JPH0257723B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an audio signal amplifier with a single amplification stage and a push-pull amplification stage at the output end stage.

[Technical background of the invention and its problems]

2. Description of the Related Art Conventional audio signal amplifiers include those shown in FIGS. 1 and 2, for example.

The audio signal amplifier shown in FIG. 1 has a single amplification stage as the final output stage, and includes a transistor 1 for power amplification, and a transformer 2 for impedance matching between a load 3 and the output of the transistor 1. When using this audio signal amplifier,
Transistor 1 is designed so that the output signal can swing equally on both the (+) side and (-) side with respect to the input signal.
The operating point of is chosen to be the midpoint of the active region. Therefore, current amplification is performed on the input signal in the linear region of transistor 1, so in the audio signal amplifier shown in Figure 1, the linearity of the output signal is good, but the amplitude is determined by the linear region of transistor 1, resulting in a large output. There was a drawback that I couldn't get it.

The audio signal amplifier shown in FIG. 2 has an output final stage consisting of a push-pull amplification stage, which electromagnetically couples the output signals of the transistors 4 and 5 to power amplification transistors 4 and 5, and further impedance matching with the load 7. It consists of a transformer 6. This audio signal amplifier consists of transistors 4 and 5.
For example, a positive phase input signal is input to transistor 4, a negative phase input signal is input to transistor 5, the current is amplified, and the outputs of transistors 4 and 5 are electromagnetically coupled by a transformer 6. , supplies an output signal to the load 7. That is, since the positive side of the input signal is amplified by the transistor 4 and the negative side is amplified by the transistor 5, switching is performed at the 0 point of the output signal.

However, when using the audio signal amplifier shown in Fig. 2, transistors 4 and 5 only need to amplify the positive and negative sides of the input signal separately, and by deepening the bias and shifting the operating point, a large amplitude output signal can be generated. However, as the bias deepens, it becomes class AB or class B, which causes problems due to discontinuity or nonlinearity of the operating point at the zero point crossing, and has the drawback of increasing so-called switching distortion. .

[Purpose of the invention]

The present invention has been made in view of the above, and provides an audio signal amplifier which eliminates the above-mentioned drawbacks and improves the distortion rate for small signals by eliminating the switching distortion that occurs when the output signal is at zero point in the push-pull amplification stage. The purpose is to provide

[Embodiments of the invention]

FIG. 3 is a block diagram showing one embodiment of the present invention.

The output of the preamplifier 11 is supplied to an amplifier 12 with a single final stage and an amplifier 13 with a push-pull final stage for current amplification. supply,
The output of the amplifier 13 is supplied between the other end of the primary winding of the transformer 14 and the intermediate tap, and a load 15 is connected to the secondary winding of the transformer 14.

The inputs of amplifiers 12 and 13 are both supplied with the output signal of preamplifier 11, but the ground side is the same as the ground side of preamplifier 11 in the case of amplifier 12, and the ground side of transformer 1 in the case of amplifier 13.
4 as the intermediate tap, ie, the hot side of the amplifier 12. Further, the voltage amplification degree of the amplifiers 12 and 13 is "1" when the transformer 14 is loaded.

The operation of one embodiment of the present invention constructed as described above will be explained with reference to FIG.

When a small input signal is supplied to a point A, that is, the preamplifier 11, a signal obtained by amplifying the input signal is outputted to a point B, that is, the output terminal of the preamplifier 11.
The signal is supplied to amplifiers 12 and 13. The amplifier 12 is within the linear region with respect to the signal level at point B. As a result, the voltage waveform at the output end of the amplifier 12, ie, the point C, is the same as the voltage waveform at the point B. On the other hand, since the voltage waveform at point B and the voltage waveform at point C are the same, the input to the amplifier 13 is relatively zero. As a result, no output appears at the output end of the amplifier 13, that is, at point D. Further, the transformer 14 in this case functions simply as an impedance converter and outputs a signal to the load 15, and the entire system equivalently functions as a single amplifier.

Next, when a large input signal is supplied to point A, assuming that this large input signal is within the linear region of the preamplifier 11, the linear output of the input supplied to point A is displayed at point B. You will be killed. This signal at point B becomes the input to amplifiers 12 and 13. Since the amplifier 12 is out of the range for the signal level at point B, the voltage waveform at point C becomes a waveform that is clipped at the top and bottom. On the other hand, the difference between the voltage at point B and the voltage at point C is supplied to the amplifier 13 as an input signal, and the output waveform of the amplifier 13 is at the point CD, which is the same as the clip part waveform shown by the broken line in FIG. The waveform becomes intermittent and discontinuous.

A voltage with a clipped waveform at point C is applied to the intermediate tap of the transformer 14, and a voltage with a discontinuous waveform at point D is applied to the other end of the transformer 14.
The discontinuous waveform at point is an addition to the clipped waveform at point C, so if the electromagnetically coupled waveform is viewed from the reference ground, the clipped waveform at point C and D
The waveform is a superimposed waveform of the discontinuous points, and is the same as the waveform at point B. Therefore, the output waveform at point E is no longer distorted.

That is, as the amplified output, an output having the same waveform as that which would have been generated if the linear region of the amplifier 12 was wide is obtained by electromagnetic coupling, and signal switching is performed at the clip point of the amplifier 12.

In the embodiment of the present invention described above, the case where the voltage gain of the amplifier 12 is 1 has been explained. However, when the gain is 1 or more, as shown in FIG. A similar effect can be achieved by inserting a preamplifier 16 with a gain equal to the gain.

〔Effect of the invention〕

As explained above, according to the present invention, the zero point crossing portion of the signal is entrusted to a single amplifier, and since it is a continuous portion in the operating region of this amplifier, switching distortion does not occur at the zero point crossing, and the distortion rate in small signals is reduced. Improvements will be made.

A large signal input is amplified by a push-pull amplifier, and it is possible to obtain a large output, which is the inherent advantage of a push-pull amplifier. Furthermore, since switching is performed at a point where the linearity of a single amplifier is lost, even if switching distortion occurs at this level, it will be a small value in terms of relative ratio to the output signal.

[Brief explanation of drawings]

1 and 2 are circuit diagrams of a conventional audio amplifier, FIG. 3 is a block diagram showing an embodiment of the present invention, FIG. 4 is a waveform diagram for explaining the operation of an embodiment of the present invention, and FIG. FIG. 5 is a block diagram showing an application example of one embodiment of the present invention. 11 and 16... preamplifier, 12 and 1
3...Amplifier, 14...Transformer, 15...Load.

Claims (1)

[Claims] 1. A preamplification stage that voltage amplifies an input signal, a class A single current amplification stage that current amplifies the output of the preamplification stage, and an output voltage of the preamplification stage and an output of the class A single current amplification stage. A class A, class AB, or class B push-pull current amplification stage that amplifies current by inputting the difference between the two current amplification stages, and a push-pull current amplification stage that serves as an output load for both the current amplification stages and electromagnetically couples the outputs of the two current amplification stages from the secondary side. and a transformer for obtaining an output signal superimposed on the audio signal amplifier.