JPS6112109A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To set accurately the input/output current ratio of a current mirror circuit by connecting a base-collector of an input TR of the current mirror circuit via a TR and connecting a TR to TRs forming a differential amplifier circuit in cascode. CONSTITUTION:TRs 5, 7, 12 form the current mirror circuit. Then a resistor 21 inserted between a base of the TR12 and a common base of the TRs 5, 7 applies beta compensation of the current mirror circuit. Further the early effect is excluded by inserting TRs 19, 20 to the collector of the TRs 1, 2 and a TR22 between the base and collector of the TR12. Then the input/output current ratio of the current mirror circuit is set accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a current mirror circuit of a current source connected to the emitter of a transistor.

[Technical background of the invention]

FIG. 4 is a circuit diagram showing an example of a differential amplifier including a conventional current mirror circuit of this type. The collectors of the transistors 1 and 2 constituting the differential amplifier circuit are connected to the voltage source Vcc via a resistor 3.4, and the collector of the transistor l is connected to the voltage source VCCK via a transistor 5 and a resistor 6ft. The collector of 's transistor 2 is connected to the voltage source Vcc via a transistor 7 and a resistor 8.

The emitters of transistors 1 and 2 are connected to each other by a resistor 9, and the emitters of transistors 1 and 2 are each grounded via a current source 10, 11. The bases of transistors 5.7 are connected in common, and these bases are also connected to the base of transistor 120. The emitter of the transistor 12 is connected to the voltage source Vcc through a resistor 13, and the collector is connected to ground through a current source 14. Further, the base and collector of this transistor 120 are connected. Each base of the transistor 1.2 is connected to an input terminal 15.16, and each collector is connected to an output terminal 17.18. When differential input Vin is applied to terminals 15.16, differential output Vout of transistors 1 and 2 is outputted to terminals 17.18.

Incidentally, the gain M of the differential amplifier with respect to the differential input VinK is expressed by the following equation, where the differential output is Vout.

Here, RL is the resistance value of the resistors 3 and 4, . ■Ti
The thermoelectromotive force of the 1t transistor 1.2 is shown. It is also assumed that I, = I2.

In addition, the DC potential of the output terminals 17 and 18 Vout p □
is expressed by the following formula.

Voutpc=Vcc-RLIRLII:VCCh (
II ICMI ) = - (3) where % IRL is the current flowing through resistors 3 and 4. Ml indicates the current flowing through the resistor 6.

Now, let us consider a case where the gain must be increased without changing the input signal amplitude Vinpp and the bias currents Il and I2, and separately, the output DC potential VoutDC must be determined to a target value. In commonly used differential amplifiers, the value of the resistance ratio is set large in order to increase the gain, but in this case, the output DC potential V is uniquely
In other words, use equation (3). The value is determined to be M1=0. Therefore, if a current mirror is used, the output DC potential Vout
nO can be determined independently.

By the way, in the current mirror circuit consisting of transistors 5, 7.12 and resistors 6, 8.13 shown in FIG. 4, the following approximately holds true. That is, the input current IC! (
Output current (collector current of input transistor 12). The ratio of llIC2 is 6.4.1 for each emitter resistor.
By appropriately setting the resistance ratio of 3 and the emitter area ratio of each transistor 5°7.12, υ is constant. When the input/output current ratio = 1, the emitter resistance ratio = 1 and the emitter area ratio = 1. becomes.

[Problems with background technology]

In the conventional differential amplifier as described above, the following problems arise when high accuracy of the output DC potential VoutpcK is required. That is, the noisy current I,
, I2. Even if the required current value for I3 is accurately obtained, the actual input/output current ratio of the current mirror circuit described above will not be equal to the set value for the following two reasons. Here, it is assumed that the input/output current ratio of the current mirror circuit is set to H1 after υ. One of the above reasons is the input current ■. Since S supplies the base current of both input and output transistors 5, 7, 12, there is a problem of β compensation in which even though the collector currents of these input and output transistors 5, 7, 12 are equal, the input and output currents are not equal. .

Therefore, the problem of this β compensation will be described below.

In the current mirror circuit shown in Figure 4, the transistor 5°7.1
Assuming that the two devices are formed on the same semiconductor substrate and that matching is ideally obtained, the input current]. 3 and output current■.

1 and engineering. 2 is expressed by the following equation, where βF is the forward current amplification factor of the transistor 5.7.12. That is, as shown in equation (4), an error occurs due to the linear term of βr.

2I'i of the above reason, input/output transistor 5゜7.
This is an early effect problem in that if the collector-emitter voltages of each of the 12 differ, the collector current also differs. Now, in Fig. 4, the collector-emitter voltages of transistors 5 and 7゜12 are respectively vCEs z''%Dp'VGE
1! and the base-emitter voltage is %i
# When VBICt and VBK+□, the following formula holds true.

However, it is assumed that the transistors 5, 7, and 12 have ideal characteristics, Is is the forward saturation current of each transistor, and A is the early voltage of each transistor. Here, VBICII = Vgxy = Vaxu (By transforming equations (5) and (6) using the D relationship, the following equations are obtained. From equations (8) and (9), input/output transistor 5
．． If the collector-emitter voltage of 7.12 is different, the input/output transformer C1*rc- will also be different.

In conclusion, it can be said that the current mirror circuit used in the conventional differential amplifier shown in FIG. 1 does not operate accurately due to the two separate factors mentioned above. Therefore, the output DC potential VoutD□ generated at the load resistor 3.4 also deviates from the expected value.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above drawbacks, it is an object of the present invention to provide a current mirror circuit capable of setting a positive mK input/output current ratio.

[Summary of the invention]

The present invention includes an input transistor whose collector is connected to each collector of a plurality of transistors each having a current source at its emitter and whose polarity is opposite to that of the plurality of transistors, and an output transistor which supplies an input current to these input transistors. In a current mirror circuit, the bases of an input transistor and an output transistor are commonly connected, and the collectors of these input/output transistors are connected to a common voltage source. The plurality of transistors are connected to the voltage source via the emitter-collector, and the plurality of transistors are connected between the base and collector of the input transistor. The above object is achieved by providing a second transistor with a polarity and applying a predetermined reference voltage to a common base of the first and second transistors.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. explain. FIG. 1 is a circuit diagram showing an embodiment of a differential amplifier to which the current mirror circuit of the present invention is applied. The collector of the transistor 1 constituting the differential amplifier circuit is connected to the voltage source VCC via the emitter collector of the transistor 19 and the resistor 3, and the collector of the transistor 2 is connected to the voltage source VCC via the emitter collector of the transistor 20 and the resistor 4. It is connected to the.

In addition, a transistor 12 constituting a current mirror circuit
The base of the resistor 21 is connected to the common base of transistors 5 and 7.
Further, the Jl base of the transistors 5 and 7 and the collector of the transistor 12 are connected through the collector-emitter of the transistor 22.

The bases of transistors 19, 20, 22 are connected in common, and these bases are connected to terminal 23. terminal 2
3 is applied with a reference voltage Vref. The other configurations are the same as those of the conventional example, so explanations will be omitted.

Next, the operation of this embodiment will be explained. Tranrasta 1
A resistor 21 inserted between the base of transistor 2 and the common base of transistors 5 and 7 performs β compensation, which is a problem with the current mirror circuit described in the conventional example. That is, when the resistor 21 is inserted into the base of the transistor 12 constituting the current mirror circuit, the following equation is established.

is the same as the conventional example. In equation (10), Rat-=
If you choose a value of 3Rau+ (= 3Raux),
Engineering. □Uni. 3, and the influence of p can be ignored. As a result, the problem of β compensation is solved in the circuit of FIG.

Next, transistor 1゜2 of trunk cluster 19.20
and the base of the transistor 12,
Transistor 22 can be inserted between the collectors without deteriorating the performance of the differential amplifier.
This was done to solve the problem of keeping the collector-emitter voltages the same.

That is, by selecting an appropriate value for the reference voltage Vref applied to the common base of the transistors 19 and 20 connected to the collector side of the transistors 1 and 2 in cascode and the transistor B, the transistors 5 and 7 are connected by the transistors 19 and 20. The collector-emitter voltage of the transistor 12 can be fixed by the transistor 22. Therefore, transistors 5, 7, and 12 in the current mirror circuit operate with the same collector-emitter voltage. Therefore, Vcgs
:VcE4 :■Eδ was explained in the conventional example (8
) to (9), the following relationships are obtained.

I, :I. , ...(11) I. , :I. , -...(12) This reduces variations in the collector-emitter voltage of transistors 5, 7, and 12 due to the Early effect,
These collector and emitter voltages can always be made equal, so as mentioned in the conventional example (8) and (9)
1 can always be made equal.

According to this embodiment, β compensation is performed by inserting the resistor 21, and the output current of the transistor 5.7 is reduced to ■. 1゜■. 2, and furthermore, transistors 19, 20 .
Input/output current IC1 due to the Arealy effect due to the insertion of 22
? It is possible to eliminate the deviation that occurs between IC0T I (1). Therefore, the gain of the differential amplifier circuit composed of transistors 1 and 2 is increased, and in addition to this, the output potential VoutDck is accurately set to the desired value. Furthermore, since the transistors 19 and 20 are connected in cascode with the transistors 1 and 2 forming the differential input circuit, the input capacitance of the transistors 1 and 2 can be greatly reduced by the mirror capacitance of the transistors 19 and 20. It is possible to improve the high frequency characteristics of the amplifier and achieve a wide band.

FIG. 2 is a circuit diagram showing another embodiment of the β-sweeping circuit in the portion surrounded by the broken line in FIG. 1.

That is, the base and collector of the transistor 12 are connected via the emitter-base and collector-emitter of the transistor 24 and 22, and the base of the transistor 12 is connected to the first
Both transistors 5 and 7 in the figure are directly connected to the i base. Since the β compensation circuit of this example is used in exactly the same circuit as the circuit shown in FIG.
) than the expression βν. The influence on I is reduced and β compensation can be performed.

FIG. 3 is a circuit diagram showing another embodiment of the present invention. This circuit consists of transistor 5 that constitutes a current mirror circuit.
．． Transistors 25, 26 and resistor n on the emitter side of 7
This is a differential amplifier circuit constructed by adding a differential amplifier circuit to the circuit shown in FIG. 1, and the emitters of transistors 25 and 26 are grounded via current sources 28 and 29. Further, the bases of the transistors 2 and 25 are connected in common, and further connected to the input terminal 30. The base of transistor 26 is connected to input terminal 16. Therefore, this circuit has a differential pair consisting of transistors 1 and 2 and transistors 25 and 26 on the load side of transistors 5 and 7 constituting the current mirror circuit, and a common base transistor is connected to each adder circuit in cascode. It constitutes a connected two-man power addition circuit.

This embodiment also includes transistors 19, 20, 22 and resistor 2.
1, similarly to the embodiment shown in FIG.
It is possible to make the settings □ and improve the high frequency characteristics.

〔Effect of the invention〕

As described above, according to the current mirror circuit of the present invention, the first transistor group is cascode-connected to the collector of each output transistor of the differential amplifier circuit connected to the output side of the current mirror circuit, and the current mirror The base and collector of the input transistor of the circuit are connected via a second transistor, and the base of the first transistor group and the base of the second transistor are connected in common, and a predetermined voltage is applied to these bases. By applying a reference voltage, the input/output current ratio of the current mirror circuit can be set with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of a differential amplifier to which the current mirror circuit of the present invention is applied, Fig. 2 is a circuit diagram showing another embodiment of the β compensation circuit shown in Part 1; FIG. 3 is a circuit diagram showing another embodiment of the present invention, and FIG. 4 is a circuit diagram showing an example of a conventional differential amplifier circuit. 1, 2.5.7.12.19.20.22.24...
Transistor 3, 4, 6, 8, 9, 13.21-...
Resistance Agent Patent Attorney Noriyuki Chika Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1) An output transistor whose collector is connected to each collector of a plurality of transistors having a current source at the emitter, the polarity of which is opposite to that of the plurality of transistors, and an input current is supplied to these output transistors. In a current mirror circuit comprising an input transistor, the bases of the input transistor and the output transistor are commonly connected, and the emitters of these input/output transistors are connected to a common voltage source, wherein the plurality of transistors a first group of transistors having the same polarity and the same number as the plurality of transistors, the emitter of which is connected to each collector of the input transistor, and the collector of which is connected to the voltage source via a load resistor; A current mirror circuit comprising: a second transistor having the same polarity as the plurality of transistors connected through the current mirror circuit; and applying a predetermined reference voltage to a common base of the first and second transistors. 2) a third transistor of a different polarity from the second transistor, which connects the collector of the second transistor provided between the base and collector of the input transistor to the base of the input transistor via a base emitter; 2. A current mirror circuit according to claim 1, further comprising a current mirror circuit.