JP2721163B2 - Synchronous compression scrambler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a synchronous compression scrambler used in a cable television (hereinafter, referred to as CATV) system. (Prior Art) In a CATV system, a pay broadcast program is scrambled and transmitted, and measures are taken so that only subscribers having key data for descrambling can view the program. There are various scramble methods, and among them, a synchronous compression method is one that can be relatively easily realized. This method is a method in which a synchronizing signal section of a video signal is level-compressed and transmitted with respect to a high frequency or an intermediate frequency of a broadcasted television signal. The control signal for notifying the timing of the level compression is superimposed on the voice FM signal in the form of AM modulation and transmitted to the subscriber terminal. On the receiving side, the control signal is extracted, and the level compression section of the scrambled television signal is expanded based on the timing of the control signal. As a result, the demodulated video signal is normally displayed. Here, if the transmission timing of the control signal coincides with the horizontal synchronization section, it is relatively easy to eavesdrop on.
In order to prevent this eavesdropping, a method of transmitting the control signal with a timing shifted (with a delay amount) with respect to the horizontal synchronization section has been considered. In the case of such a method, it is possible to make piracy difficult by changing the delay amount from time to time. (Problems to be Solved by the Invention) According to the above-described scrambling method, when a control signal is reproduced on the receiving side, an extended pulse synchronized with a synchronous compression position is generated by using the reproduced control signal. If the detection is not performed accurately, the phase of the extension pulse will be out of order, and the video signal will be damaged. In order to accurately detect the control signal, the control signal is preferably a square wave. However, when a square wave is superimposed on an audio FM signal in the form of AM, there is a problem that the spread of the spectrum is large and the video signal and the audio signal are disturbed. Conventionally, there has been a system in which a rectangular wave is superimposed on an FM audio signal to notify a receiving side of a synchronous compression position. For reference, FM with conventional system
The audio signal is shown in FIG. 6 (6d). When the control pulse is superimposed and transmitted as described above, if the composite intermediate frequency is descrambled, the FM audio signal contains a rectangular wave as shown in FIG. 6 (6e), which is reproduced as noise. Had to be done. Conventionally, in order to reduce such interference, a method of transmitting a control signal through a low-pass filter on a transmitting side to form a blunt waveform and transmitting the signal has been considered. , The accurate phase information cannot be obtained, and the timing of the extension pulse deviates from the position of the synchronization signal. SUMMARY OF THE INVENTION It is an object of the present invention to provide a synchronous compression scrambler capable of achieving stable and accurate descrambling (descrambling) without interference with image quality and sound quality. [Means for Solving the Problems] According to the present invention, the level of the horizontal synchronizing signal position of the video intermediate frequency is compressed on the transmitting side by the synchronous compression pulse, and the level of the synchronizing position is extended on the receiving side. In a system that performs rumble, the transmitting side AM-modulates an audio intermediate frequency with a sine wave having a specific phase relationship with the horizontal synchronization frequency and two frequencies shifted from each other in time, and synchronously compresses the horizontal synchronization signal. The position information is transmitted by a combination state of the two sine waves. On the receiving side, the two sine waves are obtained by AM detection from the AM-modulated audio intermediate frequency.
Decomposing the combination state of two sine waves to determine the expansion timing of the horizontal synchronization signal, generate an expansion pulse, and use this expansion pulse to extend the level of the synchronization signal position of the received video intermediate frequency It is. (Operation) By the above means, the sine wave as the control signal superimposed on the audio FM signal in the form of AM has no spread of the spectrum and does not adversely affect the image quality and the sound quality. Further, regarding the prevention of eavesdropping, since the generation timing of the extension pulse can be changed by a combination of the two sine waves, sufficient security can be obtained. Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a transmitting encoder according to an embodiment of the present invention. An audio signal is supplied to the input terminal 11,
The input terminal 15 is supplied with a video signal. The audio signal is FM-modulated in the intermediate frequency modulator 12. The FM audio intermediate frequency is converted into a digital analog (D /
A) The sine wave from the converter 27 is superimposed in the form of AM, and the FM audio intermediate frequency on which the sine wave is superimposed is mixed with the video intermediate frequency in the mixer 14 and input to the high-frequency modulator 18 to be input to the high-frequency modulator 18
Converted to RF. On the other hand, the video signal is supplied to the intermediate frequency modulator 16
Is converted to the video intermediate frequency. The video intermediate frequency is subjected to scramble processing in a gain control circuit 17 constituting a level compression means, and the level of the synchronization signal is compressed by a compression pulse from the monomultivibrator 24,
The scrambled video intermediate frequency is FM-mixed by mixer 14.
It is mixed with the audio intermediate frequency and converted into a high frequency signal by the high frequency modulator 18. Further, the video signal is supplied to the sync separation circuit 21, and the vertical
The horizontal sync signal is separated. The separated vertical and horizontal synchronization signals are supplied to the counter 22. The counter 22 supplies the count data to the decoder 23. The decoder 23 can obtain the synchronous compression timing from the count content, and supplies the timing pulse to, for example, the mono multivibrator 24. The compressed pulse obtained from the mono multivibrator 24 is supplied to the gain control circuit 17, and compresses the horizontal synchronization signal position of the video intermediate frequency by, for example, 6 dB. FIG. 3 (3a) shows the video intermediate frequency before scrambled, FIG. 3 (b) shows the compressed pulse, and FIG. 3 (c) shows the scrambled video intermediate frequency. Returning to FIG. 1, the description will be continued. The vertical and horizontal synchronization signals separated by the synchronization separation circuit 21 are also supplied to the decoder 25. The decoder 25 supplies a frequency switching signal (specifically, a switching signal between fH and 4fH, fH is a horizontal frequency) to the conversion table circuit 26, and the switching timing is synchronized with the separated synchronization signal. The conversion table circuit 26 constituting the sine wave generation means stores sine wave generation data, and is driven by a clock from the counter 22. The output data of the conversion table circuit 26 is a D / A converter 27
Is supplied to the sine wave superimposing circuit 13 as an analog sine wave. Therefore, according to the above encoder, normally, a sine wave of 4fH is superimposed on the FM audio intermediate frequency in the form of AM, and when transmitting data to the receiving side, when the fH wave is superimposed on three waves, "0" If "1" is set when six fH waves are superimposed, data can be freely transmitted to the receiving side. FIG. 4 (4a) shows an example of a sine wave demodulated on the receiving side. T1 and T3 are 4fH sine wave periods, and T2 is fH
Is the period of the sine wave. This example means that the data “1” has been transmitted because there are three sine waves of fH. Returning to FIG. 1, the description will be continued. When data is transmitted as described above, the data content is determined by the switching timing of the switching signal output from the decoder 25. The decoder 25
When transmitting data to be held on the receiving side, data of a format determined in advance for each vertical cycle or a plurality of vertical cycles is transmitted, for example. Furthermore, this decoder
25, after transmitting the data, corresponding to this data,
The key information required to descramble is fH and 4fH
Is transmitted by a combination of sinusoidal waves of This function will be further described with reference to FIG.
This will be described with reference to FIG. FIG. 2 shows a decoder. The high-frequency signal introduced to the input terminal 31 is converted by the tuner 32 into a composite intermediate frequency signal. The composite intermediate frequency signal includes a video intermediate frequency signal and an audio intermediate frequency signal. The intermediate frequency signal is output from the gain control circuit 33 as a signal whose horizontal synchronizing signal is expanded by an expansion pulse and is descrambled.
Derived to 34. On the other hand, a sine wave is extracted from the FM audio intermediate frequency signal in the AM detection circuit 35 constituting the sine wave reproducing means.
FIG. 4 (4a) shows an example of the extracted sine wave.
The output of the AM detection circuit 35 is supplied to an fH filter 36 that extracts a frequency component of fH and a 4fH filter 37 that extracts a frequency component of 4fH. The 4fH sine wave extracted by the 4fH filter 37 is
While being supplied to the clock input terminal of the counter 40,
The signal is supplied to the 4fH detection circuit 38. The counter 40 has fH
The output of the filter 36 is also supplied, and the counter 40
When the output of the filter 36 exists, the counting operation is stopped. When detecting the 4fH sine wave, the 4fH detection circuit 38 supplies the detection output to the counter 40 and also supplies the data to the data separation circuit 39. 4 (b) shows the output of the fH filter 36, FIG. 4 (c) shows the output of the 4fH filter 37, and FIG. 4 (d) shows the detection output of the 4fH detection circuit 38. In FIG. 4, since there are three fH sine waves, it means that data "1" has been transmitted as described above. This data is determined by a data separation circuit 39. When the data is transmitted in a predetermined format in a vertical period, the data separation circuit 39 holds a predetermined number of bits in a parallel state and outputs the data. I do. Next, during periods other than the vertical synchronization period, 4f shown in FIG.
At the rise of the H detection signal, a process for descrambling is started. That is, the vicinity of the period TX in FIG. 4 is enlarged and shown in FIG. When detecting the 4fH sine wave after the fH sine wave, the 4fH detection circuit 38 raises the detection signal (FIG. 4 (4d)) (at the time). When this detection signal is input, the counter 40 starts counting from the time when the 4fH signal first rises (time) after the time when the output of the fH filter 36 first crosses zero, and counts each time the zero crossing occurs. Proceed. However, in this case, the counter 40 is a data separation circuit 39
The data held in is preset as desired data. In the case of this embodiment, the data preset in the counter 40 is 5 (decimal), and the counter 40 is an octal counter. When the counter 40 advances counting to 5, 6, 7 and becomes 0,
The contents of this counter are detected by the decoder 41. When the counter 40 becomes 0, the decoder 41 generates an expansion timing pulse and supplies it to the mono multivibrator 42.
The mono-multi vibrator 42 generates an expansion pulse having a predetermined width when the expansion timing pulse is input, and expands the compressed synchronization signal, that is, performs descrambling. FIG. 5 (5c) shows the counting state of the counter 40, and FIG. 5 (5d) shows the extension pulse. Thereafter, the above operation is repeated when fH arrives again, or 4fH
Is continuous, the counter 40 counts in octal, and
, An extension pulse is generated. Further, the output of the 4fH detection circuit 38 is also supplied to the integration circuit 43. When the sine wave of 4fH is not detected for a long time, the integration circuit 43 determines that the current signal has not been scrambled, and stops the operation of the decoder 41. As described above, the present invention realizes the timing at which an extension pulse is to be generated by combining two sine waves in the time axis direction. Further, data transmission as obtained by the data separation circuit 39 is performed by combining two sine waves. In the above embodiment, m times fH (M
= 4) and a sine wave having a frequency n times (n = 1) is realized. And by this combination, the counter 40
Is transmitting preset data. Here, it is clear from the above description that the generation timing of the extension pulse can be changed by changing the preset data. The fact that the generation timing of the extension pulse can be changed means that in the above embodiment, the time interval between the switching point of the sine wave of fH and 4fH and the synchronous compression position can be changed. Therefore, even if the sine wave of fH is illegally detected to generate an extension pulse and the scramble is canceled, it is impossible to know the generation timing. When changing the preset data, for example, two sine waves can be combined and transmitted in a predetermined format during the vertical synchronization period and changed, and when the format is detected, the data separation circuit takes in the preset data. . FIG. 6 is a signal waveform diagram for explaining the effect of the present system on an FM audio signal. Since the FM audio signal (FIG. 6 (6a)) modulated by the sine wave in the form of AM is included in the composite intermediate frequency signal, when passing through the gain control circuit 33 shown in FIG. Under the influence of (FIG. 6 (6b)), there is a period of expansion as shown in FIG. 6 (6c). Since the synchronous compression was performed only on the video intermediate frequency signal, it is actually only necessary to perform the video intermediate frequency signal, but in order to do so, once the video intermediate frequency and the FM audio intermediate frequency And must be separated. If the separation is performed in this manner, the configuration becomes complicated. Therefore, in the present system, the synchronous expansion is performed in the state of the composite intermediate frequency. As a result, the FM audio signal has a level extension section as shown in FIG. 6 (6c). However, in this device, the signal superimposed on the FM audio signal is a sine wave, so that the spectrum spreads. Instead, it is played back as this expanded part noise,
No distortion is given to the stereo component of the audio signal. When a control pulse as shown in FIG. 6 (6d) is superimposed on a conventional FM audio signal and transmitted, when the composite intermediate frequency is descrambled, the FM audio signal becomes a rectangular wave as shown in FIG. 6 (6e). , Which may be reproduced as noise. However, in this embodiment, there is no problem as in the prior art, and a good reproduced sound can be obtained. [Effects of the Invention] As described above, the present invention can provide a synchronous compression scrambler capable of obtaining stable and accurate descrambling (descrambling) without disturbing image quality and sound quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an encoder according to an embodiment of the present invention, FIG. 2 is a block diagram of a decoder according to an embodiment of the present invention, and FIG. FIGS. 4 and 5 are signal waveform diagrams shown for explaining the operation of the decoder, and FIGS.
FIG. 3 is a signal waveform diagram shown to compare and explain the state of the FM audio signal on the decoder side with the conventional system on the decoder side. 12 ... intermediate frequency modulator, 13 ... sine wave superimposing circuit, 14 ...
Mixer, 16: Intermediate frequency modulator, 17: Gain control circuit,
18 High frequency modulator, 21 Synchronous separation circuit, 22 Counter, 23 Decoder, 24 Mono multivibrator, 25 Decoder, 26 Conversion table circuit, 27
D / A converter, 32 Tuner, 33 Gain control circuit, 35
…… AM detection circuit, 36 …… fH filter, 37 …… 4fH filter, 38 …… 4fH detection circuit, 39 …… data separation circuit, 40…
... Counter, 41 ... Decoder, 42 ... Monomultivibrator.

Claims (1)

(57) [Claims] On the transmission side, a compression pulse generation means for generating a synchronization compression pulse synchronized with a horizontal synchronization signal; a level compression means for level-compressing a horizontal synchronization signal position of a video intermediate frequency by the synchronization compression pulse; And a frequency generating means for generating first and second frequencies that are integer multiples of the horizontal frequency. The first and second frequencies are switched at specified timings, and the first and second frequencies are switched. A sine wave generating means for repeatedly arranging a sine wave of frequency 2 in the time axis direction, a sine wave switching timing of the first and second frequencies arranged in the time axis direction, and synchronous compression of the level compression means The time difference information with respect to the position is determined based on the switching position in the time axis direction of the first and second frequencies and the first or second frequency from the switching position. Control means for expressing the information by combination information with the count value of the sine wave; and controlling the switching timing of the one sine wave from the other to control the compressed horizontal position from the switching timing to a lapse position corresponding to the time difference information. Means for notifying that a synchronization signal is present; AM modulation means for AM-modulating an audio intermediate frequency with the two sine waves arranged in succession; and outputs of the level compression means and AM modulation means. Means, a receiving side, a sine wave reproducing means for obtaining two sine waves of the first and second frequencies from the AM-modulated audio intermediate frequency by AM detection, and a switching timing of the second sine wave; Means for obtaining the time difference information based on the combination information with the count value of the sine wave of the first or second frequency; After detecting the switching point of the sine wave, determine the time after the elapse of the time corresponding to the time difference information as the generation timing of the expansion pulse, and generate an expansion pulse to generate an expansion pulse. A synchronous compression scrambler, comprising: a decompression means for level decompression. 2. The extension pulse generating means has a counter for presetting the time difference information after the period of the one sine wave has elapsed and counting the other sine wave, and when the value of the counter reaches a predetermined value. 2. The synchronous compression scrambler according to claim 1, wherein the decoder outputs the generation timing of the expansion pulse.