JPS5890808A - Pulse width modulating amplifier - Google Patents

Abstract

PURPOSE:To obtain a pulse width modulating amplifier with a good distortion factor, by modulating the pulse width of input signals and applying the amplitude modulation using the input signal. CONSTITUTION:A sound signal inputted to a terminal 10 is amplified by amplifiers 1, 2. A clipper 3 clips the sound signal at a prescribed level before a power amplifier becomes nonconductive (zero output). A clipped output is modulated for the pulse width at a comparator 5. Signals of the same pulse width are arranged for the clipped part. This pulse modulated wave is amplified at a pulse amplifier 6 and enters the clipper 7. The clipper 7 clips the pulse width modulating wave by taking an audio signal from the audio amplifier 2 as a bias voltage. The part clipped to this audio signal has a constant pulse width and the amplitude is proportional to the audio signal. This signal is amplified for pulse power. Thus, an output signal without distortion in the demodulated waveform can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse width modulation amplifier, and a pulse width modulation amplifier for use in medium and short wave broadcasting equipment, which amplifies the power of audio by 50%.

Generally, this type of pulse width modulation amplifier has a single-ended pulse power amplifier at the final stage.

However, in a single-ended pulse power amplifier, a falling waveform of the pulse is formed due to the output capacitance of the power amplification element. Figure 1 shows a low-pass filter (L) for demodulating this pulse power amplifier (TR, D).
1, L2, C1, C2) and loads, and FIGS. 2 and 3 show waveforms at points A and B of the circuit of FIG. 1, respectively. When the pulse width of the pulse width modulation signal becomes narrower and the conduction time (TON) becomes shorter than a certain value,
The output suddenly drops to zero due to the output capacitance. (FIG. 2) When such a waveform is demodulated using a low-pass filter, a part of the demodulated wave becomes the ground potential as shown in FIG. 3, resulting in a waveform with so-called protrusions.

In order to eliminate this pop-up, the conventional power method eliminates the pop-up and improves it, but it has the disadvantage that the distortion rate worsens because it is doubly modulated by pulse width modulation and pulse amplitude modulation, resulting in a hill. This increases the distortion rate, so the distortion rate also increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pulse oscillation modulation amplifier with no jumps in the demodulated waveform and with less distortion.

A pulse width modulation amplifier according to the present invention includes: a first clipper that clips an input signal at a predetermined DC bias level; a means for pulse width modulating the output of the first clipper to output a pulse width modulated wave; a second clipper that clips the pulse width modulated wave with the input signal to amplitude-modulate the portion of the pulse modulated wave corresponding to the input signal removed by the first clipper with the input signal; and an output of the second clipper. The power amplifier is configured to include a power amplifier receiving the power, and means for demodulating the output of the power amplifier.

In the present invention, pulse width modulation is not performed on the portion of the modulated wave where the pulse width would be narrowed if pulse width modulation is performed, and pulse amplitude modulation is performed with the pulse width kept constant.

Next, the present invention will be described in detail with reference to the drawings. FIG. 4 is a block diagram showing one embodiment of the present invention.

This pulse width modulation amplifier includes an audio input terminal 10, an audio amplifier 1 that amplifies this audio signal, and an audio amplifier 1 that amplifies this audio signal.
an audio amplifier 2 that further amplifies the output of the audio signal, a clipper 3 that removes (clips) the portion below a certain level of the audio signal, and a triangular wave generator 4 that compares and amplifies the clipped audio signal and the triangular wave to determine the pulse width. A comparator 5 that modulates the pulse width modulated wave, a pulse amplifier 6 that amplifies the pulse width modulated wave, a clipper 7 that clips the amplified pulse width modulated wave using the audio signal as a bias voltage, a pulse power amplifier 8, and a pulse width modulated wave that amplifies the pulse width modulated wave. It consists of a low-pass filter 9 for demodulation. Negative feedback is applied from the low-pass filter 9 to the audio amplifier 1 to reduce distortion. Further, a load 10 is connected to the low-pass filter 9. FIG. 5 shows waveforms of various parts of the pulse width modulation amplifier 1 shown in FIG. Audio input terminal 10
The incoming audio signal is amplified by the audio amplifier 1.2.

Waveform 1 shows the input and output of the stage width device. (fflL, the magnitude of the amplitude is abstract). The clipper 3 clips the audio signal at a certain level before the pulse power amplifier 8 becomes a non-conducting state (output zero) K (waveform 2).
As explained with reference to FIG. 1, this happens suddenly when the pulse width of the pulse width modulated wave becomes narrower than a certain value. 1lI
A triangular wave (waveform 3) serving as the l carrier wave is generated by the triangular wave generator 4. This triangular wave is input to the comparator 50 together with the clipped audio signal. The signal pulse width modulated by the comparator 5 (waveform 4) has the same pulse width in a portion (time width T) corresponding to the audio signal clipped by the clipper 3. This pulse width modulated wave is transmitted to the pulse amplifier 6
It is amplified by Kuritsuno (enters 7).

The clipper 7 is a peak clipper that uses the audio signal input from the audio amplifier 2 as a bias voltage to clip the pulse width modulated wave. Since the pulse width of T) is constant and the amplitude is proportional to the audio signal, it becomes a pulse amplitude modulated wave.The pulse power amplifier 8 is
The power of the pulse width modulated wave and pulse amplitude modulated wave output from the clipper 7 is amplified. Both the pulse width modulated wave and the pulse amplitude modulated wave are demodulated by the low pass filter 9. Here, the audio input to the audio input terminal 10 is power amplified without distortion, and a demodulated wave (waveform 1) with a good distortion rate can be obtained without any jumps in the demodulated signal.

As explained above, according to the present invention, it is possible to obtain a pulse width modulation amplifier with no jumps in the demodulated waveform and a good distortion rate.

2 and 3 are signal waveform diagrams at points A and B of the circuit shown in FIG. 1, respectively, FIG. 4 is a block diagram showing an embodiment of this invention, and FIG. FIG.

In FIG. 5, waveform 1 is the input/output waveform of the audio amplifier 1.2 and the output of the low-pass filter 9, waveform 2 is the output waveform of the clipper 3, waveform 3 is the output waveform of the triangular wave generator 4, and waveform 4 is the comparison waveform. Waveform 5 shows the output waveforms of the clipper 7 and the pulse power amplifier 8, respectively.

Claims (1)

[Claims] a first clipper for clipping an input signal at a predetermined DC bias level; means for pulse width modulating the output of the first clipper to output a pulse width modulated wave; a second clipper that amplitude-modulates a portion of the pulse-modulated wave that corresponds to the input signal removed by the first clipper with the input signal; a power amplifier that receives the output of the second clipper; and means for demodulating the power amplifier output.