JPS60246419A - Constant-current source circuit - Google Patents

Abstract

PURPOSE:To suppress a constant-current output variation caused by an influence of an Early effect and a load variation, by performing a negative feedback so that the potentials of two voltage references become equal. CONSTITUTION:In case when the potential of a point C rises, and a collector current of PNP transistors (hereinafter called TR) 27, 28 is increased by an Early effect, the potential by diodes 14, 15 and a resistance 16 is varied to V'B2 from VB, and the potential by a diode 20 is varied to V'B1 from VB. Also, a differential amplifying circuit constituted of NPNTRs 17, 18 becomes an unbalance, and the base potential of the TR17 becomes higher than the base potential of th TR18, therefore, a base current of a PNPTR23 decreases. The PNPTRs26-28 constitute a current mirror circuit mirror circuit, the collector current of the TRs27, 28 decreases, the current flowing to the diode 14 and 15 side and the diode 20 decrease, and in the end, a point L in the figure, namely, both the potentials become VB equally.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a constant current source circuit used in an integrated circuit.

Conventional Structure and Its Problems FIG. 1 shows a conventional low voltage operation constant current source circuit used in integrated circuits. In FIG. 1, the base and collector of NPN) transistor 1 and the base of NPN) transistor 2 are connected to form a current mirror circuit, and the collector of NPN) transistor 1 is connected to the collector of transistor 4 and The collector of is PNP
Connected to the collector of transistor 4, PNP
The collector and base of the transistor 3 are connected to the base of the PNP transistor 40, and the NPN transistors 3 and 4 also constitute a current mirror circuit.

NPN transistor 2 pcs NPN) transistor 1
Since the element area is larger than NPN), the sum of the base-emitter contact potential of transistor 2 and the voltage drop across resistor 6 due to the emitter current of transistor 2 is N P N
The circuit enters an equilibrium state when the contact potential between the base and emitter of transistor 1 becomes equal to the contact potential between the peak and the peak. (That is, the second
Equilibrium occurs at point F in the figure.

(The curve E is the characteristic of the transistor 2 side in FIG. 1.) Further, VB is the potential between the 0 point and ground in FIG. 1, and ■ is the emitter current of the transistor 1.2.

The current is extracted as a collector current of a PNP transistor whose base and emitter are respectively connected to the PNP transistor 3. The value of this current can be adjusted by the ratio of the sizes of PNP transistors 1 and 2 and the value of resistor 6.

In conventional circuits, changes in current due to the Early effect sometimes caused problems. In other words, when the potential at point A increases, the current amplification factor of transistor 4 increases due to the Early effect, so the collector current of transistor 4 increases,
(NPN) transistor 1's collector current and emitter current also increase.

On the other hand, the collector current and therefore the emitter current of transistor 2 also increase due to the Early effect. transistor 1,
Since the base potentials of transistors 2 and 2 are equal, in FIG. 2, the transistor 1 side is at the F2 point and the transistor 2 side is at the Fl point, which is an equilibrium state, and the emitter current increases by (I, -1).

Since the base of PNP) transistor 0 is at a common potential with the base of PNP) transistor 4, the current supplied to the circuit as the collector current of transistor 6 is also approximately (I2
-1) increase. When the potential at point A decreases, the opposite is true, and the equilibrium point is F3. Go to F4 and (I
'-I3) When actually using an integrated circuit, AC ripple components are often added to the DC power supply, and as a result, changes in the current source current due to the Early effect may become a problem. There is. In addition, if the current amplification factor decreases due to variations in the current amplification factor of the transistor, the effect of the pace current of the transistor that supplies current to the circuit, such as the PNP transistor shown in Figure 1, becomes noticeable, and the constant current The equilibrium state of the circuit changes, and the current source current value changes. This has a more pronounced effect as the number of transistors supplying current to the circuit increases. In order to improve this problem, there is a circuit shown in FIG. 3 as a circuit for reducing the base current dependence of the output transistor in a balanced state. In this circuit, transistors 9, 10, 12
Since a base current of 9°10 is supplied, the transistor 9°10
．． The influence of the pace current of transistor 12 is reduced to 1/(PNP) current amplification factor of transistor 11). However, this circuit can only guarantee reduced voltage operation up to about 14V.

Purpose of the Invention The present invention solves the above-mentioned problems, and detects the current change due to the Early effect, performs error amplification, and applies feedback to eliminate the current change due to the Early effect and to reduce the current change due to power supply voltage fluctuations. It is an object of the present invention to provide a constant current source circuit that can not only improve stability but also improve current stability due to variations in current amplification factors of transistors (especially when they decrease) without deteriorating voltage reduction characteristics. This is the purpose.

'Structure of the Invention The constant current source circuit of the present invention has two voltage references, and negative feedback is performed by a differential amplifier circuit and an error current amplifier circuit so that the potentials of both are equalized, thereby reducing the Early effect and the load. The structure is such that constant current output fluctuations due to fluctuations can be eliminated and stable constant current output can be supplied down to low voltages.

DESCRIPTION OF THE EMBODIMENT FIG. 4 shows an embodiment of the present invention. (NPN) transistors 17 and 18 form a differential amplifier, and in a balanced state, the base potentials of transistors 17 and 18 are equal. A series circuit of a diode 14, 15 and a resistor 16 is connected between the base of the NPN transistor 1 and the ground.
N) A diode 2o is connected between the base of the transistor 18 and the ground. Diodes 14 and 15 are PNP
Due to the transistor 27, the diode 20 is NPN)
Current is supplied by the transistor 28, and since the base potentials of the transistors 27 and 28 are the same, if the transistors 27 and 28 have the same electrical characteristics, the collector currents of both transistors will also be equal, and the L point in FIG. In other words, the parallel circuit of diodes 14 and 15, the series circuit of resistor 16, and diode 20 are in equilibrium when the current flowing through them and the potential at both ends are equal, and the equilibrium current value in this state, that is, as shown in the figure. PNP as a constant current) transistor 27.28. !
: PNP to which the pace and emitter are connected) This is the current value that can be supplied to the circuit by the transistor 29. 6th
In the figure, curve ■ is on the diode 14.15 side, and curve K is on the diode 14.15 side.
is the voltage-current characteristic on the diode 2o side. The current value can be adjusted by the number of diode elements and the value of the resistor 16. - As an example, when n elements having the same characteristics as the diode 2Q are connected in parallel to the diode 14.15 side of the diode 20@IC, and the resistance value of the resistor 16 is R, the current value is given by the following equation.

I=VTRnn/R However, VTzkT/q k: Boltzmann constant q: Electron charge T: Absolute temperature Here, the diodes 14 and 15 may be replaced with diodes having a lower contact potential than the diode 2Q.

In FIG. 4, a differential amplifier circuit consisting of NPN transistors 17 and 18 and a PNP transistor 27.
28 is connected via a PNP transistor 23 and NPN transistors 24 and 26.

Now, assuming that the potential at point C rises and the collector current of the PNP transistor 27.28 increases due to the Early effect, (the diode 14.16 side and the diode 2o
The potential across the diode 14, 15 and the resistor 16 increases from VB to "B2" in FIG.
Similarly, the potential at diode 20 changes from VB to v'B1 in FIG. In other words, NPN)
The base potential of the run raster 1F0 becomes V'B2 and the base potential of the 1NPN transistor 18 becomes V'BIK, and the differential amplifier circuit constituted by both transistors becomes unbalanced. In this case, since the base potential of the transistor 170 is higher than the base potential of the transistor 18, the collector current of the transistor 17 increases and the collector current of the transistor 18 decreases. Therefore, the current flowing into the intersection of transistor 18 and PNP transistor 22, ie, the base current of PNP transistor 23, decreases.

As a result, the collector current of the transistor 23 decreases,
In a current mirror circuit composed of NPN) transistors 24 and 25, the collector current of the transistor 26,
In other words, the collector current of the PNP transistor 26 also decreases, and since the terminal and base of the transistor 26 are connected to each other and have a common potential, the transistor 27.
28, the collector current of transistors 27 and 28 decreases, and the current flowing to the diode 14 and 15 side and diode 2o decreases, and finally reaches point L in FIG. 6, that is, the potential of both. When the common pace potential of PNP transistors 27 and 28 rises, the reverse operation occurs.

Since the circuit configuration uses an error amplification circuit and a feedback circuit in this way, the equilibrium point of this circuit does not change even if the power supply voltage fluctuates, and the constant current output supplied as the collector current of the PNP transistor 29 is It is constant and is not affected by the Ally effect. However, in reality, the differential amplifier circuit composed of NPN) transistors 17 and 18 in FIG. The amplification factor changes and transistor 1
Since the equilibrium conditions of 7.18 change, the output current changes, but the ratio of the base current of transistor 23 to the collector current of transistor 26 is extremely small, so its effect is extremely small. It is also possible that the fluctuations are due to the characteristics of the transistors 17 and 18 not being the same, but if they are formed with the same dimensions on the same silicon chip,
Since most of the characteristics are the same, there is no problem. Similarly, even if an AC ripple component is superimposed on the power supply voltage and the potential at point C changes, changes in the constant current output due to the ripple component can be kept extremely small. Next, when many circuits are driven as loads, that is, when a plurality of load circuit current supply transistors 5 (same as transistor 27 in FIG. 4) in FIG. 1 are used, their base currents cause In the conventional circuit, the circuit balance was destroyed and the output current value changed, but in this example circuit, the PNP in Figure 4
) Since the current is passed through the current amplification circuit using the transistor 23, the influence of the pace current can be greatly reduced. If the current amplification factor of the transistor 23 is low, it is also possible to improve the current gain by inserting a resistor between the emitters of the NPN transistors 24 and 26 and ground to further improve the stability. It is. In order to prevent abnormal oscillation, please connect the power line C1 as necessary.
A small capacitor may also be inserted between the base of the transistor 23.

The voltage reduction operation of this circuit is approximately 0 even in the circuit path where the operable voltage is the highest because its value is the sum of the base-emitter contact voltage of the forward transistor and the collector-emitter saturation voltage of the transistor. .9
It is possible to operate up to VV and can be used as a constant current source circuit for low voltage operation integrated circuits.

In addition, as shown in FIG. 6, a resistor 16 and a diode 20
Even when both are grounded through the resistor 3o, the base potentials of the transistors 17 and 18 only rise by the voltage drop due to the resistor 3o, and the operation is the same as that of the circuit shown in FIG. This circuit is used when it is necessary to raise the base potential of the transistors 17 and 18 due to the circuit configuration, and when it is actually incorporated into an integrated circuit.
It is also effective as a means for correcting variations in the current value due to variations in the resistance value of the resistor 16.

Effects of the Invention The present invention makes it possible to supply a constant current that is extremely stable against fluctuations in power supply voltage down to low voltages in an integrated circuit.
It can be kept extremely low compared to conventional circuits.

[Brief explanation of drawings]

Figure 1 is a connection diagram of a conventional constant current source circuit, Figure 2 is a characteristic diagram of the current reference section in the circuit of Figure 1, and Figure 3 is a circuit diagram of the circuit of Figure 1 with improved stability against load fluctuations. 4 is a wiring diagram of a constant current source circuit in an embodiment of the present invention. FIG. 6 is a characteristic diagram of the voltage reference section in the circuit of FIG. 4. FIG. 7 is a wiring diagram of a constant current source circuit in another embodiment. C...Power supply line for each circuit, 16, 19.30
...Resistance, 14, 15, 20---Diode, 1
7゜18, 24, 25...NPN) transistor, 21゜22.23.26.27.28.29...
...PNP transistor. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 4 Figure 5 Figure 6 Procedural amendment (voluntary) December 1980, 1o8 2. Name of the invention Constant current source circuit 3. Relationship with the person making the amendment Patent application Address Kadoma City, Osaka Prefecture Oaza Kadoma 1006 address name (
582) Matsushita Electric Industrial Co., Ltd. Representative Toshihiko Yamashita 4 Agent 571 Address 61 Matsushita Electric Industrial Co., Ltd. 1006 Kadoma, Kadoma City, Osaka Prefecture Contents of amendment (1) The scope of claims in the specification will be corrected as shown in the attached sheet. (2) Page 3, lines 3 to 7 [(that is...
It is... '' [In other words, the state of equilibrium is reached at point F in FIG. Here, the curve is the transistor 1 in FIG.
Side 1 curve E is the characteristic of transistor 2 side, and VB
is the potential between the 0 point and ground in FIG. 1, and is the emitter current of transistors 1 and 2. ” will be corrected. (3) Correct "Resistance 6" on the 11th line of page 3 to "Resistance 6". (4) Correct "emitter current" in the fourth line of page 4 to "emitter current of transistor 2". (6) "PNP transistor 4" on page 4, lines 6-6
" is corrected to rPNP) transistor 3". (6) r(I-rs)J on page 4, line 10 of the same page as “(
I-1°)". (7') [14vJ on page 5, line 9] "1.4v"
will be corrected. (8) "Ochitsuku," in the third line of page 10 will be corrected to "Ochitsuku." (9) Page 1Q, line 10 [...not accepted. ”
Next, ``Similarly, an AC ripple component is superimposed on the xi voltage, and even if the potential at point C changes, the change in constant current output due to the ripple component can be kept extremely small.''
Insert and put on. (10) Delete "Can be done in the same way" from lines 3 to 6 on page 11. 2. Claims First and second NPN) A differential amplifier circuit is constructed by grounding the emitter of the transistor via a resistor or a constant voltage circuit, and a transistor is connected between the base of the first NPN transistor and the ground. 1 diode and this second NPN
) A series circuit of a plurality of parallel-connected diodes or a second diode and a resistor having a contact voltage lower than that of the first diode is connected between the base of the transistor and the ground, and the collector output signal of this differential amplifier circuit is The fourth and sixth PNPs have a common emitter and base.
) the collector of this fourth PNP transistor is connected to the base of said first NPN transistor, and the collector of this sixth PNP transistor is connected to the base of said second NPN) transistor. A constant current source circuit characterized in that a current negative feedback circuit is configured by using a current negative feedback circuit.

Claims (1)

[Claims] A differential amplifier circuit is constructed by grounding the emitters of the first and second NPN) transistors via a resistor or a constant voltage circuit, and between the base of the first NPN) transistor and the ground. A first diode is connected, and a plurality of parallel-connected diodes or a series circuit of a diode and a resistor having a contact voltage lower than that of the first diode are connected between the base of this second NPN transistor and ground. , the collector output signal of this differential amplifier circuit is the emitter. In addition to the bases of the fourth and fifth PNP transistors having a common base, the collector of this fourth PNP transistor is connected to the base of the first NPN transistor, and the collector of this fifth PNP transistor is connected to the base of the first NPN transistor. A constant current source circuit characterized in that it is connected to the base of the second NPN transistor to form a current negative feedback circuit.