JPH066708A - Picture display device - Google Patents

Abstract

PURPOSE:To prevent the generation of disturbance on the screen of a television(TV) at the time of changing a mode by increasing the number of scanning lines and mutually aligning vertical synchronizing signals in internally and externally generated composite video signals. CONSTITUTION:When a synchronizing switching signal S1 is inputted, a synchronizing signal generating circuit 10 outputs a vertical synchronizing signal V1 included in an internally generated composite video signal whose period is changed in accordance with an inputted clock signal CLK to a 3-input NAND circuit 35 through an inverter circuit 31. When the vertical synchronizing signal of the internally generated composite video signal and that of an externally generated composite video signal are mutually aligned at the time of inputting the signal S1 for instructing switching from an internal synchronizing mode to an external synchronizing mode, a synchronizing switching signal S2 is generated from a 2-input NAND circuit 33 and inputted to an inverter circuit 4. Thereby the continuity of these composite video signals can be held before and after the switching and the generation of instantaneous disturbance on the TV screen can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to characters on a television screen,
The present invention relates to a screen display device for displaying a pattern or the like, and more particularly to a screen display device for synthesizing a superimpose signal or a blueback signal with an externally synchronized or internally synchronized video signal to perform superimposed display or blueback display.

[0002]

2. Description of the Related Art FIG. 1 is a block diagram showing a configuration of a conventional screen display device, which mainly shows the flow of a composite video signal of external synchronization or internal synchronization related to the present application, and another configuration. Illustration of parts is omitted.
In FIG. 1, 3 is a superimposing circuit 1 for synthesizing a superimposing signal with an external composite video signal.
And a composite video signal generating circuit 2 for generating an internal composite video signal and synthesizing a blue back signal with the internal composite video signal. The superimposing circuit 1 is connected to an analog switch 6 that controls the transmission of its output signal, and the composite video signal generating circuit 2
Is an analog switch 7 that controls the transmission of its output signal.
It is connected to the. A synchronization switching signal S1 is input to each of the analog switches 6 and 7 through the inverter circuits 4 and 5, and the synchronization switching signal S1 switches on and off of the analog switches 6 and 7 so that the external synchronization mode and the internal synchronization are synchronized. Only one of the composite video signals is output depending on the mode.

Next, the operation will be described. When a character is superimposed on the composite video signal input from the outside, the superimposing circuit 1 combines the characters to be superimposed on the input composite video signal. On the other hand, when a composite video signal is generated from the inside, a blue back signal is combined in the composite video signal generation circuit 2 by various signals from a synchronization signal generation circuit (not shown). Then, in the external synchronization mode, the synchronization switching signal S1
By the control of 1, the analog switches 6 and 7 are turned on and off, respectively, and the external composite video signal in which the superimpose signal is combined is output. On the other hand, in the internal synchronization mode, the control of the synchronization switching signal S1
The analog switches 6 and 7 are turned off and on, respectively, and the internally generated composite video signal in which the blue back signal is combined is output.

[0004]

Since the conventional screen display is constructed as described above, when the blue back signal of the internal synchronization of the composite video signal generated from the inside is switched to the external synchronization mode, the composite display is changed. Since the video signal becomes discontinuous, there is a problem that the TV screen is disturbed at that moment.

The present invention has been made in view of such circumstances, and when switching from the internal synchronization mode to the external synchronization mode, the continuity of the composite video signal can be maintained, and the television screen is momentarily disturbed. It is an object of the present invention to provide a screen display device that can prevent such a situation.

[0006]

A screen display device according to the present invention is provided with an internal sync mode for a composite video signal internally generated when switching from an internal sync mode for a composite video signal internally generated to an external sync mode for a composite video signal externally input. The position of the vertical sync signal of the composite video signal to be generated is matched with the position of the vertical sync signal of the external composite video signal in an extremely short time, and then the internal sync mode is switched to the external sync mode. To do.

In the first invention, the number of scanning lines in one field is increased to align the positions of the vertical synchronizing signals of the internally generated composite video signal and the external composite video signal. In the second aspect of the invention, the time for one scanning line is increased to align the positions of the vertical sync signals of the internally generated composite video signal and the external composite video signal. In the third invention, the number of scanning lines in one field is increased or decreased to align the positions of the vertical synchronizing signals of the internally generated composite video signal and the external composite video signal. According to the fourth aspect of the present invention, a specific scanning line within the vertical sync blanking period in one field is deleted to align the positions of the vertical sync signals of the internally generated composite video signal and the external composite video signal.

[0008]

In the screen display device of the present invention, the position of the vertical synchronizing signal of the composite video signal generated from the inside is made to coincide with the position of the vertical synchronizing signal of the external composite video signal in an extremely short time, and then the internal synchronization mode is set. Switch to external sync mode. As a result, the continuity of the composite video signal is maintained before and after this switching, and the television screen is not disturbed even for a moment.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments.

FIG. 2 is a block diagram showing the configuration of the characteristic portion of the screen display device according to the present invention, and the illustration of the other configuration portions not directly related to the present invention is omitted. In FIG. 2, reference numeral 3 denotes a superimpose circuit 1 for synthesizing a superimpose signal with an external composite video signal, and a composite video signal generating circuit 2 for generating an internal composite video signal and synthesizing a blueback signal therewith. It is a video mixer composed of and. The superimpose circuit 1 is connected to an analog switch 6 that controls the transmission of its output signal, and the composite video signal generation circuit 2 is connected to an analog switch 7 that controls the transmission of its output signal. A synchronization switching signal S2 is input to each of the analog switches 6 and 7 via the inverter circuits 4 and 5, and the synchronization switching signal S2 switches the analog switches 6 and 7 on and off, thereby providing an external synchronization mode and an internal synchronization. Only one of the composite video signals is output depending on the mode.

The above-mentioned basic structure is the same as that of the conventional example, but the synchronous switching signal for controlling the ON / OFF of the analog switches 6 and 7 is different from the conventional one. The configuration for outputting the synchronization switching signal S2 will be described below. In the figure, 10 is a synchronizing signal generating circuit whose period can be changed by the synchronizing switching signal S1. The synchronizing signal generating circuit 10 is for generating an internally generated composite video signal whose period is changed according to an input clock signal CLK. The vertical synchronizing signal Vi is output to one input terminal of the 3NAND circuit 35 via the inverter circuit 31. At the other two input terminals of the 3NAND circuit 35,
The vertical synchronizing signal Vo and the synchronizing switching signal S1 of the external composite video signal are inputted respectively via the inverter circuit 32. The output signal of the 3NAND circuit 35 is input to one input terminal of the 2NAND circuit 33. 2NAND is applied to the other input terminal of the 2NAND circuit 33
The output signal of the circuit 34 is input. At the two input terminals of the 2NAND circuit 34, the output signal of the 2NAND circuit 33 and the synchronization switching signal S1
Is entered. With the above configuration, when the synchronization switching signal S1 for switching from the internal synchronization mode to the external synchronization mode is input, the operation of the synchronization signal generation circuit 10 and other peripheral circuits causes the internally generated composite video. Only when the position of the vertical synchronizing signal between the signal and the external composite video signal is aligned, is the synchronizing switching signal S2 for controlling the on / off of the analog switches 6 and 7 changed to the 2NAND circuit.
It is generated from 33 and input to the inverter circuit 4.

Next, the operation will be described. When a character is superimposed on the composite video signal input from the outside, the superimposing circuit 1 synthesizes the character to be superimposed on the input composite video signal. On the other hand, when a composite video signal is generated from the inside, a blue back signal is combined in the composite video signal generation circuit 2 by various signals from a synchronization signal generation circuit (not shown). And
In the external synchronization mode, the analog switches 6 and 7 are turned on and off by the control of the synchronization switching signal S2, and the external composite video signal in which the superimpose signal is combined is output. On the other hand, in the internal synchronization mode, the analog switch 6 and 7 are turned off and on, respectively, by the control of the synchronization switching signal S2, and the internally generated composite video signal in which the blue back signal is combined is output.

The above-described operation is basically the same as that of the conventional example, but the content of the synchronization switching signal for controlling the analog switches 6 and 7 is different from the conventional one. According to the present invention, when the synchronization switching signal S1 is input, the synchronization switching signal S2 is output and the internal switching is performed only when the positions of the vertical synchronization signals of the internally generated composite video signal and the external composite video signal are aligned. Switching from the synchronous mode to the external synchronous mode is performed. FIG. 3 shows a time chart of this operation. When the synchronous switching signal S1 changes from L level to H level,
The position of the vertical synchronizing signal Vi of the internally generated composite video signal is shifted to the position of the vertical synchronizing signal Vo of the external composite video signal (indicated by a dotted arrow in the figure). Then, only when the positions of the vertical synchronizing signals of the both are aligned, the synchronous switching signal S2 for controlling the OFF and ON of the analog switches 6 and 7 is generated, and the analog switch 7 is switched from the ON state to the ON state of the analog switch 6. Can be switched.

Several methods can be considered for the processing operation in the sync signal generating circuit 10 for aligning the position of the vertical sync signal of the internally generated composite video signal with the position of the vertical sync signal of the external composite video signal. . Hereinafter, these processing operations will be described. In the following explanation,
Take the NTSC method as an example.

(First Embodiment) FIG. 4 is a block diagram showing the internal structure of the synchronizing signal generating circuit 10 of the first embodiment. The synchronizing signal generating circuit 10 of the first embodiment is capable of providing accurate one scanning time. 1H generating circuit 11 for generating the signal and a 1V generating circuit 22 for increasing the number of scanning lines in one field.
In this embodiment, when the sync switching signal S1 is input, the 1V generating circuit 22 acts so that the sync switching signal is not provided until the vertical sync signal between the internally generated composite video signal and the external composite video signal matches. S2 is generated to control ON / OFF of the analog switches 6 and 7.

FIG. 5 is a time chart in the first embodiment.
Shown in. When the synchronization switching signal S1 changes from the L level to the H level, the 1V generating circuit 22 causes an accurate 1V period (V: 1 vertical period), that is, 262.5H lines (H: 1 horizontal scanning period) to 1V + nH lines (n: 1) to be an integer)
By increasing the number of scanning lines in the field, the position of the vertical sync signal Vi of the internally generated composite video signal is forcibly aligned with the position of the vertical sync signal Vo of the external composite video signal so that the positions of both vertical sync signals are The synchronization switching signal S2 is generated for the first time when they match, and the analog switch 7 is switched from the on state to the analog switch 6 on state.

(Second Embodiment) FIG. 6 is a block diagram showing the internal structure of the synchronizing signal generating circuit 10 of the second embodiment. The synchronizing signal generating circuit 10 of the second embodiment has one scanning line time. It is composed of a 1H generating circuit 12 that can increase the number and a 1V generating circuit 21 that generates an accurate number of scanning lines. In this embodiment, when the synchronization switching signal S1 is input, the 1H generation circuit 12 acts so that the synchronization switching signal is not output until the vertical synchronization signals of the internally generated composite video signal and the external composite video signal match. S2 is generated to control ON / OFF of the analog switches 6 and 7.

FIG. 7 is a time chart in the second embodiment.
Shown in. When the synchronous switching signal S1 changes from the L level to the H level, the 1H generating circuit 12 increases the time for one scanning line so as to be 1H + nCLK (n: an integer) from the accurate 1H period, and the internally generated composite signal is generated. The position of the vertical synchronizing signal Vi of the video signal is set to the vertical synchronizing signal Vo of the external composite video signal.
Is forced to the position of, and the sync switching signal S2 is generated only when the positions of the vertical sync signals of both are aligned,
From the ON state of the analog switch 7, the analog switch 6
Is switched on.

(Third Embodiment) FIG. 8 is a block diagram showing the internal structure of the synchronizing signal generating circuit 10 in the third embodiment, and FIG. 9 is a diagram showing the time chart in the third embodiment. The sync signal generating circuit 10 of the third embodiment has a 1H generating circuit 11 for generating an accurate one scanning time and a 1V generating circuit 23 for increasing or decreasing the number of scanning lines in one field.
The 1V generation circuit 23 generates a vertical sync signal of an internally generated composite video signal and an internal sync vertical sync signal (hereinafter, referred to as V / 2 inverted signal) which changes at a position of V / 2 relative to the vertical sync signal.
Output as shown in FIG. Further, the synchronization signal generation circuit 10
An inverter circuit 42 which receives the synchronous switching signal S1 and
Inverter circuit 43 that inputs the V / 2 inverted signal, inverter circuit 44 that inputs the vertical synchronizing signal of the external composite video signal, and 3NAND that outputs the outputs of inverter circuits 42 and 44 and the V / 2 inverted signal Circuit 51 and inverter circuits 42, 4
3NAND circuit 52 which inputs each output of 3, 44 and 2NAND which inputs the output of 3NAND circuit 51 and the output of 2NAND circuit 48
A circuit 47, a 2NAND circuit 48 that receives the output of the 3NAND circuit 52 and the output of the 2NAND circuit 47, a 2NAND circuit 49 that receives the output of the 2NAND circuit 47 and the synchronization switching signal S1, and a 2NA
An inverter circuit 46 that receives the output of the ND circuit 49, an inverter circuit 45 that receives the synchronization switching signal S1, and a 2NA
It has a 2 NOR circuit 50 which receives the output of the ND circuit 47 and the output of the inverter circuit 45. In this embodiment, when the synchronization switching signal S1 is input, the 1V generation circuit 23 acts so that the synchronization switching signal is not output until the vertical synchronization signal between the internally generated composite video signal and the external composite video signal matches. S2 is generated to control ON / OFF of the analog switches 6 and 7.

The position of the vertical synchronizing signal of the external composite video signal can be roughly classified into two patterns (C or D) as shown in FIG. When the position of the vertical synchronizing signal of the external composite video signal is the C pattern, 1V
The E signal is input to the generation circuit 23. In this case, the 1V generation circuit
At 23, the number of scanning lines in one field is increased so as to be 1V + nH lines (n: integer). On the other hand, when the position of the vertical synchronizing signal of the external composite video signal is the D pattern, the F signal is input to the 1V generating circuit 23, and in this case, 1V.
In the generating circuit 23, the number of scanning lines in one field is reduced so that the number of lines becomes 1V-nH (n: integer). Then, the position of the vertical sync signal of the internally generated composite video signal is forcibly aligned with the position of the vertical sync signal of the external composite video signal, and the sync switching signal S2 is generated only when the positions of the vertical sync signals of both are aligned. Then, the on state of the analog switch 7 is switched to the on state of the analog switch 6.

In the third embodiment, the increase or decrease in the number of scanning lines in one field is selected according to the position of the vertical synchronizing signal of the external composite video signal, so that only the number of scanning lines is increased in the first embodiment. Compared to the example, the alignment of both vertical synchronization signals can be performed more efficiently.

(Fourth Embodiment) FIG. 10 is a block diagram showing the internal structure of the synchronizing signal generating circuit 10 in the fourth embodiment. And a 1V generating circuit 24 for reducing the number of scanning lines in one field by deleting a specific scanning line in the vertical synchronization blanking period in one field. In this embodiment, the synchronization switching signal S1
When 1 is input, the 1V generating circuit 24 operates to generate the sync switching signal S2 only when the vertical sync signal between the internally generated composite video signal and the external composite video signal is matched, and the analog switch 6, 7 ON / OFF control is performed.

When the synchronous switching signal S1 changes from the L level to the H level, the 1V generating circuit 24 deletes a specific scanning line from one field as shown in FIG.
Accurate 1V period (V: 1 vertical period), that is, 262.5H lines (H: 1 horizontal scanning period) to 1V-nH lines (n: integer)
The number of scanning lines in one field is reduced so that Then, the position of the vertical sync signal of the internally generated composite video signal is forcibly aligned with the position of the vertical sync signal of the external composite video signal, and only when the positions of the vertical sync signals of both are aligned, the synchronization switching signal S2 Is generated, the analog switch 7 is switched from the on state to the analog switch 6 on state.

[0024]

As described above, in the screen display device of the present invention, when the internal sync mode is switched to the external sync mode, the position of the sync signal of the composite video signal generated internally is synchronized with that of the external composite video signal. After matching the signal position in an extremely short time, the internal sync mode is switched to the external sync mode, so that the continuity of the composite video signal can be maintained before and after this switch, and the screen on the TV screen is momentarily disturbed. The present invention exerts excellent effects such as the following.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a conventional screen display device.

FIG. 2 is a block diagram showing a configuration of a screen display device according to the present invention.

FIG. 3 is a time chart in the screen display device of the present invention.

FIG. 4 is a block diagram showing a configuration of a characteristic part of the first exemplary embodiment of the present invention.

FIG. 5 is a time chart in the first embodiment.

FIG. 6 is a block diagram showing a configuration of a characteristic part of a second exemplary embodiment of the present invention.

FIG. 7 is a time chart in the second embodiment.

FIG. 8 is a block diagram showing a configuration of a characteristic part of a third exemplary embodiment of the present invention.

FIG. 9 is a time chart in the third embodiment.

FIG. 10 is a block diagram showing a configuration of a characteristic part of a fourth exemplary embodiment of the present invention.

FIG. 11 is a diagram showing a vertical blanking period of a vertical synchronizing signal in the fourth embodiment.

[Explanation of symbols]

 1 Superimpose circuit 2 Composite video signal generation circuit 3 Video mixer 4,5 Inverter circuit 6,7 Analog switch 10 Synchronous signal generation circuit 11, 12 1H generation circuit 21, 22, 23, 24 1V generation circuit S1 Synchronous switching signal S2 Synchronous switching signal

Claims (4)

[Claims] 1. A screen display device for switching and outputting an external video signal and an internally generated video signal, comprising a synchronization signal generation circuit capable of changing the cycle by increasing the number of scanning lines in one field, When switching from the sync mode to the external sync mode, the video signal is switched by the operation of the sync signal generation circuit when the position of the vertical sync signal between the external video signal and the internally generated video signal is aligned. A screen display device characterized by the above. 2. A screen display device for switching between an external video signal and an internally generated video signal for output, comprising a sync signal generation circuit capable of changing the cycle by increasing one scanning line time, and an internal sync mode. When switching from the external sync mode to the external sync mode, the video signal is switched by the operation of the sync signal generation circuit when the vertical sync signals of the external video signal and the internally generated video signal are aligned. Characteristic screen display device. 3. A screen display device for switching and outputting an external video signal and an internally generated video signal, and comprising a synchronization signal generation circuit capable of changing the cycle by increasing or decreasing the number of scanning lines in one field. When switching from the internal synchronization mode to the external synchronization mode, the number of scanning lines in one field is increased by the synchronization signal generation circuit according to the difference in the position of the vertical synchronization signal between the external video signal and the internally generated video signal. A screen display device, characterized in that it is configured such that the positions of the vertical synchronizing signals of both video signals are matched with each other and that the video signals are switched when the positions of the vertical synchronizing signals of both video signals match. 4. A screen display device for switching between an external video signal and an internally generated video signal for output and changing the cycle by deleting a specific scanning line within a vertical synchronization blanking period in one field. A synchronizing signal generating circuit is provided, and when the internal synchronizing mode is switched to the external synchronizing mode, the operation of the synchronizing signal generating circuit causes the vertical synchronizing signal of the external video signal and the internally generated video signal to be aligned with each other. A screen display device characterized by being configured to switch video signals.