JPS63126380A - Charged television decoder - Google Patents

Abstract

PURPOSE:To make the response speed of a clamp faster and to prevent the energy of a satellite system from being diffused by synchronously separating the output of a synchronizing shift device from a video signal and adding the pedestal clamp of a vertical period from the synchronizing pulse. CONSTITUTION:A synchronizing component is separated from the video signal obtained by returning the synchronizing signal of the output of the synchronizing shift device 10 to an original position in a synchronizing separator 12 and the clamp signal is generated in a vertical clamp pulse generator 13. Only the vertical period is extracted sampled in an AND gate 7 and the vertical clamp pulse is added to the horizontal clamp pulse of a horizontal clamp pulse generator 4 in an OR gate 14. Accordingly, the clamp of the vertical period is effectively carried out, a clamp holding time can be shortened and speeded up.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pay television decoding device for decoding scrambled video signals.

BACKGROUND OF THE INVENTION In recent years, pay television (hereinafter referred to as pay television), centered on CATV, has developed, and this technology is being applied to satellite broadcasting media. Pay TV requires signal processing (this is called scrambling) that cannot be received by ordinary television receivers, and a decoder is required to decipher this scrambling.

A conventional pay TV decoder will be described below with reference to the drawings. FIG. 2 is a block diagram of a pay television decoder used in conventional CATV. In the scramble, the synchronizing signal is shifted into the video as shown in FIG. In FIG. 2, 1 is an input terminal that receives the timing to return the synchronous shift, 2 is a timing receiving device that demodulates it and shapes the waveform, 3 is a horizontal synchronous shift pulse generator that reproduces the horizontal synchronous shift pulse, 4 is a horizontal clamp pulse generator that reproduces from the falling edge of the timing signal from the timing receiver. 8 is an input terminal for a scrambled baseband video signal. Reference numeral 9 represents a pedestal clamp device that applies pedestal clamping using a pedestal clamp pulse generated from a horizontal clamp pulse generator, and 1o represents a synchronous shifter that shifts the synchronous signal to a normal position using a synchronous shift pulse. 11 is an output terminal for the decoded video signal.

6 is a vertical synchronization shift pulse generator that generates a pulse for returning the synchronization shift of the vertical synchronization period from the timing signal of the timing receiver, and θ is a gate for creating the logical sum of the horizontal synchronization shift pulse and the vertical synchronization shift pulse. The descrambled video signal is supplied to the television receiver from the output terminal 11 either directly or via an RF modulator, so that each subscriber can view a synchronized normal video.

The pay TV decoder device configured as described above will be explained in detail with reference to timing charts 4 in FIGS. 3 and 4. FIG. 3 is a timing chart for the horizontal mode, and FIG. 4 is a timing chart for the vertical mode.

First, the horizontal mode will be explained. A timing signal received by the timing receiver a1 of the synchronously shifted video signal is shown in b. A horizontal synchronous shift pulse generator 4 generates a pulse that starts a synchronous shift pulse from the rising edge of a timing signal and stops immediately before the end of the synchronous shift period.

This is shown in C. This pulse causes the synchronous shifter 10 to return the synchronous signal to its original position. The synchronously shifted video signal is shown in d. A horizontal clamp pulse is generated at the falling edge of the timing signal of the timing receiver 2, a pedestal clamp is applied, and the DC component of the video signal is fixed before being synchronously shifted. This pedestal clamp pulse is shown in e. In this way,
A normal synchronization signal can be created by performing a synchronization shift of the horizontal period.

Next, the timing of the vertical mode will be explained using FIG.

a shows a scrambled video signal synchronously shifted in vertical mode. b shows a timing signal from the timing receiving device 2 in vertical mode. The vertical equalization pulse period and vertical synchronization signal period are all shifted,
As a result, the television receiver cannot perform vertical synchronization.

During the other vertical retrace periods, like the horizontal mode, only the synchronizing signal is shifted, so the pay TV decoder operates like the horizontal mode. Therefore, the timing receiving device 2
A vertical synchronization shift pulse is created from the timing signal from , and a horizontal synchronization shift pulse is added to this to create a synchronization shift pulse. This synchronous shift pulse is shown in C.

The pedestal clamp generation circuit does not operate during this vertical synchronous shift pulse period, and operates only for synchronous shifting. Therefore,
It must have the ability to maintain the pedestal level of the image during this period using direct current.

Problems to be Solved by the Invention However, when the scrambling and decoding techniques are applied to a satellite system with the above configuration, a problem arises due to the energy dispersion process of the satellite system. That is, energy dispersion processing in a satellite system is usually performed using a method in which amplitude modulation is performed using a triangular wave that has a vertical frequency and is synchronized with a vertical signal.

Regarding the portion excluding the vertical period, the hollow triangular wave component can be removed by the pedestal clamp pulse, but since the vertical period is not clamped, it remains as it is.

Furthermore, since it is necessary to slow down the response speed of the clamp in order to hold the DC component in the vertical period, the triangular wave component cannot be completely removed even in the horizontal mode. This results in unstable synchronization of the television receiver, resulting in a flickering phenomenon on the screen.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a pay TV decoding device that can add a vertical period pedestal clamp, thereby increasing the response speed of the clamp.

Means for Solving the Problems A pay TV decoding device according to the present invention is a conventional pay TV decoding device which is equipped with a pedestal clamp for separating the synchronization from the video signal output from the synchronous shifter and for vertical period from the synchronization pulse. It is.

With this configuration, the response speed of the pedestal clamp can be increased and energy dispersion in the satellite system can be eliminated.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a pay TV decoding device in an embodiment of the present invention. Blocks with the same numbers as in Figure 2 perform simultaneous operations, so
The explanation will be omitted.

12 is a sync separator that separates the sync component from the video signal that returns the sync signal output from the sync shifter to its original position; 13 is a vertical clamp pulse generator that generates a clamp signal from the rising edge of the separated sync signal; 7 is an AND gate that extracts only the vertical period from the output of the vertical clamp pulse generator, and the gate is operated by the output of the vertical synchronization shift pulse generator 6. The OR gate 14 adds a vertical clamp pulse to the horizontal clamp pulse of the horizontal clamp pulse generator 4. FIG. 4 shows the output of the KAND gate 7, and q shows the pedestal clamp pulse that is the output of the OR gate 14.

Effects of the Invention As described above, according to the present invention, by adding a vertical clamp pulse to the conventional example, the vertical period can be reliably clamped, the clamp holding time can be shortened, and the speed can be increased. , it is possible to remove the triangular wave modulation for energy diffusion in the satellite system mentioned above, and it is possible to obtain the effect of reproducing a flicker-free screen.

Furthermore, it goes without saying that by employing this means in a CATV system, the clamping effect can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a pay television decoding device according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional pay television decoding device, FIG. 3 is a timing chart of its horizontal mode, and FIG. The figure is a timing chart of the vertical mode. 1... Timing modulation signal input terminal, 2... Timing receiving device, 3... Horizontal synchronization shift pulse generator, 4... Horizontal clamp pulse generator, 5... Vertical synchronization shift pulse generator, 6
, 14...OR gate, 7...AND
Gate, 8...Song scrambled baseband video input terminal, 9...Pedestal clamp device, 1o
... Synchronous shifter, 11 ... Decoded video output terminal, 12 ... Synchronous separator, 13.
Curved/vertical clamp pulse generator. Name of agent: Patent attorney Toshio Nakao and one other person
Illusion Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) a timing receiving device that receives a descramble timing signal; a synchronous shift pulse generator that reproduces a synchronous shift pulse from the timing receiving device; a pedestal clamp device that applies a pedestal clamp to the synchronously shifted video signal; a synchronous shifter that shifts synchronization with a shift pulse from a synchronous shift pulse generator;
A pay television decoder comprising: a pedestal clamp pulse generator that reproduces a pedestal clamp signal from the timing signal from the timing receiver and the synchronous shifter output video signal. (2) A horizontal synchronous shift pulse generator and a vertical synchronous pulse generator that the synchronous shift pulse generator reproduces from the output of the timing receiver, and a gate circuit that creates a logical sum of the horizontal synchronous shift pulse and the vertical synchronous shift pulse. A pay television decoding device according to claim 1, comprising: (3) A pedestal clamp pulse generator generates a pedestal clamp pulse for a horizontal period from the falling edge of a timing signal from a timing receiver, and a synchronous separation performs synchronous separation of a video signal after synchronous shift. a vertical clamp pulse generator that generates a pedestal clamp pulse from the rising edge of the synchronization signal separated by the synchronization separator, and a gate that creates an AND between the output clamp pulse of the vertical clamp pulse generator and the vertical synchronization shift pulse. 2. A pay television decoding device according to claim 1, comprising a gate for creating a logical sum of the output thereof and a horizontal clamp pulse output from a horizontal clamp pulse generator.