JPH03175512A - Linearity compensating current source circuit - Google Patents

Abstract

PURPOSE:To keep the linearity of an input current well even at the time of reduction of a supply voltage by providing a resistance which connects emitters of two transistors TRs of a current source circuit. CONSTITUTION:The current source circuit including a first TR Q2 which has the emitter connected to the ground through a resistance R4, a second TR Q1 which has the collector connected to a voltage source Vcc and has the emitter connected to the base of the first TR Q2 and is connected to the ground through a resistance R3, a pair of resistances R1, R2 connected in series between the voltage source Vcc and the ground, and a voltage dividing circuit which applies the voltage generated at the connection point between resistances R1 and R2 to the base of the second TR Q1 is provided with a resistance R5 which connects the emitter of the first TR Q2 and that of the second TR Q1. Thus, the linearity of the current characteristic for an input current path is kept well even in a low voltage area where voltages between bases and emitters of TRs Q1 and Q2 are varied.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to current source circuits. More specifically, the present invention relates to a novel current source circuit configuration that can maintain good linearity particularly against fluctuations in power supply voltage.

2. Description of the Related Art A constant current source circuit used for the purpose of distributing bias current, constant current load, current ratio, etc. is a circuit that is extremely widely used in various electronic circuits.

FIG. 4 is a circuit diagram showing a typical configuration of this current source circuit.

As shown in the figure, this circuit includes a transistor Q1 that forms a first current path between the power supply voltage Vcc and ground, and a transistor Q1 whose emitter is connected to the base to control the first current path. It mainly consists of a transistor Q2 that forms a second current path that operates below. Here, the collector of transistor Q2 constitutes a constant current source.

In order to explain the operation of the current source circuit as described above, FIG.
2 is a graph showing the relationship between collector current (collector current) and power supply voltage Vcc.

Now, in the circuit shown in FIG. 4, the voltage division ratio S between the resistors R1 and R2, which determines the base bias of the transistor Q1, is expressed as in the following equation (1).

The current (2) manually applied to this current source circuit can be expressed as shown in equation (2) below.

1-(SVCC2VBE) /R4...(2) [
However, VBE represents the base-emitter voltage of transistors Q1 and Q2. ] Here, it is generally considered that the base-emitter voltage VBE of transistors Q1 and Q2 is constant (for example, 0.7 V>) with respect to fluctuations in the power supply voltage VCC. The characteristics of the input current of the current source circuit are supposed to maintain linearity as shown by the thick dotted line in FIG. 5 (the thin dotted line is an auxiliary line).

Problems to be Solved by the Invention However, in reality, the base-to-emink voltage VBp of a transistor fluctuates as shown in FIG. do. Therefore, in a region where the power supply voltage Vcc is low, the input terminal of the current source circuit actually exhibits nonlinear characteristics as shown by the solid line in FIG.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a novel current source circuit that solves the above-mentioned problems of the prior art and maintains the linearity of its input current well even when the power supply voltage decreases. The purpose is

Means for solving the problem, ie, according to the invention, a first transistor whose collector is connected to the input current path and whose emitter is connected to ground via a resistor; connected to the base of the first transistor, and
a second transistor connected to ground via a resistor;
The second transistor includes a pair of resistors connected in series between the voltage source and ground, and is configured to apply a voltage generated at the mutual connection point of the resistors to the base of the second transistor. A current source circuit including a voltage circuit, further comprising a resistor connecting an emitter of the first transistor and an emitter of the second transistor. # Compensation current source circuit provided.

Operation The current source circuit according to the present invention has a first current path formed by a transistor connected between a voltage source and ground, and a second current path formed by a transistor connected between an input current path and ground. Its main feature is that the emitters of each transistor are interconnected via a resistor.

That is, in the current source circuit according to the present invention, even in a low voltage region where the voltage between the base and emitter of the transistor fluctuates, the voltage fluctuation is compensated for in the second current path through the added resistor. Therefore, the linearity of the current characteristics with respect to the input current path is well maintained.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 is a diagram showing a specific example of a current source circuit constructed according to the present invention.

The current source circuit shown in the figure is the conventional current source circuit shown in FIG. 5, with the addition of a resistor R3 connecting the emitter of the transistor Q1 and the emitter of the transistor Q2.

Here, the above-mentioned equation (2) can be applied to this circuit as well. That is, the current 11 flowing through the resistor R4 in this circuit can be expressed as follows.

I+ = (SVCC2VBE) /R4...(
2) [However, VBE is transistor Q1 and Q2
represents the base-emitter voltage of ] On the other hand, the current I2 flowing through the resistor R6 can be expressed as in the following equation (3).

l2=vBE/R5・・・・・・・・・・・・(3) Second
The figure is a graph corresponding to FIG. 5, showing the current characteristics of the current source circuit as described above.

As shown in the figure, the current 1 in this circuit changes as shown by the thick dotted line in the figure, similar to the current characteristics of the conventional current source circuit. On the other hand, the current I2 flowing through the resistor R3 is a linear function of the base-emitter voltage VBH of the transistor, as shown in equation (3). It also changes as shown by the thin dotted line in Figure 2.

Here, the input terminal I for this current source circuit is as shown below (
4) It can be expressed as follows.

11=I+r2...(4) (1=1.-I2) Therefore, the nonlinear characteristic of current 11 in the low voltage region is compensated by the change in current I2, and the input terminal ■ of this current source circuit is As shown by the solid line in FIG. 2, substantially linear characteristics are exhibited over the entire region.

In this way, in the current source circuit configured according to the present invention, the power supply voltage V. Since variations in C are effectively compensated, linear characteristics are well maintained even in a region where the power supply voltage VC0 is particularly low.

FIG. 3 is a circuit diagram showing an example of the configuration of an amplifier circuit to which the current source circuit according to the present invention as described above can be advantageously applied.

As shown in the figure, this amplifier circuit includes a transistor Q for level matching, a transistor Q1 for amplification, and a transistor Q13 for emitter follower, and compensates for fluctuations in the power supply voltage Vcc. Transistor Q+□
A current source circuit I is provided to stabilize the collector current. Here, the current IR flowing through the resistor R1 connecting the collector of the transistor Q12 and the power supply VCC can be expressed as in the following equation (5).

IR= (Vcc V) /R++ ” ” ” (
5) On the other hand, if IQ is the collector-emitter current of transistor Q, 2, which is connected substantially in parallel between resistor R11 and ground, and ■ is the current flowing through current source circuit I, then the relationship between the two is can be expressed as in the following equation [6].

1,=IR-1・・・・・・・・・・・・(6) Here,
When I=O, the bias current of transistor Q12 is 1
．． -IQ, so the gain of transistor Q+□ is V. Affected by fluctuations in 0. That is, transistor Q1
In order for the collector current IQ of 2 to be constant, it is desirable that the right side of equation (6) be constant.

Here, the current IR is the power supply voltage V. Since it is a linear function of 0, if the current I does not have linear characteristics with respect to the power supply voltage VCC, the bias current 1. cannot be held constant. Therefore, it is extremely effective to use the circuit according to the present invention as a current source circuit of such an amplifier circuit.

As described in detail, the current source circuit according to the present invention has a function of compensating for nonlinearity in input current characteristics caused by fluctuations in power supply voltage. Therefore, it can be advantageously used in applications where highly accurate current control is required over a wide range, such as bias current control of amplifier stage transistors in a wideband amplifier.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a specific configuration example of the current source circuit according to the present invention, FIG. 2 is a diagram showing the characteristics of the current source circuit shown in FIG. 1, and FIG. 3 is a diagram showing the characteristics of the current source circuit shown in FIG. , FIG. 4 is a diagram showing a typical configuration of a conventional current source circuit, and FIG. 5 is a diagram showing an application example of the current source circuit according to the present invention. FIG. FIG. 6 is a diagram showing general characteristics of the base-emitter type pressure of a transistor. [Main reference symbols] Q Q2, Q13 ・Transistor, R2, R3, R4, R5,

Claims (1)

[Claims] A first transistor whose collector is connected to an input current path and whose emitter is connected to ground via a resistor; whose collector is connected to a voltage source and whose emitter is connected to the base of the first transistor; and a second transistor connected to ground via a resistor, and a pair of resistors connected in series between the voltage source and ground, and the voltage generated at the mutual connection point of the resistors. a voltage divider circuit configured to apply a voltage to the base of the second transistor, further connecting the emitter of the first transistor and the emitter of the second transistor. A linearity compensation current source circuit comprising a resistor.