JPS5894280A - Character and pattern signal superposing circuit - Google Patents

Abstract

PURPOSE:To obtain a character and pattern circuit which is free from time delay of a character signal against a video signal, and signal leakage, by connecting in multistage a switching circuit operated in an unsaturated area. CONSTITUTION:To an input terminal 12 and an input terminal 13, a video signal and a character signal are applied, respectively. Subsequently, from a switching circuit 20 of the first stage, a signal 14 is outputted, and from a connecting point 15 of a resistance connected in series to a supply voltage circuit, a bias signal is supplied. In this state, resistances 16, 17 show leakage of the switching circuit 20 of the first stage, and a signal 18 of a switching circuit of the second stage is outputted. Since the circuit 20 is a circuit operated in an unsaturated area, in this example, 2 circuits 20 are connected in series. A character signal for executing the switch-control of these 2 circuits 20 is connected so as to switch both circuits 20 simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a character/graphic signal superimposing circuit for reproducing characters, solid objects, etc. on a turpentine image surface by superimposing them on video.

As television receivers became more widespread, various types of visual information reproducing functions were developed that allowed them to be used not only for reproducing television broadcast programs, but also for reproducing other information at the same time. Information services were proposed and put into practical use.

An example of this is an information service in which other information, such as characters and graphics, is superimposed on the television program being received. (For example, regarding Akiyoshi Maehara's standards for teletext broadcasting: Television Science and Technology Report Vol. 4. NQ 7 (198
June 0) i 1T42-1) In such a case,
Signals such as characters and figures (
Hereinafter, it will simply be referred to as a character signal. ) must be superimposed.

Therefore, character signal superimposition circuits for this purpose have been conventionally used.

The simplest conventional technology is Ei 1 #2 (Fig. 1 (A)
) k character signal (FIG. 1(B)) is added. However, with this method, the brightness of the character signal differs depending on the brightness of the video signal, so only the ``#J'' image was produced, which was extremely difficult to see. 1. That is, when a character signal is superimposed on a video signal, it is necessary to keep the brightness of the character ('PI) constant. This is shown in the waveform diagram of FIG. 1. Like this'
In other words, the character signal can be clearly distinguished from the surrounding video signal.

In addition, a patent application has been filed for technology that makes the brightness of character signals constant.
]855-4607.

According to this technique, it is possible to obtain a waveform like that shown in Figure 1 (q). 1. In other words, it is a method in which a character signal is cut out from a video signal and a signal of a certain level is inserted later. However, this method has the disadvantage that a gap is created at the boundary between the video signal and the text signal, and the space between the text/figures and the video appears black.

As a method of keeping the brightness of the character signal constant and preventing gaps from forming at the boundary between the video signal and the character signal, the method shown in Figure 2 (a) is used.
), there is no way to think of a way to switch between the Hakugo and a constant bias at high speed using a character signal and output the output.

Figure 2 (b) shows a specific example of a circuit with a large cross section of 1° In Figure 2 (b), 1 to 6 are resistors, 7 to 10 are transistors, 11 is a capacitor, and 12 is a video signal. signal, 1
6 is a character signal, 14 is an output, and 15 is a constant bias. When this switching dog circuit is completely cut off by the character signal 15) and operated with saturation, the output is not the ideal waveform shown in Fig. 1q, but is slower than the ideal waveform as shown in Fig. 1. If this is obtained, the result will be a superimposed circuit in which the video gI signal and the character signal are not clearly separated.This is caused by the slow switching speed of the switching circuit.

Therefore, it is possible to construct a switching circuit using an element with a fast Nuwitching speed, but this has the disadvantage that a fast-speed element is very expensive.

In order to achieve high-speed output using relatively inexpensive elements, the signal amplitude of the character signal 13 in Fig. 2(b) is reduced to a small node vj4, and the cutting circuit is placed in the unsaturated region. I can't think of a way to use it as a working differential amplifier. In this case, the differential amplifier switches at high speed, but since it is used without being completely switched, the non-universal signal is added to the normal output. This is expressed as an equivalent circuit as shown in No. 26 (C). That is, Fig. 2(a)
is represented as a complete switching circuit with a leakage resistor 16.17. When such an unsaturated large switching circuit is used, the speed is high, and the time delay of the signal is eliminated.

However, as shown in FIG. 5(1), it is not possible to obtain an output signal in which leakage from the video signal is not superimposed when a constant bias is selected. Therefore, the brightness of the characters and figures is not constant, resulting in the disadvantage that the characters and figures become unclear.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the conventional technique described above and to provide a character/solid weight circuit which is free from time delay of a character signal with respect to an image signal and no signal leakage.

In order to achieve the above object, the present invention connects switching circuits operating in an unsaturated region in multiple stages to reduce leakage in the switching circuits.

FIG. 4 is an equivalent circuit diagram showing an embodiment of the present invention.

The configuration of FIG. 4 will be explained below. In FIG. 4, 12 is a video signal input terminal, 13 is a character signal input terminal, 14 is an output signal of the first stage switching dog circuit, 15 is a constant bias, 1
6.17 indicates leakage in switching large circuit, 1 resistor, 18 indicates 2nd resistor.
The output signal of the switching circuit in the third stage, 20, is a switching circuit. Here, a specific example of the switching circuit 20 is one in which one path of BL is used as a switching circuit operating in an unsaturated region as shown in FIG. Furthermore, the character signal controlling the switching circuits 20 in the first stage and the second stage is connected so that both switching circuits 20 are switched at the same time.

Next, the operation of FIG. 4 will be explained. In the first stage switching circuit, the video gI signal 12 and constant bias 15 are switched in accordance with the character signal. When the character signal is L°, the 5g1 stage switching circuit outputs the video g1 flaw signal. In addition, a constant bias is transmitted to the output 14 via the 11it'l resistor 17, resulting in the video signal 12 to which the DC level has been added. By first lowering the level of the image g1 signal, the DC component can be added without affecting the screen at all.

On the other hand, when the character signal is °H1, a constant bias 15 is outputted to the output 14 of the first stage switching large circuit. At this time, the video signal is transmitted to the output 14 via the resistor 17, so in addition to the constant bias 15, the video gI! Signal also output 1
Appears in 4.

Here, if the leakage rate of the uncontrollable input signal power of the switching circuit 20 to the output 14 is R, then from the above definition, R≦1. In an ideal switching circuit, it is R-o, but in the present invention, since switching is large in the unsaturated region, it is set to R-α1 as an example.

The remark waveform corresponding to the output 14 in FIG. 4 is as shown in FIG. 5 (0). Figure 5 (f in Q means letter signal l)
This is a leak from Hakugo Riki and others from the time of 1. In this case, there is some leakage, but since the switching speed of the large switching circuit 20 is fast,
There is no waveform distortion at the time t'+'P of the character signal superimposition position.

The output 14 in FIG. 4 is added to the switching λ circuit 20
1, waveforms like those shown in FIGS. 5() and 5() are obtained.

In the second stage large switching circuit shown in Fig. 4, the character signal 13
When is +I, +, the output 14 of the first stage is outputted to the output 18 of the second stage. In addition, there is a constant bias of 15
is applied to the output 18 via the leakage resistor 17, but as in the case of the first stage, there is no effect on the screen of the image ('i! No. 12) at all.

On the other hand, when the character signal 13 is l ) J l, the constant bias 15 is output to the output 18 of the second stage switching circuit. At this time, output 14 passes through leakage resistor 17 to output 18.
Therefore, in addition to the constant bias 15, the output 14 of the first stage is also transferred to the output 18 of the second stage.

By the way, the output 140 waveform diagram of the first stage is shown in Fig. 5 (q).The leakage f of Fig. 5 (q) is as large as the image g1.

Furthermore, the leakage of the second stage switching circuit when the character signal is +H' is calculated by multiplying the leakage rate R by the sum of f of C4 and constant bias 15 (Fig. 5). If the multiplication amount is P, the leakage of the output 18 of the second stage cut-off circuit 20 is (f + constant bias) xR, that is, (PXR + constant bias) xR.The latter constant bias x R is Since it is a constant, there is no problem as long as the brightness level of the text/figure multiplication changes slightly.Therefore, only Px)iF can be treated as leakage. When R-0,1, the leakage becomes αo1×P. If you look at the waveform diagram, it will look like the one shown in Figure 5 (0).

In Figure 5, g is the leakage of the second stage switching λ circuit. By stacking the switching circuits 20 in two stages in this manner, a switching circuit having an st'+ ratio of W is realized as a whole. Since W is 1, this leakage rate is so small that the leakage rate of the image 4a signal to the character signal is almost unnoticeable. In order to further reduce the leakage rate, it is sufficient to connect n large switching circuits 20 in multiple stages, which is another application example of the present invention.

By carrying out the present invention, it is possible to realize a character-graphic superimposition circuit that has no temporal deviation in the superimposition position of a character signal on a video signal and is free from omissions.

It is also economically advantageous because the circuit can be configured without using expensive transistors for high-speed switching.

[Brief explanation of drawings]

1 (5) to (G) are waveform diagrams for explaining the operation of a character/graphic signal large amount circuit, FIG. 5), (B1. ■ is a waveform diagram for explaining its operation, FIG. 4 is a block diagram showing an embodiment of the character number figure signal superimposition circuit according to the present invention, and FIG. 5 (
Q and U are waveforms for explaining the operation, and FIG. 6 is a block diagram showing another embodiment of the present invention. 12: Video signal 13: Character signal 14: Output signal of the first stage switching circuit 15 Ni constant bias 16: Resistor 17: Resistor 18: Output signal of the second stage switching circuit 20: Switching circuit agent Patent Attorney Susuki 1) Toshiyuki O 1 Figure (I)) Sai 3 Figure

Claims (1)

[Claims] In the text/figure signal superimposing circuit which is provided with a large switching means for switching between a video g1 signal and a constant signal, and reproduces characters/figures etc. by switching and superimposing them on a television video by the switching means, A means for operating the switching means in an unsaturated region and a means for connecting a plurality of the large switching means in series and simultaneously switching the plurality of switching means. circuit.