JPS6243907A - Amplitude modulation circuit - Google Patents

Abstract

PURPOSE:To reduce the distortion against the fluctuation of a power voltage by inserting a multiplication amplifier to an amplifier section of an input signal to control the amplitude of an amplification pulse to a constant value. CONSTITUTION:The DC fluctuation at a DC power supply input terminal 8 is compensated by a sound amplifier 3 through a sound amplifier 6 by the DC feedback from a low-pass filter 10 to keep the DC output of a pulse width amplifier 9. Further, the DC feedback is given to a multiplication amplifier 13 to vary the sound amplification factor thereby compensating the amplification factor for the change. Thus, the modulation sensitivity is kept continuously constant to attain the amplitude modulation with less distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplitude modulation circuit that is used in medium wave and short wave broadcasting equipment and performs serial modulation using pulse width modulation to amplify audio.

[Conventional technology]

Traditionally, medium-wave broadcasting equipment using pulse width modulation uses an unregulated power supply with rectified hc* voltage as the final stage power supply for the sys power amplifier.As a system diagram of a conventional broadcasting equipment, , as shown in Figure 4.

In the figure, %1 is an audio input terminal, 2, 3.6 is an audio amplifier, 4
is a comparator, 5 is a pulse amplifier, 7 is a 100K [(z subcarrier oscillator, 8tj DC power input terminal, 9il pulse power generator, IOH low pass filter, 11 is a high frequency amplifier, and 12ij is an amplitude modulation output terminal.

Since this broadcasting machine uses a series modulation method, the pulse power amplifier 9 works equivalent to a one-way DC-knee DC converter, so the power supply fluctuates due to the hawk feedback from the low-pass filter IO. High frequency amplifier 1
Since the pulse power amplifier 9 stabilizes the high frequency output power, the output can be stabilized even if the DC power source is unstable. is.

On the other hand, since this broadcaster requires amplitude modulation,
Pulse width modulation is performed in which the ON and OFF cycles of the pulse power amplifier 9 are changed by the audio signal.

FIG. 5 (al and bl are waveform diagrams showing the operation of this pulse width modulation. For example, when the ON and oppO ratios of the pulse power amplifier 9 in the non-modulated state are In the case of A versus B as shown in FIG. 1a) VC, when adjusting to 100 degrees, the width A varies from 0 to 2 people depending on the amplitude of the audio signal. Next, when the KDC power supply voltage changes by +α, as shown in FIG. In this case, the pulse power amplifier 9 Q)
(JN width is 1/(l+α).

[Problem that the invention seeks to solve]

In order to perform 100 modulation in this state, the VC must be changed by 0 to 2 A/1, so the modulation sensitivity will fluctuate by α, and this power supply voltage fluctuation will appear as distortion of the amplitude modulated wave. It happens.

The purpose of the present invention is to eliminate such problems, and to control the audio amplifier by increasing the audio amplifier + 19Jtk DC feedback.
It is an object of the present invention to provide a discontinuous modulator in which φ with respect to the '&' movement of the electric f@voltage is reduced.

[Means for solving problems]

The configuration of the small invention is to amplify the input signal 17 and generate a predetermined subcarrier V.
In the amplitude modulation circuit that performs pulse width modulation from C, amplifies this pulse, and amplifies the input signal by using the amplified pulse A1~, the input signal is adjusted so that the amplitude of the pre-Me amplification pulse is controlled to be constant. The feature is that a multiplication amplifier is inserted in the amplification section.

[Principle of the invention]

In the present invention, when the pulse power amplifier 9 performs the operation shown by the solid line in FIG. 5 (bl), the amplitude modulation degree O1 (
However, if 100-modulation is performed when the audio input amplitude is Y, the period A changes from 0 to 2 people as indicated by the broken line.

If the DC power source power fluctuates to (l+α) in this state,
For DC feedback, A, which is the ON period when no modulation is performed, must be A/(1+α) as shown in FIG. There is a fluctuation in this DCil source input (Nevertheless, in order to prevent the audio input amplitude Y from changing, the pulse width has to be changed by 10 A, resulting in a modulation of more than 100%. In the present invention, this amplitude control is performed using a multiplication amplifier, and the output can be increased by a factor of 101.

(Actually, it is used as a division, and as the output denominator input of the audio amplifier 2, the output of the audio amplifier 6 becomes the numerator power).

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of a transmitter including a first embodiment of the present invention. This embodiment includes an audio amplifier 2 for amplifying the audio input from the audio input terminal l, a multiplier amplifier 13, an audio amplifier 3 for amplifying the audio input and feedback input, and a subcarrier excavator 7 for pulse width modulation. , a comparator 4 that performs pulse width modulation, a pulse amplifier 5 that fully amplifies this output, and a pulse power amplifier 9 that receives DC power from an input terminal 8.
(a low-pass filter lO that demodulates the pulse width modulated wave;
A high frequency amplifier 11 that outputs an amplitude modulated output from an output terminal 12, an amplitude modulated output terminal 12, and a low deceleration filter 1.
It includes an audio amplifier 'a6 which amplifies the feedback number 1g taken out from 0.

DC fluctuations at the DC power input terminal 8 are compensated for by the audio amplifier 3 through the audio amplifier 6 through DC feedback from the low-pass filter 10, keeping the DC output of the pulse width amplifier 9 constant. In addition, this DC feedback is supplied to the multiplier amplifier 13, and the audio amplification degree is varied by this DC@feedback amount, and in order to compensate for this change in amplification degree, the modulation sensitivity is constantly kept constant. Less vibration@modulation is possible.

FIG. 2 is a block diagram of a second embodiment of the invention. This embodiment has the same configuration as the first embodiment, but the feedback output from the audio amplifier 6 is divided into I)C feedback and audio feedback, and control signals are output to each of them. This method is suitable for cases where it is necessary to multiply the DC feedback by a large amount to compensate for DC output fluctuations.

FIG. 3 is a block diagram of a third embodiment of the present invention. In this embodiment, the feedback of the second embodiment is extracted from the output of the high frequency amplifier 11 which is the final output, demodulated to audio via the demodulator 14, and the VC is supplied to the feedback audio amplifier 6. . In the case of this embodiment, it becomes possible to compensate for the distorted F'i temperature characteristics of the high frequency amplifier 11.

〔Effect of the invention〕

As explained above, the present invention has the effect of making the output fully stable at 1 u with respect to DC voltage fluctuations and lowering the distortion of the modulated output by using a multiplier for the audio amplifier.

[Brief explanation of drawings]

FIGS. 1, 2, and 3 illustrate the first embodiment of the present invention. A block diagram of a transmitter including the second and third embodiments; Figure 4 is a block diagram of an example of a medium wave transmitter using conventional pulse modulation; Figure 5 is a block diagram of an example of a medium wave transmitter using conventional pulse modulation; It is a waveform diagram explaining 1...Audio input terminal, 2, 3, 6...
Audio amplifier, 4...Comparator, 5...Pulse width amplifier, 7...Subcarrier oscillator, 8...
...DC power input terminal, 9...Pulse power amplifier, 10...Low pass filter (T, PF
), 11... High frequency amplifier, 12... Amplitude modulation output terminal, 13... Multiplication amplifier, 14... Peak... Demodulator.

Claims (1)

[Claims] In an amplitude modulation circuit that amplifies an input signal, performs pulse width modulation using a predetermined subcarrier, amplifies this pulse, and demodulates this amplified pulse to amplify the input signal, the amplitude of the amplified pulse is controlled to be constant. An amplitude modulation circuit characterized in that a multiplication amplifier is inserted in the input signal amplification section.