JPH0478044B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a current amplifier that obtains an output current corresponding to a differential voltage of input signals applied to a pair of differential input terminals, and particularly relates to a current amplifier that obtains an output current corresponding to a differential voltage of input signals applied to a pair of differential input terminals, and in particular, It is suitable for

[Background technology and its problems]

For example, it is possible to realize an instrumentation amplifier that removes the common mode component from a signal transmitted as a balanced signal and converts it into an unbalanced signal, a voltage-to-current converter whose gain can be electrically controlled, a voltage amplifier, or a variable impedance circuit. As a means for achieving this, a means for obtaining a current output by combining a differential input-differential output voltage-current conversion circuit and a multiplication circuit is required.

An example of such a current amplifier is shown in FIG. In FIG. 1, 1 is a positive power supply terminal, and 2 is a negative power supply terminal. The differential input-differential output voltage-current conversion circuit 3 includes a resistor 5 with a resistance value R ₀ connected between each output terminal of a current source 4 that supplies a pair of mutually equal currents _I It consists of PNP type transistors 6 and 7 whose emitters are connected to the connection points of the source 4 and the resistor 5, respectively. The differential input voltages supplied to the differential input terminals 8 and 9, which are the bases of these transistors 6 and 7, are converted into currents, and the differential output terminals 10, which are the collectors of these transistors 6 and 7, are converted into currents. , 11 as currents I ₁ and I ₂ . These output currents I ₁ and I ₂ are supplied to the NPN transistors 13 and 14 forming the PN junction pair 12.
are supplied respectively. Transistors 13, 14
With each base connected to its respective collector
The anode of the PN junction is formed, and the emitters serving as cathodes of these diode-connected transistors 13 and 14 are commonly connected and connected to a constant voltage source. Further, the anodes of the transistors 14 and 13 forming the PN junction pair 12 are respectively connected to the bases of NPN transistors 16 and 17 forming the common emitter transistor pair 15. These PN junction pair 12 and common emitter transistor pair 15 constitute a multiplier 18. A current source 19 connected to the common emitter of the common emitter transistor pair 15 is
A current 2I _Y is applied to determine the multiplication coefficient of the multiplier 18. Output terminals 20, 2 of multiplier 18
A current inversion (current mirror) circuit 22 is connected to the terminal 1, and the difference current between the collector output currents I ₃ and I ₄ of each transistor 16 and 17 of the common emitter transistor pair 15 is sent to the output terminal 23 as an output current i ₀ . taken out. That is, the polarity of the output current I ₄ at the terminal 20 is reversed by the current inversion circuit 22, and the difference component between the output currents I ₄ and I ₃ at the terminals 21 and 20 becomes the output current i ₀ and appears at the output terminal 23. .
Note that the current inversion (current mirror) circuit 22 is
It is composed of PNP type transistors 24 and 25.

In the configuration shown in FIG. 1, the output currents I ₁ and I ₂ of the voltage-current inversion circuit 3 are as follows: I ₁ ≒ I _X − _V /R ₀ ... I ₂ ≒ I _X + _V / R ₀ ... Therefore, the output currents I ₃ and I ₄ of the multiplier 18 are as follows: I ₃ =I ₁ (I _Y /I _X ) . . . I ₄ = I ₂ (I _Y /I _X ) . With these formulas, the output current i ₀
is, i ₀ = I ₄ − I ₃ = 2 _V I _Y /I _X R ₀ ……. Therefore, this circuit converts the potential difference between the terminals 8 and 9 into a current, and the conversion coefficient to the output current can be controlled by the current value I _Y of the current source 19. That is, this circuit has a transconductance of 2I _Y /I _X R ₀ , and this transconductance is determined by the current ratio I _Y /I _X and the resistance value R ₀ .

By the way, in the current amplifier shown in FIG. 1, the currents I ₁ and I ₂ in the above equation must be strictly taken into account the change in the base-emitter voltage due to the change in the collector current of the transistors 6 and 7. Therefore, I ₁ and I ₂ are not determined simply by _V and R ₀ . Therefore, there will be a difference in the conversion coefficients,
and generates nonlinear components.

[Purpose of the invention]

The present invention eliminates such conventional drawbacks and improves the base of the transistor in the voltage-to-current converter.
It is an object of the present invention to provide a current amplifier in which a change in the voltage between emitters does not affect the output current, a voltage-current conversion coefficient is determined only by the resistance value, and a characteristic with good linearity can be obtained.

[Summary of the invention]

That is, the characteristics of the current amplifier according to the present invention are as follows:
first and second transistors of a first conductivity type, each having its base connected to the first and second input terminals; each base connected to each emitter of the first and second transistors; a third and fourth transistor of a second conductivity type with a resistor connected between the emitters; a first current source that supplies a constant current from a reference potential to each of the emitters; and a resistor connected between the emitters. and a first conductivity type transistor whose collectors are respectively connected to the collectors of the third and fourth transistors, a DC bias is fed back from the collectors to the bases of the respective transistors, and whose emitters are connected to each other. 5. A sixth transistor, each base of which is connected to the bases of the fifth and sixth transistors, each collector connected to each of the first and second emitters, and the emitters connected to each other. a first differential transistor pair comprising seventh and eighth transistors of a first conductivity type; a second current source connected to a common emitter of the first differential transistor pair;
a second differential transistor pair consisting of a ninth and tenth transistor whose bases are connected to the bases of the fifth and sixth transistors, and whose emitters are connected to each other; and the second differential transistor. and a third current source connected to the common emitters of the pair.

〔Example〕

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

FIG. 2 is a circuit diagram showing a current amplifier as a first embodiment of the present invention. In this figure 2,
1 is a positive power supply terminal, 2 is a negative power supply terminal, and a differential input-differential output voltage-current conversion circuit 3
has a current source 4 that supplies a pair of mutually equal currents _IX from the positive power supply terminal 1, respectively.
This voltage-current conversion circuit 3 includes a resistor 5 having a resistance value R ₀ connected between a pair of output terminals of the current source 4;
Emitters are connected to the respective connection points between these output terminals and the resistor 5 to perform voltage-current conversion.
The respective emitters of NPN type transistors 31 and 32, which have PNP type transistors 6 and 7 and whose bases are connected to the first and second input terminals 8 and 9, respectively each connected to the base. NPN transistors 31 and 32 operate as emitter followers and drive PNP transistors 6 and 7, respectively. Output currents I ₁ and I ₂ from the differential output terminals 10 and 11 of the respective collectors of these transistors 6 and 7
are supplied to the collectors of the NPN transistors 13 and 14 of the PN junction pair 12 of the multiplier 18, respectively.

Each of the transistors 13 and 14 of the PN junction pair 12 of the multiplier 18 has a so-called diode-connected configuration by connecting its base and collector. The NPN type transistors 34 and 35 constituting the transistor differential pair 33 have their respective bases connected to each transistor 1 of the PN junction pair 12.
The transistors 3 and 14 are connected to their bases, and their collectors are connected to the emitters of the transistors 31 and 32, respectively, and the emitters are commonly connected to a constant current source 36 through which a current 2I _B flows.

Next, each base of the transistors 34 and 35 is
The bases of the NPN transistors 17 and 16 of the transistor differential pair 15 are connected to each other, and the common emitter of each transistor 16 and 17 receives a current of 2.
A constant current source 19 that flows _IY is connected. The respective collectors of these transistors 16 and 17 serve as multiplication output terminals 20 and 21 of the multiplier 18,
By connecting these output terminals 20 and 21 to a current inversion (current mirror) circuit 22,
The difference current between the respective output currents I ₃ and I ₄ is the output current i ₀
It is taken out from the terminal 23 as a.

In the above configuration, the transistors 34 and 35
Each base of is connected to the PN junction pair 12, so that the PN junction pair and the differential transistor pair 33 constitute a multiplier.

As a result, transistors 13 and 34 and 14
and 35, a current maintained at a constant ratio flows. The ratio is set by the ratio of the current I _X flowing through the current source 4 and the current 2I _B flowing through the current source 36. Therefore, the currents flowing through transistors 6 and 31 and 7 and 32 are kept in the same ratio. That is, the current I ₅ flowing through the transistor 31 and the current I ₆ flowing through the transistor 32 are approximately as follows: I ₅ =(I _B /I _X )·I ₁ ... I ₆ = (I _B /I _X )·I ₂ The relationship is maintained as follows. For example, when I _X = IB, the currents flowing through transistors 6 and ₃₁ and between transistors ₇ and ₃₂ are kept approximately equal. A voltage change equal to the change in the base-emitter voltage of transistors 31 and 32 occurs between the base-emitters of transistors 31 and 32. transistors 6 and 3
1, 7, and 32 cancel each other out, the input signals applied to the input terminals 8 and 9 are faithfully transmitted to both ends of the resistor 5. Therefore, the output currents I ₁ and I ₂ of the voltage-current conversion circuit 3 are determined only by the input voltage _V and the resistor 5, and high linearity can be obtained.

By the way, in the first embodiment of the present invention described above, when the current gain of the multiplier 18 is set large, the base currents of the transistors 16 and 17 cannot be ignored, so that I _Y /I _X becomes the current amplification factor h. It is necessary to set it within a sufficiently smaller range than _FE .

FIG. 3 shows a second embodiment of the present invention, and shows an example in which a current gain I _Y /I _X that exceeds the current amplification factor h _FE can also be set. In FIG. 3, parts corresponding to those in FIG. 2 are given the same reference numerals and their explanations are omitted.

According to this second embodiment, NPN transistors 41 and 4 are connected between the collectors and bases of the transistors 13 and 14 of the PN junction pair 12 of the multiplier 18.
2, and the collectors of these transistors 41 and 42 are connected to the positive power supply terminal 1, respectively.

By adding the transistors 41 and 42 that operate as emitter followers, the base currents of the transistors 16 and 17 are supplied from the transistors 41 and 42, respectively, so that a current gain I _Y /I _X exceeding h _FE is set. does not cause any operational problems.

Various applications can be considered for the current amplifier having the above structure, and for example, by having the structure as shown in FIG. 4, a variable resistance circuit can be obtained.

That is, the circuit block 51 in FIG. 4 shows the current amplifier according to the present invention, and by connecting the input terminal 9 and the output terminal 23 in FIGS. 2 and 3 to form a feedback path. , a variable resistance circuit can be constructed. At this time, the input terminal 52 and output terminal 53 of the variable resistance circuit correspond to the input terminal 8 and output terminal 23 of the current amplifier, and the equivalent circuit seen from the input and output terminals 52 and 53 of this circuit is the fifth
It can be regarded as a series connection circuit of a buffer amplifier 54 and a resistor 55 as shown in the figure. Since the resistance value of the equivalent resistance in this case can be controlled by the current of the current source, a non-grounded variable resistance circuit can be realized.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, the present invention can be applied to a current amplifier that obtains multiple outputs by connecting a plurality of common emitter transistors to a PN junction pair of a multiplier. It's also easy to do. Furthermore, the conductivity type of each of the transistors described above may be converted into PNP type and NPN type, and instead of using two parallel current sources, one current source output may be divided and used. good.

〔Effect of the invention〕

As is clear from the above description, according to the current converter according to the present invention, changes in the voltage between the base and emitter of the transistor in the voltage-current converter do not affect the characteristics, and the conversion coefficient changes to the resistance value. The linearity is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a prior art of a current amplifier according to the present invention, and FIG. 2 is a circuit diagram showing a prior art of a current amplifier according to the present invention.
3 is a circuit diagram showing a second embodiment, FIG. 4 is a block circuit diagram showing an application example of the present invention, and FIG. 5 is a circuit showing an equivalent circuit of FIG. 4. It is a diagram. 3... Voltage-current conversion circuit, 5... Resistor, 6,
7...Third and fourth transistors, 8, 9...First and second input terminals, 13, 14...Fifth and sixth transistors
transistors, 15... second differential transistor pair, 19... second current source, 31, 32... first and second transistors, 33... first differential transistor pair, 34, 35 ...Seventh and eighth transistors, 36...First current source.

Claims (1)

[Scope of Claims] 1. First and second transistors of a first conductivity type whose bases are connected to first and second input terminals, respectively; and each base of which is connected to each of the first and second transistors. third and fourth transistors of a second conductivity type connected to each emitter and having a resistor connected between each emitter; a first current source that supplies a constant current from a reference potential to each of the emitters; A resistor is connected between the emitters, each collector is connected to each collector of the third and fourth transistors, and a DC bias is fed back from each collector to the base of the transistor, and each emitter is connected to each other. 1st
conductivity type fifth and sixth transistors, each base being connected to each base of the fifth and sixth transistors, each collector being connected to each of the first and second emitters, and each emitter being connected to each of the first and second emitters; a first differential transistor pair comprising seventh and eighth transistors of a first conductivity type connected to each other; a second current source connected to a common emitter of the first differential transistor pair; a second differential transistor pair consisting of a ninth and tenth transistor, each base of which is connected to each base of the fifth and sixth transistors, and each emitter of which is connected to each other; a third current source connected to the common emitters of the pair.