JPH0677743A - Audio amplifier - Google Patents

Abstract

PURPOSE:To reduce the invasion of high frequency noise through a feedback circuit to an inverted input terminal by parallelly connecting a capacitor to an emitter resistor at the push-pull output step of the audio amplifier. CONSTITUTION:The high frequency noise invading from an output terminal 5 is absorbed through capacitors 3a and 3b to the emitters of transistors Tr 1a and 1b with low output impedances. Therefore, the rate of the high frequency noise invading through a feedback resistor 11a to the inverted input terminal of a voltage amplifying step is considerably reduced. Accordingly, the generation of distortion such as TIM distortion caused by the high frequency noise is reduced. A capacitor 4 connecting the emitters of the NPN Tr 1a and the PNP Tr 1b prevents the imbalanced operations of both of Tr 1a and 1b in a high frequency area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio amplifier.

[0002]

2. Description of the Related Art FIG. 2 shows an audio amplifier according to the prior art. In the audio amplifier, a high-frequency noise is induced in the core wire 7a of the connection cable 7 due to an inter-device current including a high frequency flowing between the devices connected via the connection cable 7, and an external noise radio wave is generated in the connection cable. High-frequency noise enters the circuit through the output terminal 6 for the reason such as entering the circuit 7. Generally, when high frequency noise is input to an input terminal of an audio amplifier, it causes harmful distortion such as TIM distortion. In the conventional audio amplifier having the push-pull output stage, since the emitter resistors 2a and 2b for stabilizing the bias currents of the transistors 1a and 1b, the high frequency noise that has entered from the output terminal 6 is generated in the transistors 1a and 1b. It is not absorbed enough by the emitter and enters the feedback circuit and the feedback resistor 11
It is input to the inverting input terminal 10a of the voltage amplification stage through a. It has been found by the research of the inventor that this causes a strain such as TIM strain. TIM distortion and the like due to high frequency noise are also very detrimental to the sense of hearing, and it has been difficult for the conventional technology to provide an audio amplifier with good sound quality.

[0003]

The problem to be solved by the present invention is to reduce the high-frequency noise that has entered from the output terminal 6 of the audio amplifier to enter the feedback circuit, and the high-frequency noise causes distortion in the amplifier. Is to provide an audio amplifier with good sound quality in terms of hearing.

[0004]

In order to achieve the above object, a push-pull output stage NPN transistor and a P-type transistor are provided.
A capacitor is connected in parallel to both emitter resistors of the NP-type transistor, and the NPN-type transistor and the PNP are connected.
The emitters of the type transistors are connected via a capacitor.

[0005]

In the audio amplifier configured as described above, the high frequency noise that has entered from the output terminal 6 passes through the capacitors 3a and 3b and is absorbed by the emitters of the transistors 1a and 1b having a low output impedance, as shown in FIG. Therefore, the proportion of high frequency noise that enters the inverting input terminal 10a of the voltage amplification stage through the feedback resistor 11a is significantly reduced. Therefore, the occurrence of distortion such as TIM distortion caused by high frequency noise is reduced. This is because the capacitor 4 in which the emitters of the NPN transistor 1a and the PNP transistor 1b are connected to each other prevents unbalanced operation of the NPN transistor 1a and the PNP transistor 1b in a high frequency region.

[0006]

EXAMPLE FIG. 1 shows an example of the present invention, in which 1a is an NP.
N transistor, 1b is PNP transistor, 2 is emitter resistance, 3 is a capacitor added according to the present invention, 4 is
Is a capacitor added by the present invention, 5 is an output resistance,
6 is an output terminal, 7 is a connection cable, 8 is a power supply, 9 is a bias circuit, 10 is a voltage amplification stage, 10a is an inverting input terminal,
10b is a non-inverting input terminal, 11 is a feedback resistor, and 12 is an input terminal.

[0007]

With such a structure, the high frequency noise that has entered from the output terminal 6 of the audio amplifier passes through the output resistor 5, the capacitors 3a and 3b, and the transistors 1a and 1b having a low output impedance. Is absorbed by the emitter of. Therefore, high frequency noise is less likely to enter the feedback circuit, and distortion caused by high frequency noise such as TIM distortion is reduced. Further, the higher the high frequency high frequency noise that the voltage amplification stage becomes unable to follow and the more easily TIM distortion is generated, the lower the impedance of the capacitors 3a and 3b, so that the transistors 1a and 1b are effectively absorbed. Therefore, an audio amplifier with extremely good sound quality can be obtained.

Further, the capacitor 4 is for averaging the characteristic differences such as the output impedance of the NPN type transistor and the PNP type transistor in the high frequency region and preventing unbalanced operation with respect to high frequency noise.

In the above embodiment, the NPN type transistor and the P
An audio amplifier having an output stage composed of NP-type transistors has been described. The N-type field effect transistor and the P-type field effect transistor are combined, and the emitter is replaced with the source, the base is replaced with the gate, and the collector is replaced with the drain. Therefore, it is possible to replace the audio amplifier with the push-pull output stage.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an audio amplifier according to the present invention.

FIG. 2 is a circuit diagram of a conventional audio amplifier.

[Explanation of symbols]

1 Transistor 1a NPN-type transistor 1b PNP-type transistor 2 Emitter resistance 2a NPN-type transistor emitter resistance 2b PNP-type transistor emitter resistance 3 Condenser according to the present invention 3a NPN-type transistor emitter resistance according to the present invention Capacitor 3b Capacitor according to the present invention connected in parallel to the emitter resistance of the PNP type transistor 4 Capacitor according to the present invention for connecting the emitter of the NPN type transistor and the emitter of the PNP type transistor 5 Output resistor 6 Output terminal 7 Connection cable 7a Core wire of connection cable 8 power supply 8a positive power supply 8b negative power supply 9 bias circuit 10 voltage amplification stage 10a inverting input terminal 10b non-inverting input terminal 11a feedback resistor 11b feedback resistor 12 input terminal

Claims (2)

[Claims] 1. An audio amplifier having a push-pull output stage composed of an NPN type transistor and a PNP type transistor, wherein a capacitor is connected in parallel to an emitter resistance of the output stage and an NPN type transistor and a PNP type transistor are provided. An audio amplifier that is characterized by connecting the emitters of each other through a capacitor. 2. In an audio amplifier having a push-pull output stage composed of an N-type field effect transistor and a P-type field effect transistor, a capacitor is connected in parallel to the source resistance of the output stage, and N Amplifier, wherein the sources of a P-type field effect transistor and a P-type field effect transistor are connected via a capacitor.