JPH11308598A - Scrambler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a received image signal without distortion by the scrambler employing an amplitude suppression system adopted by a CATV. SOLUTION: A video amplitude modulator 71 at a transmitter side A applies AM modulation to a vestigial side band VSB-AM wave (c) based on a timing signal (b) for a period including a synchronizing signal from a video signal (a) extracted by a timing generator 11 to generate a transmission video signal where the synchronizing signal is suppressed. A timing demodulator 81 at a receiver side B extracts the timing signal (b) including periods for the synchronizing signal from a demodulated VSB-AM wave and a voltage controlled amplifier VCA amplifies and expands signals for the synchronizing signal periods, then the synchronizing signal component is accurately demodulated and a TV image signal without distortion is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention limits the so-called reception when a specific channel or program is charged separately in cable broadcasting such as CATV or when a specific channel or program is charged in wireless TV broadcasting. The present invention relates to an improvement of a scrambling device used for performing the above.

[0002]

2. Description of the Related Art Scrambling for broadcasting and communication includes video, audio, and data signals. Among them, scrambling for video signals is widely used in broadcasting on CATV and the like.

[0003] Among the video scrambling methods, there is a so-called synchronization signal suppression method in which the amplitude of a synchronization signal is compressed on the transmission side and transmitted, and the reception side expands the amplitude of the compressed synchronization signal to perform descrambling. It is often adopted as a device that can be realized with a relatively simple configuration.

[0004] A conventional scrambling device in the synchronous signal suppressing system has been configured as shown in FIG.

First, on the transmitting side A, a TV signal composed of a video signal a and an audio signal b is supplied to an IF modulation circuit 1, and the output of the IF modulation circuit 1 passes through a scramble modulation circuit 2 and a transmission frequency conversion circuit 3. , For example, via a CATV transmission path. That is, a synchronization signal such as a horizontal synchronization signal is multiplexed and a video signal a to be scrambled as shown in FIG.
Generator 11 and residual sideband (VSB) -A
It is supplied to each of the M modulators 12.

The timing generator 11 introduces the video signal a, synchronizes with the horizontal synchronizing signal having a pulse width h included in the video signal, and generates a pulse signal corresponding to the horizontal blanking period H, as shown in FIG. Is generated.

The timing signal b is a synchronizing signal included in the transmission video signal, that is, a compressed pulse signal for suppressing the horizontal synchronizing signal, and has a pulse width H 'as shown in FIG. 5B corresponds to a horizontal retrace period included in the video signal as shown in FIG. 5B, and includes a pulse width h region of the horizontal synchronizing signal.

Therefore, the timing signal b is supplied to the video amplitude modulator 21 and the audio amplitude modulator 22 of the scramble modulation circuit 2, respectively.

The video amplitude modulator 21 expands the VSB-AM modulated wave from the VSB-AM modulator 12 with the timing signal b and expands the region including the horizontal synchronizing signal as shown by a solid line in FIG. AM modulates the amplitude by about 50% in the negative direction,
VSB-A in which the amplitude of the region including the horizontal synchronization signal is compressed
An M-modulated wave, that is, a scrambled video modulation signal d shown in FIG.
Feed to 1.

On the other hand, the audio amplitude modulator 22 is arranged as shown in FIG.
Since the FM audio signal from the FM modulator 13 shown in FIG. 4 is similarly AM-modulated in the negative direction by 50% using the timing signal b, a scrambled audio modulated signal f as shown in FIG. The synthesizer 31 of the frequency conversion circuit 3
Supplied to

Therefore, the synthesizer 3 of the transmission frequency conversion circuit 3
1 synthesizes the scrambled video modulation signal d and the scrambled audio modulation signal f, converts them into a transmission frequency signal by a frequency converter 32, and
It is transmitted to each subscriber on the receiving side B.

As described above, the transmitting side A transmits the VSB-AM modulated wave in which the amplitude of the horizontal synchronizing signal component is AM-modulated in the negative direction by 50% by the scramble signal b and the amplitude of the horizontal synchronizing signal component is compressed. Even if the TV signal is received by a general receiver, the horizontal synchronization signal cannot be separated and taken out,
The screen of the receiver becomes distorted, and a normal video output cannot be obtained.

Therefore, a descrambler device is prepared for a subscriber who has installed a terminal which has been lent or controlled to operate according to a contract. First, a received TV signal is converted into a reception frequency conversion circuit as shown in FIG. After being frequency-converted at 4 and separated into a video IF signal and an audio IF signal, one of the video IF signals is supplied to the AM modulator 51 of the descrambling modulation circuit 5. The other audio IF signal is supplied to the FM demodulator 61 of the reception IF demodulation circuit 6 and demodulated, taken out as a TV audio signal, and supplied to the AM demodulator 52 of the descrambling modulation circuit 5.

The AM demodulator 52 outputs the AM
The timing signal added as a component is shown in FIG.
The extracted timing signal g is supplied to an AM modulator 51 for a video signal as shown in FIG.

The AM modulator 51 performs descrambling by AM-modulating the synchronization signal included in the received video IF signal in the amplitude extension direction in accordance with the timing signal g.
The original VSB-AM signal shown in (c) is obtained, and thereafter, is supplied to the VSB-AM demodulator 61 of the reception IF demodulation circuit 6 in FIG. 3 and has an appropriate amplitude level that can be supplied to a predetermined TV receiver. A TV video signal including a synchronization signal is obtained.

As described above, the AM modulator 51 is descrambled based on the timing signal g generated by demodulating the audio signal by extending the amplitude of the synchronization signal component in the opposite manner to the modulation on the transmitting side A. A video signal is taken out.

The audio FM signal output from the reception frequency conversion circuit 4 contains an AM modulation component corresponding to the timing signal b. The AM modulation component is removed by the amplitude limiter in the FM demodulator 61. Is done.

[0018]

As described above, in the conventional scrambler, in the descrambling modulation circuit on the receiving side, the amplitude of the synchronization signal component is determined based on the timing signal generated by the AM demodulator of the FM audio signal. Extension was performed.

Incidentally, on both the transmitting side and the receiving side, the audio signal undergoes frequency conversion together with the video signal.
On the transmitting side, the audio signal and the video signal are simultaneously subjected to AM modulation by the timing signal b.

However, since the audio signal band is outside the video signal band, for example, in the 4.5 MHz band, and on the transmission line after the transmission frequency conversion circuit, both signals are merely synthesized waves, so that they are separated from each other after the reception frequency conversion. The audio signal and the video signal that are extracted as described above are not always accurately synchronized. Therefore, in the AM modulator on the receiving side, a shift often occurs on the time axis between the timing signal and the synchronizing signal in the video signal.
As shown in (g), a timing difference Δt occurred. This timing difference Δt hinders normal expansion (demodulation) of the synchronization signal component included in the video signal, and noise is generated in the demodulated video signal as shown by a circle in FIG. , Reduced image quality.

In CATV, long-distance transmission is often performed, and an FM audio signal is amplified by a relay amplifier in order to correct signal attenuation in the middle. Since amplitude limiting processing is performed in the amplification of the FM modulated wave, in the above-described conventional scrambling device, the timing signal added by the AM component to the FM audio signal is lost, so that there is a case where scrambling is not formed.

[0022]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and a video signal in which the amplitude of an area including a synchronization signal is compression-modulated by a timing signal synchronized with the synchronization signal. Transmitting means for transmitting a TV signal comprising: a TV signal from the transmitting means; and an amplitude of a region including a compressed synchronization signal in the video signal, based on the timing signal extracted by demodulation. In a scrambler comprising a receiving means for expanding, the timing signal for expanding the amplitude of a region including the synchronization signal is generated from a video signal in the TV signal received by the receiving means. And

As described above, the apparatus of the present invention generates a timing signal for extending the amplitude of the area including the synchronization signal from the video signal of the TV signal received by the receiving means.
A good reproduced image can be obtained without being affected by the difference in the transmission speed between the audio signal and the video signal in the transmission system as in the related art.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the scrambler according to the present invention will be described below in detail with reference to FIGS. The same components as those of the conventional configuration shown in FIG. 3 are denoted by the same reference numerals, and detailed description is omitted.

That is, as shown in FIG.
Is composed of an IF modulation circuit 1 to which a TV signal composed of a video signal a and an audio signal is supplied, and a scramble modulation circuit 7 and a transmission frequency conversion circuit 3 connected to the IF modulation circuit 1.

The video signal a on which the synchronizing signal as shown in FIG. 2A to be scrambled is superimposed is supplied to the timing generator 11 of the IF modulation circuit 1 and the VSB-AM modulator 1.
2 respectively.

The timing generator 11 introduces the video signal a and synchronizes with the horizontal synchronizing signal included in the video signal as shown in FIG. Since the timing signal b having the width H 'is generated, the timing signal b is used as a compression pulse signal for suppressing the horizontal synchronization signal.

The timing signal b is supplied to the video amplitude modulator 71 of the scramble modulation circuit 7, and the video amplitude modulator 71 receives the timing signal b and
The VSB-AM modulated wave from the B-AM modulator 12 is approximately 50
VSB-AM modulated wave that is AM-modulated in the negative direction and the amplitude of the region including the horizontal synchronization signal is compressed, that is, FIG.
Is generated and supplied to the combiner 31 of the transmission frequency conversion circuit 3.

Since the audio signal FM-modulated by the FM modulator 13 is supplied to the synthesizer 31, the frequency converter 32 synthesizes the audio signal with the scrambled video modulation signal.
The transmission frequency is converted to a transmission frequency, and transmitted as a TV transmission signal in which a synchronization signal in a CATV or the like is suppressed by a transmission path to each subscriber on the receiving side B.

As described above, from the transmitting side A, the VSB-AM modulated wave in which the AM is modulated by the scramble signal b in the negative direction by about 50% and the horizontal synchronizing signal is compressed is synthesized with the FM-modulated audio signal. Transmitted.

On the other hand, on the receiving side B, the TV signal for suppressing the synchronizing signal received via the transmission line is supplied to a descrambled reception frequency conversion circuit 4 constituting a terminal, where it is frequency-converted, Similarly, video I
F signal and audio IF signal are separated and output.
The F signal is supplied to the VSB-AM demodulator 61 of the reception IF demodulation circuit 6.
Is supplied to the FM demodulator 62 and demodulated to be derived as a predetermined TV audio signal.

VSB-A with added suppressed synchronizing signal
The M modulated wave is AM-demodulated by the VSB-AM demodulator 61,
The signal is supplied to a timing demodulator 81 and a voltage control amplifier (VCA) 82 of the IF demodulation unit 8.

The timing demodulator 81 is constructed in the same manner as the AM demodulator 52 shown in FIG. 3, and extracts the added timing signal e for amplitude expansion from a predetermined TV video signal demodulated by the VSB-AM demodulator 61. , To the voltage controlled amplifier 82.

Accordingly, the voltage control amplifier 82 amplifies the amplitude of the synchronizing signal in the demodulated video signal in the extension direction based on the timing signal e extracted by the timing demodulator 81, as shown in FIG. A predetermined VSB-AM signal that has been descrambled and that can be supplied to a general TV receiver including a regular synchronization signal is obtained.
As described above, the IF demodulation unit 8 amplifies and expands the amplitude of the area including the synchronization signal component in reverse to the modulation on the video transmission side, based on the timing signal e generated by demodulating the video signal, thereby decompressing. Since the scrambled video signal is extracted, there is no difference on the time axis between the synchronization signal and the timing signal e in the descrambling, and a TV received image signal without distortion can be obtained.

As described above, according to the device of the present invention,
Since the timing signal is generated from the demodulated wave of the transmitted video signal, descrambling without a timing difference between the synchronization signal and the synchronization signal is performed and a good received TV image is formed. The effect is obtained.

[0036]

According to the present invention, a descrambling timing signal is generated from a demodulation synchronization signal in a video signal, and the synchronization signal of the received video signal is expanded and amplified. It has a great practical effect.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a scrambling device according to the present invention.

FIG. 2 is a signal waveform diagram of the device shown in FIG.

FIG. 3 is a configuration diagram showing a conventional scrambling device.

4 is a signal waveform diagram of the device shown in FIG.

FIG. 5 is a partially enlarged view of the signal waveform diagram shown in FIG. 4;

6 is an enlarged view of a main part of a TV video demodulated signal of the device shown in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 IF modulation part 11 Timing generator 12 VSB-AM modulator 13 FM modulator 3 Transmission frequency conversion part 4 Reception frequency conversion part 6 VSB-AM demodulation part 7 Scramble modulation part 71 Video amplitude modulator 8 IF demodulation part 81 Timing demodulation vessel

Claims (4)

[Claims] 1. A transmitting means for transmitting a TV signal composed of a video signal whose amplitude in a region including a synchronizing signal is compression-modulated by a timing signal synchronized with the synchronizing signal, and receiving a TV signal from the transmitting means, A scrambling device comprising: receiving means for expanding the amplitude of a region including a compressed synchronization signal in the video signal based on the timing signal extracted by demodulation; and extending the amplitude of the region including the synchronization signal. A scrambling device for generating the timing signal for use from a video signal in the TV signal received by the receiving means. 2. The transmitting means synthesizes an FM-modulated audio signal and an AM-modulated video signal whose amplitude in a region including a synchronization signal is compression-modulated by a timing signal synchronized with the synchronization signal, and transmits the combined signal. The scrambler according to claim 1, wherein the scrambler is configured. 3. The receiving means comprises: a vestigial sideband-AM demodulation circuit for demodulating a received modulated video signal; a timing signal forming circuit connected to the circuit for generating the timing signal; 2. A signal amplification circuit receiving a timing signal and extending the amplitude of the synchronization signal in a video demodulation signal derived from the vestigial sideband-AM demodulation circuit. The scrambler according to claim 2. 4. The receiving means is configured to derive an audio signal demodulated by an FM demodulator and the video demodulated signal whose synchronization signal has been expanded in amplitude by the signal amplifying circuit. The scrambler according to claim 3, wherein