GB2288060A

GB2288060A - Electron gun for a colour CRT

Info

Publication number: GB2288060A
Application number: GB9421245A
Authority: GB
Inventors: In-Kyu Park; Myung-Hwan Lee; Duk-Ho Kim
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1994-04-01
Filing date: 1994-10-21
Publication date: 1995-10-04
Anticipated expiration: 2014-10-21
Also published as: CN1061168C; TW289121B; KR100322443B1; GB2288060B; DE19511377A1; CN1118932A; JPH07282740A; KR950030199A; GB9421245D0

Description

2288060 I ELECTRON GUN FOR COLOR CATHODE RAY TUBE The present invention

relates to an electron gun for color cathode ray tube and, more particularly, to an electron gun having a uniform static convergence characteristic throughout a screen, at the same time, easy to assemble, making an electron beam elongated satisfactorily even with low dynamic voltage, thereby improving the shape of focus of electron beam.

A cathode ray tube includes an electron gun that generates an electron beam, a deflection yoke deflecting the above electron beam, a shadow mask to make the electron beam landed positively, and a panel whereon fluorescent material is spread that emits light when the electron beam strikes, and is applied to all kinds of display devices such as television picture tube or computer monitors and the like.

Generally, the resolution of the above cathode ray tube is greatly influenced by the size and the shape of the electron beam released from electron gun, and unless the diameter of an electron beam is small and the shape of the electron beam is similar to circle, high-quality resolution can not be obtained.

In a conventional single focus type, as shown in Fig. 1, when an electron beam is deflected by a lopsided deflection magnetic field such as a pin-cushion is magnetic f ield for horizontal deflection and a barrel mqnctig field for vertical d@flgetiall D, f8r aelf- convergence, the size or the shape of the electron beam is distorted to cause a problem that the picture quality of screen around color cathode ray tube is deteriorated as shown in Fig. 2.

As shown in Fig. 1, the deflection power that deflects electron beam horizontally focuses the electron beam vertically and forms spot 1 by pin cushion magnetic field D H I so that a screen is pressed vertically, and the deflection power that deflects electron beam vertically radiates the electron beam horizontally and forms spot 2 by barrel magnetic f ield Dv, so that the screen is extended horizontally.

Accordingly, the electron beam receives both focusing power vertically and radiation power horizontally, and a halo as shown in Fig. 2 is generated on the screen, to deteriorated the resolution.

To solve the above problem, there is a method that the shape of the electron beam in center of the screen of the color cathode ray tube is distorted intentionally, and the distortion of relatively larger area, that is, peripheral parts of the screen is compensated. But this method has a problem that the resolution in center of color cathode tube screen is deteriorated.

Therefore, as a method of solving the above 7 c 1 3 problem, dynamic focus type, namely double f ocus type electron gun was developed and has been used which is synchronized by deflection electric current of deflection yoke and varies the shape of electron beam, simultaneously with varying focusing distance of electron beam.

There was disclosed the technique about the above dynamic focus type electron gun in Korean Patent Application Examined Published No. 90-6172 published on August 24, 1990 and entitled "A Cathode Ray Tube", and No. 92-3357 published on April 30, 1994 and entitled "An Electron Gun for Color Picture Tube".

The above cathode ray tube comprises a plurality of electron guns formed at the neck of a glass sealed body and a deflection coil mounted on the outside of a panel.

Each electron gun is formed of a group of cathode, a group of accelerating electrodes, a group of front focusing electrodes, and a group of rear focusing electrodes arranged sequentially in the tube-axial direction.

The front focusing electrode comprises first and second lattice electrodes arranged sequentially in the tube-axial direction and having beam apertures to pass an electron beam. A predetermined focusing voltage is applied to the first lattice electrode, and dynamic focusing voltage changed slowly according to the change 4 of deflection quantity of electron beam, is applied to the second lattice electrode, thereby the electron beam is focused lopsidedly toward beam axis.

Additionally, the above electron gun for color picture tube comprising a control electrode, an accelerating electrode, a focusing electrode and an anode arranged along the axis of electron gun on the basis of a cathode shooting out electron beams and arranged in the horizontal scanning direction, wherein the above focusing electrode is formed with the first focusing electrode formed near the above accelerating electrode and the second focusing electrode formed around the above anode.

The first focusing electrode includes vertical or three circular electron beam apertures according to the number of electron beam, and these electron beam apertures are supported by a plurality of parallel flat electrodes, namely vertical plate adhered to the second focusing electrode along the direction of the first focusing electrode, additionally these parallel flat electrodes are surrounded with rim electrode, according to the number of contained electron beam horizontal or three circular electron beam apertures are supported in vertical to the direction of the arrangement of electron beam, namely vertical direction by a pair of or three pairs of parallel flat electrode, namely horizontal 1 Q p level plate which is adhered to the second focusing electrode along to the direction of the first focusing electrode, thereby the both electron beam apertures of each electrode secures the same distance from the axis of the electron gun, and therefore, an inline type electron gun without displacement can be assembled.

However, the above conventional dynamic focus type electron gun is difficult to assemble, at the same time, the electron beam can be made longer vertically, only when the peak to peak of dynamic voltage reaches a predetermined voltage or more.

2'1 1 Therefore it is an object of this invention to solve problems with an electron gun for color cathode ray tube which has a static convergence which is uniform throughout a screen, is easy to assemble, at the same time, makes an electron beam elongated satisfactorilly low dynamic voltage, thereby improves the shape of focus of electron beam.

To achieve this object, a preferred embodiment of this invention provides an electron gun for color cathode ray tube which comprises a control electrode, an accelerating electrode, an anode, and a focusing electrode which is divided into first and second focusing electrodes. A predetermined static focusing voltage independently of deflection period is applied to first focusing electrode which locates near the control 6 electrode and accelerating electrode, parabolic waveform dynamic focusing voltage that varies according to deflection period is applied to the second focusing electrode which locates near the anode. The first focusing electrode has three electron beam apertures, around each electron beam aperture, vertical parallel plates are mounted at the same interval in the direction opposite to the direction of electron beams. The centers of the left and right electron beam apertures among the three apertures are respectively eccentric to left and right sides in the same degree as the vertical parallel plate, because the distances from the center of the middle electron beam aperture to each center of left and right electron beam apertures are longer than the distances between the centers of vertical parallel plates.

This invention can be more fully understood from the following detailed description, by way of example only, when "Caken in conjunction with theaccomDanying drawings, wherein:

h! - Fig. 1 shows a distortion of electron beams by a pin cushion magnetic field for horizontal deflection and barrel magnetic field for vertical deflection which are generated from a self convergence type deflection yoke;

Fig. 2 shows a problem that picture quality of a peripheral part of a screen of a cathode ray tube is deteriorated by the distortion of electron beams; Z 1 7 Fig. 3 shows a state that electron gun for color cathode ray tube is mounted on the rear end portion of cathode ray tube according to a preferred embodiment of the present invention; Fig. 4 is a structural picture of the electron gun for color cathode ray tube according to the preferred embodiment of the present invention; Fig. 5 is a front view and plan view of the first focusing electrode of electron gun for color cathode ray tube according to the preferred embodiment of the present invention, Fig. 6 is a front view and plan view of the second focusing electrode of electron gun for color cathode ray tube according to the preferred embodiment of the present invention, Fig. 7 shows that the electron beam emitted from electron gun for cathode ray tube is elongated vertically by focusing electrode, Fig. 8 is a wave form of voltage that is applied to the first and second focusing electrodes of electron gun for color cathode ray tube according to the preferred embodiment of the present invention.

The preferred embodiment will now be described-further.

Fig. 3 shows a state that an electron gun for color cathode ray tube is mounted on the rear end portion of a cathode ray tube according to a preferred embodiment of the present invention.

8 As shown in Fig. 3, a cathode ray tube comprises a panel 5 whereon fluorescent material is spread that emits light when electron beam strikes and shadow mask is mounted, a funnel 4 combined with the panel 5 by band and the like, a deflection yoke 3 which is mounted on the neck of the funnel 4 and electron gun 6 which is sealed up and mounted on the rear end portion of the funnel 4.

Fig. 4 shows a structure of the electron gun for color cathode ray tube according to the preferred embodiment of the present invention.

As shown in Fig. 4, the electron gun for color cathode ray tube according to the preferred embodiment of the present invention includes a control electrode 10 whereon electron beam apertures through which electron beams pass are made; an accelerating electrode 20 whereon the electron beam apertures through which electron beams which have passed the control electrode 10 pass are made; a first focusing electrode 30 which has a vertical parallel plate 31 which is projected in the direction opposite to the direction of the electron beams on the left and right electron beam apertures, since the distance S2 between the centers of left and right apertures is longer than the distance Sl between the centers of left and right apertures of the control electrode 10 and accelerating electrode 20, left and right apertures are eccentric; a second focusing Q 1 1 9 electrode 40 which is projected in the direction opposite to the direction of electron beams on upper and lower parts of respective three electron beam apertures, and has a horizontal parallel plate 41 which is introduced into the electron beam aperture of the above first focusing electrode 30, not being electrically connected with the above first focusing electrode 30; an anode 50; and a thermoelectron emitting section 60 which is shown in Fig. 3.

Fig. 5 is a front view and plan view of the first focusing electrode of the electron gun for thecolor cathode ray tube according to the preferred embodiment of the present invention.

As shown in Fig. 5, the first focusing electrode 30 is includes a vertical parallel plate 31 whose height is W and the length is L and which is mounted at the same interval in the direction opposite to the direction of electron beams; three square electron beam apertures formed between vertical parallel plates. The distance from the center of the middle electron beam aperture H-C to the centers of left and right electron beam apertures H-S are longer than the distance between the center of vertical parallel plates mounted at the same interval, so that the left and right electron beam apertures are eccentric to left and right respectively as much as dcds against the vertical parallel plate 31.

Fig. 6 is a front view and plan view of the second focusing electrode of the electron gun for the color cathode ray tube according to the preferred embodiment of the present invention.

As shown in Fig. 6, the inventive second focusing electrode 40 includes a horizontal parallel plate 41 whose width is DH and length is DL which is mounted at the same interval Si with having DW interval on upper and lower parts of three electron beam apertures in the direction opposite to the direction of electron beams; circular electron beam apertures formed respectively between horizontal parallel plates 31 of the upper and lower sides. The distance from the center of the middle electron beam aperture to the centers of left and right electron beam apertures are the same.

is Since the above horizontal parallel plate 41 of the second focusing electrode 40 must be introduced into the electron beam aperture without electrical contact, the width DH and the height DW of the horizontal parallel plate 41 must be made smaller than the size of electron beam aperture H-C, H-S of the first focusing electrode 30.

Additionally, since the above horizontal parallel plate 41 of the second focusing electrode 40 must form electrical field duplicated with the vertical parallel plate 31 of the first focusing electrode 30, the length DL of the horizontal parallel plate 41 of the second focusing electrode 40 is designed to have full length.

1 Z 11 In the embodiment of the present invention, the above first focusing electrode 30 and vertical parallel plate 31 are used as a united member, but the technical range of the present invention is not limited hereto, and the vertical parallel plate 31 can be used, being made as a different one and welded to the other members.

Additionally, in the embodiment of the present invention, the above second focusing electrode 40 and horizontal parallel plate 41 are used as a separate member, but the technical range of the present invention is not limited hereto, and the second focusing electrode 40 may be formed to be integral with the horizontal parallel plate.

The operation of the electron gun for the color cathode ray tube according to the preferred embodiment of the present invention having the above structure is as follows.

A high-voltage power is applied to the electron gun 6 for a cathode ray tube, then thermoelectron is emitted from a thermoelectron emission part 60 of the electron gun 6, and applied to the control electrode 10.

The control electrode 10 of the electron gun 6 controls the quantity of electron beams, and the brightness of the screen is controlled according to the size of voltage applied to the control electrode 10.

The electron beams which pass the aperture of the 12 control electrode 10 of the electron gun 6 are applied to the accelerating electrode 20, the speed of the same is accelerated by the accelerating electrode 20, and then the beams are applied to the first focusing electrode 30.

Static focus voltage Vfs regardless of deflection period 1H of electron beams as shown in Fig. 8 is applied to the first focusing electrode 30 and vertical parallel plate 31, to the second focusing electrode 40 and horizontal parallel plate 41, dynamic focus voltage Vd which varies according to deflection period 1H of electron beams as shown in Fig. 8, whereby the first focusing lens 30 and the second focusing lens 40 focusing electrode form a dynamic focus lens.

Fig. 8 is a figure of wave form of voltage that is applied to the first and second focusing electrodes of the electron gun for the color cathode ray tube according to the preferred embodiment of the present invention.

As shown in Fig. 8, the above dynamic focus voltage Vd has a parabolic wave-form voltage which has a mininum value when there is no deflection power applied to electron beams, that is, in the middle of the screen, and the more deflection power applied to electron beams increases, the higher voltage is.

Accordingly, between the first focusing electrode 30 to which static focus voltage Vfs is applied and the t 13 second focusing electrode 40 to which dynamic focus voltage is applied, the dynamic focus lens is formed which is varied according to deflection period 1H.

If electron beams pass the aperture on the rear end portion of the first focusing electrode where the dynamic lens is formed as mentioned above, the electron beams become elongated vertically as shown in Fig. 7.

Fig. 7 shows that the electron beams emitted from the electron gun for the cathode ray tube are elongated vertically by focusing electrode.

Accordingly, in the middle of the screen, the size of the static focus voltage Vfs is the same as that of the dynamic focus voltage Vd, and the dynamic lens does not work, and circular electron beam is formed. The size of the static focus voltage Vfs, however, is different from that of the dynamic focus voltage Vd in peripheral parts of the screen, so that the farther from the center of the screen the electron beam is, the more by dynamic lens the electron beam elongated vertically.

Such a phenomenon that the electron beam is elongated vertically as shown in Fig. 7 becomes more obvious by the structure of the first and second focusing electrodes 30 and 40 according to the present invention.

That is, if the electron beams pass the aperture on the rear end portion of the first focusing electrode 30, the electron beams are effectively elongated and at the 14 same time, characteristic of the static convergence is changed because the left and right apertures H-S of the f irst focusing electrode 30 is eccentric and electric f ield by horizontal parallel plate 41 of the second focusing electrode 40 is duplicated on the upper and lower parts of the first focusing electrode 30.

Therefore, according to the structure of the present invention, electron beams can be elongated vertically enough even with the dynamic focus voltage Vd which is smaller than the voltage needed in the conventional art.

Additionally, since the distances ds, dc from the centers of left and right apertures of the first focusing electrode 30 to vertical parallel plate 31 mounted on both sides of the aperture are different each other, the electron beam which passes the left and right apertures is naturally converged to center beam, thereby decline of resolution can be revised in case that dynamic voltage is applied to the second focusing electrode 40 and the voltage of the second focusing electrode 40 rises, the effect of main lens formed between the second focusing electrode 40 and anode 50 is weakened, the character of static convergence is weakened, thereby the resolution is declined.

The electron beam which is elongated vertically with passing the first 30 and the second 40 focusing electrode can improve the resolution throughout the Z j Z screen by correcting the distortion of electron beams by lopsided magnetic field generated from self-convergence type deflection yoke, as shown in Fig. 1.

The above preferred embodiment provides electron gun f or the color cathode ray tube which is easy to assemble, the electron beams are elongated vertically enough even with small valued dynamic voltage, whereby the shape of focus of electron beam can be improved.

The effect of the present invention can be used for design, manufacture and sale of the electron gun which is an essential element of the cathode ray tube.

16

Claims

CLAIMS is 4 k.

An electron gun for color cathode ray tube comprising a control electrode, an accelerating electrode, an anode, and focusing electrodes divided into first and second focusing electrodes, a static focusing voltage predetermined independently of deflection period is applied to said first focusing electrode locating near said control electrode and accelerating electrode, a parabolic waveform dynamic focusing voltage varying according to deflection period is applied to the second focusing electrode locating near said anode; said first focusing electrode having three electron beam apertures, vertical parallel plates being mounted around each electron beam aperture in the direction opposite to the direction of electron beams; and centers of the left and right electron beam apertures among said three apertures being eccentric respectively to left and right sides in the same degree with vertical parallel plate, because the distance from the center of middle electron beam aperture to the centers of left and right electron beam apertures are longer than the distances between the centers of the 1 A.

17 vertical parallel plates.
2. An electron gun as claimed in claim 1 wherein said vertical parallel plates are mounted around each electron beam aperture at equally spaced intervals.
3. An electron gun according to claim 1 or 2, wherein said second focusing electrode has three apertures which electron beams can pass, a pair of horizontal parallel plates are mounted on the upper and lower sides of each of said electron beam apertures, in the direction opposite to the direction of electron beams; and said horizontal parallel plates are introduced into the electron beam apertures of the first focusing electrode without electrical contact.
4. An electron gun according to claim 1, 2 or 3 wherein the distance ds from the centers of left and right sides apertures to the parallel plates mounted in the direction of neck wall are shorter than the distance dc to the parallel plates in the direction of the middle electron beam aperture.
5. An electron gun according to any one of claims 1 to 4 wherein the distance SI between centers of the parallel plates mounted on the electron beam apertures formed in anode of said first focusing electrode to which dynamic focus voltage is applied, is shorter than 18 the distance between electron beam aperturesof the electrode to which dynamic focus voltage is applied, or the distance S2 between electron beam apertures is longer than the distance between electron bean apertures formed in the electrode to which dynamic focus voltage is applied.
6. An electron gun according to any one of claims 1 to 5, wherein the distance S2 between electron beam apertures formed in electrode part to which dynamic focus of said first focusing electrode is applied is longer than the distance between electron beam apertures formed in a control electrode, an accelerating electrode or an accelerating electrode of the first focusing electrode.
7. An electron gun substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.