JPH05219506A - Video synchronization compression scramble method, and its transmitter and receiver - Google Patents

Abstract

PURPOSE:To attain reproduction of a video image with fidelity to an original video signal by allocating a pulse superimposed on a sound FM signal only for a vertical blanking period of the video signal at the transmission of a timing pulse for synchronization reproduction. CONSTITUTION:A timing pulse D superimposed on a sound FM intermediate frequency signal C for a synchronization compression period of a synchronization compression video intermediate frequency signal B consists of a horizontal synchronizing pulse corresponding one to one to a horizontal synchronizing signal (8-12H) located for the vertical blanking period for a vertical synchronization timing pulse and a base band video signal A. The pulse D is recovered by discriminating a horizontal synchronizing frequency from the sent horizontal synchronizing timing pulse with respect to the deficient horizontal synchronization timing pulse equivalent to one field and converted into a reproduction expansion signal E. The signal E is a key pulse used to convert the signal B into a descramble video intermediate frequency signal F. Thus, noise appearing at the horizontal synchronizing signal portion of the video signal is limited to noise for the vertical blanking period only.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video synchronous compression scramble method for cable television broadcasting such as CATV, and a transmitter and a receiver thereof.

[0002]

2. Description of the Related Art Conventionally, in cable television broadcasting, as shown in FIG. 4, in order to prevent eavesdropping, the transmitting side transmits the base band video signal shown in FIG. A scramble system is used in which a compressed compressed video intermediate frequency signal is compressed, converted to a broadcast frequency and transmitted, and the synchronization signal cannot be reproduced on the receiving side. In this case, in order to reproduce the compressed sync signal on the receiving side, a timing pulse indicating the position information of that portion is generated as shown in FIG.
As shown in (1), the audio FM signal is superimposed and transmitted in a one-to-one correspondence. AM modulation is used to superimpose the timing pulse on the audio FM signal, and the timing pulse is extracted by the AM detection in addition to the FM detection of the audio on the receiving side.
The extracted timing pulse is separated into horizontal and vertical sync,
The waveform is shaped and converted into a reproduction decompression signal indicating the position and period of the compressed synchronization signal as shown in FIG. 4D, whereby the intermediate frequency signal of the received video signal is AM-modulated, In the intermediate frequency amplification stage on the receiving side, the synchronous compressed video intermediate frequency signal (scramble intermediate frequency signal) shown in FIG. 4B is restored to the descramble video intermediate frequency signal shown in FIG. 4E.

[0003]

In this conventional scrambling method, the AM is used for the video synchronous compression period and the audio FM signal.
The positions of the timing pulses to be superimposed by the modulation overlap in a one-to-one correspondence when considered on the time axis. Therefore, first, the sideband generated when the audio FM signal is AM-modulated by the timing pulse on the transmitting side enters into the video signal band.
On the receiving side, when the synchronously compressed video signal is AM-modulated and reproduced, the audio FM signal and the audio FM signal are re-A
Since it is M-modulated (AM-modulated twice), this sideband also enters the video signal band. When these sidebands undergo AM demodulation of the video signal, they become noise in the horizontal synchronizing signal portion that overlaps in time, which causes jitter in the horizontal synchronization, which causes the problem of image quality deterioration.

[0004]

Therefore, in order to achieve the above-mentioned object, a first aspect of the present invention is to compress a sync signal of a baseband video signal and to output a timing pulse for reproducing the sync signal as an audio FM signal. In the video synchronous compression scramble method for transmitting by superimposing AM modulation on the audio FM, the timing pulse is audio FM only during the vertical blanking period of the video signal.
It is superimposed on the signal.

The transmitter of the second aspect of the present invention is a video IF modulation circuit for AM-modulating an input baseband video signal to convert it into a video intermediate frequency signal, and a horizontal and vertical direction from the input baseband video signal. A horizontal and vertical sync separation circuit for separating the sync signal, and one vertical synchronization timing pulse based on the separated horizontal and vertical sync signals,
A timing pulse generation circuit for generating a horizontal synchronization timing pulse corresponding to a horizontal synchronization signal within a vertical blanking period of a video signal, and compression for synchronous compression based on the separated horizontal and vertical synchronization signals. A compression timing signal generation circuit for generating a timing signal, a synchronization compression circuit for inputting the compression timing signal to compress the synchronization signal portion of the video intermediate frequency signal and converting it to a synchronization compression video intermediate frequency signal, and the input base Audio IF for FM modulation of band audio signal and conversion to audio FM intermediate frequency signal
A modulation circuit, an AM modulation circuit that AM-modulates and superimposes the output of the timing pulse generation circuit on this audio FM intermediate frequency signal, mixes the output from this AM modulation circuit and the synchronous compressed video intermediate frequency signal, and sets a predetermined value. And an RF modulation circuit for converting to a television channel frequency and outputting the same.

The receiver of the third aspect of the present invention compresses the synchronizing signal of the baseband video signal, and the timing pulse for reproducing this synchronizing signal is audio F only during the vertical blanking period of the video signal.
A tuner circuit for receiving a signal superimposed on M signal by AM modulation and converting it into a synchronous compressed video intermediate frequency signal and an audio FM intermediate frequency signal, and timing for separating and extracting timing pulses from this audio FM intermediate frequency signal Based on the pulse detection circuit, the horizontal and vertical synchronization timing pulse separation circuit for separating the horizontal and vertical synchronization timing pulse from the output of the timing pulse detection circuit, and the separated and extracted horizontal synchronization timing pulse, Lack 1
1 field horizontal synchronization timing pulse reproducing circuit for reproducing horizontal synchronization timing pulse for field,
A reproduction timing pulse generating circuit for generating the reproduction timing pulse by synthesizing the output of the 1-field horizontal synchronizing timing pulse reproducing circuit and the output of the vertical synchronizing timing pulse separating circuit, and a synchronous compressed video with the reproducing timing pulse. A reproduction decompression signal generation circuit that generates a reproduction decompression signal while synchronizing with the intermediate frequency signal, and a descrambling circuit that inputs the reproduction decompression signal and converts the synchronous compression video intermediate frequency signal into a descrambling video intermediate frequency signal, A video detection circuit that detects the descrambling video intermediate frequency signal and outputs a baseband video signal, and a base station that detects the audio FM intermediate frequency signal from the tuner circuit.
And a voice detection circuit for outputting a voice signal in a band.

[0007]

According to the present invention, the timing pulse superimposed on the audio FM signal is within the vertical blanking period of the video signal when considered on the time axis, and the noise due to the sideband generated on the transmitter side is vertical. It only affects the video signal during the blanking period and does not appear on the TV screen. Also, since the voice FM signal that has been AM-modulated twice at the receiver side only needs to be AM-modulated once, the noise on the horizontal synchronizing signal portion can be reduced and the jitter does not appear on the screen.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. 1 is a signal waveform diagram showing a timing pulse of a video synchronous compression scramble method according to the present invention, FIG. 2 is a block diagram showing a transmitter (scramble encoder), and FIG. 3 is a receiver (scramble decoder). It is a block diagram shown.

In the signal waveforms shown in FIG. 1, the synchronous compression period of the synchronous compressed video intermediate frequency signal shown in FIG.
The timing pulse superimposed on the audio FM intermediate frequency signal shown in FIG. 1 (C) is put in one vertical synchronization timing pulse and the vertical blanking period of the baseband video signal shown in FIG. 1 (A). The horizontal synchronizing signal (8 to 12H) has a one-to-one correspondence with the horizontal synchronizing timing pulse. The lacking one-field horizontal sync timing pulse finds its horizontal sync frequency from the transmitted horizontal sync timing pulse, and reproduces the playback timing pulse shown in FIG. It is converted into the reproduction expansion signal shown in (E). The reproduction / expansion signal is a key pulse for converting the synchronous compression intermediate frequency signal into the descramble video intermediate frequency signal shown in FIG.

A scramble encoder (transmitter) 11 shown in FIG. 2 is a video IF modulation circuit 12 for AM-modulating an input baseband video signal to convert it into a video intermediate frequency signal.
And a compression timing signal for generating a compression timing signal for synchronous compression based on the horizontal and vertical synchronization signals separated and extracted by the horizontal synchronization separation circuit 13 and the vertical synchronization separation circuit 14 from the input baseband video signal. A generation circuit 15, a synchronization compression circuit 16 which receives a compression timing signal, compresses a synchronization signal portion of a video intermediate frequency signal, and converts it into a synchronization compression video intermediate frequency signal, and FM-modulates an input baseband audio signal. An FM modulation circuit 17, an audio IF modulation circuit 18 for converting its output into an audio FM intermediate frequency signal, a horizontal sync separation circuit 13 and a vertical sync separation circuit 14.
Figure 1 using horizontal and vertical sync signals separated and extracted by
A timing pulse generation circuit 19 for generating one vertical synchronization timing pulse shown in FIG. 6C and a horizontal synchronization timing pulse corresponding to the horizontal synchronization signal within the vertical blanking period of the video signal, and this timing pulse generation. Circuit 1
AM modulation circuit 20 for superimposing the output of 9 on the audio FM intermediate frequency signal by AM modulation, and a mixer for mixing the output from this AM modulation circuit 20 and the synchronous compressed video intermediate frequency signal from the synchronous compression circuit 16 21 and an RF modulation circuit 22 for converting the output of the mixer 21 into a desired television channel frequency (scrambled television signal).

A scramble decoder (receiver) 31 shown in FIG. 3 selects a scrambled television signal output from the scramble encoder 11, and outputs the synchronous compressed video intermediate frequency signal and audio shown in FIG. 1 (B). A tuner circuit 32 for converting to an FM intermediate frequency signal, a timing pulse detection circuit 33 for separating and extracting a timing pulse from the audio FM intermediate frequency signal, and an output of the timing pulse detection circuit 33 are received, and FIG. The horizontal synchronization timing pulse separation circuit 34 and the vertical synchronization timing pulse separation circuit 35 for separating the horizontal and vertical synchronization timing pulses are shown.
And a 1-field horizontal synchronization timing pulse reproduction circuit 36 for reproducing a 1-field shortage horizontal synchronization timing pulse based on the separated and extracted horizontal synchronization timing pulse, and the 1-field horizontal synchronization timing pulse reproduction circuit 36. The output of the timing pulse reproduction circuit 36 for horizontal synchronization and the output of the timing pulse separation circuit 35 for vertical synchronization are combined to produce the output shown in FIG.
A reproduction timing pulse generation circuit 37 for generating a reproduction timing pulse shown in FIG. 1 and FIG. 1E while synchronizing with the synchronous compressed video intermediate frequency signal by this reproduction timing pulse.
A reproduction expansion signal generating circuit 38 for generating a reproduction expansion signal, a descrambling circuit 39 for converting the synchronous compressed video intermediate frequency signal into a descramble video intermediate frequency signal by using this reproduction expansion signal, and the descrambling video intermediate frequency. It comprises a video detection circuit 40 for obtaining a baseband video signal from the signal and an audio detection circuit 41 for obtaining a baseband audio signal from the audio FM intermediate frequency signal from the tuner circuit 32.

In this embodiment, by adopting such a method and configuration, the influence of the side band on the video signal generated when the timing pulse is superimposed on the audio FM signal by AM modulation on the transmitter side is affected by the television. Only during the vertical blanking period that does not appear on the screen, and when the receiver side demodulates the video signal that has been synchronously compressed by AM modulation, the audio FM signal is A only once during the vertical blanking period.
Since M modulation is sufficient, the sideband can be halved as compared with the conventional one, and appears in the horizontal synchronizing portion of the video signal due to the influence of the sideband of the audio FM signal generated on the conventional transmitter side and receiver side. It is possible to satisfactorily eliminate noise, and it is possible to reproduce an image faithfully to the original image signal without horizontal synchronization jitter due to the noise.

[0013]

As described above, according to the present invention, when transmitting the timing pulse for synchronous reproduction of the video synchronous compression scramble method, the timing pulse to be superimposed on the audio FM signal is only within the vertical blanking period of the video signal. Placed in
The method of reproducing insufficient timing pulses on the receiver side has an effect on the sideband video signal generated when the transmitter side superimposes the timing pulse on the audio FM signal by AM modulation. Only during the vertical blanking period, which is not shown in Fig. 5, when the audio signal FM is synchronously compressed by the receiver and descrambled by AM modulation, the audio FM signal is A
Since M modulation is sufficient, sideband generation can be halved as compared with the conventional case, and noise that appears in the horizontal synchronizing portion of the video signal due to the influence of the sideband of the audio FM signal generated on the conventional transmitter side and receiver side. Is excellently eliminated, there is no horizontal synchronization jitter due to the noise, and a scramble system capable of reproducing an image faithful to the original image signal can be constructed.

[Brief description of drawings]

FIG. 1 is a signal wave system diagram showing timing pulses of a video synchronous compression scramble method of the present invention.

FIG. 2 is a block diagram showing a scramble encoder according to the present invention.

FIG. 3 is a block diagram showing a scramble decoder according to the present invention.

FIG. 4 is a signal wave system diagram showing timing pulses in a conventional video synchronous compression scramble method.

[Explanation of symbols]

11 transmitter (scramble encoder) 12 video IF modulation circuit 13 horizontal sync separation circuit 14 vertical sync separation circuit 15 compression timing signal generation circuit 16 sync compression circuit 17 FM modulation circuit 18 audio IF modulation circuit 19 timing pulse generation circuit 20 AM Modulation circuit 21 Mixer 22 RF modulation circuit 31 Receiver (scramble decoder) 32 Tuner circuit 33 Timing pulse detection circuit 34 Horizontal synchronization timing pulse separation circuit 35 Vertical synchronization timing pulse separation circuit 36 1 field Horizontal Timing pulse reproduction circuit for synchronization 37 Reproduction timing pulse generation circuit 38 Reproduction decompression signal generation circuit 39 Descrambling circuit 40 Video detection circuit 41 Audio detection circuit

Claims (3)

[Claims] 1. A video synchronous compression scramble method in which a sync signal of a baseband video signal is compressed, and a timing pulse for reproducing the sync signal is superimposed on an audio FM signal by AM modulation and transmitted. A video synchronous compression scramble method characterized by being superimposed on an audio FM signal only during a vertical blanking period of the signal. 2. A baseband video signal which is input
A video IF modulation circuit for M-modulating and converting to a video intermediate frequency signal, a horizontal and vertical sync separation circuit for separating horizontal and vertical sync signals from an input baseband video signal, and the separated horizontal and vertical sync signals A timing pulse generating circuit for generating one vertical synchronizing timing pulse based on the above, and a horizontal synchronizing timing pulse corresponding to the horizontal synchronizing signal within the vertical blanking period of the video signal; A compression timing signal generation circuit that generates a compression timing signal for synchronous compression based on a vertical synchronization signal, and a compression timing signal that is input to compress the synchronization signal portion of the video intermediate frequency signal to generate a synchronous compressed video intermediate frequency. Synchronous compression circuit for converting into a signal, and FM modulation of the input baseband audio signal, and into an audio FM intermediate frequency signal An audio IF modulation circuit for converting, an AM modulation circuit that AM-modulates and superimposes the output of the timing pulse generation circuit on this audio FM intermediate frequency signal, and an output from this AM modulation circuit and a synchronous compressed video intermediate frequency signal are mixed. And a RF modulation circuit for converting and outputting to a predetermined television channel frequency, a video synchronous compression scramble transmitter. 3. A signal in which a synchronization signal of a baseband video signal is compressed and a timing pulse for reproducing the synchronization signal is superimposed on an audio FM signal by AM modulation only during a vertical blanking period of the video signal, and synchronization is performed. A tuner circuit for converting a compressed video intermediate frequency signal into an audio FM intermediate frequency signal, a timing pulse detection circuit for separating and extracting a timing pulse from the audio FM intermediate frequency signal, and a horizontal and horizontal output from the output of the timing pulse detection circuit. A horizontal and vertical synchronization timing pulse separation circuit that separates the vertical synchronization timing pulse, and a horizontal synchronization timing pulse for one field that is lacking based on the separated and extracted horizontal synchronization timing pulse. 1 field horizontal synchronization timing pulse regeneration circuit, and 1 field horizontal synchronization timing pulse regeneration circuit A playback timing pulse generation circuit that synthesizes the output of the playback circuit and the output of the vertical synchronization timing pulse separation circuit to generate a playback timing pulse; and a playback timing pulse that plays back in synchronization with the synchronized compressed video intermediate frequency signal. A reproduction / expansion signal generation circuit for generating a expansion signal, a descrambling circuit for receiving the reproduction / expansion signal and converting the synchronous compressed video intermediate frequency signal into a descrambled video intermediate frequency signal, and detecting the descrambling video intermediate frequency signal And then
Video synchronization characterized by comprising a video detection circuit for outputting a sub-band video signal and an audio detection circuit for detecting an audio FM intermediate frequency signal from the tuner circuit and outputting a base-band audio signal. Compression scramble receiver.