Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1999-05-07
2001-05-29
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S414000, C313S431000
Reexamination Certificate
active
06239542
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a cathode ray tube comprising an in-line electron gun including means for generating electron beams and electrodes.
Such cathode ray tubes are known and are employed, inter alia, in television receivers and computer monitors.
In such a cathode ray tube, three electron beams are generated in the in-line electron gun, which electron beams extend in one plane, the in-line plane. These electron beams are deflected across a display screen in two mutually perpendicular directions by means of a deflection means. A color selection electrode, for example a shadow mask, is arranged between the electron gun and the display screen.
A factor which is of great importance for the quality of the image displayed is the accuracy with which the three electron beams converge. Convergence errors adversely affect the picture quality.
An external magnetic field (for example the terrestrial field) influences the electron beams and hence may cause convergence errors and adversely affect the picture quality.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a cathode ray tube comprising a means for improving the picture quality.
To achieve this, a cathode ray tube in accordance with the invention is characterized in that the electron gun comprises an electrode including: a part which comprises a soft-magnetic material, which extends at least partly transversely to the paths of the electron beams, and which is provided with apertures for allowing passage of the electron beams, and two further parts comprising a soft-magnetic material, which extend substantially parallel to the electron beams and on either side of said electron beams, and which parts are further removed from the means for generating the electron beams than the first-mentioned part.
An external magnetic field causes, in an in-line gun, two effects which both bring about a convergence error in the y-direction (transversely to the in-line plane through the three electron beams) and which are both approximately of the same order of magnitude. The overall effect is the sum of both effects.
In the cathode ray tube in accordance with the invention, the electron gun comprises parts of a soft-magnetic material which jointly form a, preferably continuous, magnetic circuit which extends both along and transversely to the electron beams. By virtue thereof, as a result of an interaction of the external magnetic field and the magnetic circuit, an additional force can be generated, in operation, which acts on the outermost electron beams and which causes the error in the y-direction to be reduced. It is important that the electron beams first pass the part having the apertures, at right angles to the electron beams, and subsequently the further parts parallel to the electron beams. Preferably, the parts lie against each other or substantially against each other, or are connected to each other. Preferably, the part and further parts are situated in front of a main lens (viewed from the means for generating electron beams) and the part and further parts form a portion of a focusing electrode.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 3772554 (1973-11-01), Hughes
patent: 4546287 (1985-10-01), Collins et al.
patent: 4748372 (1988-05-01), Noordermeet
patent: 5530315 (1996-06-01), Arimoto et al.
Dekker Martijn J.
Noordermeer Leendert J.
Guharay Karabi
Patel Nimeshkumar D.
U.S. Philips Corporation
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