JPH05325822A - Cathode-ray tube - Google Patents

Abstract

PURPOSE:To improve the resolution by reducing the aberration at the time of forming a crossover, and reducing the beam spot diameter on a phosphor screen. CONSTITUTION:A cathode-ray tube is provided with an electron gun 16 having a cathode K and plural electrodes, which include a first grid G1 and a second grid G2 arranged from the cathode K to the phosphor screen so as to be adjacent in order, and forming a crossover of the cathode K and the first and the second grids G1, G2 adjacent to the cathode K in order to emit the electron beam. The first grid G1 is formed with an electron beam passing hole, of which a hole diameter becomes minimum between the cathode K side end surface and the second grid G2 side end surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode ray tube such as a color picture tube, and more particularly to a cathode ray tube which improves the performance of an electron gun so that a small beam spot can be obtained on a phosphor screen.

[0002]

2. Description of the Related Art A color picture tube will be described as an example of a cathode ray tube. Generally, a color picture tube has an envelope composed of a panel and a funnel-shaped funnel, and blue, green, and red are provided on the inner surface of the panel. A phosphor screen composed of a dot-shaped or stripe-shaped three-color phosphor layer that emits light is formed, and a shadow mask is mounted inside the phosphor screen so as to face the phosphor screen. On the other hand, an electron gun that emits three electron beams is arranged in the neck of the funnel. Then, the electron beam emitted from this electron gun is deflected by the magnetic field generated by the deflection yoke mounted outside the funnel, and the phosphor screen is horizontally and vertically scanned to form a structure for displaying a color image. Has been done.

In the most widely used self-convergence in-line type color picture tube today, the electron gun is
The deflection yoke, which is formed in a structure that emits three electron beams arranged in a row and composed of a center beam and a pair of side beams that pass on the same horizontal plane, and which deflects the electron beam
The horizontal deflection magnetic field that deflects the electron beam in the horizontal direction is a pincushion type, and the vertical deflection magnetic field that deflects the electron beam in the vertical direction is a barrel type.

In such a color picture tube, in order to improve the resolution, it is necessary to make the diameter of the beam spot on the phosphor screen as small as possible.
For that purpose, it is necessary to improve the performance of the electron gun.

Generally, an electron gun of a cathode ray tube has a cathode, an electrode which controls an electron emission from the cathode and which constitutes an electron beam forming unit for focusing the emitted electron to form an electron beam, and the electron beam forming. It has a plurality of electrodes, such as the electrodes that form the main electron lens unit that focuses the electron beam emitted from the unit onto the phosphor screen.

FIG. 4 shows an example of the electron gun. This electron gun is composed of a cathode K, a first cathode disposed on the cathode K, and a first cathode disposed at a predetermined interval in the direction of the phosphor screen 1.
To fourth grids G1 to G4. The first and second
The grids G1 and G2 are composed of plate electrodes having relatively small electron beam passage holes. The third grid G3 is composed of a cup-shaped electrode, and the second grid G2 side end surface has a second grid G2.
An electron beam passage hole larger than the electron beam passage hole of the grid G2 is formed, and a larger electron beam passage hole is formed on the fourth grid G4 side. The fourth grid G4 is composed of a cylindrical electrode, and the fourth grid G4 is formed with an electron beam passage hole having the same size as the electron beam passage hole on the fourth grid G4 side of the third grid G3.

In this electron gun, the cathode K and the first,
Electron beam forming unit by the second and third grids G1, G2, G3
GEA is formed, and the main electron lens unit MLA is formed by the third and fourth grids G3 and G4. That is, by giving a predetermined potential to the cathode K and the first to fourth grids G1 to G4, the electrons emitted from the cathode K are formed by the cathode K and the first and second grids G1 and G2. The crossover CO is formed by KL, and then slightly focused by the prefocus lens PL formed by the second and third grids G2 and G3, forming a virtual crossover VCO and diverging to the third grid. It is incident on G3. Electron beam 2 incident on this third grid G3
Are focused on the phosphor screen 1 by the main electron lens ML formed by the third and fourth grids G3 and G4.

Therefore, in order to improve the resolution,
The diameter of the beam spot SP of the electron beam 2 focused on the phosphor screen 1 may be made as small as possible, but the electron beam from the cathode K is separated by the cathode K and the first and second grids G1, G2. The axial beam is more strongly focused than the paraxial beam and already has aberrations at the crossover CO point. Furthermore, this aberration is added by the prefocus lens PL and the main electron lens ML, so the phosphor screen 1
Even if the electron beam is optimally focused on the top, the paraxial beam is unfocused with respect to the phosphor screen 1.
On the other hand, the off-axis beam becomes overfocused. Therefore, it is difficult to reduce the diameter of the beam spot SP on the phosphor screen 1.

Conventionally, in order to reduce the beam spot diameter on the phosphor screen, there is an electron gun in which an Astig lens such as a quadrupole lens or an elliptical lens is incorporated to reduce the above-mentioned aberration. However, when such an Astig lens is used, it is possible to reduce the aberration in one direction, but on the contrary, the aberration in the other direction increases,
There arises a problem that the magnification of the electronic lens is deteriorated.

[0010]

As described above, in order to improve the resolution of the cathode ray tube, it is necessary to make the beam spot diameter on the phosphor screen as small as possible. For that purpose, the electron gun is used. It is necessary to improve the performance of. However, in general, the electron beam from the cathode is more strongly focused on the off-axis beam than on the paraxial beam due to the cathode and the first and second grids, and already has aberration at the crossover point, and also the prefocus lens and the main lens. Since the aberration is added by the electron lens, even if the electron beam is optimally focused on the phosphor screen,
The paraxial beam is unfocused with respect to the phosphor screen, while the off-axis beam is overfocused, making it difficult to reduce the diameter of the beam spot on the phosphor screen. In order to reduce the beam spot diameter on this phosphor screen, there is an electron gun that incorporates an Astig lens such as a quadrupole lens or an elliptical lens to reduce the aberration. If a lens is used, it is possible to reduce aberrations in one direction, but on the contrary, problems such as increase in aberrations in the other direction and poor magnification of the electron lens occur, and the beam spot on the phosphor screen It is extremely difficult to reduce the diameter.

The present invention has been made to solve the above problems, and an object of the present invention is to reduce the beam spot diameter on the phosphor screen to form a cathode ray tube having an extremely good resolution.

[0012]

A cathode and a plurality of electrodes including first and second grids arranged on the cathode in the phosphor screen direction so that the cathode and the cathode are successively adjacent to the cathode. In a cathode ray tube including an electron gun that emits an electron beam by forming a crossover from the cathode by the first and second grids, the first grid has a hole diameter between the end surface on the cathode side and the end surface on the second grid side. An electron beam passage hole having a minimum shape was formed.

[0013]

As described above, when the electron beam passage hole of the first grid adjacent to the cathode is formed in a shape having the minimum hole diameter between the end surface on the cathode side and the end surface on the second grid side, The curvature of the electric field penetrating from the electron beam passage hole to the cathode side can be increased near the tube axis, which strengthens the focusing power of the paraxial beam, and the crossover position of the paraxial beam is changed to the crossover of the deaxial beam. Can be brought closer to the position. In addition, the curvature of the electric field penetrating near the periphery of the cathode can be reduced, thereby enhancing the focusing force of the off-axis beam and bringing the cross-over position of the off-axis beam closer to the cross-over position of the paraxial beam. You can Therefore, the above two effects can reduce the aberration at the crossover.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the drawings.

FIG. 1 shows a color picture tube which is an embodiment of the present invention. This color picture tube consists of panel 10 and this panel
The panel 10 has an envelope formed of a funnel-shaped funnel 11 that is integrally joined to the panel 10. On the inner surface of the panel 10, a phosphor screen 12 formed of a three-color phosphor layer that emits blue, green, and red is formed. A shadow mask 13 having a large number of electron beam passage holes formed therein is mounted so as to face the phosphor screen 12. On the other hand, inside the neck 14 of the funnel 11,
An electron gun 16 that emits three electron beams 15 is provided.

In FIG. 1, reference numeral 18 is an inner conductive film formed by coating on the inner surface of the funnel 11, and 19 is a deflection yoke mounted on the outer side of the funnel 11.

The electron gun 16 has three cathodes K and three heaters (not shown) for heating the cathodes K respectively.
And a plurality of electrodes arranged on the cathode K in the direction of the phosphor screen 12 at predetermined intervals. In the illustrated electron gun, the plurality of electrodes are composed of first to fourth grids G1 to G4.

And, in particular, the electron gun 16 of this example has a cathode.
A first grid G1 adjacent to K is formed in the structure shown in FIG. That is, the first grid of the electron gun
G1 is composed of a plate-shaped electrode and has an electron beam passage hole 20 having a tapered side surface that has a minimum hole diameter between the end surface on the cathode K side and the end surface on the second grid G2 side and the maximum on both end surfaces.
Are formed. Moreover, as can be seen from a comparison with the plate-shaped first grid G1 of the conventional electron gun shown in FIG. 2B, the plate thickness t is formed thick, and the end face on the second grid G2 side is the second grid G2. Approaching

Next, specific dimensions of the first grid G1 of the electron gun 16 and its vicinity will be shown.

Electron beam passage hole diameter G1φ of the first grid G1: Electron beam passage hole diameter G1φA at point A = 0.70 mm Electron beam passage hole diameter G1φB at point B = 0.50 mm Electron beam passage hole diameter G1φC at point C = 0.70 mm Thickness of the first grid G1 G1t = 0.28 mm Distance between the points A and B in the gun axis direction G1A / B = 0.15 mm Distance between the first grid G1 and the cathode K G1 / K = 0.100
mm Electron beam passage hole diameter of second grid G2 G2φ = 0.50 mm Thickness of first grid G1 G2t = 0.20 mm Distance between first grid G1 and second grid G2 G1 / G2 = 0.
15mm The thickness of the plate-shaped first grid of a normal electron gun is 0.10.
Since it is about mm, the plate thickness of the first grid G1 of the above electron gun
G1t is quite thick.

The first grid G1 having such a large plate thickness and the electron beam passage hole having a special shape is etched,
Alternatively, it can be formed by a method such as laminating a plate in which required apertures are formed.

By the way, the electron beam passage hole 20 having the above shape is formed.
In the above, when the opening edge on the cathode K side is A, the minimum position of the hole diameter is B, and the opening edge on the second grid G2 side is C, the gun axis of the electron gun is defined by points B, C and sides BC. The curvature of the equipotential line 21 near the tube axis z can be changed, and the curvature of the equipotential line 21 near the gun axis can be increased as shown in comparison with the conventional electron gun of FIG. As a result, the focusing force for the paraxial beam 15n from the vicinity of the center of the cathode K 1 can be strengthened, and the position of the crossover COn of the paraxial beam 15n can be moved to the cathode K side. This allows the off-axis beam from the periphery of the cathode K.
It is possible to reduce the difference (aberration) between the position of the crossover COn of the paraxial beam 15n and the position of the crossover COf of the off-axis beam 15f by bringing it closer to the position of the crossover COf of 15f. According to the calculation of the electron orbit, the closer the point C is to the second grid G2, the larger the curvature of the equipotential line 21 near the gun axis can be made.

Although it is difficult to increase the curvature of all equipotential lines 21 from the cathode K to the vicinity of the second grid G2 only at the point C, the hole diameter at the point B should be smaller than that at the point C. This makes it possible to increase the curvature of the equipotential line 21 near the gun axis of the electric field penetrating the region near the cathode K 1.

However, as described above, the point C is set to the second grid G2.
Or the hole diameter at the point B is reduced, the cutoff potential of the second grid G2 increases. Normally, the cutoff potential of the second grid G2 is set to a predetermined value in the TV set, so that the increase of the cutoff potential of the second grid G2 must be avoided. In this respect, by changing the position of the point A close to the cathode K, the cutoff potential of the second grid G2 can be lowered.

If the hole diameter at the point A is increased, the curvature of the equipotential line 21 near the peripheral portion of the cathode K can be reduced. The electric field penetrating near the peripheral portion of the cathode K greatly affects the off-axis beam 15f from the peripheral portion of the cathode K, and the off-axis beam 15f is largely bent by the electric field near the peripheral portion of the cathode K 1. Therefore, if the curvature of the equipotential line 21 near the periphery of the cathode K is reduced as described above, the focusing force for the off-axis beam 15f can be weakened, and the position of the crossover COf of the off-axis beam 15f can be set to the second grid. By moving to the G2 side, it is possible to further reduce the difference between the position of the crossover COn of the paraxial beam 15n and the position of the crossover COf of the off-axis beam 15f.

That is, the first grid G1 composed of plate electrodes
The electron beam passage hole 20 having the smallest hole diameter between the end surface on the cathode K side and the end surface on the second grid G2 side and the maximum on both end surfaces is formed, and the plate thickness is increased to form the second grid.
When the end face on the G2 side is brought closer to the second grid G2, the curvature of the electric field near the gun axis is increased to enhance the focusing force for the paraxial beam 15n, and the crossover COn position of the paraxial beam 15n is set to the cathode K side. Can be moved to
The position of crossover COn of paraxial beam 15n is decentered beam
The position of the crossover COf of 15f can be approached. In this case, the end surface of the second grid G2 side is the second grid
By approaching G2, the cutoff potential of the second grid G2 rises, but this rise of the cutoff potential of the second grid G2 is reduced by increasing the hole diameter at the point A on the cathode K side, Can be set to a cutoff potential of. Moreover, by making the hole diameter at the point A larger than the hole diameter at the point B, the curvature of the electric field in the vicinity of the peripheral portion of the cathode K is made small, and the focusing force for the off-axis beam 15f is weakened. Beam 15f crossover COf
The position of can be moved to the second grid G2 side.
As a result, the difference between the position of the crossover COn of the paraxial beam 15n and the position of the crossover COf of the off-axis beam 15f, that is, the aberration at the crossover can be reduced. Moreover, since the curvature of the electric field near the peripheral portion of the cathode K becomes small, the aberration at the time of a large current in which electron emission also occurs from the peripheral portion of the cathode K can be reduced. As a result, it is possible to improve the resolution by reducing the diameter of the beam spot on the phosphor screen 12 not only when the current is small but also when the current is high.

In the above embodiment, the electron beam passage hole of the first grid has a tapered side surface having a minimum hole diameter between the cathode side end surface and the second grid side end surface and a maximum of both end surfaces. However, as shown in FIG. 3A, the shape of the electron beam passage hole of the first grid has a minimum hole diameter over a certain width between the end face 23 on the cathode side and the end face 24 on the second grid side. The minimum hole diameter portion 25 and both end faces 23, 24 may have a tapered side surface. Further, as shown in (b), the hole diameter is minimized over a certain width between the end surface 23 on the cathode side and the end surface 24 on the second grid side, and the minimum hole diameter portion 25 has a flat protruding portion. It may be one. Further, as shown in (c), it may be formed in a cup shape, and an opening having a tapered side surface that minimizes the inner hole diameter may be formed in the end surface 23 on the cathode side, and other various structures. Can be used.

[0028]

When the electron beam passage hole of the first grid is formed in a shape having a minimum hole diameter between the end face on the cathode side and the end face on the second grid side, the electron beam passage hole of the first grid is formed on the cathode side. It is possible to increase the curvature of the electric field penetrating into the vicinity of the gun axis, thereby enhancing the focusing power of the paraxial beam and making the crossover position of the paraxial beam closer to the crossover position of the off-axis beam. .. Also, the curvature of the electric field penetrating near the periphery of the cathode can be reduced, which enhances the focusing force of the off-axis beam,
The position of the off-axis beam crossover can be brought closer to the position of the paraxial beam crossover. Therefore, due to the above two effects, the aberration at the crossover can be reduced, the cutoff voltage of the second grid can be adjusted, the beam spot diameter on the phosphor screen can be reduced, and the resolution can be improved. ..

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a color picture tube which is an embodiment of the present invention.

FIG. 2A is a diagram for explaining the structure and action of the first grid, and FIG. 2B is a diagram showing the structure and action of a conventional first grid shown for comparison. is there.

FIG. 3 (a) to FIG. 3 (c) are different from each other.
It is a figure which shows the structure of a grid.

FIG. 4 is a diagram for explaining the structure and operation of a conventional electron gun.

[Explanation of symbols]

 10 ... Panel 12 ... Phosphor screen 15 ... 3 Electron beam 16 ... Electron gun K ... Cathode G1 ... First grid G2 ... Second grid

Claims (1)

[Claims] 1. A cathode and a plurality of electrodes including a first grid and a second grid, which are sequentially arranged on the cathode in the phosphor screen direction so as to be adjacent to each other. In a cathode ray tube including an electron gun that forms a crossover from the cathode by the second grid and emits an electron beam, the first grid has a hole diameter between the end surface on the cathode side and the end surface on the second grid side. A cathode ray tube having an electron beam passage hole having a minimum shape.