JPS625513B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates primarily to a television signal scrambling system used for pay television broadcasting.

The applicant has developed a television signal scrambling method that allows normal reception only on specific receivers for which a reception fee has been paid or a reception contract has been established.

In this method, on the transmitting side, the level of the television signal to be sent is repeatedly changed using a separately generated rectangular wave control signal, in other words, it is scrambled and sent out, and on the receiving side,
The level change of the received television signal on the transmitting side is canceled out by a control signal synchronized with the control signal on the transmitting side, that is, it is descrambled.

According to this method, if the TV receiver is not equipped with a descrambling means, an incorrect scrambled television signal will be received, and a correct image will not be reproduced. Correct images can only be reproduced if

Further, the present invention has excellent advantages such as being able to use existing transmitters and existing TV receivers as they are, and requiring only simple attachments to be added to each, resulting in less economical burden.

However, in TV receivers with fast AGC response, the level of the television signal is determined by the AGC.
The circuit may compensate to some extent, reducing the scrambling effect. Also, if the horizontal oscillation frequency is set accurately in the TV receiver,
Even if a synchronization signal is not detected from the television signal, the screen may not shift suddenly and a sufficient scrambling effect may not be obtained.

The present invention attempts to eliminate such inconveniences.

The illustrated embodiment will be described below.

Figure 1 shows the circuit on the transmitting side, and Figure 2 shows the circuit on the transmitting side.
FIG. 3 is a block diagram showing a circuit on the receiving side.

The transmitter shown in FIG. 1 periodically changes the DC level and signal level of the composite video signal at the front stage of the existing video transmitter 1. That is, an encoder 2 is provided that performs scrambling processing and superimposes a pseudo synchronization signal on the composite video signal.

The encoder 2 has the configuration shown in the figure, and supplies a normal composite video signal to the pedestal clamp circuit 21.
CV ₁ is introduced, its pedestal level (level of synchronization signal) is controlled to be constant, and then it is branched into three directions, one of which is directly supplied to the signal switch 23, and the other is The level shift circuit 22 lowers the DC level and the signal level by a predetermined amount, and the signal switch 23
3A and B at different levels.
Two composite video signals CV ₂ and CV ₃ shown in are sent to the parallel signal switch 23. The remaining one is sent to the synchronization signal detection circuit 25, where the horizontal synchronization signal is extracted, and the horizontal synchronization signal is sent to the control signal generation circuit 26 and the pseudo synchronization signal generation circuit 27.

The control signal generation circuit 26 creates a rectangular wave control signal (switching signal) from the horizontal synchronization signal, and sends this to the signal switching 23 and the pseudo synchronization signal generation circuit 27.

According to the control signal, the signal switching device 23 switches the two composite video signals CV ₂ and CV ₃ of different levels introduced in parallel alternately and during the horizontal retrace period, and outputs them serially. A scrambled composite video signal CV ₄ shown in FIG. Send to 1. Further, the signal switching device 23 obtains a reference timing signal from the control signal, cuts off the scrambled composite video signal CV ₄ based on the reference timing signal, and switches the scrambled composite video signal CV 4 to the voltage generating circuit 24 instead.
control to omit the horizontal synchronizing signal (shown with diagonal lines in Fig. 4 C and D) in the composite video signal by outputting a DC voltage from the switch and sending it to the receiving side. Used as a signal for signal synchronization. However, it is not necessary to provide this omission in response to every switching, but in order to ensure synchronization on the receiving side, it is desirable that the omission occurs once every few times.

The pseudo synchronization signal generation circuit 27 receives the horizontal synchronization signal and the control signal, and generates a signal from all the video signals during the low level period mXH in the scrambled composite video signal CV ₄ or the appropriately selected video signal.
A pseudo synchronization signal is generated that temporally corresponds to the overscan point 2 to 5 μsec after the end, and whose peak value is almost the same as the horizontal synchronization signal during the high level period nXH, and the mixer Send to 28.

The mixer 28 superimposes the pseudo synchronization signal on the scrambled composite video signal CV ₄ and sends the composite video signal CV ₅ shown in FIG. 3D, which is then sent to the video transmitter 1. Pulse P in FIG. 3D is a pseudo synchronization signal.

The video transmitter 1 receives the scrambled composite video signal CV ₅ on which a pseudo synchronization signal is superimposed, converts it into a signal in an appropriate frequency band through modulation, and transmits the signal from the antenna 3 to the television. Send as a signal.

Furthermore, since the video transmitter 1 is equipped with an internal pedestal clamp circuit, a part of the control signal is introduced to stop the circuit. As a result, the scrambled composite video signal CV ₅ is sent to the pedestal.
The clamp circuit prevents the image from being corrected to a normal appearance.

On the receiving side of FIG. 2, a decoder 5 is installed upstream of the existing TV receiver 4 to descramble the incoming television signal and restore it to a normal television signal.

The decoder 5 has the configuration shown in the figure, and inputs the television signal received by the antenna 6 to the amplifier 51 via the changeover switch 7, where it is amplified and converted into a normal television signal by the electronically controlled attenuator 52. It is corrected and sent to the TV receiver 4 via the changeover switch 8.

The electronically controlled attenuator 52 operates by receiving a control signal that synchronizes with the transmitting side and a pseudo synchronizing signal sampling signal, but the control signal branches a part of the television signal from the output side of the electronically controlled attenuator 52, This is demodulated into a composite video signal by a demodulator 53,
Furthermore, the synchronization signal detection circuit 54 extracts the horizontal synchronization signal, detects the lack of the horizontal synchronization signal, that is, the control signal synchronization signal, and based on these, the control signal generation circuit 55 generates a rectangular waveform that is synchronized with the transmitting side. Build at the traffic light. In other words, a control signal that is synchronized with and has the same shape as the control signal on the transmitting side is generated.

Further, the pseudo synchronization signal extraction signal is generated by branching and introducing the horizontal synchronization signal from the synchronization signal detection circuit 54 in the pseudo synchronization signal extraction control circuit 56, and based on this, a pulse having the same timing as the pseudo synchronization signal on the transmitting side is generated. Form.

The electronically controlled attenuator 52 that receives such a pseudo synchronization signal sampling signal and control signal corrects the level of the television signal to a uniform normal state according to the control signal, and at the same time corrects the level of the television signal to a uniform normal state. The signal is controlled ON/OFF to lower the level of the pseudo synchronization signal superimposed on the television signal to the pedestal level. This state is shown in the form of a composite video signal as shown in FIG. 3E.

The television signal is then sent to the TV receiver 4 via the changeover switch 8, and the TV receiver 4 reproduces the correct image.

At this time, since the pseudo synchronization signal remains at a low level, it will affect the image, but since the pseudo synchronization signal is inserted at an overscan point, it does not actually appear on the screen.

As mentioned above, if the pseudo synchronization signal is inserted during the low level period mXH in the scrambled composite video signal CV ₄ , it may be inserted here and there even if it is inserted into each video signal of all cycles during that period. However, the sampling signal on the reception side corresponding to this may be generated only within the low level period mXH, or may be generated throughout the entire period including the high level period nXH. If each case is illustrated as appearing on the screen, Figures 4 A to D
become that way. In the figure, the black portion is the portion where the pseudo synchronization signal appears in black, the shaded portion is the portion where the pseudo synchronization signal extraction signal appears in white, and A is
If a pseudo synchronization signal is inserted into each cycle of the low level period mXH, and a pseudo synchronization signal sampling signal is made to correspond to all of the low level period mXH and high level period nXH, B is the pseudo synchronization signal in A above. If the sampling signal corresponds to all during the low level period, C inserts a pseudo synchronization signal here and there during the low level period, and corresponds to the pseudo synchronization signal sampling signal throughout the low level period and the high level period. In this case, D is a case in which the pseudo synchronization signal sampling signal corresponds to all of the low level periods in C above.

In addition, from the point of view of AGC and AFC characteristics of commercially available TV receivers, if the low level period is 10 to 20 horizontal periods, A or B is used, and if it is longer, the pseudo synchronization signal is 10 to 20 horizontal periods. Turn ON/OFF with C or D
It is effective to adopt

By the way, it is not equipped with the above-mentioned decoder 5.
When a TV receiver receives a scrambled television signal, the level of the television signal changes at regular intervals, so shading appears on the screen and it is difficult to detect the horizontal synchronization signal. Over time, the synchronization gets disrupted and the screen starts to drift.

Additionally, if the TV receiver is equipped with a peak type AGC circuit or a keyed AGC circuit with a quick AGC response, the AGC circuit attempts to correct the low level portion of the television signal, but in the former case, the AGC circuit attempts to correct the low level part of the television signal. , because the pseudo sync signal is at a high level, it is fooled and does not produce a correction effect, and in the latter case, when it first becomes low level, it detects the drop in the horizontal sync signal level and acts to compensate, but after that Since a pseudo sync signal with a large level comes in at the same period as the horizontal sync signal, it is regarded as a horizontal sync signal and follows it, returning to the original state. Then, when a pseudo sync signal is input, the horizontal synchronization is dragged, so the screen begins to shift to the left, and after several to several tens of cycles, it becomes completely synchronized with the pseudo sync signal, and the screen shifts to the left. It will completely collapse. This occurs even if the horizontal oscillation frequency is set accurately in the TV receiver.

Therefore, in any case, a TV receiver not equipped with the decoder 5 cannot reproduce a normal image from the above-mentioned television signal, and is extremely unsuitable for pay television broadcasting.

In the decoder 5, the front and rear two changeover switches 7 and 8 are provided for the purpose of excluding the decoder 5 when receiving normal television broadcasting that has not been scrambled.

In addition to the above-mentioned means, the means for transmitting the control signal may include transmitting the control signal itself or a control signal synchronization signal through a public line such as a telephone, a separately provided wireless line,
It may also be transmitted by a subcarrier inserted into a television audio channel.

According to the present invention, AGC with quick response can be used in TV receivers.
Even if a circuit is provided, it will not be fooled by a pseudo synchronization signal and correct the level of the scrambled television signal, and
Even if the horizontal oscillation frequency is set accurately in the TV receiver, the image will be streamed by a pseudo synchronization signal with a timing shift, and therefore a descrambling processing device, that is, a decoder, should not be attached to the TV receiver. It can prevent image reproduction as reliably as possible, and is extremely effective and suitable for use in pay television broadcasting.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; Fig. 1 is a block diagram showing the circuit on the transmitting side, Fig. 2 is a block diagram showing the circuit on the receiving side, Fig. 3 is a signal waveform diagram, and Fig. 4 is a screen explanation. It is a diagram. 1...Video transmitter, 2...Encoder, 4...TV receiver, 5...Decoder.

Claims (1)

[Claims] 1 A control signal in which the level of the television signal to be transmitted is repeatedly changed by a separately generated control signal on the transmitting side, and the level change on the transmitting side of the television signal received at the receiving side is synchronized with that on the transmitting side. In a television signal scrambling method configured to cancel each other out, a pseudo synchronization signal whose timing is shifted from the horizontal synchronization signal is superimposed on the television signal sent from the transmitting side, and the pseudo synchronization signal is transmitted on the receiving side. A television signal scrambling method characterized in that the television signal is scrambled.