JPH10191362A - Video output switching method in ntsc encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video output switching method which reduces D/A converters, low pass filters and amplifiers and also is never expensive. SOLUTION: It is discriminated whether a Y/C cable 37 is connected to an S terminal 32, either a Y signal or a composite signal is selected in an NTSC encoder 31 based on a discrimination result, the Y signal is outputted from the terminal 32 when the Y signal is selected and the composite signal is outputted from a video terminal 33 when the composite signal is selected. When the cable 37 is connected to the terminal 32, the Y signal is selected in the encoder 31 and the Y signal is outputted from the terminal 32. When the cable 37 is not connected to the terminal 32, the composite signal is selected in the encoder 31 and the composite signal is outputted from the terminal 33.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a video output switching method in an NTSC encoder.

[0002]

2. Description of the Related Art Conventionally, when an RGB signal output from a personal computer or the like is output to a television or the like,
A video output switching device is used, and the RGB signal is converted into a video signal conforming to the NTSC system by the video output switching device. For this purpose, the video output switching device is provided with an NTSC encoder.

FIG. 2 is a diagram showing a conventional three-system video output switching device. In the figure, reference numeral 11 denotes an NTSC encoder, and when an RGB signal, that is, an R signal, a G signal, and a B signal are input to the NTSC encoder 11, N
The TSC encoder 11 generates a Y signal representing light and dark, a C signal representing color, and a composite signal obtained by combining the Y signal and the C signal based on the R signal, the G signal, and the B signal.

The Y signal and the C signal are both a D / A converter DAC for performing digital / analog conversion, a low pass filter LPF for smoothing an analog output signal and removing high frequency noise, and an amplifying signal. The Y / C signal is output from the S terminal 12 via the amplifier AMP, and the composite signal is output from the D / A converter DAC, the low-pass filter LPF, and the amplifier AM.
It is output as a composite video signal from the video terminal 13 via P. In this case, NTSC encoder 1
The D / A converter DAC, the low-pass filter LPF, and the amplifier AMP are required three each between the S terminal 1 and the S terminal 12 and the video terminal 13, and the number of components increases.

A description will now be given of a two-system video output switching device that combines the outputs of the amplifiers AMP. FIG. 3 is a diagram showing a conventional two-system video output switching device. In the figure, reference numeral 21 denotes an NTSC encoder.
When the signal is input, the NTSC encoder 21 generates a Y signal and a C signal based on the R signal, the G signal, and the B signal.

The Y signal and the C signal are both a D / A converter DAC and a low-pass filter LPF.
The signal is output as a Y / C signal from the S terminal 22 via the amplifier AMP. The Y signal and the C signal are both a D / A converter DAC and a low-pass filter L.
Via PF and amplifier AMP, analog adder 2
4 and becomes a composite signal. The composite signal is output from the video terminal 23 as a composite video signal. In this case, the analog adder 24 combines the Y signal and the C signal output from each amplifier AMP.

Therefore, there is no need to generate a composite signal in the NTSC encoder 21, and the D / A
Since only two converter DACs, two low-pass filters LPF, and two amplifiers AMP are required,
We can reduce by set.

[0008]

However, in the conventional video output switching device, the analog adder 2 is used.
4, the cost increases. The present invention solves the problems of the conventional video output switching device, and provides a video output switching method that can reduce the number of D / A converters, low-pass filters, and amplifiers, and does not increase the cost. The purpose is to do.

[0009]

For this purpose, the present invention provides
In the video output switching method in the TSC encoder, it is determined whether or not a Y / C cable is connected to the S terminal, and based on the determination result, one of the Y signal and the composite signal is selected in the NTSC encoder, and the Y signal is selected. If so, the Y signal is output from the S terminal, and if the composite signal is selected, the composite signal is output from the video terminal.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a video output switching device according to a first embodiment of the present invention. In the figure, reference numeral 31 denotes an NTSC encoder.
When a signal is input, the NTSC encoder 31 generates a Y signal, a C signal, and a composite signal based on the R signal, the G signal, and the B signal. A selector 35 is provided in the NTSC encoder 31. The C signal is directly output from the NTSC encoder 31, while one of the Y signal and the composite signal is selected by the selector 35, and the Y signal and the composite signal are output. One of the signals is output from the NTSC encoder 31.

The C signal is a D / A converter DAC,
The signal is output from the S terminal 32 via the low-pass filter LPF and the amplifier AMP1. When the Y signal is selected by the selector 35, the D / A converter DAC,
The Y / C signal is formed together with the C signal via the low-pass filter LPF and the amplifier AMP2, and is output from the S terminal 32. Then, the composite signal is supplied to the selector 3
5 is output as a composite video signal from the video terminal 33 via the D / A converter DAC, low-pass filter LPF, and amplifier AMP2.

Further, a switch (not shown) for determining whether or not the Y / C cable 37 is connected is built in the S terminal 32, and the result of the determination based on the ON / OFF of the switch is sent to the selector 35 as a control signal. The S terminal 32 and the selector 35 are connected by a control line L1. Next, the operation of the video output switching device having the above configuration will be described.

[0013] The C signal is transmitted to the NTSC terminal irrespective of whether the Y / C cable 37 is connected to the S terminal 32 or not.
D / A converter DA output from encoder 31
C, the signal is always output from the S terminal 32 via the low-pass filter LPF and the amplifier AMP1. And S terminal 3
2 is connected to the Y / C cable 37, the selector 35
Is Y according to a control signal sent via the control line L1.
Select a signal. As a result, a Y signal is output from the NTSC encoder 31 and output as a Y / C signal together with a C signal from the S terminal 32 via the D / A converter DAC, low-pass filter LPF, and amplifier AMP2.

When the Y / C cable 37 is not connected to the S terminal 32 and a video cable (not shown) is connected to the video terminal 33, the selector 35 operates in accordance with the control signal sent through the control line L1. Select As a result, a composite signal is output from the NTSC encoder 31 and output as a composite video signal from the video terminal 33 via the D / A converter DAC, low-pass filter LPF, and amplifier AMP2.

As described above, according to whether the Y / C cable 37 is connected to the S terminal 32, one of the Y signal and the composite signal is selected by the selector 35, and the Y signal is selected.
Since the signal is output from the S terminal 32 and the composite signal is output from the video terminal 33, the D / A
The converter DAC, the low-pass filter LPF, and the amplifier AMP2 can be shared. Therefore, D /
A converter DAC, a low-pass filter LPF, and an amplifier AMP (see FIG. 2) can be reduced, and there is no need to use an analog adder, so that the cost does not increase.

Next, a second embodiment of the present invention will be described. FIG. 4 is a diagram showing a video output switching device according to a second embodiment of the present invention. In the figure, reference numeral 41 denotes an NTSC encoder.
When the R signal, G signal and B signal are input to
The encoder 41 generates a Y signal, a C signal, and a composite signal based on the R signal, the G signal, and the B signal. Also, the NTSC encoder 41 supplies the select signal T
The ESTSEL is input and the test signal TE fixed to 1 [V] in the NTSC encoder 41.
ST is generated. Furthermore, NT
The SC encoder 41 is provided with selectors 45 and 46. One of the C signal and the test signal TEST is selected by the selector 45, and either the C signal or the test signal TEST is output from the NTSC encoder 41. One of the Y signal and the composite signal is selected by the selector 46, and either the Y signal or the composite signal is output from the NTSC encoder 41.

When the C signal and the test signal TEST are selected by the selector 45, the D / A converter D
The signal is output from the S terminal 42 via the AC, the low-pass filter LPF, the amplifier AMP1, and the resistor R1. Also, Y
When the signal is selected by the selector 46, the D / A converter DAC, the low-pass filter LPF, the amplifier AM
A Y / C signal is formed together with the C signal via P2 and the resistor R2, and is output from the S terminal 42. When the composite signal is selected by the selector 46, D
It is output as a composite video signal from the video terminal 43 via the / A converter DAC, low-pass filter LPF, amplifier AMP2, and resistor R2.

Further, a Y / C cable 47 is connected to the S terminal 42.
Is connected between the resistor R1 and the S terminal 42 to send a result of the determination by the control signal generating means 51 to the selector 46 as a control signal. The control signal generator 51 and the selector 46 are connected by a control line L2.

The control signal generating means 51 comprises a comparator 55 and a flip-flop F / F. One input terminal of the comparator 55 receives a voltage between the resistor R1 and the S terminal 42, and the other input terminal. A voltage of 0.6 [V] is input to the terminal as a reference voltage, and the output terminal of the comparator 55 is connected to the input terminal of the flip-flop F / F. Further, the synchronization signal Vsync is input to a reset terminal of the flip-flop F / F, and the control line L2 is connected to an output terminal.

Reference numeral 52 denotes a television as a device on the other end, and 53 denotes an S terminal 42 via the Y / C cable 47.
And a television-side terminal R3 connected to the Y-C cable 47 and a ground. The resistance value of each of the resistors R1 to R3 is 75 [Ω].
To be. Next, the operation of the video output switching device having the above configuration will be described.

FIG. 5 is a time chart showing the operation of the video output switching device when the Y / C cable according to the second embodiment of the present invention is not connected, and FIG. 6 is a second embodiment of the present invention. 6 is a time chart showing the operation of the video output switching device when the Y / C cable is connected in FIG. In the figure, Vsync is a synchronization signal, a is a point between the amplifier AMP1 (FIG. 4) and the resistor R1, b is a point between the resistor R1 and the S terminal 42, c is a comparator 55 and a flip-flop F / F. , D is a point between the flip-flop F / F and the selector 46, and e is a selector 4
6 shows a point between the D / A converter 6 and the D / A converter DAC.

The output of the comparator 55 goes high when the voltage at the point b is 0.6 [V] or more,
If it is less than 0.6 [V], it becomes low level. The flip-flop F / F outputs a control signal of the voltage level at the point c every time the synchronization signal Vsync rises (changes from low level to high level).
Reference numeral 6 selects a composite signal when the control signal from the flip-flop F / F is at a high level, and selects a Y signal when the control signal is at a low level.

The selector 45 outputs the select signal T
When ESTSEL is at a low level, the test signal TE
When ST is at a high level, the C signal is selected. The select signal TESTSEL is a signal obtained by delaying the synchronization signal Vsync by two clocks of NTSCCLK (14.3 [MHz]). Therefore, for example, the select signal TESTS input to the selector 45
When EL is at the low level, the test signal TEST is selected, and a voltage of 1.0 [V] is output to the point a. In this case, while the synchronizing signal Vsync is at a low level and before and after the synchronizing signal Vsync, nothing is displayed on the television 52 during the vertical blanking period. Even if the test signal TEST is sent to the television 52 via the Y / C cable 47, the screen display of the television 52 is not affected.

By the way, the Y / C cable 47
When the terminal 42 and the television terminal 53 are connected, a point b
Is obtained by dividing the voltage at the point a by the resistors R1 and R3. Therefore, the select synchronization signal TESTSEL input to the selector 45 becomes low level,
When the test signal TEST is selected and a voltage of 1.0 [V] is output to the point a as shown in FIG. 6, the voltage of the point b becomes 0.5 [V]. As a result, the comparator 55
Becomes low level, and the control signal output from the flip-flop F / F becomes low level at the rise of the synchronization signal Vsync, so that the selector 46 selects the Y signal.

On the other hand, when the Y / C cable 47 does not connect the S terminal 42 and the television terminal 53, the point b
Is equal to the voltage at point a. Therefore, the select signal TESTSEL becomes low level, and the selector 4
5, the test signal TEST is selected, and the points a.
When a voltage of 0 [V] is output, the voltage at point b becomes 1.0
[V]. As a result, the output of the comparator 55 goes high, and the control signal output from the flip-flop F / F goes high at the rising edge of the synchronization signal Vsync, so that the selector 46 selects the composite signal.

Therefore, when a Y / C cable 47 is connected to the S terminal 42 and a video cable (not shown) is connected to the video terminal 43, when the Y / C cable 47 is connected to the television terminal 53, the Y signal is When the selected Y / C signal is output from the S terminal 42 and sent to the television 52, while the video cable is connected to a terminal (not shown) of the television 52, a composite signal is selected by the selector 46 and the composite signal is selected. It is output from the video terminal 43 and sent to the television 52. That is, if the Y / C cable 47 is connected on the S terminal 42 side but not on the television terminal 53 side, a composite signal is selected by the selector 46 and the composite signal is transmitted to the video terminal 43.
Output from

As described above, the selector 46 selects the Y signal or the composite signal in accordance with whether the television terminal 53 is connected to the S terminal 42 via the Y / C cable 47. Therefore, since the composite signal is output from the video terminal 43, the D / A converter DAC, the low-pass filter LPF, and the amplifier AMP2 can be used in common. Therefore, the D / A converter DAC, the low-pass filter LPF, and the amplifier AMP (see FIG. 2) can be reduced, and there is no need to use an analog adder, so that the cost does not increase.

A Y / C cable 47 is connected to the S terminal 42.
However, even when a video cable is connected to the video terminal 43, a Y / C signal or a composite signal is output from a terminal (not shown) to which the television 52 is connected. It should be noted that the present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0029]

As described above in detail, according to the present invention, in the video output switching method in the NTSC encoder, it is determined whether or not the Y / C cable is connected to the S terminal, and based on the determination result. In the NTSC encoder, one of the Y signal and the composite signal is selected. If the Y signal is selected, the Y signal is output from the S terminal. If the composite signal is selected, the composite signal is output from the video terminal. .

In this case, when a Y / C cable is connected to the S terminal, a Y signal is selected in the NTSC encoder, and the Y signal is output from the S terminal. Also,
If no Y / C cable is connected to the S terminal, N
A composite signal is selected in the TSC encoder, and the composite signal is output from a video terminal.
Therefore, the D / A converter, the low-pass filter, and the amplifier between the NTSC encoder and the S terminal and the video terminal can be made common, so that the number of the D / A converter, the low-pass filter, and the amplifier can be reduced. Further, since there is no need to use an analog adder for synthesizing the Y signal and the C signal to generate a composite signal, the cost does not increase.

[Brief description of the drawings]

FIG. 1 is a diagram showing a video output switching device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a conventional three-system video output switching device.

FIG. 3 is a diagram showing a conventional two-system video output switching device.

FIG. 4 is a diagram showing a video output switching device according to a second embodiment of the present invention.

FIG. 5 is a time chart showing an operation of the video output switching device when a Y / C cable is not connected according to the second embodiment of the present invention.

FIG. 6 is a time chart showing an operation of the video output switching device when a Y / C cable is connected according to the second embodiment of the present invention.

[Explanation of symbols]

 31, 41 NTSC encoder 32, 42 S terminal 33, 43 Video terminal 35, 45, 46 Selector 37, 47 Y / C cable 52 TV Vsync Synchronization signal TEST Test signal

Claims (3)

[Claims] (A) determining whether a Y / C cable is connected to an S terminal; (b) selecting one of a Y signal and a composite signal in an NTSC encoder based on a result of the determination; and (c). If the Y signal is selected,
A video output switching method in an NTSC encoder, comprising: outputting a Y signal from an S terminal; and outputting a composite signal from a video terminal when a composite signal is selected. 2. The video output switching method in an NTSC encoder according to claim 1, wherein whether or not a Y / C cable is connected to the S terminal is determined based on on / off of a switch built in the S terminal. 3. When a synchronization signal is input to an NTSC encoder, a test signal is generated in the NTSC encoder, output from an S terminal, and based on a voltage of the test signal output from the S terminal, the Y signal is output. 2. The video output switching method in the NTSC encoder according to claim 1, wherein it is determined whether or not a device on the other end is connected to the / C cable.