JPS62295128A - Constant electric current circuit - Google Patents

Abstract

PURPOSE:To normalize an action with a low power source voltage by using a transistor to form a base to a feedback transistor at the activating base area of a low concentration. CONSTITUTION:A constant current circuit is composed of the first - third transistors (hereinafter, Tr) 1 - 3, a starting resistance 4, the fourth Tr5, a shunt resistance 6, the fifth Tr7, the sixth Tr9 of a current mirror circuit 8 and a feedback Tr10, and an output terminal 11 is connected to the seventh Tr12 controller. At this time, Tr with the base as the activating base area of the low concentration is used to the feedback Tr10. Thus, since the Tr10 has the current rise characteristic of an emitter base junction better than the conventional Tr, a carrier transporting efficiency at the base is high, it can be normally operated up to a greatly reduced electric power source voltage Vcc.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a constant current circuit, and more particularly to a constant current circuit with significantly improved voltage reduction characteristics.

(b) Conventional technology low 1! As a constant current circuit that operates with a source voltage, there is, for example, a circuit described in Utility Model Application No. 193264/1983.

FIG. 4 shows such a circuit, with a first . a second transistor (1) (2), whose base and emitter are the first and second transistors (1);
) (2), a diode-connected third transistor (3) connected in common with the base and emitter of (2), and a starting resistor (4) connected to the collector of the third transistor (3);
a fourth transistor (5) whose collector is connected to the collector of the first transistor (1);
) is connected in parallel between the collector and emitter of the shunt resistor (
6), a fifth transistor (7) that is current mirror connected to the fourth transistor (5) and whose collector is connected to the collector of the second transistor (2); (7) A current mirror circuit (β) that takes out the difference current in the collector current and a current mirror circuit (β)
A sixth transistor (9) constituting the bag, and a feedback transistor (with which the base and emitter are commonly connected and whose collectors are connected to the common base of the first to third transistors (1), (2), and (3)); 10), and the seventh transistor (1
2). This circuit is Vs! +Vc
t (where vll! is the base of the third transistor (3)
The emitter voltage, vc, is the lowest voltage f1. of the collector-emitter voltage of the feedback transistor (10). Voltage V. C
It is useful as a constant current circuit that operates at

When such a circuit is made into an IC, the fourth to sixth NPN type and feedback transistors (5), (7), (9) and (1
0) used the following transistors.

FIG. 5 shows the structure of such a transistor, which includes an N-type epitaxial layer (22) laminated on a P-type semiconductor substrate (21), and an N''-type buried layer (22) formed on the surface of the substrate (21). 23), an island region (25) which becomes a collector and is formed by junction-separating the epitaxial layer (22) by a P0 type isolation region (24), and a P type base region (26) formed on the surface of the island region (25). , an N0 type emitter region (27), a collector contact region (28), an oxide film (29), and an electrode (30) disposed on each region via a contact hole formed in the oxide film (29). configured.

(c) Problems to be Solved by the Invention However, when a conventional constant current circuit is driven by a power source in which the power supply voltage VCC decreases depending on the usage time and usage conditions, the voltage 't1. There was a drawback that normal operation could not be performed with high voltage, or that the period of operation could not be achieved at an early stage.

For example, if the electric FA voltage VCC decreases to 0.8■, V CCV Cl' = 0.6V between the collector and emitter of the fourth to sixth transistors (5) <7> (9).
(V ct is the voltage between the collector and emitter of the first and second transistors (1) and (2)) is applied, and this becomes a high hFt.
It can be operated in the following conditions. However, since a diode-connected third transistor (3) is connected to the collector between the collector and emitter of the feedback transistor (10), V CC -0,65 = 0.15V.
L cannot be applied completely, and h□ of this transistor drops extremely. And the electric vffA voltage ■. As the value of 0 continues to decrease, the ability to draw a predetermined collector current is eventually lost, and the output current cannot flow through the output terminal (11).

If we define that the feedback transistor (10〉) loses its ability when its h□ drops to 30, then in the transistor shown in Fig. 5, ■. = 0.11V, that is, the power supply voltage Vco is 0.65 + 0.11 When the voltage drops to = 0.76V, the limit of use is reached.

(d) Means for Solving the Problems The present invention has been made in view of the above-mentioned drawbacks. Of the NPN transistors constituting the constant current circuit, at least the feedback transistor (10) has an island region (35 )
A P-type active base region (36) formed on the surface, an N1-type emitter region (37) formed on the surface of the active base region (36), and a P-type active base region (36) partially overlapped with the active base region (36).
By using the transistor formed with the type base contact region (38), the power supply voltage VC is considerably reduced.
This provides a constant current circuit that can operate normally even in C. .

(E) Effect The transistor used in the present invention has a base formed of a lightly doped active base region (36), so it has better current rise characteristics at the emitter-base junction than conventional transistors.
Carrier transport efficiency is high on a transport basis. Therefore, even if the collector potential is insufficient, there is a high probability that minority carriers (electrons) injected from the emitter will reach the collector, and V
CI! Maintains high hrt even in extremely low hrt ranges.

Therefore, according to the present invention, since such a transistor is used as the feedback transistor (10), normal operation can be achieved even in a region where the power supply voltage vec is considerably reduced.

(f) Example Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 shows a constant current circuit according to the present invention, in which (1) is a PNP type first transistor whose emitter is connected to a power supply;
(2) is a PNP type second transistor whose base and emitter are commonly connected to the base and emitter of the first transistor; (3) is the first transistor; Second transistor (1) (2)
(4) is a starting resistor for flowing a starting current to the third transistor (3); (5) has a collector connected to the collector of the first transistor (1); (6) is a resistor that shunts the collector current of the first transistor (1); (7) is the fourth transistor (5);
(9) is a current mirror circuit that extracts the difference current between the collector currents of the second and fifth transistors (2) and (7), and (9) is a current mirror circuit (β). A sixth NPN transistor (10) constitutes one of the current mirror circuits (10), and the collector thereof is connected to the first to third transistors (1) (2).
(3) a feedback transistor connected to the common base of (
11) is an output terminal connected to the collector of the seventh transistor (12) which is connected in a current mirror manner to the sixth transistor (9).

When the voltage R (V cc ) is applied, the collector current I of the third transistor (3) flows due to the starting resistor (4).
Accordingly, the first. A collector current of I flows through the second transistors (1) and (2), respectively. First transistor (1
)'s collector current 1 is shunted to the resistor (6) and the collector of the fourth transistor (5), respectively, so that the current flows to the collector of the resistor (6) and the collector of the fourth transistor (5).
The collector current of transistor (7) also becomes I4. However, since the collector current of I is flowing through the second transistor (2), the difference current ItIa=Is flows through the current mirror circuit (Dan), and the feedback transistor (10
) and the collector current of the seventh transistor (12) are also equal to , respectively.

For example, the first. If the mirror ratio of the second transistor (1) (2) and the third transistor (3) is set to 2=1 and the current I is set to Io, the collector current (emitter The collector current of the feedback transistor (10) is 1. So, the first. The collector current of the second transistor (1) (2) is 2
Engineering. becomes stable.

Therefore, the collector current of the fourth transistor (5) is also reduced.

Therefore, the output terminal (11) connected to the collector of the seventh transistor (12) has ■. The stable output ′w, the current flows.

In the circuit described above, the most distinctive feature of the present invention is that
The point is that a transistor having the following structure is used as the NPN type feedback transistor (10).

Figure 1 shows a transistor with a P-type semiconductor substrate (3
1) N-type epitaxial layer (32
) and an N-type buried layer (33) buried in the surface of the substrate (31).
), an island region (35) serving as a collector formed by junction-separating the epitaxial layer (32) by a P4 type isolation region (34), and a P-type active base region (36) formed on the surface of the island region (35). ), an N3 type emitter region (37) formed on the surface of the active base region (36), and a base contact region (38) partially overlapping the active base region (36).
), an N+ type flexor contact region (39), an oxide film (40), and an electrode (
41). Base contact area (38
) is the emitter region (3) to lower the base extraction resistance.
7), and the active base region (36) may be shallower or deeper than the base contact region (38) as desired.

However, it goes without saying that the diffusion depth must be deeper than the emitter region (37) and sufficient to obtain a predetermined withstand voltage. Further, the base contact region (38) is formed in a base diffusion process of an NPN l-transistor, and the emitter region (37) and collector contact region (39) are formed in an emic diffusion process of an NPN)-transistor. The impurity concentration of the active base region (36) is the same as that of the base contact region (36).
8) Lower, about 10"cm"-3.

Since the transistor formed in this manner has a base formed of a lightly doped active base region (36), it has better current rise characteristics at the emitter-base junction than conventional transistors, and also has higher carrier transport efficiency at the base. Therefore, even if the first position of the collector is insufficient, there is a high probability that the minority carriers (electrons) injected from the emitter will reach the collector.
Not only is h□ high in the saturated region, but it continues to be high even in regions close to the non-saturated region where Vct is low.

Figure 3 (A) and (B) respectively show the transistor shown in Figure 1 and the fifth transistor.
A Vct Ic characteristic diagram of the transistor shown in the figure is shown. As is clear from the figure, the transistor voltage V ct in FIG.
= 0. In contrast, in the transistor shown in FIG. 1, the current rise characteristic is abrupt, so that hFt=about 160 is still maintained at Vci=0.11V.

Therefore, according to the present invention, since such a transistor is used as the feedback transistor (10), the output current I, which exceeds a predetermined value due to insufficient vc of the feedback transistor (10),
The minimum value of the power supply voltage VCC at which the current cannot flow (operational limit) is smaller than that of the conventional system. For example, if the operation limit is reached when h□ of the feedback transistor (10) drops to 30, then in the transistor shown in FIG. 5, VC! =0.11V is the lower limit, and the minimum operating power supply voltage VCC is 0.65+0.11-0.76V.

On the other hand, the transistor TE in FIG. 1 is v, t=o, o
Since svmate11rt=30 or more is maintained, the constant current circuit according to the present invention has a minimum operating power supply voltage VCC of 0.65+0.05=0.70V.

In the above embodiment, in order to equalize the characteristics of both transistors constituting the electric KE mirror circuit (Dan), the sixth. It is preferable to use the transistors shown in FIG. 1 for the seventh transistors (9) and (12). It is preferable to use it also for the fifth transistors (5) and (7).

(g) As described in detail, according to the present invention, at least the feedback transistor (10) is provided with a base in a low concentration active base region (
Since the transistor formed in 36) is used, it has the advantage of being able to operate normally even at a considerably lower power supply voltage VCC. Moreover, since the rise characteristics of Ic are good,
It has the advantage of maintaining high bit until near the operating limit and exhibiting good characteristics. Furthermore, the transistor shown in Figure 1 requires only the addition of a diffusion process for the active base region (36) to a normal NPN transistor, so it can be used efficiently for specific transistors on the same chip without particularly increasing the chip area. Can be formed. Therefore, the constant current circuit of the present invention has the advantage of being easily integrated into an IC.

[Brief explanation of the drawing]

1 and 2 are a cross-sectional view and a circuit diagram, respectively, for explaining the present invention, and FIGS. 3(A) and 3(B) are Vc of the transistor.
The xIc characteristic diagram, FIGS. 4 and 5 are a circuit diagram and a sectional view, respectively, for explaining the conventional technology. (1), (2), and (3) are the first . Second. The third transistor (4) is a shunt resistor, (5), (7), (9) and (12) are NPN type fourth transistors. Fifth. The sixth and seventh transistors (10) are NPN type feedback transistors, (3
1) is a P-type semiconductor substrate, (35) is an island region, (36) is a P-type active base region, and (38) is a P-type base contact region. Applicant Sanyo Electric Co., Ltd. and one other agent Patent attorney Takuji Nishino and one other person Figure 1 Figure 2 Figure 3 54 (Ino VCH (mV')

Claims (1)

[Claims] (1) first and second transistors whose bases and emitters are commonly connected; a diode-connected third transistor whose bases and emitters are commonly connected to the bases and emitters of the first and second transistors; a diode-connected fourth transistor connected to the collector of the first transistor; a fifth transistor connected in a current mirror to the fourth transistor, and whose collector is connected to the collector of the second transistor;
a resistor connected in parallel between the collector and emitter of the fourth transistor; a current mirror circuit for extracting a difference current between the collector currents of the second and fifth transistors; a sixth transistor constituting the current mirror circuit; In a constant current circuit comprising a feedback transistor whose emitters are commonly connected and whose collectors are connected to a common base of the first to third transistors, at least the feedback transistor is provided with a collector formed on the surface of an island region. A transistor comprising a low concentration active base region of a conductivity type, an emitter region of an opposite conductivity type formed on the surface of the active base region, and a base contact region partially overlapping the active base region. constant current circuit.