JPH11168329A - Base current compensation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier circuit of small current consumption and high accuracy. SOLUTION: To a 5th PNP output transistor 5, a current I2 for which the current I2/A flowing through a 7th PNP transisstor 7 for constituting a current mirror circuit is multiplied by A with an 8th PNP transistor 8 is supplied. As a result, I2/β (β is a current amplification factor in common to the PNP transistors of this circuit) flows to its base, then it flows into a 4th NPN transistor 4. In the meantime, a current almost equal to the sum of the base currents of the 7th and 8th PNP transistors 7 and 8, that is the current of (1+1/A)I2/β, flows to a 10th PNP transistor 10 and it flows into the collector of a 3rd NPN transistor 3. The magnitude of this current is made almost equal to the base current of the 5th PNP transistor 5 by enlarging A which is the emitter area ratio of the 8th PNP transistor 8 to the emitter area of the 7th PNP transistor 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base current compensation circuit in an amplifier circuit widely used as a semiconductor integrated circuit (IC, LSI, etc.), and more particularly to a base current compensation circuit which realizes a reduction in current consumption. It is.

[0002]

2. Description of the Related Art Conventionally, as an amplifier circuit of this type which is formed into a semiconductor integrated circuit (IC, LSI, etc.), there is, for example, one shown in FIG. Hereinafter, referring to FIG.
If its configuration, operation, etc. are briefly described, first,
This amplifying circuit is mainly configured with a differential amplifier composed of first and second PNP transistors Q1 and Q2. That is, a differential input is applied to the bases of the first and second PNP transistors Q1 and Q2, and the third and fourth active loads become so-called active loads on the respective collector sides. NPN transistors Q3 and Q4 are provided. And the second PN
The output obtained on the collector side of P-type transistor Q2 is the fifth
Is finally output through a so-called emitter follower by the PNP transistor Q5.

In the above-mentioned conventional circuit, the base of the fifth PNP transistor Q5 is connected to the second PNP transistor Q5.
Connected to the collector of the fourth NPN transistor Q4 together with the collector of the second PNP transistor Q2, the collector of the fourth NPN transistor Q4 and the fifth PNP transistor Q2. P
The base current of the NP transistor Q5 flows. In contrast, the collector of a so-called diode-connected third NPN transistor Q3 has:
If the base of the sixth PNP transistor Q6 is not connected as shown in FIG.
And the sixth PNP transistor Q6 is provided similarly to the provision of the fifth PNP transistor Q5 from the viewpoint of avoiding such circuit unbalance. , The base current I2 / 'of the fifth PNP transistor Q5 is the same as that of the fifth PNP transistor Q5.

[0004]

However, in the above-mentioned conventional circuit, the sixth PNP transistor Q6
In order to make the base current I2 '/ β of the fifth PNP transistor Q5 the same as that of the fifth PNP transistor Q5, the emitter current of the fifth PNP transistor Q5, A constant current source that outputs the same current as I2 is required, but since the output current is generally relatively large, flowing the same current is
This leads to an increase in current consumption, that is, an increase in power consumption of the entire circuit, which is not preferable in this type of circuit that requires low power consumption.

The present invention has been made in view of the above circumstances, and provides a base current compensating circuit which realizes a reduction in current consumption. Another object of the present invention is to provide a highly accurate amplifier circuit by performing base current compensation.

[0006]

According to a first aspect of the present invention, there is provided a base current compensating circuit having a base on an output side of the second transistor among first and second transistors constituting a differential amplifier. A base current compensation circuit in an amplifier circuit configured to obtain the output of the second transistor via an output transistor connected to operate as an emitter follower. A current mirror circuit is provided, and one of the transistors constituting the current mirror circuit is connected to the output transistor so that a DC bias current is supplied to the output transistor, and the other transistor is connected to the other transistor. Is connected to a constant current source and the base of the transistor for base current compensation. A first transistor which connects the base current compensating transistor so that the other transistor is in a diode-connected state via a transmitter, and the output side of the base current compensating transistor constitutes the differential amplifier And the emitter area of one transistor constituting the current mirror circuit is set to a predetermined multiple of the emitter area of the other transistor, and the constant current source is connected to one of the transistors constituting the current mirror circuit. Thus, a current of a value obtained by dividing the DC bias current value supplied to the output transistor by the predetermined multiple is output.

In such a configuration, the emitter area of one of the transistors forming the current mirror circuit is set to, for example, A times the emitter area of the other transistor. , I.e., the current flowing as a DC bias current to the output transistor is I, and the current amplification factor of the two transistors constituting the current mirror circuit is β. , (1 + 1 / A) I / β flows. By increasing A, this current is calculated as I / β
This current value is approximately equal to the current I / β flowing through the base, assuming that the current amplification factor of the output transistor is also β.
Therefore, unlike the conventional case, the transistor for base current compensation does not flow a current as large as the output current,
Base current compensation is performed, and current consumption is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The members, arrangements, and the like described below do not limit the present invention, and can be variously modified within the scope of the present invention. First, a configuration of an amplifier circuit to which a base current compensation circuit according to an embodiment of the present invention is applied will be described with reference to FIG. This amplifying circuit is roughly divided into a differential amplifier 12, an output circuit 13, and a base current compensating circuit 14 according to an embodiment of the present invention. The dynamic amplifier 12 has two input terminals 10
After the difference between the signals input to a and 10b is amplified, an output signal is obtained from the output terminal 15 via the output circuit 13.

The differential amplifier 12 includes first and second PNP
Type transistors ("Q1", "Q
2 "), which is composed mainly of 1 and 2
And the emitters of the second PNP transistors 1 and 2 are:
They are connected to each other and to a power supply line to which a power supply voltage Vcc is applied via a first constant current source 16. On the other hand, the collectors of the first and second PNP transistors 1 and 2 are connected to third and fourth NPN transistors as so-called active loads acting as load resistances ("Q3" and "Q3" in FIG. 1, respectively). The collectors of the third and fourth NPN transistors 3 and 4 are grounded, respectively. In addition,
The collector and the base of the third NPN transistor 3 are connected to each other, and the third NPN transistor 3 is in a so-called diode connection state.

The bases of the first and second PNP transistors 1 and 2 are connected to the first and second PNP transistors 1 and 2 to which a signal is input.
Input terminals ("-IN", "+ I
N) 10a, 10b are connected. An output signal of the differential amplifier 12 is supplied to a fifth PNP transistor ("Q5" in FIG. 1) as an output transistor.
After the current is amplified by 5), the output terminal (FIG. 1)
In this case, the data is output from an “OUT” 15). That is, the fifth PNP transistor 5
Is connected to the connection point between the collector of the second PNP transistor 2 and the collector of the fourth NPN transistor 4, while the emitter thereof connects a part of the base current compensation circuit 14 described below. While connected to a positive power supply line via an eighth PNP transistor (denoted as “Q8” in FIG. 1) 8, the collector is grounded.

The base current compensating circuit 14 includes seventh and eighth PNP transistors (indicated as "Q7" and "Q8" in FIG. 1, respectively) constituting a current mirror circuit.
8, a so-called Darlington-connected tenth PNP transistor (referred to as “Q10” in FIG. 1) 10 connected to the seventh PNP transistor 7 for base current;
And a second constant current source 17. That is,
The seventh and eighth PNP transistors 7, 8 have their bases connected to each other, and their emitters are both connected to a power supply line to which a power supply voltage Vcc is applied. The collector of the seventh PNP transistor 7 is grounded via the second constant current source 17, while the collector of the seventh PNP transistor 7 is connected to the eighth constant current source 17.
The collector of the PNP transistor 8 is connected to the fifth PNP transistor.
Output terminal 15 connected to the emitter of transistor 5
It is connected to the.

A tenth PNP transistor 10 for base current compensation has its base connected to the collector of the seventh PNP transistor 7 and its emitter connected to the seventh and eighth PNP transistors 7,8. While connected to the base, its collector is connected to the collector of the first PNP transistor 1 constituting the differential amplifier 12 via the bases of the third and fourth NPN transistors 3, 4. It has become. Therefore, the seventh PN
The P-type transistor 7 is in a so-called diode-connected state via the base and the emitter of the tenth PNP transistor 10.

Here, each of the seventh and eighth PNP transistors 7 and 8 constituting the current mirror circuit of the base current compensation circuit 14 has an emitter area equal to the emitter area of the seventh PNP transistor 7. Is set to 1, the area of the emitter of the eighth PNP transistor 8 is formed to have a size A which is a predetermined multiple.

In the above configuration, in the amplifier circuit to which the base current compensation circuit according to one embodiment of the present invention is applied, current consumption is reduced as follows. First, the output current of the second constant current source 17 is set to I2 / A. here,
A is the seventh PNP transistor 7 as described above.
PNP transistor 8 for the emitter area of
The eighth PN when the emitter area of the seventh PNP transistor 7 is 1,
It is the emitter area ratio of the P-type transistor 8, in other words, the gain of the current mirror circuit. Also, I2 is
This is the magnitude of the DC bias current to be passed through the fifth PNP transistor 5.

Here, if the collector current of the seventh PNP transistor 7 is I _C7 , the base current is I _B7 , and the base current of the eighth PNP transistor 8 is I _B8 ,
The following relationship is established between the output current of the second constant current source 17, the collector current of the seventh PNP transistor 7, and the base current of the tenth PNP transistor 10.

I 2 / A = I _C7 + I _B10 = I _C7 + (I _B7 + I _B8 ) / β

Here, β is the current amplification factor of the tenth PNP transistor 10. Therefore, if β is sufficiently large, the current flowing from the bases of the seventh and eighth PNP transistors 7 and 8 to the second constant current source 17 via the base of the tenth PNP transistor 10 is made sufficiently small. The seventh PNP transistor 7
Of the collector current I _C7 ≒ I 2 / A.

Then, a current that is A times the collector current I _C7 of the seventh PNP transistor 7, that is, I 2 flows through the eighth PNP transistor 8 by the action of the current mirror circuit. Therefore, the current amplification factor of the fifth PNP transistor 5 is equal to the tenth PN transistor.
Assuming β as in the PN transistor 10, a current of I2 / β flows through the base of the fifth PNP transistor 5.

On the other hand, the tenth PNP transistor 10
Assuming that the current I _C10 on the collector side is substantially equal to the current on the emitter side, I _C10 = I _B7 + I _B8 . Here, assuming that the current amplification factors of the seventh and eighth PNP transistors 7 and 8 are also the same as those of the tenth PNP transistor 10, the base currents I _B7 and I _{B8 become}
It can be expressed as:

I _B7 = I _C7 / β = (I 2 / A) / β

I _B8 = I 2 / β

Therefore, from these relations, I _C10
The following formula can be _summarized as I _C10 = (I 2 / A) / β + I
2 / β = (1 + 1 / A) I2 / β. That is, the first
A current of (1 + 1 / A) I2 / β flows into the collector of the first PNP transistor 1 as the collector current of the PNP transistor 0. Where A
Is set to a sufficiently large value, 1 + 1 / A ≒ 1, and
As a result, the current flowing into the first PNP transistor 1 becomes approximately I2 / β, which is equivalent to the fifth PNP described above.
This is substantially equal to the base current of the NP transistor 5.

In this embodiment, as described above, the base current of the fifth PNP transistor 5 = the tenth PNP transistor
Not only can the base current of the fifth PNP transistor 5, which is the transistor for output of the amplifier circuit, be compensated as the collector current of the transistor 10, but also the tenth PNP transistor for base current compensation. The current I2 / β, which is 1 / β of the current I2 flowing through the fifth output PNP transistor 5, may be applied to the transistor 10, so that the current consumption is greatly reduced.

In the above-described embodiment, the third and fourth NPN transistors 3, 4 serving as active loads are used.
, Except that the third and fourth transistors 3 and 4 may be of PNP type and the other transistors may be of NPN type. . Further, a part may be constituted by a so-called FET instead of the bipolar transistor.

[0025]

As described above, according to the present invention, the base current compensation is performed by using the gain of the current mirror circuit. This has the effect of saving power by reducing the current. Further, since the base current compensation is reliably performed, it is possible to provide an amplifier circuit having a high amplification factor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration example of an amplifier circuit having a base current compensation circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional circuit example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st PNP transistor 2 ... 2nd PNP transistor 5 ... 5th PNP transistor 12 ... Differential amplifier 13 ... Output circuit 14 ... Base current compensation circuit

Claims (5)

[Claims] An output transistor having a base connected to an output side of the second transistor and operating as an emitter follower, among first and second transistors constituting a differential amplifier. A base current compensation circuit in an amplifier circuit configured to obtain an output of the second transistor, wherein a current mirror circuit using two transistors is provided, and one of the transistors constituting the current mirror circuit is Connecting one of the transistors to the output transistor so that a DC bias current is supplied to the output transistor, connecting a constant current source to the other transistor,
The base current compensating transistor is connected via the base and the emitter of the base current compensating transistor so that the other transistor is in a diode-connected state, and the output side of the base current compensating transistor is connected to the difference side. The constant current source is connected to an output side of a first transistor constituting a dynamic amplifier, and an emitter area of one transistor constituting the current mirror circuit is set to a predetermined multiple of an emitter area of the other transistor. A base current compensating circuit for outputting a current obtained by dividing a DC bias current value supplied to the output transistor by one of transistors constituting a current mirror circuit by the predetermined multiple. 2. The output side of the first and second transistors constituting the differential amplifier is provided with an active load composed of two transistors, the bases of the two transistors are connected, and one of the transistors is connected to the other. 2. The transistor according to claim 1, wherein the first transistor is diode-connected to an output side of the first transistor, and the other transistor is connected to an output side of the second transistor.
The described base current compensation circuit. 3. The base current compensation circuit according to claim 1, wherein the transistor is a PNP transistor. 4. The base current compensation circuit according to claim 1, wherein the transistor is an NPN transistor. 5. The base current compensation circuit according to claim 1, wherein the transistor is an FET.