JPH10145154A - Current mirror circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the base current dependence of an output Tr and to realize a low voltage operation by controlling a second reference current source with a transistor for base current correction Tr and setting the bias of 1VBE top respective Tr voltage in the reference voltage sources. SOLUTION: Trs Q1 and Q3 for base current correction operate to enlarge the reference current Iref3 of the second reference current source 2, when the power amplification rate β of Tr is small, namely, when base current is large. When the reference current of a first reference current source 1 is set to be Iref1 , the base current value of current mirror input and output Trs Q2 and Q4 to be Iref2 , the collector current value of TrQ3 for base current correction to be Iref3 -Iref2 , the base current value of TrQ1 for base current correction to be IB, the collector current value of TrQ2 to be IIN, an output current value to be Iout and a value Iref3 -Iref2 to be values IIN and IOUT, IOUT=Iref1 /(1.1/β<2> ) is obtained, the base current dependence of each Tr can be improved. Then, 1VBE bias is set to respective Tr voltage by the first and second reference voltage sources 3 and 4, so as to realize a low-voltage operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a current mirror circuit, and more particularly to a current mirror circuit in which the dependence on the base current of a transistor is improved and which operates at a low voltage.

[0002]

2. Description of the Related Art Conventionally, a current mirror circuit having a configuration as shown in FIG. 5 is known (co-authored by Gray / Meyer, translated by Minoru Nagata, November 30, 1990, published by Baifukan, "Analog Integration"). Circuit Design Technology ”, Vol. 1, p. 218). This current mirror circuit includes a transistor Q101 having a collector and a base connected to a power supply _Vcc via a resistor R, and an emitter connected to GND;
And a transistor Q102 whose base is connected to its base and whose emitter is connected to GND.

In a current mirror circuit as shown in FIG. 5, the input reference current is I _ref , the collector current of the transistor Q101 is I _IN , and the transistor Q101 is
, Q102 and β, and the transistors Q1 and Q2 have the same shape, the output current I _OUT
Is approximately expressed by the following equation (1). I _ref −I _IN −2 I _OUT / β = 0 I _OUT ≒ I _ref / (1 + 2 / β) (1) where I _OUT = I _IN .

The current mirror circuit shown in FIG. 5 can operate at a low voltage (power supply voltage V _CC = 1 V), but it can be seen from the above equation (1) that the output current greatly depends on β.

A conventional current mirror circuit having a configuration as shown in FIG. 6 is also known (see page 221 of the above-mentioned document). This current mirror circuit comprises three transistors Q101, Q102,
In the current mirror circuit constituted by Q103, the output current I _OUT is represented by the following equation (2) due to the base current correction effect of the transistor Q103. I _ref −I _IN −2 I _OUT / β ² = 0 I _OUT ≒ I _ref / (1 + 2 / β ² ) (2) where I _OUT = I _IN . From the equation (2), the output current I _OUT is larger than the output current in the conventional example shown in FIG.
It can be seen that the base current dependency of the β-fold transistor is improved.

[0006]

By the way, in the conventional current mirror circuit in which the dependency of the output current on the base current is improved, there is no description on the viewpoint of low power supply voltage operation. That is, in the current mirror circuit shown in FIG. 6, when considering the minimum power supply voltage operation level, the V _{BE of} all the transistors is about 0.7 V, and the input reference current I _ref is generated by the constant current source using the transistors. _Assuming that the minimum operating voltage V _CEsat between the collector and the emitter of the transistor is about 0.2 V, V _BE of the transistors Q 1 and Q 3 and V V of the transistor forming the constant current source connected to the collector of the transistor Q 1 are assumed.
_CEsat makes the minimum power supply voltage about 1.7V. on the other hand,
The current mirror circuit shown in FIG. 5 can operate at a low power supply voltage (power supply voltage of about 1.0 V), but has a large dependence on the base current of the transistor, and is not suitable for a circuit requiring high accuracy.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem in the conventional current mirror circuit, and can operate even at a low power supply voltage of about 1.0 V and has a dependency on the base current of the transistor. It is an object to provide a small current mirror circuit.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides first and second reference current sources each having one end connected to a first reference voltage source. A first transistor having a base connected to the first reference voltage source at the other end of the source, a collector connected to the other end of the first reference current source, and a base connected to the other end of the second reference current source; A second transistor having an emitter connected to the second reference voltage source, and a second transistor having a base connected to the collector of the first transistor.
And the collector is connected to the second reference voltage source.
A third transistor connected so as to control the reference current source of the first and second transistors, and a fourth transistor current mirror-connected to the second transistor, so that an output current is obtained from a collector of the fourth transistor. To form a current mirror circuit.

In the current mirror circuit configured as described above, the first and third transistors for correcting the base current are used to connect the second transistor connected to the base of the current-mirror-connected fourth transistor in the output stage. Is controlled, and the base current dependency of the output transistor in the current mirror output current is improved. Also,
The voltage of each transistor is bias-set at 1 V _BE by the first and second reference voltage sources, so that low voltage operation is possible.

[0010]

Next, an embodiment will be described. FIG. 1 is a circuit diagram showing a first embodiment of a current mirror circuit according to the present invention. In FIG. 1, 1
Is a first reference current source having one end connected to the first reference voltage source 3, and 2 is a second reference current source having one end connected to the first reference voltage source 3. The other end of the first reference current source 1 is connected to the base of a transistor Q1 for correcting base current whose emitter is connected to the first reference voltage source 3, and the other end of the second reference current source 2 Is connected to the base of a current mirror input transistor Q2 having an emitter connected to the second reference voltage source 4 and a collector connected to the other end of the first reference current source 1. The collector of the transistor Q1 is connected to the base of a transistor Q3 for base current correction, the emitter of which is connected to the second reference voltage source 4,
The collector of the transistor Q3 is connected to control the second reference current source 2. The current mirror output transistor Q4 is current mirror connected to the current mirror input transistor Q2 to form a current mirror circuit.

In the current mirror circuit configured as described above, the transistors Q1 and Q3 are connected to the second reference current source 2 when the current amplification factor β of the transistors is small, that is, when the base current flows much. Current I
_Works to increase _ref3 . Therefore, the reference current I _ref1 of the reference current source 1, the base current of the transistor Q2 and Q4 I _ref2, the collector current of the transistor Q3 (I _ref3 -I _ref2), the base current I _B of the transistor Q1, the collector of the transistor Q2 The current is defined as I _IN, and as described in the following second embodiment, I _IN
By setting the _{ref3 -I ref2 = I IN = I} OUT, the output current I _{OUT is, I OUT = I ref1 / (} 1-1 / β 2) , and the addition, the voltage of the transistors of the first and second The bias voltage is set at 1 V _BE by each of the reference voltage sources, so that the base current dependence of the transistor is small and low voltage operation is possible.

Next, a second embodiment will be described with reference to FIG. This embodiment shows a specific example in which the first and second reference current sources 1 and 2 in the first embodiment shown in FIG. 1 are constituted by transistors, and the first reference current source is a PNP. It comprises transistors Q6 and Q7 and a current source 5, and the second reference current source comprises a PNP transistor Q8 and an NPN transistor Q5. The transistor Q6 has an emitter connected to the first reference voltage source 3, a base and a collector connected to the second reference voltage source 4 via the current source 5, and a transistor Q7 has an emitter connected to the first reference voltage source 4. 3, the base is connected to the base of the transistor Q6, the collector is connected to the base of the transistor Q1 and the collector of the transistor Q2, and the transistor Q8 has the emitter connected to the first reference voltage source 3, and the base connected to the transistors Q6 and Q7. Has a collector connected to the collector of the transistor Q3 and a collector and base of the transistor Q5. The transistor Q5 has a base connected to the bases of the transistors Q2 and Q4, and an emitter connected to the second reference voltage source 4.

Next, the operation of the second embodiment configured as described above will be described. The collector current of transistor Q7 is I _ref1 and the collector current of transistor Q8 is I _ref1 .
_Assuming that _ref3 , the collector current of the transistor Q5 is I _ref2 , the base current of the transistor Q1 is I _B , and the collector current of the transistor Q2 is I _IN , the output current I _OUT and I _ref1 , I _ref2 , and I _ref3 are represented by the following equations ( There are the relationships shown in 3) and (4). I _ref1 + I _B −I _IN = 0 (3) I _B = (I _ref3 −I _ref2 ) / β ² (4) where , I _ref3 −I _ref2 = I _IN = I _OUT , the output current I _OUT of the current mirror is expressed by the following equation (5). I _OUT = I _ref1 / (1-1 / β ² ) (5)

Therefore, if I _ref3 -I _ref2 = I _OUT is set, the current mirror circuit according to this embodiment can obtain a base current dependency substantially equal to the output current in the conventional example shown in FIG. Can be. Further, since the voltage of each transistor is biased at 1 V _BE by the first and second reference voltage sources, low power supply voltage operation is possible.

Next, a third embodiment will be described with reference to FIG. In this embodiment, the method of controlling the collector current of the transistor Q8 constituting the second reference current source in the second embodiment shown in FIG. 2 is changed. That is, the resistors R1, R2 are connected between the emitters of the transistors Q6, Q7, Q8 and the first reference voltage source 3.
2 and R3, and the transistor Q3
Is connected to the emitter of transistor Q8,
It constitutes a collector current I _ref2 of the transistor Q8 to control by the transistor Q3. The third embodiment thus configured differs from the second embodiment in that the current control of the transistor Q8 is controlled by the emitter terminal instead of the collector terminal. However, the same operation and effect as those of the second embodiment or the first embodiment can be obtained by setting the current.

Next, a current mirror circuit according to a fourth embodiment will be described with reference to FIG. In this embodiment, the polarity of the transistor used in the second embodiment shown in FIG. 2 is reversed, that is, the PNP transistor is replaced by an NPN transistor,
The N transistor is replaced with a PNP transistor, and each corresponding transistor is shown with a dash. The operation and effect of this embodiment are the same as those of the third embodiment, that is, the first and second embodiments.

[0017]

As described above with reference to the embodiments, according to the present invention, it is possible to realize a current mirror circuit which can operate even at a low power supply voltage and has a small dependence on the base current of a transistor. .

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a current mirror circuit according to the present invention.

FIG. 2 is a circuit configuration diagram showing a second embodiment.

FIG. 3 is a circuit configuration diagram showing a third embodiment.

FIG. 4 is a circuit configuration diagram showing a fourth embodiment.

FIG. 5 is a circuit configuration diagram showing a configuration example of a conventional current mirror circuit.

FIG. 6 is a circuit configuration diagram showing another configuration example of a conventional current mirror circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first reference current source 2 second reference current source 3 first reference voltage source 4 second reference voltage source 5 current source

Claims (1)

[Claims] A first reference current source having one end connected to the first reference voltage source, a base connected to the other end of the first reference current source, and an emitter connected to the first reference voltage source. A second transistor having a collector connected to the other end of the first reference current source, a base connected to the other end of the second reference current source, and an emitter connected to the second reference voltage source; A second base connected to the collector of the first transistor;
And the collector is connected to the second reference voltage source.
A third transistor connected to control the reference current source of the first and second transistors, and a fourth transistor current mirror-connected to the second transistor, so that an output current is obtained from a collector of the fourth transistor. A current mirror circuit characterized by comprising.