JPS6251553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a blanking device for a television receiver.

Usually, a television receiver uses a picture tube for display purposes. The picture tube is a horizontal beam of electrons,
The image is reproduced on the fluorescent surface by vertical scanning. The sawtooth waves used for this horizontal and vertical scanning are shown in FIGS. 1a and 1b, respectively. The periods of these sawtooth waves are determined by broadcasting standards, and one horizontal period T _H is approximately 63.5 μs, and one vertical scanning period T _V is approximately 16.7 m.
It is written as s. The horizontal flyback period T _H2 is approximately 17% of one horizontal period T _H , and the remaining 83% is the image transmission period T _H1 . Further, the vertical retrace period T _V2 is approximately 8% of one vertical scanning period T _V , and the remaining 92% is the image transmission period T _V1 .

Figure 2 shows the vertical retrace period and its surroundings in a conventional television signal, where a is a received signal, b is an explanatory diagram of receiver deflection scanning, and c is an explanatory diagram of an effective screen. , d in the figure shows a blanking pulse. Further, e in the same figure shows a blanking pulse according to the present invention. In the figures, H represents the horizontal period, and the subscript at the bottom of each figure is the number of the horizontal period,
In other words, it indicates the number H.

As shown in FIG. 2a, the vertical retrace period of the received signal is 21H. As is well known, conventional vertical deflection circuits start deflection using the vertical synchronization signal as a trigger signal, so the vertical retrace line is from the 3rd to the 5th H.
It starts between. This is illustrated in Figure 2b. Figure c illustrates an effective screen, and the overscan area in the figure is 28H in total. This overscan section is 28H in total. This overscan portion is a portion that protrudes from the effective fluorescent surface of a picture tube or the effective screen portion of a projection television. Therefore, this overscan area does not become an effective screen. d in the figure is a blanking pulse, which has the same pulse width as the vertical retrace period of the deflection circuit.

In conventional television receivers, the scanning linearity deteriorates at the beginning and end of the image transmission period _TV1 , so in order to prevent this deterioration from appearing on the screen, the scanning linearity is shown in Figure 2c. So, about 10%
An overscan (excessive amplitude deflection) was performed.

That is, as a result, only about 90% of the transmitted information was configured to be visible. This has the advantage that the beginning (lower edge of the screen) and the end (upper edge of the screen) of scanning are hidden, and a poor quality image does not appear on the screen.

Television receivers are commonly provided with blanking circuitry to cut off the scanning electron beam during retrace. The width of the blanking pulse output from this blanking circuit is
As can be seen from FIGS. 2c and 2d, the purpose of blanking is achieved since it is matched with the vertical blanking period of the deflection circuit. However, since the electron beam was not cut off for the 10% overscan, the electron beam flowed through the cathode ray tube unnecessarily, resulting in wasted power consumption.

In addition, the overscanned electron beam is abnormally reflected by the upper and lower walls of the picture tube and generates secondary electrons, which collide with the fluorescent surface again, deteriorating the contrast ratio of the screen. There was a problem.

In addition, front projection television receivers developed in recent years use a method that optically projects light onto the screen surface, so overscanning light that extends beyond the screen surface may hit the wooden frame around the screen and cause abnormalities. There was a drawback that the over-scan light that generated interference light and even beyond the wooden frame hit the ceiling or wall behind the screen and generated abnormal light.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, eliminate unnecessary power consumption, prevent deterioration of contrast, and prevent the occurrence of abnormal light. The purpose is to improve the brightness and contrast of the screen.

The present invention provides a device that uses two pulse counters and flip-flop means to make the width of a blanking pulse wider than the width of a conventional blanking pulse, thereby cutting off the electron beam in the overscan region. It has characteristics.

FIG. 3 is a schematic diagram of a television receiver to which the present invention is applied. In the figure, 1 is a tuner and intermediate frequency circuit, 2 is a video circuit, 3 is a synchronization separation circuit, 4 is a horizontal deflection circuit, 5 is a vertical deflection circuit, and 6 is a blanking pulse generation circuit of the present invention.

The present invention improves the pulse width of the blanking pulse, and one embodiment thereof will be explained with reference to FIG. In the figure, 12 and 13 are pulse counters, and 14 is a pulse counter.
RS flip-flop, 15 is a horizontal pulse input terminal, 16 is a vertical pulse input terminal. A horizontal pulse is applied to terminal 15 and pulse counter 12,
13 clock input terminals. Also, the vertical pulse is applied to the terminal 16, and the pulse counter 1
It is added to the reset terminals 2 and 13. Each counter 12, 13 is reset at the rising edge of the vertical pulse (4th H).

The operation of the blanking pulse generating circuit described above will be explained with reference to FIG. FIG. 5 is a timing chart of the output signals of each block shown in FIG. Note that the scale in FIG. 5 indicates the horizontal period number (H).

When a vertical pulse is input to the terminal 16, the pulse counters 12 and 13 both detect the rising edge (first pulse) of the vertical pulse.
4H). Therefore, signal 12
a, 13a becomes L level. Next, when the 33rd H horizontal pulse is applied to the terminal 15, the output 12a of the pulse counter 12 becomes H level. As a result, the RS flip-flop 14 is reset and the F output 17 becomes L level. Next, when the 250H horizontal pulse is applied to the terminal 15,
The output 13a of the pulse counter 13 changes to H level, and the F output 17 of the RS flip-flop 14 changes to H level.
become the level. By repeating the above operations, blanking pulses of H level are obtained from 250H to 33H shown in FIG. 2e or 17 in FIG.

As described above, according to this embodiment, since the blanking pulse width is from the 250th H to the 33rd H, it is possible to cut off the scanning electron beam in the overscan portion. Therefore, the drawbacks of the conventional television receiver described above can be eliminated.

In addition, although the above embodiment has been explained using an example using a counter, a monostable multivibrator for delay may be used instead of the counters 12 and 13. In this case, horizontal pulses are unnecessary and only vertical pulses are used.

As described above, according to the present invention, the width of the blanking pulse can be expanded and the electron beam in the overscan portion can be cut off compared to the conventional technology. Therefore, approximately 10% of the high-voltage power was wasted in the overscan section, which previously was approximately 10%.
can be reduced. Furthermore, by utilizing this power for effective screen display, a brighter and more beautiful image can be provided. Furthermore, it is possible to prevent contrast deterioration due to straying of the electron beam in the overscan area in the prior art. Furthermore, when applied to a projection television, it becomes possible to eliminate interfering light in the outer frame of the screen, etc.

Furthermore, since the horizontal period is counted by a pulse counter and the blanking pulse is created based on the result, it is possible to create a blanking pulse with an accurate pulse width. Another advantage is that the front and back of the pulse can be changed independently.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of sawtooth waves used for horizontal and vertical scanning, Fig. 2 is an explanatory diagram of an effective screen and blanking pulse, and Fig. 3 is a block diagram of a television receiver to which the present invention is applied. FIG. 4 is a block diagram of a blanking pulse generator according to an embodiment of the present invention, and FIG. 5 is an output waveform diagram of each block in FIG. 6...Blanking pulse generation circuit, 12,1
3...Counter, 14...RS flip-flop, 17...Blanking pulse.

Claims (1)

[Claims] 1. In the blanking device of a television receiver, it is reset by the vertical pulse of the television signal, and when the horizontal pulses before and after the 33rd H (H represents the horizontal period) are input, the blanking device is reset. a first pulse counter that outputs a signal; a first pulse counter that is reset by the vertical pulse;
The second pulse counter outputs a set signal when the horizontal pulses before and after the 250th H or around it are input, and the first pulse counter enters the first state by the set signal of the first pulse counter. 2
Blanking of a television receiver, characterized in that the flip-flop means is brought into a second state by a signal set from a pulse counter of the television receiver, and the flip-flop means blanks during the second state. Device.