JPH0515525U - Power Amplifier - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a flat frequency characteristic for a power amplifier that amplifies an audio signal. [Structure] Transistors Q ₁ , Q ₃ and Q ₂ , which are used for both an amplification path (A) for amplifying a positive signal and an amplification path (B) for amplifying a negative signal in an input audio signal. Q ₄
Are used as emitter followers, respectively.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a class AB amplification power amplifier, and more particularly to a power amplifier in which input and output transistors are respectively connected to emitter followers.

[0002]

[Prior Art]

 A video signal recording / reproducing apparatus such as a VTR has a power amplifier for amplifying the power of the video signal, and the amplified video signal is supplied from the output terminal of the VTR to the input terminal of the video signal of the television.

FIG. 2 shows an example of a conventional power amplifier circuit. In this circuit, 1 is a video signal input terminal, Q _{11 to} Q ₁₅ are transistors, 10 and 11 are constant current sources, D is a diode for generating an idling current, and Z is an impedance connected to the output terminal 2. Dance, R is a resistance, and V _CC is a power supply.

Among the video signals input to the input terminal 1, the positive signal component flows through the path of the dotted line (A) passing through the emitter electrodes of the transistors Q ₁₁ and Q ₁₂ , while the negative signal component is the transistor. The power-amplified video signal is output to the output terminal 2 via the capacitor C through the path of the solid line (B) passing through Q ₁₃ , Q ₁₄ , and Q ₁₅ .

[0005]

[Problems to be solved by the device]

In the route of (B), the signal is inverted by the collector of the transistor Q ₁₃ , and also inverted by Q ₁₅ and amplified by a certain amplification degree. However, in the emitter follower circuit of the route of (A), such signal inversion is performed. And does not have an amplification factor of 1 or more.

As a result, the signal flowing through the path (B) has a phase delay and is amplified as compared with the signal output through the path (A). As a result, the frequency characteristic of the signal output to the output terminal 2 has a peak in the 20 to 30 MHz band as shown by the dotted line in FIG. When the frequency characteristic is extended in this way, an oscillation phenomenon may appear.

Further, the negative signal waveform that has passed through the path (B) has various problems that ringing occurs as shown in FIG.

An object of the present invention is to provide a power amplifier that solves the above conventional problems.

[0009]

[Means for Solving the Problems]

 In the power amplifier according to the present invention, the bases of the first PNP transistor and the second NPN transistor are connected to the input terminals, respectively, and the base of the third NPN transistor is connected to the emitter of the first transistor. The emitter of the second transistor is connected to the base of the fourth PNP transistor, and the emitters of the third and fourth transistors are connected to the output terminal via a capacitor.

[0010]

[Action]

 Since the amplification transistors of the (A) path through which the positive signal of the input signal passes and the (B) path through which the negative signal passes are all connected in the emitter follower type, the (A) and (B) paths are the same. It is formed by the amplifier circuit with the configuration, and both are amplified under the same condition, and the frequency characteristic can be made flat.

[0011]

【Example】

 FIG. 1 shows an embodiment of the power amplifier according to the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

Q _{1 to} Q ₄ are transistors, and 20 and 21 are constant current sources. Z is the input impedance of the video input terminal of the television connected to the output terminal 2. The emitters of the transistors Q ₁ and Q ₂ are connected to the power source V _CC and the ground via the constant current sources 20 and 21.

The amplification path indicated by the dotted line (A) is the transistor Q.₁, Q₃, Each of which has an emitter follower connection. On the other hand, the amplification path of the solid line (B) is the transistor Q.₂, Q _Four , And these are also used as emitter follower types, respectively.

Transistor Q₁, Q₂Does class A operation, Q₃, Q_FourIs designed to perform class AB operation. Depending on the level of the positive signal component in the video signal input to the input terminal 1, the transistor Q₁Emitter current decreases, and the current from the constant current source 20 is Q ₃ Flows as a base current, is amplified by current, and is output (E) to the output terminal 2 via the capacitor C.

On the other hand, in the negative period of the video signal, a current flows through the emitter of the transistor Q ₂ in accordance with the level, and when the current is small, the base current of Q ₄ increases and the current width increases. The generated emitter current of Q ₄ is supplied (F) from the capacitor C. It should be noted that the transistors Q ₃ and Q ₄ are made to have an idling current of 2 to 3 mA by the V _F of Q _{1 to} Q ₄ and the constant current sources 20 and 21 to perform class AB operation. Improves signal waveform distortion.

Since both the paths (A) and (B) have the same configuration as the emitter-follower type amplifier circuit, the gains of both paths are substantially the same and there is no phase difference. Therefore, a peak does not occur in the frequency characteristic as in the conventional circuit, and a flat characteristic can be obtained over the desired band as shown by the solid line in FIG. In addition, there is no fear of oscillation, no ringing occurs in the negative period of the video signal, and no distortion of the output signal waveform.

The power amplifier circuit according to the embodiment of FIG. 1 has been described as an example applied to a wide band video amplifier, but it is also suitable for use in a narrow band audio amplifier at a lower frequency.

[0018]

[Effect of the device]

 According to the power amplifier according to the present invention described above, a flat frequency characteristic can be obtained, there is no fear of oscillation and distortion of the output signal waveform, and the number of parts can be reduced as compared with the conventional one, and the circuit configuration is simple. It has various great effects such as

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of an example of a conventional power amplifier.

FIG. 3 is a diagram showing frequency characteristics of the present invention and a conventional one.

FIG. 4 is a diagram showing a conventional output waveform.

[Explanation of symbols]

1 Input Terminal 2 Output Terminal Q ₁ First Transistor Q ₂ Second Transistor Q ₃ Third Transistor Q ₄ Fourth Transistor C Capacitor

Claims (1)

[Scope of utility model registration request] 1. A base of a first PNP type transistor and a base of a second NPN type transistor are respectively connected to an input terminal, and a base of a third NPN type transistor is connected to an emitter of the first transistor. A power amplifier in which the base of a fourth PNP transistor is connected to the emitter of the second transistor, and the emitters of the third and fourth transistors are connected to the output terminal via a capacitor.