JPH0737521A - Electron gun for color cathode-ray tube - Google Patents

Abstract

PURPOSE:To improve focusing performance in the whole region of a face plate and the whole current region of an electron beam and also reduce the occurrence of moire at the time of low current. CONSTITUTION:A color cathode-ray type electron gun is provided with a prefocus part consisting of a negative electrode K, first and second grid electrodes 1 and 2, and afocus acceleration part consisting of a third-nth grid electrodes N. Slits 2-3 having a long side in a horizontal direction are provided on an electron beam pass hole of the second grid electrode 2 oh the opposite surface side of the third grid electrode 3. Also slits 1-2 having a long side in a vertical direction are provided on an electron beam pass hole of the first grid electrode 1 on the opposite surface side of the second grid electrode 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun for a cathode ray tube, and more particularly to an electron gun for a color cathode ray tube capable of reducing the occurrence of moire without deteriorating the focus characteristics at the time of a large current.

[0002]

2. Description of the Related Art A cathode ray tube used for displaying a color image (color cathode ray tube) is a vacuum container composed of a panel portion which is an image screen, a neck portion, and a funnel portion connecting the panel portion and the neck portion. An electron gun is housed in the neck portion of the vacuum container, and a shadow mask as a color selection electrode is suspended on the panel portion.

At least three color phosphors are coated on the inner surface of the panel portion, and a magnetic shield connected to the shadow mask is provided inside the funnel portion. The three electron beams emitted from the electron gun are deflected by a deflection yoke mounted on the transition region of the neck portion and the funnel portion, pass through a large number of apertures formed in the shadow mask, and undergo color selection. An image is formed by landing on a predetermined phosphor screen.

In the electron gun, it is necessary that the spots of the electron beam of the electron gun exactly match the phosphors of the phosphor screen formed on the phosphor screen. Therefore, it is required that the electron beam spots on the phosphor screen maintain a sufficiently focused state both in the central portion and the peripheral portion of the phosphor screen.

FIG. 6 is a schematic diagram for explaining an example of the structure of a conventional electron gun for a color cathode ray tube, in which K is a cathode and 1 is a first.
Grid electrode, 2 is a second grid electrode, 3 is a third grid electrode, 4 is a fourth grid electrode, 5 is a fifth grid electrode, and 6 is a sixth grid electrode. In the figure, the electron gun includes a cathode K, a three-pole portion including a first grid electrode 1 and a second grid electrode 2, and a prefocus portion including a second grid electrode 2 and a third grid electrode 3. And the third grid electrode 3, the fourth grid electrode 4, and the fifth
The main lens portion is composed of the grid electrode 5 and the sixth grid electrode 6.

A crossover is formed in the prefocus portion formed by the first grid electrode 1 and the second grid electrode 2 in the electron flow generated in the three-pole portion. This crossover is focused and accelerated by the main lens unit and deflected and scanned horizontally and vertically by a deflection yoke (not shown) to form an image on the screen (fluorescent screen). FIG. 7 shows the second grid electrode 2 of the electron gun described above.
3A is a front view for explaining the structure of FIG. 3A, and FIG. 4B is a cross-sectional view taken along line AA of FIG.

In the figure, 2 is a second grid electrode, 2
a is a center electron beam passage hole, 2b and 2c are side electron beam passage holes, and 2-3a, 2-3b and 2-3c are horizontally long slits. As shown, the second grid electrode 2
Horizontal slits 2-3a, 2-3b, and 2-3c having long sides in the horizontal direction are formed on the third grid electrode 3 side of each of the electron beam passage holes 2a, 2b, and 2c.

The lateral slits 2-3a, 2-3b, 2
-3c reduces the deflection aberration of the electron beam and improves the focus characteristic in the peripheral portion of the screen. The prior art relating to the electron gun for this type of color cathode ray tube is disclosed, for example, in Japanese Utility Model Publication No. 56-5164.
No. 8 and JP-A-59-215640 can be mentioned.

[0009]

In the above electron gun structure of the prior art, the electron beam spots are vertically elongated in the central portion of the screen, and the vertical lines formed on the phosphor screen tend to be too thin. Moire occurs when current is applied. As a measure against this, for example, horizontally long slits 2-3a and 2-3
A possible method is to make the depths b and 2-3c shallow to thicken the vertical line in the central portion of the screen when the current is low, but this also thickens the vertical line when the current is high, degrading the focus performance. There was a problem.

An object of the present invention is to solve the above-mentioned problems of the prior art, to improve the focusing performance in the entire area of the screen and in the entire current range of the electron beam, and to reduce the occurrence of moire at low current. An object is to provide an electron gun for a cathode ray tube.

[0011]

In order to achieve the above-mentioned object, the present invention provides a pre-focus portion including a cathode K, a first grid electrode 1 and a second grid electrode 2, and a third grid electrode 3. In the electron gun for a color cathode ray tube, which comprises a focusing accelerator composed of a fourth grid electrode 4, a fifth grid electrode 5 and a sixth grid electrode 6, the second grid electrode 2 faces the third grid electrode 3. A laterally long slit 2-3 having a long side in the horizontal direction is provided in the electron beam passage hole on the surface side, and the first grid electrode 1 is provided.
The vertical slits 1-2 having long sides in the vertical direction are provided in the electron beam passage holes on the opposite surface side of the second grid electrode 2.

The type of electron gun is not limited to the above-mentioned type, and the present invention can be applied to a multistage focusing type electron gun having a structure with fewer grid electrodes or up to the nth grid electrode N.

[0013]

The vertical slit having a long side in the vertical direction provided on the side of the electron beam passage hole of the second grid electrode facing the third grid electrode reduces the thinning of the vertical line at the center of the screen when the current is low. At the same time, deterioration of the focus performance at high current is prevented. In order to prevent the vertical line from becoming thin in the central portion of the screen, it is necessary to make the cross-sectional shape of the electron beam in the electron gun closer to a circle as the current value becomes smaller.
However, in the case where the horizontally elongated slit having the long side in the horizontal direction is provided on the second grid electrode side of the electron beam passage hole of the first grid electrode, the cross-sectional shape of the electron beam becomes horizontally elongated as the current value decreases. . This is because as the current becomes lower, the crossover position in the prefocus portion approaches the cathode side, and the slit effect becomes greater.

On the other hand, by providing a vertical slit having a long side in the vertical direction in the electron beam passage hole on the surface of the first grid electrode facing the second grid electrode, the horizontal direction is provided before the crossover. Exerts a focusing force on. In this case, due to the crossover position, the slit effect becomes larger as the current becomes higher. If the slit effect of the first grid electrode is made larger than the slit effect of the second grid electrode, a laterally elongated electron beam cross section can be obtained as the current becomes higher (that is, a circular shape becomes as the current becomes lower).

As a result, the deterioration of the image quality due to the occurrence of the moire can be prevented.

[0016]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic view of an essential part for explaining an embodiment of an electron gun for a color cathode ray tube according to the present invention, in which K is a cathode, 1 is a first grid electrode, 2 is a second grid electrode, and 3 is a third grid electrode. The grid electrode 4 is a fourth grid electrode. It should be noted that the figure shows only one half which is symmetrical with respect to the beam passing axis of the central electron beam which constitutes the three-electron gun, and the configuration of the fifth grid electrode and below is omitted.

In this electron gun, the cathode K, the first grid electrode 1 and the second grid electrode 2 form a three-pole portion, and the second grid electrode 2 as in the conventional electron gun described above.
And the third grid electrode 3 constitute a prefocus portion, and the third grid electrode 3 and the fourth grid electrode 4 ... Configure a main lens portion. On the second grid electrode 2 side of the first grid electrode 1, a vertically long slit 1-2 having a long side in the vertical direction is formed in the electron beam passage hole, and the third grid electrode of the second grid electrode 2 is formed. On the third side, a laterally long slit 2-3 having a long side in the horizontal direction is formed in the electron beam passage hole.

FIG. 2 is a schematic perspective view for explaining the structure of the side of the first grid electrode facing the second grid electrode,
1a is a center electron beam passage hole, 1b and 1c are side electron beam passage holes, 1-2a is a vertical slit provided in the center electron beam passage hole 1a, 1-2b and 1-2c are side electron beam passage holes 1b and 1c. It is a vertical slit provided in.

FIG. 3 is a schematic perspective view for explaining the structure of the side of the second grid electrode facing the third grid electrode,
2a is a center electron beam passage hole, 2b and 2c are side electron beam passage holes, 2-3a is a vertical slit provided in the center electron beam passage hole 2a, 2-3b and 2-3c are side electron beam passage holes 2b and 2c. It is a horizontal slit provided in the. This horizontally long slit is the same as that described in FIG.

As described above, the longitudinal slits 1-2a, 1- provided in the first grid electrode 1 and the second grid electrode 2 are formed.
2b and 1-2c apply a focusing force to the electron beam in the horizontal direction before the crossover formed by the prefocus lens composed of the second grid electrode 2 and the third grid electrode 3. Then, the horizontal slits 2-3a, 2-3b, 2-3c of the second grid electrode 2 suppress the thinning of the vertical line at the time of low current in the central portion of the screen.

Therefore, the focusing performance is not deteriorated over the entire screen and in the entire current region of the electron beam, and the vertical line in the central portion of the screen at the low current is brought about without causing the focus deterioration at the high current. It is possible to suppress the occurrence of moire due to the thinning of the. FIG. 4 is a side view illustrating the appearance of a color electron gun having a grid electrode structure according to the present invention. The same reference numerals as in the above embodiment correspond to the same parts, 5 is a fifth grid electrode, and 6 is a sixth grid. An electrode, 7 is a shield cup electrode, 8 is a bead glass for fixing and holding each electrode, and 9 is a stem.

The first grid electrode 1 and the second grid electrode 2 of this electron gun have the structure described with reference to FIGS. 2 and 3. FIG. 5 is a cross-sectional view for explaining an example of a color cathode ray tube equipped with the electron gun of the present invention. 10 is a face panel constituting a screen, 11 is a fluorescent screen, 12 is a shadow mask, 20 is a neck, 21 is 21. Electron gun, 30 is a funnel, 31 is a magnetic shield, 32 is an internal conductive film, 40
Is a deflection yoke.

The electron gun 21 in the figure is the electron gun described in FIG. 4, and the electron beam emitted from this electron gun is deflected horizontally and vertically by the deflection yoke 40, and the shadow mask 12 selects the color. A color image is reproduced by receiving and colliding with the required fluorescent substance which comprises the fluorescent surface 11.

[0024]

As described above, according to the present invention,
It is possible to provide a high-quality electron gun for a color cathode ray tube that can improve the focusing performance over the entire screen and in the entire current range of the electron beam, and can reduce the occurrence of moire at a low current.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part for explaining an embodiment of an electron gun for a color cathode ray tube according to the present invention.

2 is a second grid of the first grid electrode of the electron gun shown in FIG.
It is a schematic perspective view explaining the structure of the side which opposes a grid electrode.

3 is a third view of the second grid electrode of the electron gun shown in FIG.
It is a schematic perspective view explaining the structure of the side which opposes a grid electrode.

FIG. 4 is a side view illustrating the appearance of a color electron gun having a grid electrode structure of the present invention.

FIG. 5 is a cross-sectional view illustrating an example of a color cathode ray tube equipped with the electron gun of the present invention.

FIG. 6 is a schematic diagram illustrating a configuration example of a conventional electron gun for a color cathode ray tube.

FIG. 7 is an explanatory diagram of a structure of a second grid electrode of a conventional electron gun for a color cathode ray tube.

[Explanation of symbols]

 K cathode 1 1st grid electrode 1-2a, 1-2b, 1-2c Vertical slit 2 2nd grid electrode 2-3a, 2-3b, 2-3c Horizontal slit 3 3rd grid electrode 4 4th grid electrode 5th 5 grid electrode 6 6th grid electrode 7 shielding cup electrode 8 bead glass 9 stem.

Claims (1)

[Claims] 1. An electron gun for a color cathode ray tube, comprising: a cathode, a pre-focusing part composed of a first grid electrode and a second grid electrode, and a focusing acceleration part composed of a third grid electrode to an nth grid electrode. In the electron beam passage hole of the second grid electrode on the opposite surface side of the third grid electrode, a horizontally elongated slit having a long side in the horizontal direction is provided, and the first grid electrode faces the second grid electrode opposite surface. An electron gun for a color cathode ray tube, wherein a vertical slit having a long side in the vertical direction is provided in the electron beam passage hole on the side.