JPS5845728B2 - Micro current source circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a minute current source circuit suitable for integration into an integrated circuit.

Conventionally, a micro current source circuit in an integrated circuit is known that is configured as shown in FIG.
A three-stage resistor (diode) bias method current sink circuit consisting of Q is connected in series.

If the reference current ■1 flowing through the diode-connected front-stage transistor Q1 in the first-stage mill is 11=1 mA, then
Set the emitter resistance R0 of the subsequent transistor Q2 to R1=1.
The current flowing through Q2 as β in 2 is 12=10 μA.
becomes.

Further, if the emitter resistance of the second-stage rear-stage transistor Q4 is set to R2-12 as β, the current 3 flowing through the transistor Q4 becomes 3 μA.

Similarly, when the emitter resistance R3 of the third-stage rear-stage transistor Q6 is R, and ρ is set to 12, the output current I flows through the transistor Q6.

becomes 1.5μA.

Here, Q5. Each of Q5 is diode-connected, and the current flowing therein is equal to I, , I3.

In other words, if we increase the emitter resistance of each diode and the latter stage of the bias method current sink circuit as much as possible in this way, the current in the latter stage will be smaller than that in the former stage, so we can obtain the desired minute current from now on. It is something to do.

However, in such conventional circuits, the emitter resistor that can be formed using integrated circuit technology is approximately 12
However, it is difficult to form a larger resistance than this, and it is also disadvantageous in terms of cost.

Therefore, there is a limit to obtaining the desired minute current, for example, O
In order to obtain a minute current of about 0.01 μA or less, the number of cascaded stages increases unnecessarily and the configuration becomes complicated, which is not practical.

For this reason, there is an idea to use the base current of the transistor, but in this case, the characteristics of the transistor used must be controlled and manufactured, which is extremely difficult.

Therefore, the present invention has been made in view of the above points, and it is an object of the present invention to provide an extremely good microcurrent source circuit that can easily and reliably obtain a desired microcurrent and is particularly suitable for integrated circuit implementation. The purpose is to

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, as shown in FIG. 2, the diode-connected transistor Q11 has its common base and collector connected to the resistor R1,
It is connected to the power supply +Vcc via the transistor Q12 and to the base of the transistor Q12, and its emitter is grounded.

The collector of the transistor Q12 is connected to the power supply +Vcc via the diode-connected transistor Q13, and is also connected to the base of the transistor Q14.
Moreover, its emitter is grounded via a resistor R12 and connected to the emitter of a transistor Q15.

Also, the emitter of the transistor Q14 is connected to the power supply +Vcc.
, and its collector is grounded via a diode-connected transistor Q16, and is also connected to the base of the transistor Q15.

Here, the collector of the transistor Q, 5 is connected to the output terminal OUT from which a desired minute current is obtained.

In the above configuration, the reference current ■1□ flowing through the diode-connected transistor Q1 is IH-1mA, and the emitter resistance R12-12KQ of the transistor Q12 is
Then, the current 112 flowing through Q12 is 10 μA as in the conventional case.

The current 112 of this Q1□ is equal to the current 113 flowing through the transistor Q14 and the diode-connected transistor Q16, and is equal to the output current I flowing through the transistor Q15.

is a very large value, that is, ■1□-10μA = ■13
)■.

The relationship is as follows. On the other hand, assuming that each transistor has the same characteristics, the base-emitter voltage VBB has the following relationship: BE - Tln (E/).

However, ■E is an emitter current, Is is a saturation current, and ■T is a thermovoltage component expressed as so-called ■T=KT/(26 mV/3000K).

This gives us the relationship, sort this out A relationship was obtained, and in the end ■.

It is represented by .

In addition to the above-mentioned ■il = 1 mA, 112-113
= 10μA and find ■o, Io = 0.1μA
It can be seen that an extremely small current can be obtained.

In other words, in this case, the voltage generated across the emitter resistor R□2 is used to drive the transistor Q15, which becomes a minute current source.
By reducing the potential between the base and emitter of the device and controlling it in the cut-off direction, it has become possible to easily and reliably obtain a minute current of about 0.1 μA, which was previously difficult.

Furthermore, if a resistor similar to the conventional one (indicated by a broken line in the figure) is inserted into the emitter of the transistor Q14 in the above, the current can be made even smaller.

As is clear from the above explanation, the minute current obtained is determined only by the constant component T and the resistor R12, and does not respond in a first-order manner to parameters that vary easily, such as the current amplification factor (hFE) of the transistor. ,
A desired microcurrent can be stably obtained.

FIG. 3 shows another embodiment, in which the diode-connected transistor Q13 and transistor Q14 in FIG. 2 of the previous example are omitted, and the diode-connected transistor Q
, 6 are controlled from the common base and collector of a diode-connected transistor Q1 via a resistor R13.

In this case, a resistor R14 is inserted between the base and collector of the transistor Q16.

That is, even in this configuration, I 11 = 1 mA
, R1□-12, Q.

■12-101iA, ■13 is the resistor R13
Since there is a relationship based on this, it is R13-12! 2 as ■1□
It becomes 10 μA, which is the same as .

Here, when R14-OQ is assumed, ■.

follows the precedent.

In other words, all that is needed is to obtain a small current 113.

By the way, in this case, for When R14 takes a finite value Because the relationship is established, To sort this out Therefore is obtained.

Here, when R,=R13, This results in an extremely small current.

In the case of the embodiment shown in FIG. 3, when it is integrated into an integrated circuit, the transistor Q16 and the resistor R131 are integrated as shown in FIG.
Since R14 can be formed integrally, it becomes much easier to integrate the circuit.

In FIG. 4, 11 is a P type substrate, 12 is an N type collector layer, 13 is a base diffusion layer, P114 is an emitter diffusion layer N.
115 is a separation region, Qll・Q16, Q15
? R12, R13, R14, and ■0 are elements and connection electrodes corresponding to the circuit diagram in FIG. 3, respectively.

In this case, the resistance value of the resistors R13t and R14 can be increased by forming the resistors R13t and R14 in a thin shape when viewed from the surface.

Furthermore, the collector layers of transistors Qll and Q16 may be connected at locations A and A' in the figure.

In this way, the separation area of elements related to the size of an integrated circuit can be reduced, so when integrating the circuit, the size can be kept small and a relatively large resistance value can be obtained, making it possible to create a microcurrent source circuit. It is suitable as

5 to 7 also show other different embodiments. First, in the case of FIG. 5, the diode-connected transistor Q13 and the transistor Q14 controlled by it in FIG. This is shared by the t-transistor Q1□.

Q17 has a diode function because its first collector is shared with its base, and its second collector is grounded through a resistor R15 and connected to the emitter of the output transistor Q16'. 3 collector is grounded via a diode-connected transistor Q16' and connected to the base of Q15'.

According to this configuration, the output transistor Q15'
The emitter potential of Q, from the emitter potential of 2, R15/
Since the current is multiplied by 12, it is possible to obtain an even smaller current than the embodiment shown in FIG.

Further, FIG. 6 shows an example in which the output transistor Q15'' and the others are expressed by diodes Q11', Q1□', and Q16'.

Furthermore, in FIG. 7, the emitter area of the transistor Q12 in FIG. 2 is enlarged and is represented as Qll.

This can be similarly applied to Q12 in FIGS. 2 and 3 and Q16 in FIGS. 5 and 6, and by increasing the emitter area, the current can be made even smaller.

Such a minute current source circuit can be used as a bias circuit that requires setting with a minute current, a reference current source, etc., and can also be used as a substitute for a large resistor of several MQ to several 10,100 ohms.

As an example of the latter, if used in a time constant circuit, for example, a triangular wave or sawtooth wave with a very gentle slope can be obtained with a small capacitor.

Therefore, as described in detail above, according to the present invention, it is possible to easily and reliably obtain a desired minute current, and it is possible to provide an extremely good minute current source circuit particularly suitable for integration into an integrated circuit. Become.

[Brief explanation of drawings]

Fig. 1 is a wiring diagram showing a conventional micro current source circuit/circuit, Fig. 2 is a wiring diagram showing one embodiment of the micro current source circuit according to the present invention, and Fig. 3 is a wiring diagram showing another embodiment. 4 are implementation diagrams of essential parts when FIG. 3 is integrated into an integrated circuit, and FIGS. 5 to 7 are connection diagrams showing other different embodiments. Q11-Q16...transistor, R11-R14...
...Resistance, +Vcc...Power supply, OUT...
Output end.

Claims (1)

[Claims] 1. A first bias means for applying a first predetermined potential by being driven by a reference current I, l, and a base coupled to the first predetermined potential point by the first bias means. a first transistor driven by a first constant current ■1□ smaller than the reference current Ill by having its emitter connected to a resistor and a first constant current ■1 caused by this first transistor; Second constant current 113 approximately equal to □
a second predetermined potential that is approximately equal to the first predetermined potential by the first bias means;
(2) from the collector by having a base coupled to the second predetermined potential point by the second biasing means and an emitter commonly coupled to the resistor. a second transistor that outputs a minute constant current of 1. A minute current source circuit characterized in that the minute current source circuit is configured to be determined as follows.