JPH0638132A - Multi-system reproduction changeover circuit and display device - Google Patents

Abstract

PURPOSE:To attain picture reproduction of a video signal of a different scanning line number or character display or the like by improving deterioration in vertical resolution of a shadow mask and production of moire when a CRT in common use for the NTSC, PAL and SECAM systems. CONSTITUTION:The display device is provided with a VG2s voltage changeover circuit 9 used to vary the shape of an electron beam spot when the broadcast system and the scanning line number are switched in the case that a picture comprising a video signal with a different number of scanning line is reproduced or a character is displayed by using a CRT having an electron gun whose electron beam spot shape is varied and with a multi-system reproduction changeover circuit 8 applying a voltage generated from the circuit 9 to a G2s.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a cathode ray tube (hereinafter referred to as CRT).
The present invention relates to a display device for image reproduction or character display, etc.

[0002]

2. Description of the Related Art In the field of television, dedicated CRTs are used to prevent moire in reproduced images of the NTSC system and the PAL / SECAM system. This dedicated C
The RT is equipped with a dedicated shadow mask for making moire less noticeable.

In order to make the moire inconspicuous, generally, either the wavelength of the moire (the degree of density of the moire manuscript) is shortened, or the degree of modulation of the moire pattern (the contrast of the moire manuscript) is decreased, or both. It is necessary to meet the condition of. More specifically, the moire changes periodically with respect to the hole pitch of the shadow mask.
When the vertical pitch is fixed, the spot diameter of the electron beam is made smaller and the resolution is made higher so that it becomes more conspicuous. Therefore, the vertical pitch of the shadow mask is usually designed coarsely as the number of scanning lines increases, without changing the beam spot diameter. Dedicated shadow mask is 525 NTSC scanning lines, P
The optimum vertical pitch is determined for each of the 625 scanning lines of the AL / SECAM system. Although moiré can be prevented even if the electron beam spot diameter is increased by keeping the hole pitch of the shadow mask constant, it is not a good idea to change the size of the circular beam spot because it extremely deteriorates the horizontal resolution of the reproduced image.

Therefore, when configuring a multi-system image receiver,
A shared CRT (shared shadow mask) is used. This shared CRT is intended for dual use, so NTSC and PA
In L-SECAM, the focusing of the electron beam spot and the vertical pitch of the shadow mask are determined on the assumption that moire is generated to some extent, so that there is still room for resolution improvement in the reproduced image.

[0005]

SUMMARY OF THE INVENTION The present invention improves the deterioration of vertical resolution of a shadow mask and the generation of moire when using a CRT shared by NTSC and PAL / SECAM, which is a disadvantage of the above-mentioned prior art, and improves the scanning line. It is intended to realize image reproduction or character display of video signals of different numbers.

[0006]

The present invention is a CRT having an electron gun capable of changing the shape of an electron beam spot.
When performing image reproduction or character display of video signals with different scanning lines by using, the multi-system reproduction switching circuit that has a voltage generation circuit that changes the electron beam spot shape at the same time as switching the broadcasting system and the number of scanning lines It is configured and uses this as a means.

[0007]

The present invention prevents the deterioration of the vertical resolution of the shadow mask and the occurrence of moire by changing the shape of the electron beam spot with the above structure. Of course, since the horizontal resolution uses the vertically long beam spot, it is possible to provide a reproduced image which is faithful to the video signal and has a high sharpness without deterioration.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an electrode structure of a CRT used in the present invention, which includes a cathode K 1, a first grating G12, a second grating G23, an auxiliary accelerating focusing electrode G2s 4, a third grating G3 5,
Consists of. This electron gun has two second electrodes, each of which has a rectangular electron beam transmission hole, and the long axes of the rectangles are orthogonal to each other, and the spot shape of the electron beam can be controlled by the voltage applied to this electrode. It has features (see Japanese Examined Patent Publication No. 61-6970).

FIG. 2 shows a multi-system reproduction switching circuit of the present invention, which includes a PAL / SECAM video signal 6, an NTSC video signal 7, a switching circuit 8 and a VG2s voltage switching circuit.
9, CRT deflection circuit 10, video signal processing circuit 11,
It is composed of a CRT drive circuit 12. The switching circuit 8 switches the broadcasting system or the number of scanning lines, and at the same time V controlled by the signal from the switching circuit 8
The voltage generated by the G2s voltage switching circuit 9 is applied to G2s to change the shape of the electron beam spot from a circular shape to a vertically long shape to prevent moire. This is an important part of the multi-system reproduction switching circuit. Since the moire pattern is generated by the interference between the hole array (phosphor dot array pattern) of the shadow mask and the scanning line (electron beam spot diameter), changing the electron beam spot shape from a circle to a rectangle etc. Prevents interference and also prevents resolution degradation. Specifically, the vertical pitch of the shadow mask is made finer than the resolution determined by the broadcasting system, and the electron beam spot shape is changed from a circular shape to a rectangular shape or the like to prevent the generation of a moire pattern. This operation is performed by the multi-method reproduction switching circuit. This circuit has a function of changing the electron beam spot shape in association with the switching of the broadcasting system or the number of scanning lines. The proposed display device is constructed using this circuit.

[0010]

As is apparent from the above embodiments, according to the present invention, when a multi-system broadcast is received using a shared CRT, moire is generated without degrading the reproducible resolution of each system. The display device can be configured without causing the generation. In addition, even in the single broadcast system, it is possible to prevent moire, which was a little in the past, and further improve the resolution. The effect is that the number of scanning lines in the NTSC system is 525, and the number of scanning lines in the PAL / SECAM system is 62.
Not only is it possible to reproduce five more faithful images, but it can also be easily applied to high-vision and wide-vision applications.

[Brief description of drawings]

FIG. 1 is a perspective view showing an electrode configuration of a CRT effective for a device according to an embodiment of the present invention.

FIG. 2 is a multi-system reproduction switching circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 Cathode K 2 1st grating G 1 3 2nd grating G 2 4 auxiliary acceleration focusing electrode G 2s 5 3rd grating G 3 6 PAL / SECAM video signal 7 NTSC video signal 8 switching circuit 9 VG 2s voltage switching circuit 10 CRT deflection circuit 11 video signal processing Circuit 12 CRT drive circuit

Claims (4)

[Claims] 1. A display device comprising a cathode ray tube capable of switching the shape of an electron beam spot. 2. A display device characterized in that a cathode ray tube capable of switching the shape of an electron beam spot is used to reproduce video signals having different scanning line numbers. 3. A multi-system reproduction switching circuit, wherein a voltage for changing the shape of an electron beam spot is generated at the same time when the broadcasting system or the number of scanning lines is switched. 4. A display device comprising the multi-system reproduction switching circuit according to claim 3.