JPH0750929B2 - Video signal transmission device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a video signal transmission device for transmitting a video signal to a distant place by compensating for a phase shift between the video signals caused by variations in a transmission circuit.

[Conventional technology]

FIG. 4 is a block diagram showing a conventional example of this type of device. In the figure, the portion surrounded by the dotted line is a transmission cable, HS is a horizontal synchronizing signal, VS is a vertical synchronizing signal, R is a video signal (red),
G is a video signal (green). In addition to the above, the video signal includes a blue signal, a luminance signal and the like, but for the sake of simplicity, the description is omitted here.

FIG. 5 is a waveform diagram of each part for explaining the device shown in FIG. 4, where HS, VS, R, G are signal waveforms on the transmission side of the above-mentioned signals, and HS ', VS', R '. , G'is the signal waveform on the receiving side.

The operation will be described below with reference to FIGS. 4 and 5.

HS, VS, R, G is taken in from an external video signal output device,
Here, as shown in FIG. 5, it is assumed that the pulses of the video signals R and G have the same phase. When this signal is transmitted to a distant place via a transmission cable, the received video signals are R'and G'in FIG.
Therefore, there is a difference in the phase of the video signal. This is because the signal transmission speed is obtained by the following equation (1) and each signal is transmitted by a different cable, so that the signal transmission speed is different due to the variation of L and C of the cable, and the transmission distance is The longer the length, the larger the phase difference.

However, V: signal transmission speed L: transmission cable inductance (distributed constant system) C: transmission cable capacity (distributed constant system) [Problems to be solved by the invention] In the conventional video signal transmission device, When a video signal is transmitted to a distant place, the transmission between the video signals is deviated, and for example, when this signal is connected to a CRT display, there is a drawback that color shift occurs, so the transmission side and CR
The distance between the T-displays was, for example, 1.5 m or more.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional apparatus. Therefore, the object of the present invention is to make the phase between video signals on the receiving side the same as the phase at the time of transmission, such as a CRT display. An object of the present invention is to provide a video signal transmission device that does not cause color misregistration when connected to.

[Means for solving problems]

In order to achieve such an object, the present invention extracts the horizontal synchronization signal when the level of the vertical synchronization signal indicates the non-display period on the transmission side and outputs the same phase to each video signal. Pulse is added as a pulse, and the phase shift amount of the pulse is detected on the receiving side, and the phase of each video signal is corrected according to this phase shift amount.

〔Example〕

 Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1,4,5,6,14,15 are AND operation elements, 2,3 are OR operation elements, 7 and 8 are counters, 9 and 10 are shift registers, 11 and 12 are data selectors, and 13 is It is a NOT operation element, and the part surrounded by the dotted line is the transmission cable.

2 and 3 are waveform diagrams for explaining the operation of FIG. 1, in which the horizontal synchronizing signal HS, the vertical synchronizing signal VS, and the video signals R and G are fetched from an external video signal output device, Is transmitted to a distant place and signals HS ′, VS ′, R ₀ and G ₀ are output.

Next, the circuit operation will be described with reference to FIGS.

The horizontal sync signal HS, the vertical sync signal VS, and the video signals R and G as shown in Fig. 2 HS, VS, R, and G are taken in from an external video signal output device, but for the sake of explanation, the pulses of the video signals R and G are taken. Are in phase. Since the time of the vertical synchronizing signal VS is high level is a non-display period, Figure 2 pulses HS ₀ of the AND operation element 1 is a vertical synchronizing signal VS horizontal synchronizing signal HS at the high level HS ₀
Taken out as shown, and use this as the video signal by OR operation elements 2 and 3.
It is added to R and G to form a signal waveform as shown in R'and G'in FIG. When these signals are transmitted to a distant place by a transmission cable, they have waveforms such as HS ', VS', R ", G" in Fig. 2. Before transmission, the pulses added to the video signals R, G have the same phase. However, there is a phase difference after transmission.

Hereinafter, a circuit operation for detecting this phase difference and correcting it so as to be in phase will be described.

A clock generating circuit (not shown) generates a clock pulse CLK such as CLK shown in FIG.
R "by AND operation element 5 and signals CLK, VS ', G" by AN
By performing the AND operation by the D operation element 6, the number of clocks in the pulse HS ₀ added to the pre-transmission video signal is obtained, and a signal waveform such as 7-CLK, 8-CLK in FIG. 2 is obtained,
These are the input signals of the counters 7 and 8, respectively.

Further, by performing an AND operation on the signals R ″, G ″, VS ′ by the AND operation element 4, a portion such as the signal RT shown in FIG. 2 in which the added pulses in the signals R ″, G ″ overlap each other is extracted. Is the reset signal for counters 7 and 8. Counter 7,8 counts the number of input pulses from the fall of the reset signal, from outputs the result to the output terminal of 3bit Q _0, the Q _1, Q _2, counter 7 Figure 2 7-Q _0, 7 “Q” like −Q ₁ and 7−Q ₂
, And the counter 8 outputs "2" as in 8-Q ₀ , 8-Q ₁ in FIG. _{2 and} 8-Q ₂ in FIG. That is, regarding the phase relationship between the transmitted video signals R ″ and G ″, the signal R ″ is the signal G ″.
It can be detected that it is advanced by 2 clocks.

On the other hand, the signals R ″ and G ″ are input to the serial input terminals D of the shift registers 9 and 10, respectively, and the output terminals Q ₀ of the shift registers 9 and 10 receive the input signal and then are output at the rising edge of the clock pulse. , Is output to the output terminal Q ₁ at the rising edge of the second clock.

The following are used for the same output terminal _{Q 2, Q 3, Q 4} , Q 5, Q 6 is delayed by one clock output, the input signal is to be outputted is 8 clock delay at the output terminal Q ₇ Therefore, for example, the output signal waveforms of the output terminals Q ₀ , Q ₁ , and Q ₇ of the shift register 9 are the third
9-Q ₀ , 9-Q ₁ , 9-Q ₇ , and the output waveforms of the output terminals Q ₀ , Q ₁ , Q ₅ of the shift register 10 are shown in FIG. 3 10-Q ₀ , 10-Q ₁ , 10 -Q
It will be ₅ .

The output signals of the output terminals Q _{0 to} Q ₇ of the shift registers 9 and 10 are input to the input terminals D _{7 to} D ₀ of the data selectors 11 and 12, respectively, and the selector terminals S ₀ , S ₁ , and S _{2 of the} data selector 11 are input. Figure 2 7-Q ₀ representing the phase difference between the above-mentioned video signal each other in, 7-
Selector signals such as Q ₁ , 7-Q ₂ are input, and similarly, select terminals S ₀ , S ₁ , S ₂ of the data selector 12 have 8-Q ₀ , 8 of FIG.
-Q ₁ and 8-Q ₂ signals are input. The data selector 11 selects the input signal from the input terminal D ₀ , that is, the signal R ″ delayed by 8 clocks, and the data selector 12 delays the input signal from the input terminal D ₃ that is the signal G ″ by 6 clocks. By selecting the signal, the data selector
Since signals such as 11-Q and 12-Q in FIG. 3 are output to the output terminals Q of 11 and 12, the phases of the video signals can be matched.

These video signals 11-Q, 12-Q and the signal VS 'are inverted by the NOT operation element 13 and the signal as shown in FIG.
By performing an AND operation by the D operation elements 14 and 15, respectively, the added pulse is cut and final video signals R ₀ and G ₀ are obtained as shown in R ₀ and G ₀ in FIG. It is clear that this coincides with the phase relationship when taken in from an external video signal output device as shown in FIGS.

〔The invention's effect〕

According to the present invention, it is possible to correct a phase shift between video signals that occurs after transmission, so that there is an advantage that it is possible to provide a video transmission apparatus that does not cause color shift when connected to a CRT display, for example.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are signal waveform diagrams of respective parts for explaining the operation of FIG. 1,
FIG. 4 is a block diagram showing a conventional example of a video signal transmission device, and FIG.
The figure is a signal waveform diagram for explaining the operation of FIG. HS: Horizontal sync signal, VS: Vertical sync signal, R: Video signal (red), G: Video signal (green), 1,4,5,6,14,15 ...
… AND operation element, 2,3 …… OR operation element, 7,8 …… Counter, 9,10 …… Shift register, 11,12 …… Data selector, 13 …… NOT operation element.

Claims (1)

[Claims] 1. A pulse adding circuit for extracting a horizontal synchronizing signal when the level of the vertical synchronizing signal indicates a non-display period and adding the same as a pulse having the same phase to a plurality of video signals transmitted to a distant place. And a phase shift amount detection circuit for detecting the phase shift amount between the video signals based on the phase difference between the pulses of the video signal transmitted by the transmission cable, and a phase for correcting the phase difference based on the phase shift amount. A video signal transmission device comprising: an adjustment circuit, which transmits a video signal to a distant place and corrects a phase shift between the video signals generated at the time of transmission.