transistors Q22 and Q23 are connected to each other. This transistor Q22. The emitter of Q23 is connected to the collector of transistor Q24 via resistors R25' and R26, respectively.

The emitter of this transistor Q24 is connected to the power supply terminal 2 via a resistor R24, and the base is connected to the transistor Q24 which forms a current mirror configuration with this transistor Q24.
25 base and collector.

The emitter of transistor Q25 is connected to power supply terminal 2 through resistor R22, and the collector is connected to power supply terminal 2 through resistor R22.
21 and to the ground terminal 22 via resistors R2 and J-.

Next, the collector of transistor Q26 is connected to the collector of transistor Q23. This transistor Q
26 forms a current mirror circuit together with a transistor Q27. That is, the collector and paste of the transistor Q26 are short-circuited, and the emitter is connected to the ground terminal 22 via the resistor R27'f. and transistor Q
The base of transistor Q27 is connected to the base of transistor Q27.

The emitter of this transistor Q27 is connected to the ground terminal 22 via a resistor R28, and the collector is connected to the next stage circuit 2.
Connected to 3.

One embodiment of the present invention is constructed as described above.

Here, the resistors R20 and R21 may be current sources.

Find collector current 125f of transistor Q25.

When you put it on, becomes.

Here, if the resistors R22 and R24 (fWk) are equal, the collector current t24 of the transistor Q24 is i24-1
25...■ If the resistors R25 and R26 are made equal, then the collector current i26 of the transistor Q26 is as follows. Further, since the reference voltage Vref is Vref = i25 .R23'...■, the output current Iout is as follows.

Therefore, by setting R23=R25, the output current I
out no longer includes the terms 1, f('f), and 'Vcc-Vj. Therefore, even if the temperature changes, the output current Iout remains stable.

FIG. 6 shows another embodiment of the invention. Parts corresponding to the configuration in FIG. 5 are given the same reference numerals and explanations are omitted, but
In this circuit, the emitter base of a transistor Q31 is connected to the base collector of a transistor Q25, and a current mirror circuit "fc #41" is formed by transistors Q24Q25 and Q31.Transistor Q25
The collector of is connected to the transistor Q21 via the resistor R31e.
Connected to the pace of. With this configuration, the base currents of transistors Q24 and Q25 are compensated to be more stable. Other operations are the same as the circuit shown in FIG.

FIG. 7 shows yet another embodiment of the invention.

In this embodiment, transistors Q32 . The collector of Q33 is connected, and the resistor R34 is connected between them. The emitters of transistors Q32 and Q33 are connected to power supply terminal 21 via resistors R32P and R33, respectively. Also, transistor Q32. Q33.
Q25 paces are commonly connected. The rest of the configuration is the same as the circuit shown in FIG. 6, so the same reference numerals are given and the explanation will be omitted.

In this circuit, if the values of resistors R22, R32, and R33 are made equal (R22=R32=R33), the output current I
out is to. However, 125 is a transistor. It is assumed that the collector current is 25 and the resistors R27 and R28 are equal.

Therefore, when the resistors R23 and R34'f are made equal, the output current has no temperature dependence.

This invention is not limited to the above embodiments. The polarity of the transistors constituting the differential amplifier may be opposite to that of the above embodiment.

That is, as shown in FIG. 8, a transistor. 35°Q3
6 is npn) radial resistor, emitter resistor R35
, R,36. Transistor Q37 supplies current to a differential amplifier composed of transistors Q35 and Q36. And this transistor Q37
forms a current mirror circuit together with transistor Q38. The emitters of transistors Q37 and Q38 are connected to ground terminal 22 via resistors R37 and R38'e, respectively.

〔Effect of the invention〕

As described above, according to the present invention, it is suitable for lower voltages, has a wide dynamic range, and is particularly resistant to temperature changes because the reference voltage generator and the current supply transistor of the comparator circuit (differential amplifier) Due to the mirror relationship, the current flowing through the current supply transistor is independent of the output current, and it is possible to provide a voltage-current converter in which the output current is not affected by temperature changes.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a conventional voltage-current converter, Figure 2 is a diagram showing voltage-current conversion characteristics, Figures 3 and 4 are circuit diagrams showing conventional voltage-current converters, and Figure 5 is a circuit diagram showing a conventional voltage-current converter. The figure is a circuit diagram showing one embodiment of the present invention, and FIGS. 6, 7, and 8 are circuit diagrams showing other embodiments, respectively. Q, 20~Q2.8, Q31, Q3.2, Q
33...Transistor, R20-R28...Resistor,
23...Next stage circuit.

Claims (1)

[Claims] A differential amplifier formed by first and second transistors each having an emitter resistor, a third transistor that supplies current to this differential amplifier, and a third transistor that forms a current mirror circuit together with this third transistor. 4 transistor, means for applying an input terminal to the base of the first transistor, and means for applying a reference voltage to the base of the second transistor with a constant potential difference from the collector potential of the fourth transistor. A voltage-current converter, characterized in that a current is drawn out from the collector of the first or second transistor.