JP3165738B2 - 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 conversion circuit for converting a voltage signal into a current signal, and more particularly to an integrated circuit driven at a low voltage.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional voltage-current conversion circuit (hereinafter simply referred to as a conversion circuit). This conversion circuit includes a differential amplifier circuit including NPN-type transistors Q ₁ and Q ₂ whose emitters are connected via a resistor R _1, and two constant current circuits connected to the emitter sides of the transistors Q ₁ and Q _2. a source 11, a transistor Q _3, Q _4, Q ₇ of the diode-connected NPN type, and the differential amplifier circuit consisting of transistors Q _5, Q ₆ of the NPN type, the constant current source I ₂
And The emitters of the transistors Q ₃ and Q ₄ are connected to the collectors of the transistors Q ₁ and Q ₂ , respectively, and the bases and collectors of the transistors Q ₃ and Q ₄ are connected to the emitter of the transistor Q ₇ . Transistor Q
The collector and base ₇ are connected to the drive power supply _Vcc .

[0005] The emitters of the transistors Q ₅ and Q ₆ are commonly connected and connected to a constant current source 13. The base of transistor Q ₅ is connected to the collector of the transistor Q _2, the base of the transistor Q ₆ is connected to the collector of the transistor Q _1. The constant current sources 11 and 12
Produces a current of the same intensity I ₁ , and the constant current source 13
Produces ₂ currents. And each of the constant current sources 11, 12, 13
Is a suction type, and allows a sucked DC current to flow to a ground power supply.

Such a voltage-current conversion circuit converts a signal voltage applied to _two input terminals IN ₁ and IN ₂ of a differential amplifier circuit composed of transistors Q ₁ and Q ₂ into a diode-connected transistor Q _3. , compressed by Q _4, converts the compressed signal into a signal current by the transistor Q _5, consisting of Q ₆ differential amplifier circuit, the collector (output terminal OU of the signal current transistor Q _5, Q ₆
T ₁ , OUT ₂ ).

Now, the base of the transistor Q ₂ is AC grounded, and the input signal voltage v is applied to the base of the transistor Q _1.
in the case of applying a _i, the relationship between the current i ₂ flowing between the collector of the signal voltage v _i and transistor Q _5, Q _6, i.e. the transconductance G _m is determined as follows.

First, each transistor Q _i (i = 1,...)
The emitter resistor of 6) and r _ei, and _{r e1 = r e2 = r e3} = r e4 and r _e5 = r _e6. Then the _{r e1 = V T / I 1} , r e5 = 2V T / I 2. Here V _T is expressed as called thermal voltage V _T = kT / q. Here, k is the Boltzmann constant, T is the absolute temperature of the transistor, and q is the absolute value of the electron charge.

[0007] Then, the transistors Q _1, resistors R _1, the v _i = _{i 1} · When the current flowing through the circuit consisting of transistors Q _2, Q _4, Q ₃ and _{i 1 (R 1 + 2r e1} ). The base of the transistor Q ₅ and the transistor Q
'When, v _i' the voltage generated between the base of the ₆ v _i becomes _{= i 1 · 2r e1 = i} 2 · 2r e5. Therefore, the transconductance G _m is Becomes Where R ₁ >> re _e1 , that is, R ₁ >> V
For _T / I _1, the transconductance G _m is G _m = I ₂
/ (2R ₁ I ₁ ), and if the current conversion ratio (I ₂ / I ₁ ) is determined, it becomes inversely proportional to the resistance value R ₁ .

[0008]

Generally, a voltage V between a base and an emitter of a diode-connected transistor is used.
_BE is

(Equation 1) It is expressed as Here I _c is the collector current, I _s represents the saturation current. V _BE varies depending on the manufacturing process, but has a value substantially equal to 0.7 V in a normal temperature range. Thus, the conventional voltage - in the current conversion circuit, the driving voltage V _cc, the collector of the transistor Q ₁ - when the voltage between the emitter and V _CE

(Equation 2) Therefore, there is a problem that a relatively high drive voltage is required.

[0009] In addition, when the driving voltage V _cc varies, transistor collector of Q _1, Q ₂ - even if the voltage V _CE between the emitter and change, the Early effect of the transistor Q _1, Q ₂ there is a problem that can not be ignored . The present invention has been made in view of the above circumstances, and has as its object to provide a voltage-current conversion circuit that can be driven at a voltage as low as possible and can ignore the Early effect.

[0010]

A voltage-current conversion circuit according to the present invention includes a first differential amplifier circuit having first and second transistors, each having an emitter connected through a resistor, and a first differential amplifier circuit having a first transistor and a second transistor. A first constant current source that extracts a predetermined current from the emitters of the first and second transistors to a first power supply, third and fourth transistors each of which is diode-connected and whose cathode side is connected in common; A second constant current source for supplying a predetermined current from a second power supply to the anode side of the third and fourth transistors, and the same polarity as the third and fourth transistors, each emitter being connected in common A second differential amplifier circuit having fifth and sixth transistors, a third constant current source connected to the emitters of the fifth and sixth transistors, and a cathode of the third and fourth transistors. First power supply A voltage drop element connected between the second current source and the first current source to cause a voltage drop by a current difference between the second current source and the first current source, wherein an anode of the third transistor has a collector of the first transistor and The fourth transistor is connected to a base of the sixth transistor, and an anode of the fourth transistor is connected to a collector of the second transistor and a base of the fifth transistor.

[0011]

According to the voltage-current conversion circuit of the present invention thus configured, the bias voltage of the first differential amplifier circuit can be biased to a predetermined voltage. Operating at low drive voltage
Early effects can be ignored.

[0012]

FIG. 1 shows the configuration of a first embodiment of a voltage-current conversion circuit (hereinafter, also simply referred to as a conversion circuit) according to the present invention. The conversion circuit of this embodiment includes a differential amplifier circuit including NPN transistors Q ₁ and Q ₂ whose emitters are connected via a resistor R ₁ , and an NPN diode-connected NPN transistor.
Type transistors Q ₃ and Q _4, and N
A differential amplifier circuit composed of PN transistors Q ₅ and Q ₆ , a resistor R _2, and a sink type constant current source 11, 12, 13
And discharge-type constant current sources 14 and 15.

The emitters of the transistors Q ₁ and Q ₂ are connected to ground power via constant current sources 11 and 12, respectively. The collector of the transistor Q ₁ is connected to the base and collector of the transistor Q _3, the collector of the transistor Q ₂ is connected to the base and collector of the transistor Q _4. The emitter of the transistor Q ₃ and Q ₄ are connected in common, are connected to the ground power supply through a resistor R _2. The collector of the transistor Q ₃ are connected to a driving power source V _cc via the constant current source 14, the collector of the transistor Q ₄ are connected to a driving power source V _cc via the constant current source 15. And the base of the transistor Q ₅ is transistor Q
It is connected to the _fourth base and the collector, the transistor Q ₆
The base is connected to the base and collector of the transistor Q _3. The emitters of the transistors Q ₅ and Q ₆ are commonly connected, and are connected via a constant current source 13 to a ground power supply. Incidentally, the constant current source 11 12 produces a constant current of the same intensity I _1, the constant current source 14 and 15 produces a constant current of the same intensity I _3.

[0014] In this first embodiment, the base of the transistor Q ₂ AC manner grounded, in the case of applying the input signal voltage v _i to the base of the transistor Q _1, and the signal voltage v _i, the transistors Q ₅ , the relationship between the current i ₂ flowing between the collector of Q _6, i.e. the transconductance G _m
Is obtained as follows. First, each of the transistors _{Q i (i = 1, ......} 6) the emitter resistance of the r _ei, and _{r e1 = r e2, r e3} = r e4, r e5 = r e6. Then _{r e1 = V T / I 1} , r e3 = V T / (I 3 -I 1), a _{r e5 = 2V T / I 2} . Here, _VT is a thermal voltage.

Next, the transistor Q _1, the resistance value R _1, the current flowing through the circuit consisting of transistors Q _2, Q _4, Q ₃ and i _1, the _{v i = i 1 · (R} 1 + 2r e1) . The 'When, v _i' the voltage generated between the base of the transistor Q ₅ and Q ₆ v _i becomes _{= i 1 · 2r e3 = i} 2 · 2r e5. Therefore, the transconductance G _m is Becomes Here, in the case of R ₁ >> re _e1 , that is, R ₁
>> In the case of V _T / I _1, the transconductance G _m is If the current conversion ratio I ₂ / (I ₃ −I ₁ ) is determined, it is inversely proportional to the resistance value R ₁ as in the conventional case.

However, in the first embodiment, the driving voltage _Vcc is

(Equation 3) Thus, the drive voltage _Vcc can be reduced as compared with the conventional case. Further, when the driving voltage V _cc is varied, the variation is absorbed by the resistor R _2, the collector of the transistor Q _1, Q ₂ - emitter voltage V _CE hardly change, be ignored Early effect it can.

Next, the configuration of a second embodiment of the conversion circuit according to the present invention is shown in FIG. The conversion circuit according to the second embodiment includes:
In the conversion circuit of the first embodiment shown in FIG. 1, the NPN transistors Q ₃ , Q ₄ , Q ₅ , and Q ₆ are replaced with PNP transistors Q ₇ , Q ₈ , Q ₉ , and Q _10. Is replaced by a discharge type constant current source 16 of the same strength. In this case, the bases and collectors of the transistors Q ₇ and Q ₈ are commonly connected, and are connected to a ground power supply via a resistor R ₂ . Transistor Q
₇ the emitter is connected to the collector and the constant current source 14 of the transistor Q _1, the emitter of the transistor Q ₈ is connected to the collector and the constant current source 15 of the transistor Q _2. The emitters of the transistors Q ₉ and Q ₁₀ are commonly connected, and are connected to a drive power supply via a constant current source 16.

[0018] In addition, the base of the transistor Q ₉ is connected to the emitter of the transistor Q _8, the base of the transistor Q ₁₀ is connected to the emitter of the transistor Q _7.
In the conversion circuit according to the second embodiment, when a signal voltage is input to the bases of the transistors Q ₁ and Q ₂ constituting the input differential amplifier circuit, the signal voltage is converted to a signal current and the output differential amplifier is output. Signal currents are output from the collectors (output terminals OUT ₁ , OUT ₂ ) of the transistors Q ₉ , Q ₁₀ constituting the circuit. It goes without saying that the conversion circuit of the second embodiment also has the same effect as the conversion circuit of the first embodiment.

[0019]

As described above, according to the present invention, it is possible to operate at a low drive voltage and to ignore the Early effect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a conventional example.

[Explanation of symbols]

Q ₁ ... Q ₆ Transistor R ₁ , R ₂ resistance IN ₁ , IN ₂ input terminal OUT ₁ , OUT ₂ output terminal 12-15 Constant current source _Vcc drive voltage

Claims (1)

(57) [Claims] 1. A first differential amplifier circuit having first and second transistors each having an emitter connected through a resistor, and a predetermined current from emitters of the first and second transistors. A first constant current source that is pulled out to a first power supply; third and fourth transistors, each of which is diode-connected and whose cathode side is connected in common; and a third constant-current source connected to the anode side of the third and fourth transistors. A second constant current source into which a predetermined current flows from the second power source; and the third and fourth constant current sources, each having an emitter connected in common.
A second differential amplifier circuit having fifth and sixth transistors having the same polarity as that of the third transistor; a third constant current source connected to the emitters of the fifth and sixth transistors; A cathode of a fourth transistor and the first transistor;
A voltage drop element which is connected between the power supply of the first transistor and the second current source, and which causes a voltage drop by a current difference between the second current source and the first current source. And the anode of the fourth transistor is connected to the collector of the third transistor and the base of the sixth transistor.
A voltage-current conversion circuit, which is connected to a collector of the transistor and a base of the fifth transistor.