JPH0750849B2 - Amplifier circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an amplifier circuit that is frequently used in various electronic devices such as audio devices, and is particularly suitable for semiconductor integrated circuits.

[Background Art] "Analog Integrated Circuit" (September 15, 1985, published by Modern Science Co., Ltd., P186-188) consists of a first stage differential amplifier circuit, class A drive amplifier circuit, and class B push-pull circuit. , + V,-
An operational amplifier that operates using two positive and negative V power supplies is disclosed.

According to a study by the present inventor regarding the operational amplifier, the operational amplifier has an extremely large open-loop voltage gain, and therefore, in order to prevent undesired oscillation when negative feedback is applied, the operational amplifier of the class A drive amplifier circuit It was found that a large-capacity phase compensation capacitor must be connected between the input and output. The operational amplifier is made into a semiconductor integrated circuit (hereinafter referred to as an IC). However, since the phase compensating capacitor is formed in the semiconductor chip, as shown in FIG. We have found that a large area is required in the semiconductor chip, which reduces the degree of IC integration.

[Object of the Invention] The present invention has been made in view of the above problems, and an object of the present invention is to perform an amplifying operation with a single power supply that can obtain only two power supply potentials and to have a DC power supply of an input terminal. An object of the present invention is to provide an amplifier circuit that can perform an amplifying operation even when the potential is near the power supply potential and that is suitable for an IC that does not require a large-capacity phase compensation capacitor.

[Outline of the Invention] The outline of the invention disclosed in the present application will be briefly described as follows.

That is, a pair of input first conductivity type transistors whose collectors are connected to one terminal of a power source, a pair of second conductivity type transistors which form a current mirror by being interposed on the emitter side of the pair of transistors, and a collector being a power source. A second conductivity type output transistor connected to the other terminal of the output follower to form an emitter follower output circuit, a level shift element interposed between the emitter follower output of the output transistor and the output terminal, and the pair of inputs. The input signal is supplied to the base of one of the transistors for use, and the negative feedback signal from the output terminal is supplied to the base of the other transistor.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

In the drawings, the same reference numerals indicate the same or corresponding parts.

1A and 1B show a first embodiment of an amplifier circuit to which the present invention is applied.

The amplifier circuit A1 shown in the figure is an IC (semiconductor integrated circuit),
Circles enclosing numbers indicate the external connection terminals of the IC.

The amplifier circuit A1 includes a first-stage amplifier circuit that amplifies a signal supplied from the input terminal (+), as shown in FIG.
An output circuit that has an output circuit that amplifies the output of the first-stage amplifier circuit and supplies it to the output terminal forms a voltage follower type amplifier circuit that performs 100% negative feedback as shown in FIG. . The operation is performed by one power supply of only Vcc and GND (ground potential).

The amplifier circuit A1 shown in FIG. 9A has the first conductivity type, that is, PN.
P-type bipolar transistors Q1 and Q2, second conductivity type or NPN-type NPN bipolar transistors Q3 to Q6, a first current source CS1 and a second current source which are constant current control circuits, respectively.
It is composed of a current source CS1 and a resistor R1.

The transistors Q1 to Q4 and the current sources CS1 and CS2 form a part of the first-stage amplifier circuit, and the transistors Q5 and Q6 and the resistor R1 form a part of the output circuit.

In this case, Q1 and Q2 are input transistors, and Q5 and Q6 are output transistors. Also, Q3, Q4
Is a current mirror, Q5 is an emitter follower output circuit, Q6
Form level shift elements, respectively.

Transistors Q1 to Q5, current sources CS1 and CS2, resistor R1
The connection state of is as follows.

That is, the input PNP bipolar transistor Q1
The base is connected to the input terminal (external terminal number 1), and the collector is connected to one terminal (Vcc) of the power supply.

NPN bipolar transistor Q3 has PNP emitter
It is connected to the emitter of transistor Q1.

The first current source CS1 is connected to the other terminal (Vcc) of the power supply and the NPN.
It is provided between the collector of the transistor Q3 and the current Io flowing from the power supply to the NPN transistor Q3 side is controlled to be constant.

The output NPN bipolar transistor Q5 has a base connected to the collector of the NPN transistor Q3 and a collector connected to the other terminal (Vcc) of the power supply.

Another output NPN bipolar transistor Q6 is for the above output with its base and collector connected.
It is provided in series between the emitter of the NPN transistor Q5 and the output terminal (external terminal number 3).

The other input PNP bipolar transistor Q2 has a base connected to the output terminal and a collector connected to one terminal (GND) of the power supply.

The NPN bipolar transistor Q4 is diode-connected by connecting the collector and the base, the emitter is connected to the emitter of the input PNP transistor Q2, and the base is connected to the base of the NPN transistor Q3.

The second current source CS2 is connected to the other terminal (Vcc) of the above power source and the above
A current I that is provided in series between the collector of NPN transistor Q4 and flows from the power supply to the side of NPN transistor Q4 above.
Control o'constantly.

With the above configuration, as shown in FIG.
A voltage-following (voltage follower) amplifier circuit that performs 100% negative feedback is formed.

The current Iout flowing through the transistor Q5 of the output circuit is
It is a current flowing with the emitter follower operation of the transistor Q5, and is controlled according to the output voltage of the first-stage amplifier circuit taken out from the collector side of the transistor Q3.

Next, the operation will be described.

Open loop voltage gain GV of amplifier circuit A1 shown in FIG. 1 (A)
When o is represented by a mathematical model, it becomes as shown in the following expression (1).

GVo = (hFEQ5 × R1) / (reQ1 ＋ reQ2 ＋ reQ3 ＋ reQ4) ……
(1) In this case, hFEQ5 is the current amplification factor of transistor Q5, reQ1
~ ReQ2 is the emitter resistance of the transistors Q1 to Q4.

That is, the first-stage amplifier circuit composed of the transistors Q1 to Q4 forms a composite differential amplifier circuit, and the gain of this composite differential amplifier circuit is limited by the sum of the equivalent emitter resistances of the four transistors Q1 to Q5. To be done.

At the same time, since the output circuit is composed of the emitter follower of the transistor Q5, the voltage gain GVo becomes small, which makes it unnecessary to provide a phase compensation capacitor between the base and collector of the transistor Q3. .

On the other hand, when the input signal Vin is supplied, the output signal Vout is obtained by the above circuit operation, but the negative feedback signal VNF is fed back through the path as shown by the arrow in FIG. If it is good, give it.

Since the input transistors Q1 and Q2 are PNP transistors and their collectors are connected to one terminal (GND) of the power supply, the DC potential of the input terminal (external terminal number 1) is almost the GND potential, The above amplifying operation can be performed using the + Vcc power supply which is one power supply.

As described above, the above-mentioned amplifier circuit A1 can be operated by one power supply that can obtain only two power supply potentials (Vcc-GND), and even if the DC potential of the input terminal is near Vcc, it is small. With the negative feedback amount, the voltage follower operation by 100% negative feedback can be stably performed.

Furthermore, since the voltage amplification gain in the absence of feedback is low, the operation can be stabilized without a large capacity phase compensation capacitor.

FIG. 2 shows an amplifier circuit according to a second embodiment of the present invention, in which the conductivity type of the bipolar transistor (PNP and NPN) is opposite to that of the first embodiment described above. As a result, the connection direction to the power supply (Vcc-GND) is also reversed.

That is, in the amplifier circuit A1 of the second embodiment, the first-stage amplifier circuit is composed of NPN bipolar transistors Q21 and Q22 and PNP bipolar transistors Q23 and Q24, and the output circuit is composed of PNP bipolar transistors Q25 and Q26. Has been done.

In the case of the second embodiment, the input transistors Q21, Q2
Reference numeral 2 is an NPN transistor, but its collector is connected to the other terminal (Vcc) of the power supply, so that the DC potential of the input terminal (external terminal number 1) can be made approximately Vcc potential.

As a result, in the case of the second embodiment as well, it is possible to operate with one power supply that can obtain only two power supply potentials (Vcc-GND), and even if the DC potential of the input terminal is near Vcc, a small negative With the feedback amount, the voltage follower operation by 100% negative feedback can be stably performed. Since the voltage amplification gain in the absence of feedback is low, the operation can be stabilized without a large-capacity phase compensation capacitor.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. There is no end.

For example, in the amplifier circuit of the present invention, the need for a phase compensation capacitor is low, but it does not prevent the use of a small capacity phase compensation capacitor.

In the above description, the case where the present invention made by the present inventor is mainly applied to an audio amplifier circuit which is a field of application which is the background of the present invention has been described. However, the present invention is not limited to this and, for example, a video amplifier circuit. Alternatively, it can be applied to an amplifier circuit for other purposes.

[Effects of the Invention] The effects of typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, the amplification operation can be performed by one power supply that can obtain only two power supply potentials, and the amplification operation can be performed even when the DC potential of the input terminal is near the power supply potential, and the voltage amplification gain when there is no negative feedback. That is, there is an effect that the open loop voltage gain can be lowered to eliminate the need for a large capacity phase compensation capacitor.

[Brief description of drawings]

1 is a circuit diagram showing a first embodiment of an amplifier circuit to which the technique of the present invention is applied. FIG. 2 is a circuit diagram showing a second embodiment of an amplifier circuit to which the technique of the present invention is applied. Description] A1 …… Amplifier circuit Q1, Q2 …… PNP bipolar transistor Q3 to Q6 …… NPN bipolar transistor Q21, Q22 …… NPN bipolar transistor Q23 to Q26 …… NPN bipolar transistor Vin …… Input signal Vout ...... Output signal GND …… Ground battery (first or second power supply potential) Vcc …… Power supply (second or first power supply potential)

Continuation of the front page (56) References JP-A-50-103955 (JP, A) JP-B 52-19423 (JP, B2) JP-B 58-24042 (JP, B2)

Claims (1)

[Claims] 1. A first conductivity type first transistor having a base connected to an input terminal and a collector connected to one terminal of a power supply; and a second conductivity type having an emitter connected to the emitter of the first transistor. A second transistor, a first current source provided between the other terminal of the power supply and the collector of the second transistor, and a base connected to the collector of the second transistor,
A second transistor of the second conductivity type having a collector connected to the other terminal of the power source, a level shift element provided between the emitter of the third transistor and the output terminal, and a base connected to the output terminal. A diode connection in which a collector is connected to one terminal of the power source, a fourth transistor of the first conductivity type, an emitter is connected to the emitter of the fourth transistor, and a base is connected to the base of the second transistor. And a second current source provided between the other terminal of the power supply and the collector of the fifth transistor.