JPH04192608A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To suppress a change in a mirror coefficient due to a change in a collector-base voltage by connecting a 2nd current mirror circuit to a 1st current mirror circuit via a resistor. CONSTITUTION:A 3rd transistor(TR) Q3 whose collector and base connect to current mirror circuits Q1,Q2 comprising 1st and 2nd TRs and whose emitter connects to ground and a 4th TR Q4 whose collector connects to an input terminal, whose base connects to a base of the 3rd TR Q3 and whose emitter connects to ground are provided to the current mirror circuit. Then a collector of the 2nd TR Q2 and a collector of the 3rd TR Q3 are connected via a resistor R1. Thus, an error in a mirror current caused by the Earley's effect of the 2nd TR Q2 is cancelled by the 2nd current mirror circuit comprising the 3rd TR Q3 and the 4th TR Q4, an error in the mirror current is reduced to suppress a change in the mirror coefficient.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current mirror circuit, and more particularly to a current mirror circuit in which fluctuations in mirror coefficients due to the Early effect are reduced.

[Conventional technology]

Conventionally, current mirror circuits are used to supply a load connected to the output with a current proportional to the current applied to the input. Second as a current mirror circuit
The circuit shown in the figure is known.

In Fig. 2, l is the input terminal of the current mirror circuit;
2 is an output terminal. The collector and base of the first transistor Q1 are connected to the input terminal 1, and the emitter is grounded. The second transistor Q2 has a collector connected to the output terminal 2, a base connected to the base of the first transistor Q1, and an emitter grounded.

In this current mirror circuit, if the characteristics of the two transistors Ql and Q2 are equal, the current amplification factor hfm is infinite, and the Early voltage vA is infinite, then the input current 11 and the output current 12 are completely equal, and 1+= The relationship L holds true.

[Problems to be Solved by the Invention] Early voltages of transistors Ql and Q2 used in the above-mentioned current mirror circuit,
is actually not infinite, but a finite value, the number 10v ~ 1
It takes a value of about 00V. Therefore, the mirror coefficient: jl/12 is determined by the collector-base voltage VC1+02 of the output side transistor, that is, the second transistor Q2.
The problem is that the changes occur.

In this case, the relationship between i and i is as follows: V cmoz: Q2 collector-base voltage ■A
: Early voltage.

Figure 3 shows the mirror coefficient and VCI in the current mirror circuit of Figure 2. The relationship between the two is shown by a broken line. In this way, the mirror coefficient is changed by the collector-base voltage VClO2 of the transistor Q2.

An object of the present invention is to provide a current mirror circuit that can suppress changes in mirror coefficients regardless of changes in collector-base voltage.

[Means to solve the problem]

The current mirror circuit of the present invention has a collector and a base connected to a current mirror circuit composed of a first and a second transistor, a third transistor whose emitter is grounded, and a third transistor whose collector is connected to an input terminal and whose base is connected to the third transistor. is connected to the base of the third transistor, and a fourth transistor whose emitter is grounded is provided, and the collector of the second transistor and the collector of the third transistor are connected via a resistor.

[Operation] According to the present invention, the error in the mirror current caused by the Early effect of the second transistor is canceled out by the second current mirror circuit constituted by the third transistor and the fourth transistor, and the error in the mirror current is eliminated. and suppress changes in mirror coefficients.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram of one embodiment of the current mirror circuit of the present invention. In the figure, 1 is an input terminal, 2 is an output terminal, Ql is a first transistor, and Q2 is a second transistor, and these constitute a circuit similar to the current mirror shown in FIG. 2.

Furthermore, the collector and base of the third transistor Q3 are connected, and the emitter is grounded. Also, the fourth
The transistor Q4 has a collector connected to the input terminal 1, a base connected to the base of the third transistor Q3, and an emitter grounded. These third and fourth
Transistor Q3. Q4 constitutes a second current mirror circuit.

The collector of the second transistor Q2 and the third transistor
It is connected to the collector of transistor Q3 via resistor 1.

According to this circuit configuration, when the collector-base voltage Vcmoz of the second transistor Q2 is >0, CIQ3 is considered to be 0.7■, so V c*oa
= V cso3= OV cto'+: 3rd
Transistor collector-base voltage VCIQ4: collector-base voltage of the fourth transistor is established, the second current mirror circuit is not affected by the Early effect, and its mirror coefficient is always constant.

Here, if the mirror coefficient of the second current mirror circuit is chosen to be 2 and the resistance value R of the resistor R1 is chosen as R=V A / I 1, then the current mirror circuit in Fig. 1 becomes the current mirror in Fig. 2. This is equivalent to increasing the Early voltage of the second transistor Q2 of the circuit by 1/2.VA/Vcmoz.

In other words, the error in the mirror current caused by the Early effect of the second transistor Q2, which is the transistor on the output side of the current mirror circuit, is detected by the resistor R1 and canceled by the second current mirror circuit, thereby eliminating the error. It becomes possible to reduce the amount of time to 1/2 ・VA/VCI.

Miller coefficient and collector-base voltage of the second transistor in the circuit of FIG. . 2 is shown by a solid line in FIG. As is clear from this figure, the circuit in Figure 1 has a lower collector-base voltage than the circuit in Figure 2. .

The influence of 2 on the mirror coefficient is reduced, making it close to ideal.

〔Effect of the invention〕

As explained above, the present invention connects a second current mirror circuit made up of a third transistor and a fourth transistor to a current mirror circuit made up of first and second transistors via a resistor. Therefore, the error in the mirror current caused by the Early effect is detected by a resistor and then reduced by the second current mirror circuit, making it possible to suppress changes in the mirror coefficient due to changes in collector-base voltage. There is.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2 is a circuit diagram of a conventional current mirror circuit, and Figure 3 is the relationship between collector-base voltage and mirror coefficient in each of the first and second circuits. FIG. 1...Input terminal, 2...Output terminal, Ql...1st
Transistor, Q2...Second transistor, Q3...
・Third transistor, Q4...Fourth transistor, R
1...Resistance. Figure 1 Figure 2 Mirai #: 1 Gu2

Claims (1)

[Claims] 1. A first transistor whose collector and base are connected to an input terminal and whose emitter is grounded; and a transistor whose collector is connected to an output terminal, whose base is connected to the base of the first transistor, and whose emitter is grounded; a third transistor whose collector and base are connected, and whose emitter is grounded; and a fourth transistor whose collector is connected to the input terminal, whose base is connected to the base of the third transistor, and whose emitter is grounded. . A current mirror circuit, characterized in that the collector of the second transistor and the collector of the third transistor are connected via a resistor.