JPS6155285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a current mirror circuit that operates stably under extremely low power supply voltage.

FIG. 1 shows a circuit connection diagram of a conventionally well-known current mirror circuit. 1st
In the figure, transistor 1 is connected via input terminal
A reference current is supplied from the collector side of the transistor 2, and an output current proportional to the reference current is taken out from the collector of the transistor 2 via an output terminal Y.

By the way, in FIG. 1, the transistor 3 is used for the purpose of improving the matching of input current and output current as much as possible. For example, when the transistor 3 is not used, the most common current mirror circuit can be constructed by connecting the base and collector of the transistor 1, but in that case, part of the reference input current is This becomes the base current of transistor 1 and transistor 2, and when the DC current amplification factor of transistor 2 is β ₂ and the input current is Ix, the output current Iy
is given by the following equation.

Now suppose _β2 is 10 and Ix is 100μA,
The output current Iy is approximately 83 μA, and not only is the input/output matching insufficient, but the ratio of input current to output current depends on the DC current amplification factor of the transistor, so if precision is required, Transistor 3 was essential.

However, by using the transistor 3, there is a problem in that the lower limit value of the current voltage applied to the positive power supply terminal B increases. For example, if the base and collector of transistor 1 are connected, it will operate satisfactorily even if the current voltage drops below 1V, but if transistor 3 is used and the current voltage drops below 1.4V, transistor 3 and transistor There was a problem that the base current of No. 1 stopped flowing.

The present invention aims to provide a current mirror circuit that solves the above-mentioned problems.

FIG. 2 is a circuit connection diagram of a current mirror circuit according to an embodiment of the present invention. In FIG. 2, the base and collector of a transistor 1 are connected, the collector is connected to a reference current input terminal X, and the emitter is connected via a resistor 4 to a positive feed line Ba. The base of the transistor 1 is connected to the base of the transistor 2, the emitter of the transistor 2 is connected to the positive feed line Ba through the resistor 5, and the collector is connected to an NPN type transistor complementary to the transistors 1 and 2. Connected to the bases of transistors 6 and 7. The emitters of the transistors 6 and 7 are both connected to the negative power supply line Ca, and between the collector of the transistor 2 and the negative power supply line Ca, a transistor 8 whose base and collector are connected serves as a current bypass means. It is connected.

Further, the emitter of the transistor 9 is connected to the emitter of the transistor 2, the base of the transistor 9 is connected to the collector of the transistor 6, the collector is connected to the current output terminal Y, and the base of the transistor 9 and the positive A resistor 10 is connected between the side feed lines Ba.

On the other hand, the base and collector of a transistor 11 and the base of a transistor 12 are connected to the collector of the transistor 7, and the emitters of the transistors 11 and 12 are both connected to the positive power supply line Ba.
The collector of No. 2 is connected to the current output terminal Y.

Now, in the circuit shown in Figure 2, resistors 4, 5, 1
The resistance values of transistors 0 are R ₄ , R ₅ , and R ₁₀ , the DC current amplification factors of transistors 1, 2, 9, 11, and 12 are all βp, and the DC current amplification factors of transistors 6, 7, and 8 are All of them are βn, and the collector currents of the transistors 1, 2, 6, 7, 8, 9, 11, and 12 are I ₁ , I ₂ , I ₆ , I ₇ , I ₈ , I ₉ ,
I ₁₁ , I ₁₂ , both base-emitter voltages are V _B
E , the relationship between the reference current Ix drawn in from the reference current input terminal X and the output current Iy drawn out from the current output terminal Y can be determined as follows.

Ix=I ₁ (1+1/βp)+I ₂ /βp…(2) R ₄ I ₁ =R ₅ (I ₂ +I ₉ )…(3) I ₂ =I ₈ (1+1/βn)+I ₆ /βn+I ₇ / βn
...(4) Assuming that the resistance value of the resistor 10 is sufficiently large and most of the collector current of the transistor 6 becomes the base current of the transistor 9, I ₆ βp=I ₉ ...(5) Also, Iy=I ₉ +I ₁₂ ...(7) By the way, assuming that I ₆ = I ₈ = I ₇ /2 ...(8) holds true, the above equations (4), (5), and (6) are ₂ = I ₈ (1+4/βn) …(9) I ₈ βp=I ₉ …(10) From equations (2) and (9), Ix=I ₁ (1+1/βp)+I ₈ /βp(1+4/β
n)...(12) From equations (3) and (9), R ₄ I ₁ = R ₅ {I ₈ (1+4/βn)+I ₉ }...(13) From equations (10) and (11), From equations (10) and (12), From equations (10) and (13), R ₄ I ₁ = R ₅ I ₉ {1+1/βp+4/βpβn}…(16
) From equations (7) and (14), From equations (15), (16), and (17), finding the relationship between Iy and Ix, we get In equation (18), for example, R ₅ = R ₄ , βp=
10, βn=40, and Ix=100 μA, the value of Iy becomes 95 μA, and the matching is better than when the base and collector of transistor 1 are shorted in FIG.

Now, in the circuit shown in Figure 2, even if a voltage drop of 100 mV is created across resistor 5, for example,
The base-emitter voltage of transistor 8 is
It is about 0.65V, and the saturation voltage of transistor 2 is
Since it is 0.2V or less, it can operate satisfactorily even if the power supply voltage is lower than 1V.

By the way, in the calculation example, it is assumed that the emitter current of transistor 7 is twice that of transistor 8. It can be easily achieved.

Further, even if the resistance value of the resistor 10 is made small so that the base current of the transistor 9 and the current flowing through the resistor 10 are approximately the same, good matching characteristics can be achieved.

In addition, as illustrated in FIG. 3, the transistor 2
Even if a resistor 13 is connected as a current bypass means between the collector of the second
The same effect as the circuit shown in the figure can be obtained.

As described above, the current mirror circuit of the present invention includes a first transistor (corresponding to Embodiment 1 described above) whose collector is supplied with a reference current and whose emitter is connected to one of the feed lines, and whose base is connected to the first transistor (corresponding to Embodiment 1 described above). A second transistor connected to the base of the first transistor and whose emitter is connected to the feed line via a resistor 5.
a transistor (corresponding to No. 2), which is complementary to the first and second transistors, and whose base current is supplied from the collector of the second transistor and whose emitter is connected to the other power supply line. A transistor No. 3 (corresponding to No. 6) and a fourth transistor (corresponding to No. 7), the emitter of which is connected to the emitter of the second transistor, and a base current supplied from the collector of the third transistor. 5 transistor (equivalent to 9)
and a sixth transistor (corresponding to No. 11) whose base and collector are supplied with the collector current of the fourth transistor, whose emitter is connected to one of the feed lines, and whose base is connected to the base of the sixth transistor. a seventh transistor (corresponding to No. 12) connected to the power supply line and whose emitter is connected to the feed line; and a current bypass means (corresponding to No. 8 or No. 13) connected between the collector of the second transistor and the other feed line. ), and the output current is obtained by adding the collector currents of the fifth and seventh transistors, and there is only one base-emitter junction of the transistor between the feed lines. Since it does not exist, it has the great effect of providing good matching characteristics even under a low power supply voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit connection diagram showing a conventional example, and FIGS. 2 and 3 are both circuit connection diagrams of a current mirror circuit according to an embodiment of the present invention. 1, 2, 6, 7, 8, 9, 11, 12...transistor, 13...resistance.

Claims (1)

[Claims] 1. A first transistor to which a reference current is supplied from the collector side and whose emitter is connected to one of the power supply lines, and whose base is connected to the base of the first transistor, and whose emitter is connected to the base of the first transistor through a resistor. a second transistor connected to the power supply line; and a second transistor complementary to the first and second transistors,
third and fourth transistors, the base current of which is supplied from the collector of the second transistor, the emitters of which are connected to the other feed line; the emitters of which are connected to the emitter of the second transistor; a fifth transistor whose base and collector are supplied with the collector current of the fourth transistor and whose emitter is connected to one of the feed lines; a seventh transistor connected to the base of the sixth transistor and having an emitter connected to the power supply line; and a current bypass means connected between the collector of the second transistor and the other power supply line; A current mirror circuit characterized in that the collector currents of the fifth and seventh transistors are added together to obtain an output current. 2. The current mirror circuit according to claim 1, wherein the current bypass means is constituted by an eighth transistor whose base and collector are connected. 3. The current mirror circuit according to claim 1, wherein the current bypass means is constituted by a resistance element.