JPS60102075A - Scramble circuit of tv signal - Google Patents

Abstract

PURPOSE:To prevent unjust interception by changing a pulse width of a key signal and generating a time difference between a level compressed part of a TV signal and the key signal so as to apply scrambling thereby making the corresponding descrambling system at the terminal device side complicated. CONSTITUTION:A synchronizing signal separated from a video input signal is used to generate a timing pulse at the horizontal and vertical blanking period at a timing pulse generator 12. The timing pulse is inputted to a gain variable amplifier 13 to which an IF video signal is inputted and the pulse is compressed to a level of the IF video signal at the horizontal and vertical blanking periods. On the other hand, the timing pulse is inputted to a pulse width converter 20, where the pulse width of the key signal is converted and the result is superposed to an IF sound signal via a delay circuit 22. The IF sound signal superposed with the key signal and the IF video signal subject to blanking period level compression are mixed and the result is outputted in scrambled state as an IFTV signal output.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a TV signal scrambling circuit in the CATV system.

Conventionally, as this type of scrambling circuit, the one shown in FIG. 1 is known. Here, the sync signal separator 1 separates and detects the sync signal from the video A48, and from this sync signal, the timing pulse generator 2 generates the timing pulse Jj of the horizontal blanking and vertical blanking period, and 11,1 predetermined from the horizontal blanking period
Key No. 151, which is input immediately before the ``?i'', is generated.The above timing pulse
'V is input to the variable amplifier 3, and the level of the horizontal blanking and vertical blanking periods of the IF video signal g is compressed. On the other hand, the above key signal is input to the amplitude modulator 4 which manually controls the 1F audio signal, and applies amplitude modulation to the IF audio signal. The IF video signal scrambled in this way and ■
``The audio signals are mixed and output as an IFTV signal.

The IF video signal scrambled in this manner is descrambled by a descrambling circuit (see FIG. 2) in the terminal.

Here, the audio signal is extracted from the IF TV signal sent to the audio filter 5, demodulated by the amplitude demodulator GT'', and then converted to the key (
Play issue 8. This regenerated key signal is used to generate a timing pulse! With ij 7, R length U is converted to a predetermined pulse width, and the timing pulse for the horizontal blanking and vertical blanking periods is 1! I will. The above timing pulse is input to the variable gain amplifier 8, which expands the level of the horizontal retrace line and vertical line portion (9ii) of LFTVI@, thereby outputting a descrambled IFTV signal.

In such a system, the descramble circuit is constructed by a relatively simple circuit assembly without using a regular circuit, and therefore has the disadvantage that it is easily viewed by surreptitious viewers.

The present invention has been made based on the above-mentioned circumstances, and it creates a time difference between the level compression part of TV video (iJ'FV) and the key signal by changing the pulse width of the key signal. This is an attempt to provide a TV double signal scrambling circuit that complicates the digital descrambling system on the terminal side and prevents eavesdropping.

For this purpose, the present invention provides a TV beam (horizontal l in the image signal).
II] Gain q for level compression of signal and vertical synchronization signal
In an amplitude modulator that superimposes a key signal indicating the level-compressed area on the TV audio signal, the 1-
1 and the level-compressed area.
The circuit for transmitting n, 'JI'l+;', -information+IJ between time and VJ is 1-11, and 1j1 is defined as 1-11.

Hereinafter, one embodiment of the present invention will be described in detail with reference to Figures 3 to 5.
is a synchronization signal separator, which separates the signal 1tll lei >'j from the video input signal. The separated synchronization signal is sent to a timing pulse generator 12.
A timing pulse for the period of horizontal 9 line erasure and vertical 11) line erasure is generated. The above timing pulse is I
It is input to the variable gain amplification 3313 which has already inputted the F video signal G, and performs level compression during the horizontal blanking and vertical b5 blanking periods of the 1F video signal. On the other hand, the timing pulse is input to the pulse width converter 20.

Turn to the pulse width converter 20, ■, 1 difference setting device 19
An output signal is input from the input terminal, which changes the pulse width of the key signal (timing pulse). For example, as shown in FIG. 5, when a time difference T2 is input to the time difference setting device 19, $-(H is converted into a pulse having a pulse width T1 by the pulse width converter 20. A pulse having a pulse width T1 is transmitted by a variable delay circuit 21 to IFl.
It is delayed so that it is placed before the level compression section C of lJ image No. 13 by a time difference Tz. 1. When another time difference T4 is input to the time difference setter 19, the pulse width converter 20 converts the key signal into a pulse having a pulse width T. This pulse is transmitted to I by the r11 variable delay circuit 21.
The level compression section C of the F video signal 4 is delayed so that it is placed before the interval T4. Then, the output pulse of the variable delay circuit 21 is input to the amplitude modulator 14, and the key number 15 is superimposed on the IF audio signal as shown at A in FIG.
It is. On the other hand, in the 4Ft variable amplifier 3, the horizontal blanking and vertical blanking periods of the IF video signal are set to B in FIG.
As shown in the figure, the level is compressed. Then, the output of the variable gain amplifier 13 and the output of the amplitude modulator 14 are mixed and output in a scrambled state as a signal to the IFTV.

This J, scrambled IFTV signal is! Descrambling is possible using a <G't'isk simple circuit as shown in FIG.

That is, here, the reputation signal is separated from the TV signal by the three-way filter 1j, and this is demodulated by the amplitude demodulator 16. This demodulated signal is input to the pulse width detector 22 and the C/C mixing generator 11. In the timing generator 17, T I shown in FIG.
A timing pulse is generated that has the time necessary to level-expand the level compression section C of the video signal.
This is because the pulse width detector 22'c detects the time 1-t and drives the variable delay circuit 23 with the information obtained by Ir/. After a delay of T2 or 4 depending on the pulse width, the signal is output to the variable amplifier 18 with a gain of 1!7. Therefore, the ``1q variable 11'' 1-width amplifier 18 performs a level expansion operation with the output of the variable delay circuit 23, and the IFT
Level compressed horizontal blanking and vertical blanking FA in V signal
The level of the erasing period is expanded and the descrambled jrmTV signal is output.

In the above embodiment, a means for transmitting time difference information using the pulse width of the key signal superimposed on the IFF voice signal is provided, but a system in which other means for transmitting data is provided is not applicable. , a means for transmitting time difference information using several pits of this data may be provided. In addition, in the above embodiment, the case where there are two types of time differences, T2 and T4, has been explained, but there may be a plurality of time differences as necessary, and by increasing the number, Jζ more complicated scrambling is achieved.

As described in detail above, the present invention is applicable to the level compression section of the IFF image signal and the key signal superimposed on the IF audio (G signal).
Multiple time differences can be set, so by changing the time difference for each TV channel, it is difficult to stealth viewing, or by randomly changing the time difference for the same TV channel, by simply adding a circuit, Since it becomes difficult for eavesdropping to occur, the scrambling effect can be fully demonstrated. Furthermore, since a normal circuit for descrambling as a terminal device is not so troublesome, a descrambling circuit corresponding to the scrambler type 11 does not significantly increase the cost.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional scrambling circuit;
Figure 4 is a block diagram of a conventional descramble circuit corresponding to this, Figure 13 is a block diagram of a scramble circuit showing an embodiment of the present invention, and Figure 4 is a block diagram of a disk simple circuit corresponding to this. Figure 5 is a diagram showing the scrambling situation of the IF video/video signal sent to the scramble circuit and the IF Otokawa: bow. 11... Synchronization signal 11Ki, 12... Timing generator, 13... Gain 1f1 variable amplifier, 14... Amplitude modulator, 15... Sound signal filter, 1G...
Amplitude demodulator, 17...timing generator, 18...
Variable gain amplifier, 19... Time difference setting device, 20...
Pulse width variation H! device, 21... variable delay circuit, 22...
- Pulse width detector, 23...variable delay circuit.

Claims (1)

[Claims] A variable gain amplifier that compresses the level of a horizontal synchronization signal and a vertical synchronization signal in a TV video signal, and an amplitude modulator that adds a key signal indicating the level-compressed location to the TV audio signal, wherein the level compression A circuit that varies the time between the level-compressed location and the key signal, and transmits time difference information between the level-compressed location and the key a@! 1. A TV signal scrambling circuit, characterized in that it comprises a l-ru circuit.