JPH06176706A - Electron gun for cathode-ray tube - Google Patents

Abstract

PURPOSE:To provide a cathode-ray tube which can control a beam spot to be small without causing the deterioration of the electron emission surface of a cathode. CONSTITUTION:A first grid G1 has a hole 4 for transmitting a beam on its top and is formed in the shape of a cone or a truncated cone. The electron emission surface 9 of a cathode K is so formed as to have an outer curved surface of a protruding part facing against the first grid G1. The distance between the first grid G1 and the electron emission surface 9 of the cathode K is so constituted as to be substantially equal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron gun used for a cathode ray tube such as a color television.

[0002]

2. Description of the Related Art Conventionally, as this type of electron gun, for example, one shown in FIG. 3 has been known. That is, in the unipotential type electron gun 11, the _first to fifth grids G ₁ to
G ₅ is arranged coaxially. Then, the electron beam 13 emitted from the cathode K emits the second and third grids G ₂ ,
A prefocus lens 14 formed by G ₃ ;
It is focused on the phosphor screen 12 by the action of the main lens 15 formed by the third to fifth grids G ₃ ~G _5. In such an electron gun 11, the electron emission surface 15 of the cathode K is formed in a flat shape.

[0003]

However, in the case of such a conventional example, the following problems have occurred when trying to increase the sharpness of an image. That is, the first grid G ₁
As the cutoff voltage Ekco is increased (the potential of the first grid G ₁ is decreased with respect to the cathode K), the generation area of the electron beam 13 on the electron emission surface 15 of the cathode K is proportional to the cutoff voltage Ekco. Becomes narrower, and the beam spot 16 on the phosphor screen 12 becomes smaller accordingly, and the sharpness of the image increases.
However, at that time, the electron beam 13 is concentrated on the electron emission surface 15 of the cathode K and the cathode K is rapidly deteriorated, so that the sharpness of the image cannot be sufficiently increased.

The present invention has been made in view of the above points of the conventional example, and an object of the present invention is to provide an electron of a cathode ray tube capable of narrowing a beam spot without causing deterioration of an electron emission surface of the cathode. To provide a gun.

[0005]

The first aspect of the invention is provided with a _first conical or frustoconical grid G ₁ having a beam transmitting hole 4 at the top, as shown in FIG. 1 or 2, for example. And In the second invention, the electron emission surface 9 is the first.
It is characterized in that the cathode K is formed so as to form a convex outer curved surface toward the grid G ₁ . Furthermore, the third invention has the first grid G ₁ of the first invention and the cathode K of the second invention, and the space between the first grid G ₁ and the electron emission surface 9 of the cathode K is substantially the same. It is characterized in that they are configured to be equidistant.

[0006]

In the present invention having such a configuration, the first grid G _{1 according to} the first invention is a cone or a truncated cone having the beam transmission hole 4 at the top, or the second invention. The electron emitting surface 9 of the cathode K is connected to the first grid G
_When a beam spot S having the same diameter is to be obtained on the phosphor screen 2 by forming an outer curved surface which is convex toward ₁ , the electron beam 3 on the electron emission surface 9 is more The generation area becomes wider. Therefore, the first
Even when the cut-off voltage Ekco applied to the grid G ₁ is increased to reduce the beam spot S diameter on the phosphor screen 2 to a small size, the concentration of the electron beam 3 on the electron emission surface 9 of the cathode K is relaxed, The electron emission surface 9 is less likely to be deteriorated. This action is further strengthened by arranging the first grid G _{1 according} to the first invention and the electron emission surface 9 of the cathode K according to the second invention to be substantially equidistant.

[0007]

Embodiments of the electron gun for a cathode ray tube according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of this embodiment. As shown in the figure, the electron gun 1 of this embodiment is of a unipotential type, and the cathode K from which electrons are to be emitted.
On the other hand, the first to fifth grids G _{1 to} G ₅ are sequentially arranged coaxially toward the phosphor screen 2.

A hole 4 for transmitting the electron beam 3 is formed in the first grid G ₁ provided adjacent to the cathode K, and a cut-off which is a bias voltage more negative than that of the cathode K for controlling the beam amount. The voltage Ekco is applied.

Further, the second grid G ₂ adjacent to the first grid G ₁ is also provided with a hole 5 for transmitting the electron beam 3, and the second grid G ₂ has a positive electrode of several hundreds of V more positive than the cathode K. A high voltage is applied. Then, the electron beam 3 is extracted from the cathode K by the electric field formed by the second grid G _2, and a point 6 where the cross-sectional area of the electron beam 3 is minimum (crossover) is formed in front of the first grid G _1. It

Second grid G₂Grid adjacent to
G₃Is an electrode for accelerating the electron beam 3,
Dead G₂Together with a prefocus lens (electrostatic focusing lens
7) is formed. This prefocus lens 7 is electronic
It serves to suppress the divergence of the beam 3. This third grid
De G₃And the fifth grid G located closest to the phosphor screen 2 side _Five
And the same potential supplied from the anode button (not shown)
High voltage is applied. Meanwhile, the third and fifth grids
G₃, G_FiveFourth grid G located in between_FourFocused on
Pressure is applied. Third grid G₃, 4th grid G_Four
And the fifth grid G _FiveThe electron beam 3 on the fluorescent screen 2 by
The main lens 8 that focuses the light is formed. And like this
With such a configuration, a predetermined beam spot S on the phosphor screen 2
The electron beam 3 is guided.

1A and 1B show the cathode K and the first grid G ₁ . As shown in the figure, the first grid G ₁ of this embodiment is formed in a conical shape (FIG. 1A) or a truncated cone shape (FIG. 1B). In this case, the first grid G
The thickness t of ₁ is t <0.5 mm. However, it is preferably at least 0.25 mm or more. The inclination angle θ of the first grid G ₁ is 0
It is preferable that <θ <20 °. In this case, the inclination angle θ means an angle with respect to a plane orthogonal to the tube axis direction, as shown in FIG. 1A or B.

On the other hand, as shown in the figure, in this embodiment, the electron emission surface 9 of the cathode K is formed in a spherical shape so as to have an outer curved surface which is convex toward the first grid G ₁ . In this case, the curvature of the electron emission surface 9 of the cathode K follows the inclination angle θ of the first grid G ₁ . That is, the distance between the first grid G ₁ and the electron emission surface 9 of the cathode K is made substantially equal. still,
The overall shape of the cathode K is cylindrical. Further, the first grid G ₁ may be formed in a cup shape, and the cathode K may be arranged in the first grid G ₁ .

In the present embodiment having such a configuration,
The first electron emission surface 9 of the cathode K has a conical or truncated cone shape.
It is to have an outside curved surface convex toward the grid G _1, further first since the distance between the electron emission surface 9 of the grid G ₁ and the cathode K are configured to be substantially equal, the phosphor screen 2 above When the beam spot S having the same diameter is to be obtained, the generation area of the electron beam 3 on the electron emission surface 9 can be made larger than in the conventional example in which the electron emission surface 15 is a flat surface. Therefore, according to this embodiment,
Even when the cutoff voltage Ekco applied to the first grid G ₁ is increased to reduce the beam spot diameter on the phosphor screen 2, the concentration of the electron beam 3 on the electron emission surface 9 of the cathode K is relaxed. Therefore, the electron emission surface 9 of the cathode K is less likely to be deteriorated. As a result, the sharpness of the image can be sufficiently increased.

In the above embodiment, the unipotential type electron gun has been described as an example, but the present invention is not limited to this and can be applied to a bipotential type electron gun, for example. It can also be applied to an electron gun for color images. Further, it can be applied to a multiple beam single electron gun in which a common grid is coaxially arranged for a plurality of cathodes.

[0016]

As described above, according to the present invention, the cone-shaped or truncated-cone-shaped first grid having the beam transmission holes at the top is provided, or the electron emission surface is convex toward the first grid. Of the beam spot diameter on the fluorescent screen by having the cathode formed to have an outer curved surface of, and in particular, by arranging the electron emitting surfaces of the first grid and the cathode to be substantially equidistant. When the aperture is narrowed down, the concentration of the electron beam on the electron emission surface of the cathode can be relaxed and the electron emission surface can be prevented from deterioration. This makes it possible to sufficiently increase the sharpness of the image. Therefore, the present invention is suitable for use in, for example, an electron gun of a high-definition color cathode ray tube.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of the embodiment.

FIG. 3 is an overall configuration diagram of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electron gun 2 Fluorescent screen 3 Electron beam 4 Hole 9 Electron emission surface G _{1 to} G ₅ 1st to 5th grid K Cathode

Claims (3)

[Claims] 1. An electron gun for a cathode ray tube comprising a first cone or frustoconical grid having a beam transmission hole at the top. 2. An electron gun for a cathode ray tube, comprising an electron emission surface having a cathode formed so as to form a convex outer curved surface toward the first grid. 3. A first grid according to claim 1 and a cathode according to claim 2, wherein the first grid and the electron emission surface of the cathode are configured to be substantially equidistant from each other. A cathode ray tube electron gun.