JPS6087582A - Rf modulation circuit - Google Patents

Abstract

PURPOSE:To eliminate buzz sound by applying a differentiation value of a video signal in opposite phase to a sound signal input side while taking a notice that an unnecessary sound component corresponds to a rate of change of the amplitude of the video signal (differentiation value of the video signal). CONSTITUTION:A sound multiplex signal is fed to a sound signal transmission system 5 through resistors R2, R3 and a coupling capacitor C2, and a composite video signal from an input terminal 1 is fed to the sound signal transmission system 5 through a capacitor C1, the resistor R3 and the capacitor C2. The said video signal is differentiated by the capacitor C1 and a combined resistor R comprising resistors R1-R4. Signals from a video signal modulator 3 and a sound signal modulator 4 are synthesized by an adder circuit 6 so as to eliminate buzz sound specific to a sound multiplex receiver generated in synchronizing with the horizontal synchronizing signal and the result is outputted from an output terminal 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an RF converter/subcircuit section added to a VTR, video disc player, etc.

(B) To display the baseband television signal reproduced by the prior art V'-TR etc. on the screen of the television receiver C: The television signal is transmitted to the antenna circuit of the television receiver. In the case of applying the signal through an RF signal, it is necessary to relay the television signal through an RF conversion circuit that converts the signal into two RF signal traces. This repeater RF switching circuit may be built into a VTR, etc., or it may be a separate product from the VTR, etc. under the name of a Q RF converter or RF adapter. In either case, the basic components, as shown in FIG. 1, include a first input terminal 111 for inputting a composite video signal containing video information, and an audio signal containing audio information corresponding to the video information. A video signal modulator (21) receives the composite video signal from the second input terminal (21) and outputs a modulated video signal obtained by amplitude modulating the first carrier wave with the composite video signal. 3) and receives the audio signal from the second input terminal (2), and receives the second carrier wave?
An audio signal modulator (4) frequency-modulated by the f-voice No.
), an audio signal transmission system (5) having a video signal modulator (
It is equipped with a mixing circuit (61) for mixing the output of the audio signal transmission system (3) and the output of the audio signal transmission system (5), and an RF multiplied signal output terminal (61) for transmitting the television signal, which is the output of the mixing circuit (6).
7).

By the way, in this RFF modulator, when a carrier wave is amplitude modulated by a composite video signal and amplified, AM-PM
It is known that conversion occurs, which causes a buzz in the output of a television receiver. Unnecessary M-PM conversion occurs at a modulation stage that amplitude-modulates a carrier wave with a composite video signal and at a subsequent amplification stage, resulting in a phase change. especially,
This results in a sudden phase change in the sync signal pulse portion. This phase change can be equivalently considered as the FM component, so
The video carrier wave undergoes a sudden frequency change in the sync signal portion. On the other hand, a normal TV receiver uses an audio intercarrier reception system, which is a difference signal obtained by mixing audio and video carrier waves (4 in the 'NT' SO system).
．． 5MHz) and demodulates the audio signal. Therefore, when the video carrier frequency changes, the relative -2 becomes the same as when the audio carrier changes. Therefore, the synchronization signal part C
The change in the video carrier frequency at 2 is demodulated as an unnecessary pulse of the FM detection output, resulting in a buzz.

Normally, the problem with buzz is mainly the harmonic components of the vertical synchronization signal, but in television multiplexed audio broadcasting, the double harmonics (31.5KHz) of the horizontal synchronization signal are generated in the sub-channels (16 to 5KHz). 47KHz) and causes significant buzz interference.

In order to prevent such buzz interference based on AM-PM modulation, a transmitter that outputs commercial broadcast radio waves is
As shown in Publication No. 906-2, an AM-PM conversion compensation circuit is inserted between the video carrier wave oscillator and the modulated amplifier, and the phase modulation component by the M-PM conversion is The phase modulation with the opposite polarity is canceled out by applying a carrier wave I.

However, the configuration of the M-PM compensation circuit is extremely complicated, and it is difficult to apply it to a home-use VTR or video disc player.

1. OBJECT OF THE INVENTION The present invention has been made in view of the above points, and is intended to provide an RFF adjustment circuit which has a simple structure but which performs effective buzz compensation.

B) Structure of the Invention The present invention eliminates unnecessary input M-
RF that cancels out unnecessary audio components brought about when a PM modulation component is applied to an intercarrier type television receiver, and a composite video signal is applied to an audio signal transmission system. It is related to variable circuits.

If the composite video signal applied to the RFF adjustment circuit of the present invention is a signal such as the one shown in FIG. The audio demodulation output i2 of an intercarrier television receiver outputs an unnecessary audio component (9) shown in Figure 2 even when no audio signal is being transmitted.This is the M-PM atrocious component shown above. This is an unnecessary audio component based on the horizontal synchronization signal as mentioned earlier.The delay (T) is due to the de-emphasis circuit etc. included in the audio signal transmission system.The present invention deals with this unnecessary audio component. We focused on the fact that the audio component corresponds to the rate of change in the amplitude of the video signal, that is, the differential value of the video signal, and conversely, by adding the differential signal of the video signal as an opposite phase to the audio signal input side, we canceled out the buzz. This is what we are trying to do.

GA Embodiment FIG. 3 shows one embodiment of the RF modulation circuit of the present invention.
Elements that are the same as those in the drawings are designated by the same reference numerals C and their explanations will be omitted.

(8) is an audio multi-M signal encoder which receives the signal from the f4'r2 input terminal and outputs different forms of well-known agency voice multiplex signals depending on the program content (stereo, bilingual, monaural). do. This multiplexed signal has a resistance (Iλ2)
(RA) and connect 9 capacitor (Oz) to ゛C audio (
It is attached to the No. 3 transmission system (5), and the first input terminal (1)
The composite images from 1 and 2 are capacitor (01), resistor (R
1 and is applied to the audio signal transmission system (!j) through the capacitor (C2). The capacitor (01) is an imparting circuit (9), which together with a resistor to be described later constitutes a differentiating circuit, and has a value of about 30 pF in the two embodiments. Resistance (R1)
is the output impedance of the above encoder (8) in series,
When converted into parallel, it can be expressed as a pure resistance and has a value of several tens of ohms. The resistor (R4) is connected to the above transmission system (
5) indicates an input impedance of around 50Ω. The resistor (R2) and variable resistor (R5) are connected to the encoder (8
1) The output Calpel is adjusted to the input level of the transmission system (5), and is set to values around 100, Ω-200, and Ω, respectively. On the other hand, since the composite video signal is driven by a signal source of several 1[Omega] and the input impedance of the video signal modulator (3) is approximately 1.0[Omega], it is hardly affected by the capacitor (C1). Accordingly, when a signal is input to the first input terminal (lroni in FIG. 2a), a signal having the waveform shown in FIG. 4a appears at point [Al].

When the output point (D) of the encoder (8) is set to zero and the signal shown in FIG. 2a is applied to the first input terminal (11) as described above.

Combined resistance rm of capacitor (C1) and resistors (R1) to (R4) (R=(R1+Rz)(R5+R4)/(R1
+R2+, R, 5+R4)j and (2), the video signal is differentiated. Figure A shows this differential waveform observed at point 1B. This waveform is multiplied by B5IC, R50R4), and the transmission system (5
)i Two people are supported.

A standard TV demodulator using the split carrier method that extracts and demodulates only the audio carrier from the signal from the output terminal (7) obtained under these conditions! When demodulated, the fourth
An audio signal output as shown in Figure C is obtained. Here, it can be seen that the single output waveform has an inverse 5 phase relationship in Figure 2.

As a result, the RF signal derived from the output terminal (7) of this circuit
When a double signal is applied to a normal intercarrier type television receiver, the unnecessary audio component shown in Figure 2 on the side is added to the component in Figure 4, which has the opposite phase, and the same components cancel each other out. , horizontal synchronization signal C: the resulting buzz is removed or reduced. still.

The signal level in Figure 4C used for this cancellation is the capacitor (
By appropriately selecting the capacitance value of C1), the capacitance can be adjusted from ≦2, and the buzz level can be adjusted to the lowest level.

(f) Effects of the Invention The present invention provides a composite video signal 'Ik: 8M Hesi'('Ik: 8M Hesi') that transmits the buzz originating from the AM-PM modulation component that occurs when forming an RF signal to the audio transmission system. The configuration is extremely simple because it can be removed by adding .

This figure shows a comparison between a circuit without the circuit of the present invention (characteristic P) and a circuit with the circuit of the present invention (characteristic Q). As is clear from the figure, the audio S/N has improved by approximately 8 dB.

It was confirmed that there was a sufficient effect on hearing.

[Brief explanation of drawings]

Figure 1 shows the circuit configuration of a conventional RF modulation circuit, Figure 2 a,
b is an explanatory waveform diagram of buzz generation due to M=FIM modulation, Fig. 3 is a configuration diagram of the RF modulation circuit of the present invention, Fig. 4 a, b,
c is a wave diagram explaining the generation of the cancellation signal, and FIG. 5 is a characteristic diagram showing the effect of the present invention over the conventional example. Explanation of main drawing numbers... (11(2)...1st and 2nd input terminals, (3)...
・Video signal modulator, (5)...Audio signal transmission system, (6
1... Mixed circuit. (9)...Giving circuit

Claims (3)

[Claims] (1) A first input terminal for inputting a composite video signal containing video information, a second input terminal for inputting an audio signal containing audio information corresponding to the video information, and a second input terminal for inputting an audio signal containing audio information corresponding to the video information; a video signal modulator that receives the composite video signal and outputs an unnecessary AM-PM conversion component together with a modulated video signal obtained by amplitude modulating a first carrier wave with the composite video signal; receiving the audio signal of the second
R comprising an audio signal transmission system having an audio signal modulator that modulates a carrier wave with the audio signal, and a mixing circuit that mixes the output of the video signal modulator and the output of the audio signal transmission system.
In the F modulation circuit, when the output of the RF modulation circuit is applied to an intercarrier type television receiver, the above A
RF characterized by comprising a circuit that applies the composite video signal from the first input terminal to the audio signal transmission system so as to cancel out unnecessary audio components derived based on the M-PM conversion component. Modulation circuit. (2) The imparting circuit is connected between the first input terminal and the audio signal modulator, and is a differentiating circuit that differentiates the composite video signal. 1) RF modulation circuit described in section 1). (3) Claims characterized in that the differentiation circuit is comprised of a capacitor connected to the first input terminal and the audio signal transmission system +72, and a resistor in the audio signal transmission system. RF modulation circuit according to item 21.