GB2294582A

GB2294582A - Electron gun for color cathode ray tube

Info

Publication number: GB2294582A
Application number: GB9522310A
Authority: GB
Inventors: Hak-Cheol Yang; Hun-Chang Kim; Neung-Yong Yoon
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1994-10-31
Filing date: 1995-10-31
Publication date: 1996-05-01
Anticipated expiration: 2015-10-31
Also published as: MY114283A; CN1131811A; GB9522310D0; JPH08212938A; CN1097839C; TW428198B; DE19540664A1; GB2294582B; KR100337858B1

Description

2294582 ELECTRON GUN FOR COLOR CATHODE RAY TUBE The present invention

relates to an electron gun for a color cathode ray tube (CRT), and more particularly, to an electron gun for a color CRT which can reduce spherical aberration components within apertures of the electrodes for forming electronic lenses.

Conventionally, an electron gun for a color CRT is constituted by a triode, a plurality of focus electrodes sequentially disposed adjacent to the triode, having electron beam passing holes formed therein and for forming an auxiliary lens, and a final accelerating electrode disposed adjacent to the focus electrodes and for forming a main lens.

As predetermined voltages are applied to the triode and the respective electrodes of the conventional color CRT, a unipotential electronic lens and a bipotential electronic lens is formed. In order to reduce the spherical aberration of the electronic lenses thus formed between the respective electrodes, a method for reducing the diameter of electron beams has been conventionally used.

In order to reduce the diameter of electron beams, as shown in FIG. 1 of the accompanying drawings, there has been proposed a method for relatively enlarging the electronic lenses by forming large electron beam passing holes with the neck section of the color CRT having large diameters, or a method for enlarging effective electron beam passing holes by forming a large electron beam passing hole through which all 1 of three electron beams pass, in each electrode of the electron gun for forming the electronic lenses.

The former method increases the deflection power of a deflection yoke, thereby increasing the power consumption of the CRT. If the diameter of the neck section is reduced for reducing the deflection power, the diameters of the electron beam passing holes of the electrodes becomes relatively smaller. Therefore, as shown in FIG. 2 of the accompanying drawings, the electronic lens (L) formed by the reduced electron beam passing holes has increased spherical aberration components, so that the difference between the focal lengths of an electron beam 1 passing through the center of electronic lens (L) and an electron beam 2 passing through the periphery thereof becomes large, thereby enlarging an electron beam spot 3 landed on a fluorescent film of a screen.

Also, the latter method has a structural limitation to enlarging the electron beam passing hole.

It is an object of the present invention to provide an electron gun for a color CRT which can form small and uniform electron beam spots throughout the entire fluorescent layer by reducing spherical aberration components of the electronic lenses formed by the respective electrodes of the electron gun.

According to one aspect of the present invention there is provided an electron gun for a color cathode ray tube comprising: a cathode, a control electrode and a screen electrode all together constituting a triode section; a 2 plurality of focus electrodes for forming an auxiliary lens section, and a final accelerating electrode disposed adjacent to the focus electrodes for forming a main lens section; is wherein, in use, electron beams emitted from the cathode cross in front of the main lens section by the auxiliary lens section.

According to a further aspect of the present invention there is provided an electron gun for a color cathode ray tube comprising: a cathode, a control electrode and a screen electrode all together for forming a triode section; a first group of plural focus electrodes sequentially disposed from the screen electrode for forming a first auxiliary lens for crossing electron beam passing through the triode; a second group of plural focus electrodes for forming a second auxiliary lens for pre- focusing the crossed electron beams, and a final accelerating electrode for finally focusing and accelerating the electron beams pre-focused by the second auxiliary lens.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. I is a graph showing the relationship between an electron beam spot diameter and a neck diameter; FIG. 2 schematically illustrates the state where electron beams are focused by a conventional electronic lens; FIG. 3 is a side view illustrating an embodiment of an electron gun for a color cathode ray tube according to the 3 present invention; FIGS. 4 and 5 are side views illustrating further embodiments of an electron gun for a color cathode ray tube according to the present invention; FIGS. 6, 7 and 9 are views visualizing the trails of the electron beams formed by the embodiments of electron guns according to the present invention illustrated in FIGS. 3, 4 and 5; FIG. 8 is a diagram visualizing the state where electron beams according to the conventional and the present invention pass through a main lens, and FIG. 10 is a view showing the change in angles of incidence at the front of the main lens for the conventional electron gun and an embodiment of an electron gun according to the present invention.

An electron gun for a color CRT according to the present invention is housed in the neck section of the CRT and emits thermions for enabling a fluorescent film to be luminous. As shown in the embodiment illustrated in FIG. 3, the electron gun for the color CRT according to the present invention includes a cathode 11, a control electrode 12 and a screen electrode 13 all together for forming a triode, first, second and third focus electrodes 14, 15 and 16 for forming an auxiliary lens section having a unipotential electronic lens or a bipotential electronic lens, and a final accelerating electrode 17 disposed adjacent to the third focus electrode 16, for forming a main lens section.

4 Here, as illustrated by FIGS. 3 ar)d 6, the focusing power of auxiliary lens section 100 (see Fig. 6) formed by first, second and third focus electrodes 14, 15 and 16, is much larger than that of main lens section 200 formed between the third focus electrode 16 and final accelerating electrode 17, so that a cross-over point P of the electron beams is formed in front of main lens section 200. In order that the crossover point P of the electron beams be formed between auxiliary lens section 100 and main lens section 200 as described above, auxiliary lens section 100 should have intensive focusing power. Auxiliary lens section 100 having such an intensive focusing power can be formed by increasing the voltage difference between the respective electrodes for forming the auxiliary lens section 100 and by making first and second focus electrodes 14 and 15 affecting the focusing power of the auxiliary lens longer than those of the conventional electron g-un.

By way of example, a voltage of 0 V is applied to second focus electrode 15, and a voltage of 7 KV is applied to first and third focus electrodes 14 and 16. Here, it is preferable that the length of first focus electrode 14 is within 2-4mm, and the length of third focus electrode 16 is within 10-16mm. Also, a voltage of 25 KV is applied to final accelerating electrode 17. When the lengths of the respective electrodes are adjusted in a manner described above, and the aforementioned voltages are applied to the respective electrodes, a cross-over point is formed in front of the main lens.

1.0 Another embodiment of the electron gun according to the present invention is illustrated in FIG. 4.

As shown, the electron gun includes a cathode 21, a control electrode 22 and a screen electrode 23 all together for forming a triode, five focus electrodes 24 to 28 for forming an auxiliary lens section in which a plurality of unipotential electronic lenses or bipotential electronic lenses are disposed, and a final accelerating electrode 29 disposed adjacent to focus electrode 28 for forming a main lens section. Here, the auxiliary lens section focuses electron beams in multistep by the plural electronic lenses so that electron beams cross in front of the main lens section.

In the case in which the auxiliary lens section is composed of more than two electronic lenses as described above, it is preferable that the length (L1) of a first auxiliary lens is three to five times the diameter of electron beam passing hole 25H of focus electrode 25 positioned in the middle of three focus electrodes 24, 25 and 26. Also, it is preferable that the thickness (t) of focus electrode 27 of a second auxiliary lens is 0.1 to 0.5 times the diameter of electron beam passing hole 25H of focus electrode 25.

According to experiments with regard to the present invention, in a case in which electron bean passing hole 25H of focus electrode 25 has the diameter of 3.9mm, the trails of the aforementioned electron beams crossing in front of the main lens section were obtained under the condition that a voltage of 0-800 volts was applied not only to control electrode 22 and screen electrode 23 but also to focus 6 electrode 25 of the first auxiliary lei)s, and focus electrode 27 of second auxiliary lens, the length of first focus electrode 24 of the first auxiliary lens section is 2.0-3.Omm, the length of second focus electrode 25 of the first auxiliary lens is 3.0-5.Omm, the length of third focus electrode 26 of the first auxiliary lens is 3.0-5.Omm, the thickness of focus electrode 27 of the second auxiliary lens is 0.4-2.Omm, and the length of focus electrode 27 is 10-16mm.

Still another embodiment of the electron gun according to the present invention is illustrated by FIGS. 5 and 7.

The electron gun includes a cathode 31, a control electrode 32 and a screen electrode 33 all together for forming a triode, first, second and third focus electrodes 34, 35 and 36 for forming a first auxiliary lens section having a unipotential electronic lens or a bipotential electronic lens, fourth and fifth focus electrodes 37 and 38 disposed adjacent to third focus electrode 36 for forming a second auxiliary lens section, a final accelerating electrode 39 disposed adjacent to fifth focus electrode 38 for forming a main lens section. Here, voltages having large potential differences are applied to the respective focus electrodes 34, 35 and 36, respectively so that a cross-over point P of electron beams emitted from cathode 31 of the triode is formed between the first and second auxiliary lens sections.

Hereinbelow, the operation of the electron gun for the color CRT according to the present invention will be described.

As predetermined voltages are applied to the respective 7 electrodes for forming the embodiment of the electron gun for the color CRT according to the present invention shown in FIG.

3, auxiliary lens section 100 and main lens section 200 are formed as shown in FIG. 6 by first, second and third focus electrodes 14, 15 and 16 and final accelerating electrode 17.

Thus, the electron beams emitted from cathode 11 are prefocused and accelerated by auxiliary lens section 100 and are finally focused and accelerated by main lens section 200 to then land on the fluorescent film. At this time, since the focusing power of auxiliary lens section 100 is stronger than that of main lens section 200, the electron beams passing through auxiliary lens section 100 cross in front of main lens section 200 and then are incident into main lens section 200, thereby increasing the difference in angles of incidence into main lens section 200 to reduce the influence of spherical aberration components of main lens section 200.

This will now be described in more detail with reference to FIGS. 6 and 7 showing the trails of the electron beams passing through main lens section 200.

If electron beams pass through the peripheral portion of the electronic lens, the focusing power becomes relatively large, which increases spherical aberration components. since a cross-over point P of an electron beam 401 (indicated by thick solid lines in Fig. 7) in the electron gun according to the present invention is positioned between auxiliary lens section 100 and main lens section 200, the angle of incidence of electron beam 401 passing through the peripheral portion of main lens section 200 becomes relatively large. Therefore, in 8 view of the trails of electron beams, the focal length of electron beam 401 becomes larger than that of the conventional electron beam 501 (indicated by a solid line in Fig. 7). An electron beam 402 which is incident from the cross-over point P into the central portion of main lens section 200, has an angle of incidence smaller than that of electron beam 401 passing through the peripheral portion of main lens section 200. Therefore, the change in the focal lengths of electron beams passing through the central portion of main lens section 200, i.e., the change from the focal length of electron beam 502 to that of electron beam 402, is smaller than that of electron beams passing through the peripheral portion of main lens section 200, i.e., the change from the focal length of electron beam 501 to that of electron beam 401.

The entire distribution of the change in angles of incidence described above is shown in FIG. 10. As shown, the change in angles of incidence of electron beams passing through the peripheral portion, indicated by a line B, is relatively large, and the change in angles of incidence of electron beams passing through the central portion, indicated by a line A, is relatively small.

Since the electron beam 402 which is incident from the cross-over point P into the central portion of main lens section 200 has the relatively small angle of incidence into main lens section 200, the focal length thereof becomes longer than that of conventional electron beam 502.

Therefore, as shown in FIG. 7, the size of an electron beam spot 410 focused on the fluorescent film can be made 9 smaller than that of a conventional elqctron beam spot 510.

In the electron gun shown in FIG. 4, electron beams are focused by first and second auxiliary lens sections 710 and 810, cross in front of a main lens section 910, and then pass through main lens section 910, the state of which is shown in FIG. S. The focusing operation of such electron beams has been described above.

If a cross-over point of electron beams is positioned between first and second auxiliary lens sections 710 and 810, the electron beams are focused in the following manner.

As predetermined voltages are applied to the respective electrodes for forming the embodiments of the electron gun for the color CRT according to the present invention illustrated in FIGS. 5 and 9, first and second auxiliary lens sections 700 and 800 are formed by first, second and third focus electrodes 34, 35 and 36, and third, fourth and fifth focus electrodes 36, 37 and 38, respectively, and a main lens section 900 is formed by fifth focus electrode 38 and final accelerating electrode 39.

Therefore, the electron beams emitted from cathode 11 are pre-focused and accelerated by first auxiliary lens section 700 to then be crossed, and are re-focused and accelerated by second auxiliary lens section 800 and then are finally focused and accelerated by main lens section 900 to be landed on a fluorescent film 600 of a screen.

During this process, the focusing power of first auxiliary lens section 700 is relatively stronger than those of other lenses. Thus, since the electron beams passing through first auxiliary lens section 7PO cross in front of second auxiliary lens section 800, the electron beam spot on the screen can be reduced as described above. However, due to a deflection yoke, the larger the diameter of the electron beam passing through the main lens section, the poorer the state of the electron beam spot landed on the peripheral portion of the screen. Therefore, using the second auxiliary lens section, the radius of electron beams incident into the main lens section can be reduced, thereby improving the resolution of the entire screen.

In the electron gun according to the present invention, even if the electron gun is relatively small, that is, the effective diameter thereof is decreased by 15-20% as compared with the normal one, the same sized electron beam spot can be obtained at a low current region.

As described above, an electron gun for a color CRT according to the present invention can improve focus characteristics by reducing the spherical aberration of a main lens section, thereby reducing the size of electron beam spot.

The electron gun for the color CRT according to the present invention is not limited to those embodiments and various changes and modification may be effected by one skilled in art within the scope of the invention.

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Claims

CLAIMS:

1. An electron gun for a color cathode ray tube comprising:

a cathode, a control electrode and a screen electrode all together for forming a triode section; a plurality of focus electrodes for forming an auxiliary lens section, and a final accelerating electrode disposed adjacent to said focus electrodes and for forming a main lens section; wherein, in use, electron beams emitted from said cathode cross in front of said main lens section by means of said auxiliary lens section.

2. An electron gun for a color cathode ray tube as claimed in claim 1, wherein said auxiliary lens section comprises three electrodes and, in use, a voltage applied to the middle of one of these three electrodes is lower than that applied to the other two electrodes.

3. An electron gun for a color cathode ray tube as claimed in claim 1, wherein said auxiliary lens section is constituted by one auxiliary lens, and, in use, said electron beams cross between said auxiliary lens and said main lens section.

4. An electron gun for a color cathode ray tube as claimed in claim 1, wherein said auxiliary lens section is constituted by at least two auxiliary lenses.

5. An electron gun for a color cathode ray tube comprising:

a cathode, a control electrode and a screen electrode all 12 together for forming a triode section;.

a first group of plural focus electrodes sequentially disposed from said screen electrode for forming a first auxiliary lens section for crossing electron beam passing through said triode; a second group of plural focus electrodes for forming a second auxiliary lens section for pre-focusing said crossed electron beams, and a final accelerating electrode for finally focusing and accelerating electron beams pre-focused by said second auxiliary lens section.

6. An electron gun for a color cathode ray tube as claimed in claim 5, wherein, in use, electron beams cross between said first and second auxiliary lens sections.

7. An electron gun for a color cathode ray tube as claimed in claim 5, wherein said first and second auxiliary lens sections each are formed by three electrodes, and, in use, a voltage applied to the middle one of said three electrodes is lower than that applied to the other two electrodes.

8. An electron gun for a color cathode ray tube substantially as herein described with reference to Figure 3, with or without reference to any of Figures 4 to 10 of the accompanying drawings.

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