JPS5940308A - Modulating system of video disk recorder - Google Patents

Abstract

PURPOSE:To improve both S/N and sound quality of an audio signal, by putting a filter between an FM modulator and an adder 3 to suppress the disturbance component in a video RF signal to an audio RF signal and then to reduce the disturbance of the video RF signal to the audio RF signal. CONSTITUTION:The output of a filter 5 is added to an audio RF signal delivered from an FM modulator 2 through an adder 3, and the audio RF signal is multiplied with modulation of pulse width by a limiter 4 to receive the limit of amplitude. For the frequency distribution of the output signal of the limiter 4, the audio RF signal is set at the band which is eliminated through the filter 5. Thus no component of the audio RF signal gets into the audio RF signal band. In this case, the video RF signal produces both amplitude and phase distortions by a transmission system using the filter 5 to produce distortions to a demodulated video signal. However the deterioration can be minimized for picture quality by using a notch filter to the filter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modulation system in a recording device for recording video and audio signals on a video disc.

As shown in FIG. 1, the conventional modulation system performs FM modulation on a human video signal using an FM modulator I, FM modulates an input audio signal using an FM modulator 2, and combines the output signal of the RM modulator 1 with FM modulation. Addition circuit 3
Signal processing is performed in which the output signal of the adder circuit 3 is amplitude-limited by the limiter 4.

However, the video RF modulated by the FM modulator 1
Since the modulation index is less than 1, the band required for signal demodulation is
This is the band (3.9 to 13.5 Mllz) occupied by the primary sideband of the highest frequency of the modulated frequency. For this reason, the audio subcarriers are set at 2.3 and 2.8 MHz so as not to be affected by the primary sideband. However, since audio signals are multiplexed using a pulse width modulation method in a video disc, the carrier level of the FM modulator 2 is set to about 1/10 of the video carrier level for mixing. But in the limiter 6 more
dB decrease. Therefore, the level of the secondary sideband of the video RF signal is lower than that of the primary sideband, but the level of the audio RF signal is lower than that of the primary sideband.
The signal is subject to interference by higher order, particularly secondary sidebands, of the video RF signal, which has the drawback of deteriorating the S/N and sound quality of the audio RF signal.

The present invention has been made in view of the above, and it is an object of the present invention to provide a modulation system for a recording apparatus that eliminates the above two drawbacks.

The present invention will be explained below using examples.

FIG. 2 is a block diagram showing one embodiment of the present invention.

In one embodiment of the present invention, a filter 5 for removing audio RFtW band components is further connected between the FM modulator 1 and the adder 3 in the conventional modulation system shown in FIG.

Therefore, among the high-order sideband components in the band of the video RF signal modulated by the FM modulator l, the components falling within the audio RF band are removed by the filter 5. Therefore, the conventional drawbacks are eliminated.

This is because the band of the video RF signal modulated by the FM modulator 1 is sufficient as long as the band through which the primary sideband passes is secured, and the video RF signal of the FM modulator 1 shown in FIG. The second-order lower sideband component of the RF signal is removed by the filter 5, and the signal becomes as shown in FIG. 3 (bl).

Therefore, the output signal of the filter 5 and the audio RF signal output from the FM modulator 2 are added by the adder 3, the audio RF signal is multiplexed by pulse width modulation by the limiter 4, and the amplitude is limited by the limiter 4. As shown in FIG. 3 (C1), the frequency distribution of the output signal of the limiter 4 is such that the audio RF signal is located in the band removed by the filter 5, and no video RF signal component falls within the audio RF signal band. In this case, amplitude distortion and phase distortion occur in the video RF signal due to the transmission system using the filter 5, which causes distortion in the demodulated video signal. However, by using a non-chip filter as the filter 5, the degradation of the picture area can be minimized. It is possible to do so.

Also, since the upper sideband in the video RF signal is not removed, the lower sideband in the output signal of the limiter 4 is
It appears in the F signal band, but it is suppressed. Furthermore, it is also possible to change the attenuation rate of the filter 5 in proportion to the amount of harmonics of the video RF signal generated in the audio RF band. With this configuration, it is possible to control according to the amount of interference to the audio RF signal.

As explained above, according to the present invention, interference components in the video RF signal with respect to the audio RF signal are suppressed by inserting a filter, so that interference with the audio RF signal by the video RF signal can be reduced, and the interference with the audio RF signal can be reduced. Signal S/N and sound quality can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional modulation system, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a frequency spectrum for explaining the operation of an embodiment of the present invention. 1...FM modulator, 2...RM modulator, 3...Adder, 4...Limiter, 5
······filter. Patent applicant: Pioneer Co., Ltd.

Claims (1)

[Claims] a first FM modulator that FM modulates a video signal; a second FM modulator that FM modulates an audio signal;
A filter that removes the frequency component of the audio RF signal band from the output signal of the M modulator, an adder circuit that adds the output signal of the filter and the output signal of the second FM converter 11, and an adder circuit that adds the output signal of the adder circuit. 1. A modulation system for a video disc recording device, comprising: a limiter for limiting amplitude.