JPH01128603A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To enlarge the output impedance of a current mirror circuit by executing negative feedback control with using an error amplifier and causing the input terminal voltage of the current mirror circuit to be equal to an output terminal voltage. CONSTITUTION:An error amplifier 5 causes the voltage of an input terminal 3 to be equal to the voltage of an output terminal 4 by the negative feedback control. Accordingly, the voltages between the collectors of transistors 1 and 2 go to be equal. As the result, when the characteristics of the transistors 1 and 2 are equal, an emitter current, a current amplifying rate (hfe) and a collector current are made equal and accordingly, the input current of the input terminal 3 and the output current of the output terminal 4 go to be equal. Since the current of a constant current source 7 is constant regardless of the voltage of a voltage source 8, the current of the output terminal 4 goes to be constant in the same way. This shows that the output impedance of the current mirror circuit is infinite.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current mirror circuit, and particularly to a current mirror circuit suitable for integration into an integrated circuit.

[Prior Art] A conventional current mirror circuit has a configuration as shown in FIG. 6,8
is a voltage source, and the voltage at the input terminal 3 was constant regardless of the voltage at the output terminal 4.

[Problems to be solved by the invention] The conventional current mirror circuit described above has a transistor 2
Since the early voltage of is finite, it has the disadvantage of low output impedance. This is because when the voltage at the output terminal 4 changes, the collector-emitter voltage of the transistor 2 changes, and the current amplification factor hfe of the transistor 2 changes, so the collector current of the transistor 2, that is, the output current changes. In the current mirror circuit of FIG. 7, the early voltage of transistor 2 is VA.

Collector current is ■○UT, voltage of output terminal 4 is VOUT
, the voltage of the constant current source 6 is set to VCC, the output impedance Zo of this current mirror circuit is ZO=VA+ (
VCC-VOUT)/l0UT. For example, VA=
6V, r OUT = 1mA.

When VCC=5V and VOUT=2.5V (7), the output impedance Z'0 becomes 8.5Ω from the above equation.

The graph in FIG. 3 is the simulation result, and it can be seen that the conventional example has a low output impedance, as shown by the straight line PA.

[Differences between the present invention and the prior art] The present invention differs from the conventional current mirror circuit described above in that negative feedback control is performed using an error amplifier so that the input terminal voltage of the current mirror circuit becomes equal to the output terminal voltage. have.

[Means for Solving the Problems] The current mirror circuit of the present invention includes an error amplifier that performs negative feedback control to make the input terminal voltage of the current mirror circuit equal to the output terminal voltage.

That is, the gist of the present invention is to include a first transistor whose collector is connected to an input terminal, and a second transistor whose collector is connected to an output terminal, and a base of the first transistor and a second transistor. The current mirror circuit connected to the base of the transistor includes an error amplifier that performs negative feedback control so that the collector voltage of the first transistor becomes equal to the collector voltage of the second transistor.

[Example code] First plan Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. In this embodiment, the collector is connected to the input terminal 3, the base is connected to the output of the error amplifier 6, and the emitter is connected to the constant voltage ri, 6.
, a transistor 2 whose collector is connected to the output terminal 4, whose base is connected to the output of the error amplifier 5, and whose emitter is connected to one terminal of the constant voltage source 6; An error amplifier 5 whose input is connected to the collector of transistor 1 and whose inverting input is connected to the collector of transistor 2 is included. 7 is a constant current source, and 8 is a voltage source.

Next, the operation of the embodiment will be explained. The error amplifier 5 is
Negative feedback control 2 attempts to make the voltage at input terminal 3 equal to the voltage at output terminal 4.

Therefore, the collector-emitter voltages of transistors 1 and 2 become equal. As a result, if the characteristics of transistors 1 and 2 are equal, the emitter current, current amplification factor hfe, and collector current will also be equal, and therefore the output currents of the input terminal 3 and the output terminal 4 will be equal. Since the current of the constant current source 7 is constant regardless of the voltage of the voltage source 8, the current of the output terminal 4 is also constant. This shows that the output impedance of the current mirror circuit of the present invention is infinite. As a feature of semiconductor integrated circuits, differences in characteristics between transistors on the same chip can be made small, so it is reasonable to assume that transistors 1 and 2 have the same characteristics.

FIG. 2 shows the error amplifier 5 of the first embodiment with transistors 101, 102, 103, 104, 106, 107, 1
08 and 109 and a constant current source 105. FIG. FIG. 3 shows the relationship between the output voltage and the output current of the circuit shown in FIG. 2, obtained by computer simulation, and as shown by the straight line EMI, the output current is constant regardless of the output voltage. Early voltage V of transistor 2
The calculation was performed assuming that A=6V, the current of the constant current source 7 was 1 mA, and the voltage of the constant voltage source 6 was 5V.

Emitters of transistors 1 and 2 and constant voltage source 6 in FIG.
A modified example of FIG. 4 in which a resistor is inserted between the two, and a circuit in which the PNP transistor shown in FIGS. 1 and 4 are replaced with an NPN transistor are also included within the technical scope of the present invention.

Figure 5 is a circuit diagram of a second embodiment of the present invention, which includes a transistor 1 whose collector is connected to the input terminal 3 and whose base is connected to the output of the error amplifier 5; A transistor 2 has a collector connected to an output terminal 4, a base connected to the output of an error amplifier 5, a base and a collector connected to the committer of the transistor 1, and an emitter connected to a constant voltage R.
transistor 10 connected to one terminal of transistor 6, and transistor 1 whose collector is connected to the emitter of transistor 26 and whose base is connected to the emitter of transistor 1.
1, and an error amplifier 5 whose non-inverting input is connected to the collector of transistor 1 and whose inverting input is connected to the collector of transistor 2.

Next, the operation of the embodiment will be explained. Due to the negative feedback control of the error amplifier 5, the voltage at the input terminal 3 becomes equal to the voltage at the output terminal 4. Therefore, the emitter-collector voltages of transistors 1 and 2 and the emitter-collector voltages of transistors 10 and 11 become equal. Assuming that the current amplification factor of transistors 10 and 11 is hfe, the current of constant current source 7 is IIN, and the current of the output terminal is IOUT, then I0UT=IINXhfe/hfe+
It becomes 2. Since the collector-emitter voltage of transistors 10 and 11 is constant regardless of the voltage at output terminal 4, hfe
becomes constant, and the output current also becomes constant.

Therefore, the output intensity of the current mirror circuit of this embodiment becomes infinite. The circuit in Figure 5 (EM2) and the circuit in Figure 8
Regarding the conventional example (PA) in the figure, transistor L 2
．． 16, 11 current amplification factor is 30, early voltage is 6
V, the voltage of constant voltage source 6 is 5V, and the current of constant current source 7 is 1m.
The results of computer simulation as A are shown in FIG. As can be seen from FIG. 6, the output impedance of the current mirror circuit can be increased by the second embodiment.

[Effects of the Invention] As explained above, the present invention uses negative feedback control using an error amplifier to make the input terminal voltage of the current mirror circuit equal to the output terminal voltage, thereby increasing the output impedance of the current mirror circuit. It has a positive effect.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the first embodiment of the present invention, Fig. 2 is a circuit diagram of the error amplifier of the first embodiment, Fig. 3 is a graph showing the characteristics of the first embodiment, and Fig. 4 is a graph showing the characteristics of the first embodiment. FIG. 5 is a circuit diagram showing a modification of the first embodiment, FIG. 5 is a circuit diagram showing the second embodiment, and FIG. 6 is a circuit diagram showing a modification of the first embodiment.
Graphs showing the characteristics of the embodiment, and FIGS. 7 and 8 are circuit diagrams showing conventional examples, respectively. 1.2... Current mirror circuit transistor, 3.
...Input terminal of current mirror circuit, 4...Output terminal of current mirror circuit, 5...Error amplifier. Patent Applicant: NEC Corporation Representative, Patent Attorney Kiyoshi Kuwai - Figure 1 Figure 2 Figure 5 Figure 4 Figure 5 1.0203,04.0v VOIJT (Voltage of Naruko 4) Whistle 6 factors

Claims (1)

[Claims] A current transistor having a first transistor whose collector is connected to an input terminal, a second transistor whose collector is connected to an output terminal, and a base of the first transistor and a base of the second transistor are connected. 1. A current mirror circuit comprising an error amplifier that performs negative feedback control so that the collector voltage of the first transistor becomes equal to the collector voltage of the second transistor.