JPH04257107A - Current mirror circuit - Google Patents

Abstract

PURPOSE:To approximately maximize the output current even in the case of insufficient supply of an input current. CONSTITUTION:A resistance R2 is inserted between the collector of an input side transistor TR Q1 and the base of a buffer TR Q3 to constitute a circuit. The input side TR Q1 is saturated to reduce the collector current by the input current smaller than that of a conventional current mirror circuit, and the base current of the buffer TR Q3 is more supplied, and consequently, the base current supply of an output side TR Q2 is quickly increased, and the output side TR Q2 is saturated to obtain an approximately maximum output current.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a current mirror circuit,
In particular, the present invention relates to a current mirror circuit that can function as a normal current mirror current source and as a current source that saturates a transistor depending on the magnitude of the input current.

0002

2. Description of the Related Art A conventional current mirror circuit will be explained based on the circuit diagram of FIG. Input side NPN with base connected
type transistor Q1 and output side NPN type transistor Q2, and the base is connected to the collector of input side NPN type transistor Q1, and these two transistors Q1 and Q2
A current mirror circuit is constituted by a buffer NPN transistor Q3 which supplies a base current to the buffer. In Figure 3, R1 is the load resistance at the output terminal, I' is the input current, IX' is the output current, and VCC is the power input terminal (
power supply voltage VCC).

FIG. 4 shows a characteristic diagram of the input current and output current of the current mirror circuit. In FIG. 4, in the region A', that is, in the range of input current I' from 0 to I1', the characteristics of input current I' and output current IX' are linear;
In the region B', that is, in the range where the input current I' is greater than or equal to I1', the rate of increase in the output current IX' decreases rapidly. This indicates that the output side NPN transistor Q2 in FIG. 3 has reached the saturated state. Also, output side NP
The input current required to saturate the N-type transistor Q2 is I1'.

0004

[Problem to be Solved by the Invention] However, in the current mirror circuit of the conventional configuration described above, the input current of I1' is required to saturate the output side NPN transistor Q2, that is, the output current is almost maximized. required an input current of I1'. Therefore, the input current I
There is a problem in that if the output current IX' cannot be supplied, the output current IX' cannot be made almost the maximum.

[0005] The present invention solves the above problems, and
It is an object of the present invention to provide a current mirror circuit that can substantially maximize the output current even when a sufficient input current cannot be supplied.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the current mirror circuit of the present invention includes an input side transistor and an output side transistor whose bases are connected, and a base connected to the collector of the input side transistor,
and a buffer transistor that supplies base current to two transistors, the current mirror circuit being characterized in that a resistor is inserted between the collector of the input side transistor and the base of the buffer transistor. be.

[0007]

[Operation] With the above configuration, by inserting a resistor between the base of the buffer transistor and the collector of the input side transistor, the input side transistor is saturated due to a small input current compared to a conventional current mirror circuit, and the collector current decreases, and the supply of base current to the buffer transistor increases.Therefore, the supply of base current to the output side transistor increases rapidly, and the output side transistor is saturated to obtain almost the maximum output current. Furthermore, in a region where the input current is small, almost the same output as a conventional current mirror circuit can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Note that the same components as those in the conventional example shown in FIG.

FIG. 1 is a circuit diagram of a current mirror circuit in one embodiment of the present invention. The current mirror circuit of the present invention is constructed by inserting a resistor R2 between the collector of the input NPN transistor Q1 and the base of the buffer NPN transistor Q3.

FIG. 2 shows a characteristic diagram of the input current and output current of the current mirror circuit having the above configuration. In FIG. 2, in the region A, that is, in the range of input current I from 0 to I2, the characteristics of input current I and output current IX are linear, and B
In the region where the input current I is in the range of I2 to I1, the rate of increase in the output current IX becomes rapidly large. That is, by inserting a resistor R2 between the base of the buffer NPN transistor Q3 and the collector of the input side NPN transistor Q1, when the input current I is gradually increased, in the region B, the input side NPN type Transistor Q1 becomes saturated and the collector current decreases, increasing the supply of base current to buffer NPN transistor Q3, and therefore output side NPN transistor Q
The supply of base current of 2 suddenly increases, and the output side NPN
This is because the type transistor Q2 becomes saturated. Here, the input current I1 required to saturate the output side NPN transistor Q2 satisfies I1 <I1'.

In the region C, that is, in the range where the input current I is greater than or equal to I1, the output side NPN transistor Q2 is saturated, so the rate of increase in the output current IX rapidly decreases.

In this way, the base of the buffer NPN transistor Q3 and the input side NPN transistor Q1
By inserting a resistor R2 between the collectors of the current mirror circuit, it is possible to obtain almost the maximum output current IX with a small input current I compared to a conventional current mirror circuit. It is possible to obtain almost the same output as the current mirror circuit.

[0013]

As described above, according to the present invention, the base of the buffer NPN transistor and the input side NPN
By inserting a resistor between the collectors of the type transistors, it is possible to obtain almost the maximum output current with less input current compared to conventional current mirror circuits. You can get almost the same output.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a current mirror circuit in one embodiment of the present invention.

FIG. 2 is a characteristic diagram of input current and output current of the current mirror circuit.

FIG. 3 is a circuit diagram of a conventional current mirror circuit.

FIG. 4 is a characteristic diagram of input current and output current of a conventional current mirror circuit.

[Explanation of symbols]

Q1 Input side NPN transistor Q2
Output NPN transistor Q3 Buffer NPN transistor R1 Load resistor R2 Resistor I inserted between the base of the buffer NPN transistor and the collector of the input NPN transistor Input current IX Output current VCC Power input terminal

Claims (1)

[Claims] 1. A current transistor comprising an input side transistor and an output side transistor whose bases are connected, and a buffer transistor whose base is connected to the collector of the input side transistor and supplies base current to the two transistors. 1. A current mirror circuit, characterized in that a resistor is inserted between the collector of the input side transistor and the base of the buffer transistor.