JPH088664A - Current supply circuit - Google Patents

Abstract

PURPOSE:To provide the current supply circuit which supplies a current, which corresponds to the base current of a bipolar transistor TR to which a constant current bias is given, independently of a supply voltage. CONSTITUTION:A first NPN TR N2 which has the collector connected to a first power source node, a second NPN TR N1 which constitutes a differential pair together with the first TR N2 and whose base a reference potential is given to, a constant current source 11 which is connected between the common emitter of first and second TRs N2 and N1 and a second power source node and to which the current determined by the bias potential flows, a third PNP TR P3 which has the emitter and the collector connected between the first power source node and the base of the first TR N2 and has the base connected to the collector or the second TR N1, and a fourth PNP TR P4 which has the base connected to the base of the third TR P3 and has the emitter connected to the first power source node and whose collector the current output is taken out from are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current supply circuit formed in a semiconductor integrated circuit, and more particularly to a current supply circuit for supplying a current corresponding to the base current of a bipolar transistor to which a constant current bias is applied.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a current supply circuit 60 formed in a conventional bipolar monolithic circuit. In this current supply circuit 60, a collector / emitter of an NPN transistor N1 and a constant current source circuit 61 are connected in series between a power supply node and a ground node, and between the power supply node and the base of the transistor N1. Is connected between the emitter and collector of the first PNP transistor P1. The base and collector of the first PNP transistor P1 are connected to each other, and the emitter and base of the second PNP transistor P2 are connected to the emitter and base of the first PNP transistor P1. The two PNP transistors form a current mirror circuit.

In the current supply circuit 60 having the above structure, N
The PN transistor N1 is a constant current I of the constant current source circuit 61.
Is biased by the base current IB
Minute is the first PNP transistor P of the current mirror circuit
Supplied from 1. In this current mirror circuit,
If the emitter area ratio of the two PNP transistors P1 and P2 is set to 1: 1, the collector current of the first PNP transistor P1 and the second PNP transistor P2.
Since the current value is equal to the collector current of the second PNP,
From the collector of the transistor P2 to the collector current of the first PNP transistor P1 (NPN transistor N1
It becomes possible to output (supply to other circuits) a current corresponding to the base current IB of the above.

Here, the current supply circuit 60 is used as a base current correction circuit for supplying a base current to one of the differential pair transistors of the differential amplifier circuit input stage 70 as shown in FIG. 6, for example. Consider the case.

The differential amplifier circuit input stage 70 includes NPN transistors N3 and N4 forming a differential pair, a constant current source circuit 71 connected to an emitter common connection node of the differential pair transistors N3 and N4, and the above-mentioned. An input resistance element Ri connected between the bases of the differential pair transistors,
The reference voltage Vref is applied to the base of one transistor N4 of the differential pair transistors, and the input signal is applied to the base of the other transistor N3 from the signal source 72 through the coupling capacitance Ci.

In the differential amplifier circuit input stage 70,
The base current of the NPN transistor N3 flows from the reference voltage Vref source to the input resistance element Ri, a voltage drop occurs, and a DC voltage offset occurs between the base potentials of the differential pair transistors N3 and N4, which is not preferable.

Therefore, as described above, the current supply circuit 60
From the differential amplifier circuit input stage 70 to the base (signal input node) of the other transistor N3 of the differential pair transistors.
The base current is corrected by supplying the base current of the PN transistor N3.

However, the conventional current supply circuit 60 described above is used.
In the above, since the base potential of the NPN transistor N1 depends on the power supply voltage Vcc and the supply output current has power supply dependency, the differential pair of the NPN transistor N1 and the differential amplifier circuit input stage 70 when the power supply voltage Vcc changes. Since the operating conditions of the transistors N3 and N4 are different, the base current of the differential amplifier circuit input stage 70 cannot be accurately corrected, and an error occurs in the operation of the differential amplifier circuit input stage 70.

[0009]

As described above, the conventional current supply circuit is used as a base current correction circuit for supplying a base current to the input stage of the differential amplifier circuit because the supply output current depends on the power supply voltage. When used, there is a problem that an error occurs in the operation of the differential amplifier circuit input stage when the power supply changes.

The present invention has been made to solve the above problems, and can supply a current corresponding to the base current of a bipolar transistor to which a constant current bias is applied, without depending on the power supply voltage. The purpose is to provide a circuit.

[0011]

In the current supply circuit of the present invention, a bipolar type first transistor having a collector connected to a first power supply node and having a first polarity, and the first transistor and the emitter are A second bipolar type transistor having a first polarity, which is commonly connected to form a differential pair and has a base to which a fixed reference potential is applied; and an emitter common connection node of the two transistors forming the differential pair and a second transistor. A first constant current source circuit connected between the first power supply node and the base of the first transistor, the first constant current source circuit being connected between the first power supply node and the base of the first transistor. Is connected to the collector of the second transistor, and the base is connected to the collector of the second transistor.
A bipolar-type third transistor having a second polarity opposite to the polarity type, the third transistor and the base are connected to each other, the emitter is connected to the first power supply node, and a current output is taken out from the collector. And a bipolar fourth transistor having a second polarity.

[0012]

Operation: The base current IB1 of the first transistor is I / β
n (βn is the current amplification factor of the first transistor),
The collector current of the second transistor (base current IB2 of the third transistor) is IB1 / βm (βm is the current amplification factor of the third transistor). That is, the bias current flowing through the second transistor is sufficiently smaller than the bias current flowing through the first transistor, and the bias current flowing through the first transistor is substantially equal to the constant current I flowing through the first constant current source circuit. Can be considered.

When the base potential of the first transistor fluctuates depending on the fluctuation of the potential of the first power supply node, and the magnitude of the collector current of the first transistor changes, the second transistor is commensurate with the change. The collector current of the transistor changes in the opposite direction, whereby the collector current of the third transistor changes in the direction of suppressing the change in the collector current of the first transistor. That is, the base of the first transistor operates so as to be negatively feedback-controlled by the collector potential of the third transistor. Since the third transistor and the fourth transistor form a current mirror circuit having a common base, the collector current of the third transistor from the collector of the fourth transistor (base current of the first transistor) It becomes possible to output (supply to other circuits) a current corresponding to.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the current supply circuit of the present invention. The current supply circuit 10 includes a bipolar-type (NPN-type in this example) first transistor N1 having a first polarity and a collector connected to a first power supply node.
A bipolar type second transistor N2 having a first polarity in which the first transistor N1 and the emitter are commonly connected to form a differential pair, and a fixed reference potential Vref is applied to the base; and the differential pair. A constant current source circuit 11 connected between the emitter common connection node of the two transistors N1 and N2 and the second power supply node, and the first power supply node and the first transistor N1. Of the bipolar transistor having a second polarity opposite to that of the first polarity type (in this example, PNP type). ) Third transistor P3, the third transistor P3 and the base are connected to each other, the emitter is connected to the first power supply node, and the current output is taken out from the collector. And a bipolar fourth transistor P4 having a second polarity.

In the current supply circuit 10 having the above structure, the base current IB1 of the first transistor N1 is I / β n (β
n is the current amplification factor of the first transistor N1, and the collector current of the second transistor N2 (base current IB2 of the third transistor P3) is IB1 / βm (βm is the third).
Current amplification factor of the transistor P3). That is, the second
Bias current flowing through the first transistor N1 is sufficiently smaller than the bias current flowing through the first transistor N1, and the bias current flowing through the first transistor N1 is substantially equal to the constant current I flowing through the first constant current source circuit 11. Can be considered.

Now, depending on the fluctuation of the power supply potential Vcc, the first
When the potential of the base of the transistor N1 changes and the magnitude of the collector current of the first transistor N1 changes, the collector current of the second transistor N2 changes in the opposite direction by an amount commensurate with this change. The collector current of the third transistor P3 is equal to that of the first transistor N1.
Changes in a direction to suppress the change in collector current. That is, the first potential is set by the collector potential of the third transistor P3.
The base of the transistor N1 operates as a negative feedback control. Since the third transistor P3 and the fourth transistor P4 form a current mirror circuit having a common base, the collector current of the third transistor P3 (the first transistor N1 It becomes possible to output (supply to another circuit) a current IB1 corresponding to the base current IB1).

Next, the current supply circuit 10 as described above.
Will be described as a base current correction circuit for supplying a base current to the differential pair transistors of the differential amplifier circuit input stage 20 as shown in FIG. 2, for example.
Here, the resistance element R1 is inserted and connected between the first power supply node and the collector of the first transistor N1. In addition, the first constant current source circuit 11 is, for example, NP
The N-transistor N5 is used, and a constant current determined by the bias potential Vbias applied to its base flows.

The differential amplifier circuit input stage 20 shown in FIG.
Bipolar type NPN transistors N3 and N4 having a first polarity forming a differential pair and the differential pair transistor N
A second constant current source circuit 21 (for example, composed of an NPN transistor N6) connected to the emitter common connection node of N3 and N4, and an input resistance element Ri connected between the bases of the differential pair transistors N3 and N4. And a reference voltage Vref is applied to the base of one transistor N4 of the differential pair transistors, and the other transistor N3 is provided.
An input signal is applied to the base of the signal from the signal source 22 through the coupling capacitance Ci.

Here, a reference voltage Vref applied to the base of one transistor N4 of the differential pair transistors.
Is a reference voltage Vre applied to the base of one transistor N2 of the differential pair transistors of the current supply circuit 10.
It is set equal to f.

The second constant current source circuit 21 flows a constant current determined by the bias potential Vbias, but the second constant current source circuit 21 has a bias potential common to the first constant current source circuit 11 of the current supply circuit 10. Vbias is given.

The second constant current source circuit 21 has an emitter of a current source NPN transistor N6 so that a constant current 2I, which is twice the constant current I flowing in the first constant current source circuit 11, flows. The area is set, so that the current source transistor N6 and the current source transistor N5 of the first constant current source circuit 11 of the current supply circuit 10 have the same characteristics (for good pairing characteristics). ) Is formed.

Further, the signal input transistor N3 of the differential amplifier circuit input stage 20 and the first transistor N1 of the differential pair transistors of the current supply circuit 10 have uniform characteristics (good pairing characteristics). Is formed).

According to the circuit as shown in FIG. 2, even if the base current of the signal input transistor N3 of the differential amplifier circuit input stage 20 changes depending on the fluctuation of the power supply potential Vcc, the differential amplifier circuit. Second constant current source circuit 21 for supplying bias current to the differential pair transistors of the input stage 20 and current supply circuit 1
Since a bias potential equal to that of the first constant current source circuit 11 that applies a bias current to the differential pair transistor of 0 is applied, the current supply circuit 1 responds to the change in the base current.
The output current of 0 changes, and the base current of the differential amplifier circuit input stage 20 can be corrected with a small error.

FIG. 3 shows a modification of the current supply circuit 10 of FIG. The current supply circuit 10a is different from the current supply circuit 10 shown in FIG. 1 in that a resistance is provided between the first power supply node and the emitters of the third transistor P3 and the fourth transistor P4 of the current mirror circuit. Element R
2, R3 are inserted and connected, and the resistance element R1 is inserted and connected between the first power supply node and the collector of the first transistor N1. As a result, the current mirror property of the current mirror circuit is improved.

The current supply circuit 10b shown in FIG. 4 is obtained by reversing the polarity of each transistor and the connection relation with the power supply node and the ground node in the current supply circuit 10 of FIG. 1, and P1 and P2 are PNP transistors. N7, N8
Is an NPN transistor, and 11 is a constant current source.

The current supply circuit 10c shown in FIG. 5 differs from the current supply circuit 10b shown in FIG. 4 between the emitters of the third transistor N7 and the fourth transistor N8 of the current mirror circuit and the ground node, respectively. Resistance element R2, R
3 is inserted and connected, and the resistance element R1 is inserted and connected between the collector of the first transistor P1 and the ground node. As a result, the current mirror property of the current mirror circuit is improved.

[0027]

As described above, according to the current supply circuit of the present invention, it is possible to supply the current corresponding to the base current of the bipolar transistor to which the constant current bias is applied, without depending on the power supply voltage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a current supply circuit of the present invention.

FIG. 2 is a circuit diagram showing an application example of the current supply circuit of FIG.

FIG. 3 is a circuit diagram showing a modification of the current supply circuit of FIG.

FIG. 4 is a circuit diagram showing another modification of the current supply circuit of FIG.

5 is a circuit diagram showing a modified example of the current supply circuit of FIG.

FIG. 6 is a circuit diagram showing an example of a conventional current supply circuit.

[Explanation of symbols]

10 ... Current supply circuit, 11, 21 ... Constant current source circuit, 20
... differential amplifier input stage, N1 to N8 ... NPN transistors, P1 to P4 ... PNP transistors, Vref ... reference potential, Vbias ... bias potential, R1 to R3, Ri ... resistance elements.

Claims (2)

[Claims] 1. A first bipolar-type transistor having a first polarity whose collector is connected to a first power supply node, and a common pair of the first transistor and an emitter to form a differential pair having a base. It is connected between a bipolar second transistor having a first polarity to which a reference potential is applied, an emitter common connection node of the two transistors forming the differential pair, and a second power supply node, and is connected by a bias potential. A first constant current source circuit through which a constant current is determined, an emitter and a collector are connected between the first power supply node and the base of the first transistor, and the base is the collector of the second transistor. A bipolar-type third transistor having a second polarity opposite to the first polarity, and the third transistor and the base are connected to each other, Emitter is connected to said first power supply node, the current supply circuit, characterized by comprising a fourth transistor of the bipolar type having a second polarity current output is taken from the collector. 2. The current supply circuit according to claim 1, wherein
Further, a bipolar-type fifth transistor having a first polarity, to which a base current is supplied from the collector of the fourth transistor,
And the fifth transistor and the emitter are commonly connected to form a differential pair, and the bipolar-type sixth transistor having the first polarity to which the reference potential is applied to the base and the differential pair are formed. A second transistor connected between the emitter common connection node of the two transistors and the second power supply node, and controlled by the bias potential so that a second constant current twice the first constant current flows. 2. A current supply circuit comprising: two constant current source circuits; and an input resistance element connected between the bases of the two transistors forming the differential pair.