JPH04332208A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To obtain a current mirror with less error and low operating voltage. CONSTITUTION:The emitters of the first and second transistors Q1 and Q2 and one terminal of the first resistor R1 are together connected to the first power terminal P, and the other terminal of the first resistor R1 is connected to one terminal of the second resistor of the second resistor R2 and to the emitter of the third transistor Q3. Further, the other terminal of the second resistor R2 is connected to the bases of the first and second transistors Q1 and Q2 and to the output of a constant current source CC2. Furthermore, to the collector of the first transistor Q1, the base of the third transistor Q3 and the output of a current source C1 are connected together. Moreover, the collector of the third transistor Q3 is connected to the second power terminal G.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current mirror circuit comprising at least two transistors whose emitters are connected to each other and whose bases are connected to each other.

0002

2. Description of the Related Art A current mirror circuit used to configure a constant current source consists of two transistors Q91 and Q92 whose emitters are both connected to a power supply P91, and their respective bases. They are connected to each other, and a constant current source 91 is connected to the collector of one transistor Q91, so that a current equal to the constant current source 91 is output from the collector of the transistor Q92. However, when this circuit is integrated into an IC, it is not possible to set the hfe of transistors Q91 and Q92 to a high value.
+2) When 20 is substituted into ×Iin as the value of hfe, the collector current of the transistor Q92 becomes about 91% of the current value of the constant current source 91, resulting in a circuit with many errors as a current mirror circuit.

Therefore, as shown in FIG. 3, the bases of the two transistors Q91 and Q92 are connected to the emitter of a newly provided transistor Q93, and the base of this transistor Q93 is connected to the collector of the transistor Q91. By grounding the collector of transistor Q93, transistor Q91
, Q92 is caused to flow from the emitter to the collector of transistor Q93, thereby reducing the influence of the base currents of transistors Q91 and Q92.

Note that the relationship between the input current and the output current in this circuit is hf of the transistors Q91 and Q92.
e is hfe1, hfe of transistor Q93 is h
Assuming fe2, the following formula Iin = Iout + (2×
Iout)/(hfe1×hfe2),
The value of hfe1 is 20, and the value of hfe2 is because transistor Q93 is a substrate transistor.
If the value is 100, the output current is approximately 9 of the input current.
The value is 9.9%.

[0005]

[Problem to be Solved by the Invention] When the above configuration is used, the collector-emitter voltage Vce of transistor Q91
is the base-emitter voltage Vb of transistor Q91
e1 and the base-emitter voltage Vbe3 of transistor Q93 (approximately 1.4V) cannot be lower than the sum, so if you try to apply this circuit to a device powered by a low-voltage battery such as an AF camera, Since the power supply voltage is limited, a problem has arisen in that it may not be applicable.

The present invention has been devised to solve the above problems, and its purpose is to provide a current mirror circuit that can lower the emitter-collector voltage of a transistor whose collector is connected to the output of a current source. It is about providing.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the current mirror circuit of the present invention provides a current mirror circuit in which one of a pair of power supply terminals is used as a first power supply terminal and the other one is used as a second power supply terminal. The emitters are connected together to the first power supply terminal, and the bases of each are connected to each other.
When one of these transistors is a first transistor and the other is a second transistor, a first transistor whose one terminal is connected to the first power supply terminal
a second resistor whose one terminal is connected to the other terminal of the first resistor and whose other terminal is connected to the bases of the first and second transistors; a third transistor whose emitter is connected to the connection point with the resistor of the first transistor, whose base is connected to the collector of the first transistor and whose collector is connected to the second power supply terminal; The configuration includes a constant current source whose output is connected to both bases of the transistor, and the output of the current source is connected to the collector of the first transistor. Further, the current source whose output is connected to the collector of the first transistor is a constant current source.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing the electrical configuration of an embodiment of the present invention.

In the figure, a positive power supply P, which is a first power supply terminal, connects the emitter of the first transistor Q1 and the second
the emitter of transistor Q2, and the first resistor R1
The other terminal of the first resistor R1 is led to one terminal of the second resistor R2 and the emitter of the third transistor Q3. The other terminal of the second resistor R2 is led to the base of the first transistor Q1, the base of the second transistor Q2, and one output terminal of the constant current source CC2.

At the collector of the first transistor Q1,
The base of the third transistor Q3 is connected to one output terminal of a constant current source C1, which is a current source, and the collector of the third transistor Q3 is led to a ground terminal G, which is a second power supply terminal. There is. The other terminal of the current source C1 and the other terminal of the constant current source CC2 are connected to the ground terminal G.
It is connected to the. The collector of the second transistor Q2 is sent to an external circuit (not shown) as a constant current output.

In the above configuration, in this embodiment, the first
If the value of the second resistor R1 is denoted by r1, then r1=5KΩ, and if the value of the second resistor R2 is r2, then r
2=10KΩ. Also, the current value that is the output of the constant current source C1 is Iin
When expressed using Iin = 50 μA. When the current value of the constant current source CC2 is indicated by I2, I2=30 μA.

[0012] Also, the first and second transistors Q1,
When the amplification factor of Q2 is expressed by hfe1, since these transistors Q1 and Q2 are lateral transistors, hfe1=20, and the amplification factor of the third transistor Q3 is expressed as hf.
When e2 is assumed, hfe2=100 because the third transistor Q3 is a substrate transistor.

The operation of one embodiment of the present invention will be explained below.

When the output current Iout, which is the collector current of the second transistor Q2, and the current Iin of the constant current source C1 are balanced such that Iout≈Iin, the voltage between the base emitters of the first and second transistors Q1 and Q2 is The voltage is Vbe1
Then, since the output current Iout is Iout≒50μA, when the absolute temperature is 300 degrees, V
be1≈0.7V.

Furthermore, since the value of the collector current I4 of the first transistor Q1 is equal to the collector current of the second transistor Q2, I4=Iout. Also, the first and second transistors Q1, Q2
Since the base currents of are equal, if the current value is I1 and the emitter current of the third transistor Q3 is I3, then the base-emitter voltage Vbe1 of the first and second transistors Q1 and Q2 is Vbe1=r1X (I3+I2-2XI1)+r2X(
I2-2XI1) (This formula is referred to as Formula 2).

[0016] Regarding the current I1, I1=Iout/hfe1, so substitute this equation into the second equation, and substitute a numerical value with a fixed value into the substitution equation, and set the unit of the resistance value in KΩ. and the current value is expressed in μA (the unit of current is mV), then the second equation is 700=5X(I3+30-2XIout/20)+
Shown as 10X (30-2XIout/20)
(This formula is referred to as formula 6).

Further, the current value Iin is expressed as Iin=Iout+I3/hfe2, and the current value I3 is I3=(Iin-Iout)X100, so when these equations are substituted into equation 6, 700=5
X((Iin-Iout)X100+30-2XIou
t/20)+10X(30-2XIout/20).

When this equation is solved for Iout, Iout
≈0.997XIin-0.5, and when Iin=50 is substituted, Iout≈49.35 becomes Iout/Iin≈0.987, and it operates as a current mirror circuit with little error.

Furthermore, the voltage Vr1 between the terminals of the first resistor R1
is shown as Vr1=r1X(I3+I2-2XI1) (this equation is taken as equation 12), I3=(Iout-I
in)X100 = (50-49.35)X100=6
5, I2=30 I1=Iout/hfe1=49.35/20 ≒2.
5, so by substituting these values into equation 12, we get V
r1=5X(65+30-5), and when calculated based on each unit, Vr1=450
mV, and the collector-emitter voltage Vce1 of the first transistor Q1 is Vce1=1.15V, so it operates at a low voltage.

It should be noted that the present invention is not limited to the above embodiments, and the values of the first resistor R1 and the second resistor R2 and the current value of the constant current source CC2 satisfy Vr1 < 0.7. It can be set to any value within the range.

Regarding the transistors constituting the output circuit of the current mirror, the case where only the second transistor Q2 is provided has been described, but the base and emitter of each transistor are connected to the base and emitter of the first transistor Q1. It is possible to have a configuration in which additional transistors are added.

Further, although the current source C1 has been described as a constant current source, it can be similarly applied to a case where a current source whose current value changes is used.

Regarding the first to third transistors, although the case where PNP transistors are used has been described, the same can be applied to the case where NPN transistors are used (in this case, the polarity of the power supply terminal is (invert).

[0024]

Effects of the Invention The current mirror circuit according to the present invention connects the bases and emitters of the first and second transistors, whose respective bases and respective emitters are connected to each other, from the first and second resistors. A constant current source is provided, the output of which is connected to the bases of the first and second transistors, and the emitter is connected to the connection point between the first and second resistors. and a third transistor whose base is connected to the collector of the first transistor and whose collector is connected to one of the power supply terminals.
Since the configuration includes transistors, it is possible to lower the emitter-collector voltage of the first transistor, which is a transistor whose collector is connected to a current source.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the electrical configuration of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing the electrical configuration of the prior art.

FIG. 3 is a circuit diagram showing the electrical configuration of the prior art.

[Explanation of symbols]

Q1 First transistor Q2 Second transistor Q3 Third transistor R1 First resistance R2 Second resistance C1 Current source CC2 Constant current source P First power terminal G Second power supply terminal

Claims (2)

[Claims] Claim 1: When one of a pair of power supply terminals is used as a first power supply terminal and the other is used as a second power supply terminal, the respective emitters are both connected to the first power supply terminal, and the respective bases are connected to each other. at least two transistors, one of which is a first transistor and the other is a second transistor, a first resistor with one terminal connected to the first power supply terminal; 1
a second resistor, one terminal of which is connected to the other terminal of the resistor, and the other terminal of which is connected to the bases of the first and second transistors, and a connection point between the first resistor and the second resistor; a third transistor having its emitter connected to the terminal, its base connected to the collector of the first transistor, and its collector connected to the second power supply terminal; 1. A current mirror circuit comprising: a constant current source to which the output thereof is connected; and the output of the current source is connected to the collector of the first transistor. 2. The current mirror circuit according to claim 1, wherein the current source whose output is connected to the collector of the first transistor is a constant current source.