JPH0550164B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a constant current circuit that is less affected by fluctuations in power supply voltage, and is intended to realize this using small transistors.

Prior Art and Problems There is a constant current circuit shown in FIG. In this figure, Q1 to Q4 are transistors, _R1 and _R2 are resistors, Vcc is a power supply voltage, and _I1 is a current flowing through resistor _R1 . I ₂ is the collector current of transistor Q4 and is also the output current of this circuit. Transistor Q3 is larger than other transistors, and has an emitter area n times larger. As is known, the base-emitter voltage V _BE of a transistor is the saturation current I _S ,
The emitter current is I _E , k is the Boltzmann constant, T is the absolute temperature, and q is the electric charge, and it is expressed as V _BE =KT/qlnI _E /I _S (1). If the h _FE of the transistor is large enough, the base current can be ignored and the emitter current is equal to the collector current. The potential at point P in FIG.
Since the potential is lowered by V _BE or the voltage drop of the resistor R ₂ and the potential lowered by V _BE of the transistors Q3 and Q2, the following equation holds true.

R ₂ I ₂ +KT/qlnI ₂ /nIs+KT/qlnI ₁ /Ims =KT/qlnI ₂ /Is+KT/qlnI ₁ /Is...(2) The second term, third term, the first term, and the third term on the left side of this equation The second term is for transistors Q3, Q2, Q4, and Q1.
V indicates _BE . From this equation (2), equation (3) is established.

I ₂ = 1/R ₂・KT/ql _o n ...(3) In this equation (3), R ₂ , k, q, and n are constants (temperature dependence of R ₂ is not considered here) ) The current I ₂ is determined by these constants and does not depend on the power supply voltage Vcc. The circuit thus provides a constant current source that is independent of the supply voltage and proportional to the temperature T.

However, in this circuit, the emitter of the transistor Q3 must have an area n times larger than that of the other transistors, and if n is small, the output current I ₂ will be small. In order to increase the output current I ₂ , a large-area transistor Q3 is required, but this reduces the degree of integration when used in an integrated circuit or the like. The above formula (2) indicates that I ₂ R ₂ = V _BE1 −V _BE2 , that is, the resistance R ₂ is limited to the difference between the V _BE (indicated by subscripts 1 and 2 in the above) of the two transistors, If these conditions are satisfied, a constant current circuit can be realized by other means.

OBJECTS OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide a constant current circuit that occupies a small area and is less affected by fluctuations in power supply voltage.

Structure of the Invention The present invention includes a first circuit in which a first resistor R ₂ , a first transistor Q3, and a second transistor Q4 are sequentially connected in series to a power supply, and the other end is an output terminal; third transistor Q1,
A second circuit connects a fourth transistor Q2 and a second resistor _R1 in series, and connects the base of the first transistor Q3 to the third transistor Q.
1 and the third transistor Q1
By connecting the base of R2 to the collector of the first transistor Q3, and connecting the collector and base of the fourth transistor Q2 to the base of the second transistor Q4, the voltage drop across the first resistor _R2 becomes two and a second circuit that controls the voltage difference between the base and emitter of the transistors Q1 and Q3 to be equal to the difference between the base and emitter voltages of the transistors Q1 and Q3, wherein the third transistor Q1 of the second circuit is of a multi-collector type and the collector The current ratio is set to 1:n (here n>1), and the collector on the n-times side is connected to the second resistor _R1 , and the collector on the 1-times side is connected to the fourth transistor Q2. This feature (reference numerals correspond to FIG. 2) will now be described with reference to embodiments.

Embodiment of the Invention FIG. 2 shows an embodiment of the present invention, in which Q1 to Q4 are transistors and R ₁ and R ₂ are resistors as in FIG. 1. In the present invention, transistor Q3 is the same size as the other transistors, and transistor Q3 is replaced by transistor Q3.
1 is multi-collector type (has two collectors)
The area is chosen as 1:n. In this circuit,
Again, the voltage between point P and Vcc is R ₂ , the base of Q3.
The path between the emitter and the base emitter of Q2 is the same, as is the path between the base emitter of Q1 and the base emitter of Q4, so the following formula holds true.

R ₂ I ₂ +kT/qlnI ₂ / _Is +kT/qlnI ₁ /Is =kT/qln(1+n)I ₁ /Is+kT/qlnI ₂ /Is……(4
) The second and third terms on the left side and the first and second terms on the right side of this equation are
V indicates _BE . From this equation (4), the following equation is established.

I ₂ = 1/R ₂・kT/qln (1+n) ...(5) As is clear from equation (5), the circuit in Figure 2 also
It is possible to output a constant current _I2 that is not affected by the power supply voltage Vcc. Furthermore, the transistor Q1 is of a two-collector type, as long as the ratio thereof is 1:n, and does not need to be large. Therefore, the degree of integration can be improved.

Transistors Q1-Q4 are of the pnp type, but transistors of this type are usually made in lateral form. FIGS. 3a and 3b show a schematic plan view and a cross section thereof, where E is an emitter region and C is an annular collector region. These are formed on the surface of the epitaxial growth layer EP. The epitaxial layer EP is divided into isolation regions IS, and the inside of this division becomes a base region. B is the base contact region. The size of each part has a required value, so the first
If the size of the transistor Q3 in the figure needs to be n times larger (the emitter area is n times larger), the result will be as shown in Figure 4, and as the emitter area increases, the base and collector parts will also increase, resulting in the overall size of the transistor. It gets bigger. FIG. 4 shows an example where n=4. FIG. 5 shows a transistor Q1 of the present invention,
In this case, the collector area may be divided into 1:n ratios. Therefore, it has no or little effect on the overall dimensions of the transistor.

In addition, in Figure 2, the current flowing through resistor R ₁ is (1+
n) I ₁ gives the impression that the current is larger than the current flowing through the resistor R ₁ in Figure 1, but this is just a problem with the notation and, of course, is not the case. That is, the output current is the current I ₂ flowing through transistors Q3 and Q4,
The transistors Q1 and Q2 are the same as in FIG. ₁ because the resistor R1 only handles the base current of the transistors Q3 and Q4. In Figure 2, transistor Q
The current flowing to the large-area collector side of R1 may be expressed as I ₁ and the current flowing to the small-area collector side may be expressed as I ₁ /n. In this case, the current flowing to the resistor R ₁ is (1+1/n) I ₁ , You can get the impression from the equation that it is not much different from Figure 1.

As is clear from equations (3) and (5) above, and as mentioned above, in order to increase the output current I ₂ , it is necessary to increase n, which is clear from Figures 3 and 4. As described above, the larger n is, the more effective the present invention is in reducing the area ratio of the transistor.

Effects of the Invention As explained above, according to the present invention, there is an advantage that a constant current circuit that is not affected by the power supply voltage and that changes depending on the temperature can be constructed using small-area transistors.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIGS. 3 to 5 are diagrams for comparing and explaining required sizes of transistors. In the drawing, Vcc is the power supply voltage, _R2 is the first resistor, and Q
3, Q4 are the first and second transistors, Q1, Q
2 is the third and fourth transistors, and R ₁ is the second resistor.

Claims (1)

[Claims] 1. A first circuit including a first resistor, a first transistor, and a second transistor sequentially connected in series to a power source, with the other end serving as an output terminal, and a third transistor to the power source. , a fourth transistor, and a second resistor connected in series in sequence, the base of the first transistor is connected to the collector of the third transistor, and the base of the third transistor is connected to the collector of the third transistor. By connecting the collector and base of the fourth transistor to the base of the second transistor, the voltage drop generated across the first resistor is equal to the difference in the base-emitter voltage of the two transistors. and a second circuit that controls the current to be equal to the voltage, the third transistor of the second circuit is a multi-collector type, and the collector current ratio is 1:n (where n>1). The collector on the n-times side is connected to the second resistor, and the collector on the 1-times side is connected to the fourth resistor.
A constant current circuit characterized by being connected to a transistor.