JP2003316456A - Current mirror circuit - Google Patents

Abstract

(57) [Problem] To provide a current mirror circuit capable of obtaining a current output with a small variation and a wide output voltage range. An emitter is connected to a first resistor through a first resistor.
Transistor Q1 connected to reference potential point V1 of
, The emitter of the second transistor Q2 having the collector connected to the second reference potential point V2, and the third transistor Q3 having the emitter connected to the first reference potential point V1 through the third resistor R3. And the base of the first transistor Q1, the base of the second transistor Q2, and the other end of the reference input current source I1 whose one end is connected to the second reference potential point V2. The base of the fourth transistor Q4, which is connected in common and whose emitter is connected to the first reference potential point V1, and one end of which is connected to the third transistor Q4.
Resistance R connected to the base of transistor Q3
The other end of the second transistor Q2 and the collector of the third transistor Q3 are connected in common, and a constant current is taken out from the collector of the fourth transistor Q4.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current mirror circuit, and more particularly to a current mirror circuit capable of setting a constant current output voltage range with high relative accuracy. 2. Description of the Related Art A conventional current mirror circuit for improving the relative current accuracy will be described below with reference to the drawings. FIG. 2 is a circuit diagram showing an example of a conventional current mirror circuit. In FIG. 2, Q1, Q2, Q4, and Q5 are transistors, R1 and R4 are resistors, I1 is a reference input current source, and Vo is a constant current output terminal. As shown in this circuit, resistors R1 and R4 of high relative accuracy are connected to the emitters of transistors Q1 and Q5 which are current mirror connected like transistors Q1, Q2 and Q5, and the voltage between both ends of the resistors is provided. 0.2V
It is customary to reduce the influence of the current error due to the relative voltage error (ΔVBE) between the base and the emitter of the transistor by setting the voltage to about the same level. With the increase in voltage, one end of the resistor R2 is connected to the base end of the conventional current mirror circuit and the other end is connected to the base of the transistor Q4 in order to set a wide output voltage range of a part of the current mirror circuit. Circuits for grounding the emitter are also well known. Next, the operation of the current mirror circuit shown in FIG. 2 will be described in detail. First, by inputting a reference current from the reference current source I1 to the collector of the transistor Q1, a current output I5 more accurate than the collector of the transistor Q5 and a current output Io having a wider output voltage range than the collector of the transistor Q4 are obtained. . Here, for example, to make the current output Io equal to the collector current I5 of the transistor Q5,
It is sufficient that the voltage difference V2 at both ends of the resistor R2 is equal to the voltage difference V4 at both ends of the resistor R4, and this can be expressed by the following equations (Equation 1), (Equation 2), and (Equation 3). become. (1 + hfe5) / hfe5 × I5 × R4 = I
o / hfe4 × R2 I5 / Io = 1 / hfe4 × hfe5 / (1+
hfe5) × R2 / R4 Here, to satisfy I5 / Io = 1, hfe5 / (1 + h
fe5) If ≒ 1, the condition of (Equation 3) is required. However, R2 = hfe4 × R4. However, such a configuration, that is, a current output more accurate than one reference current and a current output having a wider output voltage range. When trying to obtain a current output with a wide output voltage range in a current mirror circuit that simultaneously realizes the resistance R2
Is required to be extremely large compared to the resistance R4, and the absolute variation at the time of manufacturing the hfe4 is directly a variation in the current ratio, which causes a large variation of 0.5 to 2 times. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide a current mirror circuit capable of obtaining a current output with a small variation and a wide output voltage range. In a current mirror circuit according to the present invention, a base of a first transistor having an emitter connected to a first reference potential point through a first resistor and a collector connected to a second transistor are provided. An emitter of a second transistor connected to a reference potential point, and an emitter connected to the first transistor through a third resistor;
, The base of a third transistor connected to the reference potential point of the first transistor, the collector of the first transistor, the base of the second transistor, and one end connected to the second reference potential point. The other end of the reference input current source is connected in common, the emitter is connected to the base of a fourth transistor whose emitter is connected to the first reference potential point, and one end is connected to the base of the third transistor. The second
The other end of the resistor and the collector of the third transistor are connected in common, and a constant current is taken out from the collector of the fourth transistor. According to the present invention, it is possible to obtain a current mirror circuit capable of obtaining a current output with a small variation and a wide output voltage range. Embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals are used for the same parts as those of the related art. FIG. 1 is a circuit diagram showing a configuration of a current mirror circuit according to an embodiment of the present invention. In the current mirror circuit shown in FIG. 1, the base of the first transistor Q1 whose emitter is connected to the first reference potential point V1 through the first resistor R1, and the collector is connected to the second reference potential point V2 The emitter of the connected second transistor Q2 and the third transistor Q3 whose emitter is connected to the reference potential point V1 through the third resistor R3.
The collector of the transistor Q1, the base of the transistor Q2, the other end of the reference input current source I1 whose one end is connected to the reference potential point V2, and the emitter is connected to the base of the transistor Q1. The base of the fourth transistor Q4 connected to the potential point V1, the other end of the second resistor R2 having one end connected to the base of the transistor Q3, and the collector of the transistor Q3 are connected in common. It is configured to take out a constant current from the collector as a current output Io. Note that the type of transistor is not limited to the illustrated NPN transistor, but can be realized by a PNP transistor or a MOS transistor. The operation of the current mirror circuit configured as described above will be described below. In order to make the current output Io equal to the collector current I3 of the transistor Q3, the voltage difference V2 across the resistor R2 and the voltage difference V3 across the resistor R3 only need to be equal. (Equation 4), (Equation 5),
(Formula 6) is obtained. V2 = (I3 + Io / hfe4) × R2 V5 = (1 + hfe3) / hfe3 × I3 × R3 From these (Formula 4) and (Formula 5), (I3 + Io / hfe4) × R2 = (1 + hfe3) / hfe3 × I3 × R3 Io = ｛(1 + hfe3) / hfe3 × R3 / R2-1｝ hfe4 × I3 = ｛(1 + hfe3) / hfe4 × hfe4 / hfe × R3 / R2-1｝ hfe4 × I3 = ｛(1 / hfe3) × (R3 / R2) + (hfe3 / hfe4) × (hfe4 / hfe3) × (R3 / R2) -1｝ × hfe4 × I3 = {(1 / hfe3) × (R3 / R2) + (R3 / R2) −1} × hfe4 × I3 (equation 6) where hfe3 ≒ hfe4 = hfe, and R3 = R
When it is set to 2, since Io = I3, since I3 and I1 are current mirrors, Io and I1 are also current mirrors from I3 = I1 and Io = I1. In (Equation 6), the relative accuracy of (R3 / R2) is 1%, (R3 / R2) -1 ≒ 0, (hfe3 / hf
Assuming that the relative accuracy of e4) is 4%, the constant current output I
o becomes as shown in (Equation 8). ## EQU8 ## Io / I3 ≒ ｛(hfe4 / hfe3) × (R
3 / R2)｝ As is apparent from (Expression 8), the variation of the current output Io is determined only by the relative variation of the elements, and becomes as shown in (Expression 9). Δ (Io / I3) = {Δ (hfe4 / hfe3) ² × Δ (R3 / R2) ² } = {(4%) ² × (1%) ² } {4. 1% As described above, according to the present embodiment, the variation in the current output is determined only by the variation in the element, so that the variation can be suppressed to a small value, and a current output with a small variation and a wide output voltage range can be obtained. A current mirror circuit can be realized. In this embodiment, I1 = I3 = Io
However, when the current output Io is made to flow more than the reference current, for example, in order to make the current output Io = 2 × I3, the transistor size ratio between the transistor Q3 and the transistor Q4 is set to 1: 2, and V2 and V3 are Since V2 = V3, the following equation is obtained: (I3 + Io / hfe4) × R2 = (1 + h)
fe3) / hfe3 × I3 × R3 Io / I3 = ｛(1 / hfe) × (R3 / R2) + (R
3 / R2) -1｝ × hfe Here, from Io / I3 = 2, the following equation is obtained: (R3 / R2) = (hfe + 2) / (hfe + 1) ≒ 1 and almost the same effect can be obtained. As described above, according to the present invention, there is obtained an advantageous effect that an excellent current mirror circuit which can obtain a current output with a small variation and a wide output voltage range can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a configuration of a current mirror circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing an example of a conventional current mirror circuit. , Q2, Q3, Q4, Q5 Transistors R1, R2, R3, R4 Resistance I1 Reference input current source Vo Constant current output terminal

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Claims (1)

Claims: 1. A base of a first transistor having an emitter connected to a first reference potential point through a first resistor;
The emitter of the second transistor, the collector of which is connected to the second reference potential point, is commonly connected to the base of the third transistor, whose emitter is connected to the first reference potential point through a third resistor. A collector of the first transistor, a base of the second transistor,
One end is commonly connected to the other end of the reference input current source connected to the second reference potential point, and further, the emitter is connected to the first reference potential point.
, The base of a fourth transistor connected to the reference potential point of the second transistor, the other end of a second resistor having one end connected to the base of the third transistor, and the collector of the third transistor. A current mirror circuit for extracting a constant current from a collector of the fourth transistor.