JP2703758B2 - TV signal transmission / reception system - Google Patents

Description

The present invention relates to a transmission / reception system of a TV signal used for transmission / reception of a pay TV broadcast or the like using CATV or DBS. (2) Prior Art Conventionally, in order to prevent eavesdropping by a third party in a pay TV broadcast or the like, a circuit shown in FIGS.
The signals shown in the figure are used. FIG. 4 shows a transmitter in a TV signal transmission / reception system, and an input terminal.
Video signals and FM audio signals to be transmitted are supplied to 11 and 12, respectively. From the video signal, the sync separation circuit
At 14, the horizontal synchronizing signal and the vertical synchronizing signal are extracted and supplied to the synchronizing suppression signal generating circuit 15. Synchronous suppression signal generation circuit
15 is a signal corresponding to the signal shown in FIG.
A synchronization suppression signal C which becomes a high level in the section of each synchronization signal is generated and supplied to the synchronization suppression circuit 13 and the amplitude modulation circuit 16. In the synchronous suppression circuit 13, the portion of the synchronization signal of the video signal supplied to the input terminal 11, i.e., a horizontal sync signal in FIG. 6 point of time T ₁ (a), in place of the time T ₂ The vertical synchronizing signal is level-compressed by about 6 dB to 10 dB and supplied to the adding circuit 18. The amplitude modulating circuit 16 has a sixth synchronizing signal of the FM audio signal supplied to the input terminal 12 whose amplitude is large with respect to the synchronous suppressing signal C supplied from the synchronous suppressing signal generating circuit 15. An amplitude-modulated FM audio signal B shown in FIG. The outputs of the synchronization suppression circuit 14 and the amplitude modulation circuit 16, that is, the synchronization suppression video signal A and the amplitude modulation FM audio signal B are added by the addition circuit 18 and output from the output terminal 19.
The signal is output as a signal, and then modulation and transmission output according to the propagation path are performed. FIG. 5 shows a receiver in the TV signal transmission / reception system. In the figure, a TV signal including a synchronization-suppressed video signal A and an amplitude-modulated FM audio signal B sent from the transmitter described in FIG. 4 is supplied to an input terminal 1. Sync suppression video signal A, the horizontal sync signal in FIG. 6 point of time T ₁ as shown in (a), but also the vertical synchronizing signal at the point of time T _2,
Each level is compressed by about 6dB to 10dB. Also,
The amplitude-modulated FM audio signal B is amplitude-modulated by a synchronization suppression signal whose level changes to a high level at a point where the video signal is level-compressed (signal B in FIG. 6B). The amplitude-modulated FM audio signal B is frequency-separated from the video signal A by the audio signal filter 3 and detected by the AM detection circuit 4 (signal C in FIG. 6C). The pulse width of the output signal C of the AM detection circuit 4 is adjusted by the pulse width adjustment circuit 5,
A signal D having an increased pulse width is generated so that the synchronization-suppressed video signal A becomes a high level corresponding to a position where the horizontal synchronization signal and the vertical synchronization signal are level-compressed. The pulse width adjustment circuit 5 includes, for example, a time constant circuit and a level slicer. The synchronization suppression release signal D output from the pulse width adjusting circuit 5 becomes a high level corresponding to the position where the horizontal synchronization signal and the vertical synchronizing signal of the synchronization suppression video signal A are level-compressed. By supplying the signal to the amplifier 2 and controlling the gain, the TV signal before the scramble is restored as shown by the broken line in FIG. 6 (a). Thus, transmission and reception of the TV signal are performed. (3) Problems to be Solved by the Invention The conventional TV signal transmitting and receiving system shown in FIGS. 4 and 5 has advantages such as simplification of the circuit, but FIG. The synchronization suppression release signal D shown in FIG. 6 (d) can be easily created only by AM detection of the amplitude-modulated FM audio signal B shown in FIG. There is a problem that the purpose of the transmission / reception system cannot be achieved. On the other hand, JP-A-60-163588 "Scrambling method in pay television system" includes a technique of suppressing a level of at least one of a horizontal synchronizing signal and a vertical synchronizing signal, performing a video scrambling process, and performing an audio during this level suppressing period. The polarity of the signal is inverted, the scrambled audio signal is FM-modulated, and a TV signal is added to the synchronization-suppressed video signal and FM audio signal, with a timing signal added to specify the level suppression period. There is disclosed a TV signal transmission / reception system that cancels video scrambling and audio scrambling based on a signal. However, this is a system for scrambling a TV signal for both video and audio to prevent eavesdropping. For descrambling, a timing signal for specifying a level suppression period is replaced by a video signal or audio. It is necessary to transmit the signal separately from the signal, and it is impossible to determine the scramble period, that is, the synchronization suppression period from the received FM audio signal. Also, since the polarity of the audio signal is inverted in accordance with the synchronization suppression period before FM modulation, from the viewpoint of FM modulation, a normal signal is transmitted only during the synchronization suppression period.
Equivalent to obtaining a modulated signal with 0 degree phase inversion, resulting in FM
FM demodulation is likely to be adversely affected by the unnaturalness that the density of the modulated wave suddenly changes, and even if the synchronization suppression period of the FM demodulation output can be reproduced with the polarity restored, the polarity restored part and the original polarity remain the same. Since the continuous portion cannot be connected smoothly, there is a problem that demodulation noise is liable to be parasitic. In addition, the timing signal indicating the beginning of the synchronization suppression period has the same pulse width for both the horizontal synchronization signal and the vertical synchronization signal, and is simply modulated at a high frequency in the timing signal modulation unit and transmitted. Only. That is, too much is captured by a technical concept including a wide scrambling process such as performing synchronization suppression in at least one of the horizontal synchronization signal period and the vertical synchronization signal period, such as performing synchronization suppression in both the horizontal synchronization signal period and the vertical synchronization signal period. Under the more limited conditions, it is clear that no technical pursuit has been made to intentionally vary the pulse width in consideration of the distinction between the horizontal synchronization signal period and the vertical synchronization signal period on the receiving side. Met. Common sense is to use the high frequency used for modulation in the timing signal modulator on the transmitting side and the vertical synchronizing signal in order to allow the receiving side to identify the type of correspondence between the horizontal synchronizing signal period and the vertical synchronizing signal period. It is indispensable to take measures such as switching to a different frequency during the signal period, which complicates the configuration of the timing signal modulation unit, and also complicates the configuration of the timing signal demodulation unit prepared on the receiving side. Had a problem. (4) Means for Solving the Problems The present invention has an object to effectively prevent eavesdropping with a simple circuit configuration, and separates synchronization from a video signal and performs horizontal and vertical synchronization. Generating a synchronization suppression signal corresponding to the signal period, generating a synchronization suppression image signal by level-compressing the video signal in a horizontal synchronization signal period and a vertical synchronization signal period based on the synchronization suppression signal; A timing pulse indicating the correspondence type between the horizontal and vertical synchronization signal periods with different pulse widths is generated in synchronization with the start end of the FM audio signal in each of the synchronization signal periods by the timing pulse based on the timing pulse. The amplitude of the modulated FM audio signal is generated by differentiating the amplitude from the other periods, and the amplitude modulated FM audio signal is mixed with the synchronization-suppressed video signal to form a TV signal. A V signal transmitter, receiving the TV signal transmitted from the TV signal transmitter, extracting an amplitude modulated FM audio signal from the TV signal, amplitude demodulating the amplitude modulated FM audio signal, Extracting, performing a pulse width conversion having a different widening amount according to the pulse width on the timing pulse to generate a synchronization suppression release signal substantially corresponding to each of the horizontal synchronization period and the vertical synchronization period, and based on the synchronization suppression release signal. A TV signal receiver for canceling level compression of the synchronization-suppressed video signal included in the TV signal. (5) Function According to the present invention, the FM audio signal is not amplitude-modulated by the synchronization suppression signal corresponding to the synchronization suppression period of the synchronization suppression video signal as it is, but instead of the horizontal synchronization signal period and the vertical synchronization signal period. Since the amplitude is modulated by a timing pulse that has a different pulse width and indicates the beginning of the synchronization suppression period but does not correspond to the synchronization suppression period, the amplitude modulation is performed on the receiving side.
It is not possible to generate a synchronization suppression cancellation signal for canceling the suppression of the video signal only by amplitude demodulation of the FM audio signal, and it is possible to effectively prevent eavesdropping. (6) Example Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 and FIG. 2 are block diagrams showing one embodiment of a TV signal transmission / reception system according to the present invention. FIG. 1 shows a transmitter in a TV signal transmission / reception system. In FIG. 1, video signals and FM audio signals to be transmitted are supplied to input terminals 11 and 12, respectively. From the video signal, a horizontal synchronizing signal and a vertical synchronizing signal are extracted by a sync separation circuit 14 and supplied to a synchronization suppression signal generation circuit 15. The synchronization suppression signal generation circuit 15 generates a synchronization suppression signal that goes high in each of the horizontal and vertical synchronization signal periods, and supplies the synchronization suppression signal to the synchronization suppression circuit 13 and the pulse width converter 17. In the synchronous suppression circuit 13, the portion of the synchronization signal of the video signal supplied to the input terminal 11, i.e., a horizontal sync signal in FIG. 3 points of time T ₁ (a), in place of the time T ₂ The vertical synchronizing signal is level-compressed by about 6 dB to 10 dB, and supplied to the adding circuit 18 as a synchronizing suppressed video signal. Further, based on the synchronization suppression signal supplied from the synchronization signal suppression signal generation circuit 15, the pulse width converter 17 has a pulse width t ₁ from the beginning of the horizontal synchronization signal period, as shown in FIG. create a timing pulse C of, for generating a timing pulse C of the pulse width t ₂ from the beginning of the vertical sync signal period. The timing pulse C carries information on the beginning of the rising synchronization suppression signal. Although the magnitude of the pulse width carries information on the type of the vertical and horizontal synchronization signal periods, the width of the synchronization suppression period itself does not. The timing pulse C is supplied to the amplitude modulation circuit 16 for the amplitude modulation of the FM audio signal. The amplitude modulation circuit 16 is supplied to the input terminal 12 according to the timing pulse C supplied from the pulse width converter 17
The signal shown in FIG. 3B in which the FM audio signal is amplitude-modulated and the amplitude becomes large during the pulse period of the timing pulse C;
That is, the amplitude modulation FM audio signal B is generated. The outputs of the synchronization suppression circuit 13 and the amplitude modulation circuit 16, that is, the synchronization suppression video signal A and the amplitude modulation FM audio signal B are added by the addition circuit 18 and output from the output terminal 19 to be a TV signal. Then, the modulation and the transmission output according to the propagation path are performed. FIG. 2 shows a receiver in the TV signal transmission / reception system. In FIG. 2, a TV signal including a synchronization-suppressed video signal A and an amplitude-modulated FM audio signal B is supplied to an input terminal 1. Sync suppression video signal A, as shown in FIG. 3 (a), the horizontal synchronization signal at the point of time T _1, also the time
Vertical sync signal at the point of T ₂ is 6dB~10dB about levels of compression, respectively. Amplitude modulated FM audio signal B is amplitude modulated by the timing pulses C, the timing pulse C, as shown in FIG. 3 (c), the high level from the beginning of the horizontal synchronizing signal period by a pulse width t ₁ It sustained, also, has only the pulse width t ₃ from the beginning of the vertical sync signal period and pulse lasting a high level. Note that the amplitude modulation shown in this embodiment is
In FM audio signal B, only the last equivalent pulse included in the vertical synchronizing signal period is so that use the modulation as the signal b _4, other equivalent pulse included in the vertical synchronizing signal period is not utilized . Among the TV signals supplied to the input terminal 1, an amplitude-modulated FM audio signal B is frequency-separated and extracted by an audio signal filter 3, and is amplitude-demodulated by a subsequent AM detection circuit 4, and as shown in FIG. The indicated timing pulse C is extracted. The signal C output from the AM detection circuit 4 is supplied to a pulse width adjustment circuit 5, a pulse width detection circuit 6, and a reset terminal R of a flip-flop 7. The pulse width adjusting circuit 5 is a circuit that widens the pulse width t ₁ to the pulse width T ₁ , and includes, for example, a time constant circuit and a level slicer. May be reversed time is constituted by the monostable multivibrator of the T _1. The output of the pulse width adjusting circuit 5 is supplied to the input terminal of the OR gate 8 after the pulse width is widened as in a signal D shown in FIG. Pulse width detection circuit 6, the pulse width of the timing pulse C is a circuit for determining whether the pulse width t ₁ or the pulse width t _3, for example, triggered reversal time at the rise of the input pulse and the monostable multivibrator of t ₁ , And an AND gate that takes the logical product of the output of the mono-multivibrator and the timing pulse C. Pulse width detection circuit 6
Outputs an output signal which becomes high level when the elapsed from the rising edge of the timing pulse C ₃ shown in FIG. 3 (c) by time t _1. The output of the pulse width detection circuit 6 is supplied to the set terminal S of the flip-flop 7. The flip-flop 7 is set when the output of the pulse width detection circuit 6 rises, and is reset when the timing pulse C output from the AM detection circuit 4 rises.
Type flip-flop. The output Q of the flip-flop 7 becomes like the signal E shown in FIG. 2 (e) and is supplied to the input terminal of the OR gate 8. The OR gate 8 performs an OR operation on a signal D output from the pulse width adjustment circuit 5 and a signal E output from the flip-flop 7. The output is the signal shown in FIG. 3 (e), that is, the synchronization suppression release signal F. The sync suppression cancel signal F, since the signal becomes a high level at the point of time T ₁ and time T ₂ of the signal A, and supplies the synchronization suppression cancel signal F to the variable gain amplifier 3, only time that the high level Increase the gain. This makes it possible to restore (descramble) the TV signal before level compression (scramble) from the signal supplied to the input terminal 1. The restored TV signal is supplied from an output terminal 9 to an external TV receiver or monitor. As described above, according to the TV signal transmission / reception system, the types of correspondence between the horizontal and vertical synchronization signal periods are indicated by different pulse widths in synchronization with the start end of the synchronization suppression signal corresponding to the horizontal and vertical synchronization signal periods. Since the timing pulse C is generated and the amplitude of the FM audio signal is modulated based on the timing pulse C, the FM audio signal itself does not interfere with the phase of the carrier carrying the audio information due to the timing pulse. Since the signal is not scrambled, eavesdropping prevention cannot be expected,
The audio signal can be normally demodulated by ordinary FM demodulation, and is not related to the sound quality deterioration due to the scramble processing and the descrambling. Also, instead of amplitude-modulating the FM audio signal with the synchronization suppression signal corresponding to the synchronization suppression period of the synchronization suppression video signal as it is, the FM synchronization signal has different pulse widths between the horizontal synchronization signal period and the vertical synchronization signal period. Since the amplitude is modulated by the timing pulse C which only indicates the beginning of the period and does not correspond to the synchronization suppression period,
It is not possible to reproduce the synchronization suppression signal simply by amplitude-modulating the amplitude-modulated FM audio signal.Therefore, it is not possible to easily reproduce the synchronization suppression signal and snoop on the video signal. The timing pulse whose pulse width differs between the period and the vertical synchronization signal period is widened according to the pulse width difference, and the synchronization suppression release signal corresponding to each of the horizontal and vertical synchronization signal periods is obtained to suppress the synchronization suppression video signal Therefore, it is difficult to imitate the pulse width widening process without concealing the processing principle, and it is possible to reliably prevent video signal eavesdropping with a relatively simple circuit configuration. In the case of this embodiment, the pulse width T ₄ of the suppression release signal F
It is precisely shorter than the time T _2. Therefore, the synchronization-suppressed video signal A is output from the variable gain amplifier 2 for a short time while the level is being compressed. However, during the time T ₂ that is visible outside deviated from the image frame of TV screen even within vertical synchronizing signal period, also being outputted while the level compression is even after the last equalizing pulse Since the synchronization signal is accurately restored (descrambled), it does not affect the screen on the TV receiver or monitor connected to the output terminal 9. As described above, the present invention is not limited to the above embodiment, and the following modifications are possible. For example, instead of the flip-flop 7, is triggered by the output of the pulse width detection circuit 6, it is possible to use a monostable multivibrator inversion time T _2. In this case, even without using the signal b ₄ (last equalizing pulse during the vertical synchronizing signal period), it is possible to produce a pulse width T ₂ as a gain control signal. (7) Effects of the Invention As described above, according to the present invention, the correspondence type between the horizontal and vertical synchronization signal periods is synchronized with the start end of the synchronization suppression signal corresponding to the horizontal and vertical synchronization signal periods. Generate timing pulses with different pulse widths,
Since the FM audio signal is amplitude-modulated based on this timing pulse, the phase of the carrier carrying the audio information is not disturbed by the timing pulse, and the audio signal is not scrambled. Therefore, although it is not expected to prevent eavesdropping, the audio signal can be demodulated normally by normal FM demodulation, and there is no sound quality deterioration due to scramble processing and descrambling, and the FM audio signal is synchronized suppression video signal The amplitude is not modulated by the synchronization suppression signal corresponding to the synchronization suppression period as it is, but the horizontal synchronization signal period and the vertical synchronization signal period have different pulse widths, and the synchronization suppression period is indicated only by indicating the beginning of the synchronization suppression period. Because the amplitude is modulated by the timing pulse that does not correspond to the above, the amplitude modulated FM audio signal was amplitude demodulated. In this case, it is not possible to reproduce the synchronization suppression signal, and therefore it is not possible to easily reproduce the synchronization suppression signal and snoop on the video signal, and the receiving side uses a pulse between the horizontal synchronization signal period and the vertical synchronization signal period. It is necessary to widen the timing pulses having different widths according to the difference in the pulse width, and obtain a synchronization suppression release signal corresponding to each of the horizontal and vertical synchronization signal periods to release the suppression of the synchronization suppressed video signal. The widening process is difficult to imitate even if the processing principle is not concealed, and has an excellent effect such that the wiretapping of the video signal can be reliably prevented with a relatively simple circuit configuration.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are block diagrams each showing an embodiment of a TV signal transmission / reception system according to the present invention, and FIG.
Waveform diagrams for explaining the operation of the circuit shown in FIGS. 1 and 2, FIGS. 4 and 5 are block diagrams showing a conventional TV signal transmission / reception system, and FIG. 6 is a diagram shown in FIGS. FIG. 4 is a waveform diagram illustrating the operation of the circuit. 2 ... Gain variable amplifier 4 ... AM detection circuit 5 ... Pulse width adjustment circuit 6 ... Pulse width detection circuit 7 ... Flip flop 8 ... OR gate 13 ... Synchronization suppression circuit 15 ... Synchronization suppression signal generation circuit 16 …… Amplitude modulation circuit 17 …… Pulse width converter

Claims (1)

(57) [Claims] Synchronous separation from the video signal, generating a synchronization suppression signal corresponding to each of the horizontal and vertical synchronization signal periods, and performing level compression on the video signal in the horizontal synchronization signal period and the vertical synchronization signal period based on the synchronization suppression signal. Along with generating a synchronization-suppressed video signal, in synchronization with the start end of the synchronization-suppressed signal, a timing pulse indicating a correspondence type between horizontal and vertical synchronization signal periods with different pulse widths is generated,
Based on the timing pulse, the amplitude of the FM audio signal in each synchronization signal period is made different from the other periods by the timing pulse to generate an amplitude-modulated FM audio signal, and the amplitude-modulated FM audio signal is converted to the synchronization-suppressed video signal. Mix
A TV signal transmitter as a TV signal, receiving the TV signal transmitted from the TV signal transmitter, extracting an amplitude-modulated FM audio signal from the TV signal, and performing amplitude demodulation on the amplitude-modulated FM audio signal. The timing pulse is extracted, and the timing pulse is subjected to pulse width conversion having a different widening amount according to the pulse width to generate a synchronization suppression release signal substantially corresponding to each of the horizontal synchronization period and the vertical synchronization period. A TV signal receiver for canceling the level compression of the synchronization-suppressed video signal included in the TV signal based on the signal.
Signal transmission / reception system.