JPH05284425A - Character mix circuit - Google Patents

Abstract

PURPOSE:To use one switch circuit to mix a video signal and a character signal. CONSTITUTION:A switch circuit 1 is provided with a clamp circuit 2, which keeps a video signal to be a prescribed DC level. The clamped video signal is inputted to one input of the switch circuit 1. Furthermore, the character signal added to the DC signal is inputted to the other input of the switch circuit 1. The video signal and the character signal are mixed by controlling them with a framing signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a character MIX circuit, and more particularly to a character MIX circuit for mixing a character signal with a video signal in a video device.

[0002]

2. Description of the Related Art Recent TVs and VTRs (Video Tape Rec)
In order), some screens can display characters such as channel No, volume, and time. This is what is called the character superimpose. In the first place, superimposing means superimposing an external signal on a video signal. The video signal and the external signal are switched at high speed at the output timing of the signal of the external device, and the superimposing can be realized by this switching operation.

FIG. 3 is a block diagram of a conventional character MIX circuit. In the figure, 11 is a first switch circuit, 12 is a first clamp circuit, 13 is a second switch circuit, and 14 is a second clamp circuit. Circuits A'to G'represent signals of respective parts, and are shown in FIG.
Waveforms corresponding to (a) to (g) are shown. Figure 4
The video signal having the waveform A ′ shown in FIG.
To a constant DC level by the clamp circuit 12. On the other hand, the border signal C ′ shown in FIG.
Switch SW1 of the switch circuit 11 to the b side,
When a DC component (luminance level) is input to the waveform B'shown in FIG. 4 (c), the border signal C is mixed only in that portion, and the video signal D'shown in FIG. 4 (d) is obtained. Further, in the switch circuit 13, the mixed signal shown in FIG.
The video signal of the waveform D'shown in (d) is input, and the clamp circuit 14 maintains a constant DC level. Also, FIG.
When the SW2 of the switch circuit 13 is switched to the d side by the character signal of the waveform F ′ shown in (f) and the DC component (luminance level) of the waveform E ′ shown in FIG. F'is mixed with the video signal D ', and FIG.
A video signal G'shown in (g) is obtained.

[0004]

As described above, in the conventional character mix circuit, the first switch circuit mixes the video signal and the border signal, and the second switch circuit mixes the character signal. Therefore, there is a problem that the structure is complicated as the MIX circuit because two switch circuits are eventually required.

The present invention has been made in view of such circumstances, and an object thereof is to provide a character MIX circuit in which a video signal and a character signal are mixed by one switch circuit.

[0006]

In order to achieve the above object, the present invention inputs a clamp circuit for keeping a video signal at a constant DC level and a video signal clamped by the clamp circuit to one input section. A switch circuit for inputting the character signal added to the DC signal to the other input section,
A border signal is used to control the video signal and the character signal.

[0007]

The video signal clamped so as to maintain a constant DC level is input to one input section of the switch circuit, and the character signal added to the DC signal is input to the other input section of the switch circuit. The video signal and the character signal are controlled by the border signal, and the character signal is mixed with the video signal.

[0008]

Embodiments will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining an embodiment of a character MIX circuit according to the present invention, in which 1 is a switch circuit and 2 is a circuit.
Is a clamp circuit. 2A to 2C are diagrams showing waveforms A to E of the respective parts in FIG.

The switch circuit 1 switches between a video signal and a border signal at high speed at the timing of the border signal. The video signal A having the waveform shown in FIG. 2A is input to one input portion of the switch circuit 1, and the video signal A is clamped by the clamp circuit 2 to a constant DC signal. Since the video signal A is AC-coupled and the position of the pedestal level (black level: the blackest part in the video) fluctuates depending on the brightness of the image, if characters are inserted as is, Since the brightness of characters changes, direct current reproduction (clamping) is performed to keep the black level of the video signal constant before inputting the character signal.

Here, the video signal A is a composite
Think of it as a video signal. Generally, a composite video signal is a composite signal of three signals of a luminance signal (Y), a chroma signal (C), and a synchronizing signal (SYNC). The luminance signal (Y) is a signal that conveys the brightness of the image, the chroma signal (C) is a signal that conveys color information, and the synchronization signal (SYNC) is a signal that provides position information of the image. The video signal A shown in FIG. 2A shows the luminance signal (Y) and the synchronization signal (SYNC), but does not show the chroma signal (C).

At the other input portion of the switch circuit 1,
The signal of the waveform C shown in FIG. 2C is input. The signal of waveform C is obtained by adding the character signal of B having the waveform shown in FIG. 2B to the DC component (luminance level). In addition, the border signal D having the waveform shown in FIG. 2D is added to the control terminal of the switch circuit 1 so that the border signal D
When it is H ", SW is switched to the b side, the screen becomes white, the character signal C is output to the output of the switch circuit 1, and when the border signal D is" L ", the SW is switched to the a side. The video signal A is output to the output of the switch circuit 1, and in this way, the mix signal having the waveform E shown in (e) of Fig. 1 is obtained, in which case it is input to the switch circuit 1 as described above. It is necessary for the video signal to be clamped by a certain DC signal, and the relationship between the clamp voltage and the DC signal that gives the brightness level of the character signal becomes important. It must be higher than the voltage corresponding to the pedestal level of the video signal.

A character generator is generally used to create a character signal, but a ROM is used for the character generator and a character code is stored in the ROM. Further, as described above, the video signal handled in the character MIX circuit of the present invention does not touch on the chroma signal, but by providing a color generating function through another switch circuit, a background with a color is displayed. It is possible to mix white or black characters, and it is also possible to mix colored characters in a normal image.

[0013]

Since the present invention is configured as described above, it is possible to mix a video signal and a character signal with one switch circuit. That is, since the video signal and the character signal are controlled and mixed by the border signal, the structure of the character MIX circuit can be simplified.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a character MIX circuit according to the present invention.

FIG. 2 is a diagram showing a waveform of each part in FIG.

FIG. 3 is a diagram showing a conventional character MIX circuit.

FIG. 4 is a diagram showing a waveform of each part in FIG.

[Explanation of symbols]

 1 ... Switch circuit, 2 ... Clamp circuit.

Claims (1)

[Claims] 1. A switch circuit comprising one input section for inputting a video signal clamped to keep a constant DC level and another input section for inputting a character signal added to the DC signal, A character MIX circuit, wherein the switch circuit has a mixing means for controlling the video signal and the character signal by a border signal and mixing the character signal with the video signal.