EP0440234A2

EP0440234A2 - Electron gun structure for color picture tubes

Info

Publication number: EP0440234A2
Application number: EP91101302A
Authority: EP
Inventors: Kyungnam Kim
Original assignee: Samsung Display Devices Co Ltd; Samsung Electron Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1990-01-31
Filing date: 1991-01-31
Publication date: 1991-08-07
Also published as: KR910014663U; EP0440234A3; KR920005828Y1; JPH0466753U

Abstract

There is disclosed an electron gun structure for color picture tubes comprising a prearranged electrode, a postarranged electrode, an extension flange perpendicularly formed along the periphery of the back end of said prearranged electrode, another extension flange perpendicularly formed along the periphery of the front end of said postarranged electrode, said both extension flanges being opposed to each other, and the electron beam passing apertures being disposed relatively inside said electrodes, wherein said prearranged electrode is supplied with a static voltage and said postarranged electrode with a dynamic focusing voltage which is varied according to a deflecting signal and a synchronizing signal, so that said prearranged electrode forms a convex focusing type of lens to have a focusing type of force which acts stronger vertically than horizontally, and said postarranged electrode forms a concave diverging lens to have a diverging force which acts stronger vertically than horizontally so as to expand the landing area of said electron beam vertically, thus said two lenses serving the complementary action to make the landing area of said electron beam circular throughout the screen of said color picture tube.

Description

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an electron gun structure for color picture tubes for improving the focusing function thereof by complementing the distortions of the electron beams landed on the portions near the periphery of the screen of the color picture tube.

(2) Description of the Prior Art

As is well known in the art, the resolution of a cathode ray tube is closely related to the size of the electron beams landed on the phosphor screen thereof, and the smaller the size of the electron beam is, the better resolution is obtained.
In order to improve the focusing characteristic, the main lens system and subordinate lens system should be functionally improved.
However, the electric field distributions formed within the apertures through which the electron beams of three colors pass in the electron gun interfere with each other. Hence, the electron gun that the electron beams do not interfere with each other are required.
Generally, the cathode ray tube comprises, as shown in Fig. 5, a bulb formed of a panel A, funnel B and neck C, electron guns E mounted inside the neck C for producing electron beams, and deflecting means F mounted between the aforesaid funnel B and neck C for deflecting the electron beams to pattern raster on the screen.
In such a cathode ray tube, when the electron beam D emitted from the electron gun E is deflected, and is not influenced by any external force, the optimum focusing point is represented on a parabola G having the deflecting point as the center.
Thus, the horizontal focusing distance and the vertical focusing distance are equal to each other in order to form the optimum focusing point in the central portion of the screen. However, in fact, it is impossible to obtain the optimum focusing point in the peripheral portions of the screen since the horizontal focusing distance is shorter or longer than the vertical focusing distance so as to result in a positive(+) or negative(-) aberrations.
By the way, U. S. Patent No. 4,866,335 proposed a method for improving the focusing characteristics by reducing the initially diverging region of the electron beam and expanding the next converging region so as to minimize the diameter of the beam spot.
However, in order to form the optimum focusing point practically in the peripheral portions of the screen, the electron gun having a cathode K and the first to sixth electrodes coaxially arranged, as shown in Fig. 6, must be a dynamic focusing type of electron gun, wherein the fifth electrode G5 comprises a main electrode G5' and a subordinate electrode G5'', and the voltage applied to the subordinate electrode G5'' is varied according to the deflecting signal of the deflecting yoke and the synchronizing signal.
Referring to Fig. 7 for illustrating the voltage waveform of the dynamic focusing electron gun, the applied dynamic voltage becomes higher towards the peripheral portions of the screen. As an example, if the horizontal frequency is 15.75KHz and the vertical frequency 60Hz, the vertical dynamic voltage waveform is overlapped by 262.5 horizontal dynamic waveforms as shown in Fig. 8.
Namely, if the maximum values of the horizontal and vertical dynamic voltages are 600V and 400V respectively, the focusing voltage in the peripheral portions of the screen becomes about 1000v higher than that in the central portion of the screen, which comes to be identical with the optimum focusing voltage in the peripheral portions. However, even in this case, the aberration causes the electron beam to be transversely distorted in the peripheral portions of the screen as shown in Fig. 9.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an electron gun structure for color picture tubes, thereby eliminating the transverse distortion of the electron beam in the peripheral portions of the screen.
According to the present invention, an electron gun structure for color picture tubes comprises a prearranged electrode, a postarranged electrode, an extension flange perpendicularly formed along the periphery of the back end of said prearranged electrode, another extension flange perpendicularly formed along the periphery of the front end of said postarranged electrode, said both extension flanges being opposed to each other, and the electron beam passing apertures being disposed relatively inside said electrodes, wherein said prearranged electrode is supplied with a static voltage and said postarranged electrode with a dynamic focusing voltage which is varied according to a deflecting signal and a synchronizing signal, so that said prearranged electrode forms a convex converging lens to have a converging force which acts stronger vertically than horizontally, and said postarranged electrode forms a concave diverging lens to have a diverging force stronger vertically than horizontally so as to expand the landing area of said electron beam vertically, thus said two lenses serving the complementary action to make the landing area of said electron beam circular throughout the screen of said color picture tube.
The extension flanges are integrally formed with said prearranged electrode and postarranged electrode respectively, or by connecting additional strips to said electrodes.
The static voltage may be 400-1000V, and the dynamic voltage 7-10KV.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the drawings attached only by way of example.

Fig. 1. is a side sectional view of an electron gun structure embodying the present invention;
Fig. 2. is a side sectional view of a multi-stages focusing type electron gun according to another embodiment of the present invention;
Fig. 3. is a partially sectioned exploded perspective view of the prearranged and postarranged electrodes embodying the present invention;
Fig. 4 illustrates another embodiment of the inventive electrodes;
Fig. 5 is a schematic diagram of a conventional cathode ray tube;
Fig. 6 is a side sectional view of a conventional dynamic focusing electron gun;
Fig. 7 illustrates the voltage waveforms of the dynamic focusing electron gun, wherein A and B represent the dynamic voltage waveforms of the horizontal and vertical frequencies respectively;
Fig. 8 illustrates the dynamic voltage waveform wherein horizontal and vertical frequencies are overlapped; and
Fig. 9 illustrates the distortion of the beam in the peripheral portions of the screen of a conventional cathode ray tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Fig. 1, a cathode 10 is supplied with 100V-500V to emit electron beams. The first electrode 12 applied with the ground voltage, second electrode 14, third electrode 16, fourth electrode 18, fifth electrode 20 and sixth electrode 22 are arranged coaxially with the cathode 10, which are fixedly mounted in a bead glass not shown.
According to the present invention, the back end surface of the fourth electrode 18 and the front end surface of the fifth electrode 20 which are opposed to each other are respectively provided with horizontal extension flanges 24 and 26, and the fifth electrode 20 is supplied with dynamic focusing voltage Vd, thereby forming a quadruple lens comprising the fourth and fifth electrodes 18 and 20 respectively as prearranged and postarranged, which is different from the conventional electron gun.
The aforesaid quadruple lens effect may be obtained by supplying the second and fourth electrodes 14 and 18 with a static voltage Eg2 of 400V-1000V, the third electrode 16 with a dynamic focusing voltage Ef of 7KV-10KV, and the fifth electrode 20 with another dynamic focusing voltage Vd of 7KV-8KV.
Referring to Fig. 2 for illustrating the inventive quadruple lens which is applied to a multi-stages focusing type of electron gun comprising 8 electrodes, the first electrode 28 is respectively supplied with the ground voltage, the second, fourth and sixth electrodes 30, 32 and 34 with a static voltage Eg2, the third and fifth electrodes 36 and 38 with focusing voltage Ef. And the seventh electrode 40 is supplied with a dynamic focusing voltage Vd, so that the sixth and seventh electrodes 34 and 40 form the prearranged and postarranged ones respectively.
In order to achieve the quadruple lens effect, it goes without saying that the back end surface of the sixth electrode 34 and the front end surface of the seventh electrode 40 must be respectively provided with extension flanges 42 and 44.
In the above two embodiments, the extension flanges 24, 26, 42, 44 may integrally formed with the prearranged fourth electrode 18 (the sixth electrode 34 in case of 8 electrodes structure) and the postarranged fifth electrode 20 (the seventh electrode 40 in case of 8 electrodes structure) respectively in the form of a cup as shown in Fig. 3, otherwise a strips 46 are separately prepared and may be attached to the prearranged and postarranged electrodes by welding, etc., as shown in Fig. 4.
The aforesaid two methods are allowed to be implemented selectively since they are the same in effect.
According to the above inventive electron gun for color picture tubes, when the electron beam is deflected towards the peripheral portions of the screen, the prearranged and postarranged electrodes are supplied with voltages respectively so that the dynamic focusing voltage is varied according to the deflecting signal and synchronizing signal to apply a voltage which is higher vertically than horizontally, thereby resulting in the vertically expanded electron beam which complements the transverse distortion of the electron beam caused by the aberration of the deflecting yoke in the peripheral portions of the screen.
In other words, in the lens system comprising the prearranged and postarranged electrodes, the side of the prearranged electrode forms a convex focusing type of lens to have a focusing type of force which acts stronger vertically than horizontally so as to cause the transverse distortion of the electron beam, whereas the postarranged electrode forms a concave lens to have a diverging force which acts stronger vertically than horizontally so as to cause the vertical distortion of the electron beam. Accordingly, the focusing force and diverging force are counterbalanced to form a circular spot of the electron beam in the end.
Thus, the inventive electron gun can solve the problems of the conventional electron gun so as to attain the optimum focus throughout the screen, thereby improving the resolution.

Claims

An electron gun structure for color picture tubes in which a prearranged electrode and a postarranged electrode are opposedly formed to each other, said prearranged electrode being supplied with a static voltage and also said postarranged electrode being supplied with a dynamic focusing voltage which is varied according to a deflecting signal and a synchronizing signal so that circular electron beams may be focused on the entire surface of screen, wherein electron beam passing apertures are disposed relatively inside said electrodes by making the extension flanges on the opposing faces of the prearranged electrode and the postarranged electrode.
The electron gun structure as claimed in Claim 1, wherein said extension flanges are integrally made with said prearranged electrode and postarranged electrode respectively, or by welding additional strips to said electrodes.