JPS5925484B2 - current mirror circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a current mirror circuit, more specifically, a DC current source, an output transistor for supplying an output current, a first resistor connected to a DC power source and the output transistor, and a first resistor connected to the DC source. and a second resistor.

As is well known to those skilled in the art, a current mirror circuit outputs a direct current that is substantially equal to or has a desired ratio (transfer ratio) to the current flowing through some element in the circuit. This is a circuit that transmits information to the side.

A conventional current mirror circuit uses a pair of transistors of the same polarity, one transistor is diode-connected with its collector and base connected in common, both bases are connected in common, and both emitters are each connected to a resistor. The configuration is such that the power supply is connected to the power supply through or immediately afterward.

This is the base-emitter voltage V of both transistors.
This utilizes the fact that a current corresponding to BE flows through each transistor on the other side.

Therefore, in a small current region where the current feedback effect by the emitter resistance cannot be expected sufficiently, the VBE offset of both transistors increases the transfer ratio of the current mirror effect (
Left and right.

For example, even with well-matched elements, ±20%
It is necessary to accept some degree of variation in current.

In general, current offset increases exponentially with respect to VBF and offset, so conventional current mirror circuits have the disadvantage that even a small VBE offset gives a large current offset.

In this way, the current flowing through the negative feedback loop is influenced by the characteristics of the elements included in the feedback loop, so when trying to obtain the current itself as the output of one circuit, it is necessary to reduce the linearity of the output current. It is difficult to maintain this over the entire current range including current.

The object of the present invention is to provide a current mirror circuit that does not have these conventional drawbacks.

To provide a current mirror circuit that is not affected by variations in circuit elements (has good linearity in output characteristics) over a wide current range including a small current range.

The current mirror circuit according to the present invention controls the voltage at the base of the output transistor in response to the voltage of the second resistor connected to the DC power supply, and substantially changes the voltage of the first resistor to the voltage of the second resistor. includes a high gain amplifier connected to make it equal to .

Embodiments of a current mirror circuit according to the invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a functional diagram for explaining the principle of a current mirror circuit according to the present invention.

In this current mirror circuit 10, a resistor R is connected to the reference power supply 1.
1 and R2 are connected, and the other terminal of the resistor R1 is connected to the non-inverting input terminal side of the high gain amplifier 3 and this current mirror circuit 10.
0 input current (current supplied) 'Io''4r: Connected to the current source 5 shown.

This resistor R1 is used to apply an input voltage to the input terminal (G) of the amplifier 3 by a current flowing through it.

The output terminal 7 of the amplifier 3 is connected to the base of an output transistor Q1 that functions as a current source that generates the output current (transfer current) Ix of the current mirror circuit 10, and the emitter of the output transistor Q is connected to the other end of the resistor R2. gain amplifier 3
Connected to the 0 anti-inverting input terminal.

Output current IX is taken out from the collector of transistor Q1 to output terminal 9.

The operation of the current mirror circuit 10 in a small current region will be considered.

Assuming that the input current of amplifier 3 is sufficiently small to be ignored, the voltage drop at the non-inverting input terminal (G) is calculated by subtracting the voltage drop due to resistor R1 of input terminal IQ of current source 5 from the reference voltage ER of reference power supply 1. A voltage E1 is applied.

Namely. E, =E −IR,・・・・・・・・・
...(1)6 On the other hand, since the base current of the transistor Q1 can be considered to be sufficiently small, the gain of the amplifier 3 AC>>1) If the common base current amplification factor of the transistor Ql is α, the current of the collector of the transistor Q1 is E2 is given by ■ -.

The output voltage E,0 of amplifier 3 is given by
changes the output voltage so that the voltages at both input terminals (g) and (→ become almost equal, and a current flows through resistor R2 that causes such a voltage drop, so in an equilibrium state, is E1 and E2, and at this time, a current determined by equation (4) from equations (1) and (2) is output from the force terminal 9.

Finally, the magnitude of the output current depends on the ratio of resistors R1 and R7.

In this way, even if there is nonlinearity in the voltage-current characteristic between the base and emitter of transistor Q1 in the small current region, it is linearized by the negative feedback of amplifier 3, so linearity in the small current region・Improved.

FIG. 2 shows an embodiment in which the current mirror circuit according to the present invention is applied to a detector.

Components that are the same as in FIG. 1 are designated by the same reference numerals.

As is clear from the figure, the reference power supply 1 includes resistors R21 and R2□, diodes D2. and transistor Q21
transistor Q21 is connected to resistors R4 and R
A reference voltage is supplied to 2.

Transistors Q24 to Q2□ constitute a high gain amplifier 3, and the collector of transistor Q25 and transistor Q27
The output of the amplifier 3 is applied from a common connection point 21 of the collectors of the amplifier 3 to the base of the output transistor Q1.

The base 23 of the transistor Q250 is connected as an inverting input terminal of the amplifier 3 to the resistor R2 and the emitter of the output transistor Q, and the base 25 of the transistor Q24 is connected as the non-inverting input terminal of the amplifier 3 to the resistor R1 and the current source 5 which provides the input current. It is connected.

The current source 5 is shown schematically with an input signal source 27.

Transistors Q22 and Q23 and capacitor C2,
.

A change in the collector current of the transistor Q22 caused by the signal source 27 is applied to the amplifier 3 as a non-inverting input voltage by the resistor R1.

Amplifier 3 controls the collector current of transistor Q1 by varying the base voltage of transistor Q, such that the voltage drop across resistor R2 is substantially equal to that across resistor R1.

The output current of this circuit is taken out from terminal 9.

Note that resistor R23 is connected to transistors Q24 and Q25K.
This current is supplied to the transistor Q2□
varies depending on the collector current.

As described above, the present invention has the advantage that it is possible to provide a current mirror circuit that is less affected by variations in circuit elements over the entire current range including the minute current range and has good linearity in its output characteristics.

Furthermore, the current mirror circuit according to the present invention can be applied to a wide range of linear detectors, and can lower the distortion factor in AC amplifiers.

Furthermore, it is easily adaptable to integrated circuits, and even when assembled from individual components, it has the advantage of being able to obtain better small current region characteristics than conventional current mirror circuits.

[Brief explanation of drawings]

FIG. 1 is a functional diagram for explaining the principle of a current mirror circuit according to the present invention, and FIG. 2 is a circuit diagram showing an embodiment in which the current mirror circuit according to the present invention is applied to a detector. Explanation of main symbols, 1...DC power supply, 3...
...High gain amplifier, 10...Current mirror circuit,
Ql... Output transistor, R1...
Second resistor, R2...First resistor.

Claims (1)

[Claims] 1. A DC power supply, an output transistor that derives an output current from the DC power supply via a first resistor R2, and an output transistor to which an output voltage of the DC power supply is applied and an input current flows. A connected second resistor R1 controls the voltage at the control terminal of the output transistor in response to the voltage across the second resistor, and changes the voltage across the first resistor to the voltage across the second resistor. and a high gain amplifier connected to substantially equal the current mirror circuit. 2. The current mirror circuit according to claim 1, wherein the high gain amplifier that makes the voltage of the first resistor substantially equal to the voltage of the second resistor includes a negative feedback amplifier circuit. 3. A high gain amplifier that makes the voltage on a first resistor substantially equal to the voltage on a second resistor connects its non-inverting input terminal to the second resistor.
The inverting input terminal is connected to the first resistor and the emitter of the output transistor to provide an input signal, the output terminal is connected to the base of the output transistor, and the output current is output from the collector of the output transistor. Claim 1 characterized in that it is configured to take out the
Current mirror circuit described in section.