Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1998-10-08
2001-09-11
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000, C313S414000, C313S421000
Reexamination Certificate
active
06288481
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on application No. 97-69886 filed in Korean Industrial Property Office on Dec. 17, 1997, the content of which is incorporated hereinto by reference.
FIELD OF THE INVENTION
The present invention relates to an in-line electron gun for a cathode ray tube (CRT) and, more particularly, to an in-line electron gun suitable for a high-resolution CRT.
BACKGROUND OF THE INVENTION
Generally, CRTs are provided with an in-line electron gun where three cathodes are arranged in a horizontal line to emit thermal electrons. The thermal electrons emitted from the cathodes pass through a plurality of grid electrodes and a shield cup while being focused and accelerated to form three electron beams for exciting three different phosphors that produce the three primary colors of red (R), green (G), and blue (B).
In order to excite the correct phosphors, the electron beam should be converged on one point of the screen. For this purpose, the electron beam is deflected by a deflection yoke placed around the outer periphery of the funnel and passes through a beam-guide aperture of the color-selecting shadow mask. This convergence state becomes a critical factor for the resolution of the CRT.
It is known that the resolution of the CRT can be improved through increasing screen image constituting signals by enhancing a horizontal deflection frequency of the deflection yoke. However, with this method, the electron beam is liable to be diverged on the screen. This divergence can be explained on the basis of Lenz's law.
According to Lenz's law, when a changing magnetic field crosses a conductor, an induced electromotive force is produced across the conductor in such a direction as to oppose the change that produces it.
In this connection, the shield cup formed with conductive materials acts as the conductor. When the deflection yoke generates a strong magnetic field with the enhanced horizontal deflection frequency, the magnetic field heavily influences the shield cup. The magnetic fields are initially directed from left to right because the horizontally deflected electron beam is scanning the screen in that direction. The direction of the magnetic field is then abruptly changed from right to left to perform the scanning from the left side of the screen and, hence, an induced electromotive force is produced across the shield cup in a direction opposite to the change of the magnetic field.
Such an induced electromotive force is formed intensely in the vicinity of the G beam-guide hole of the shield cup due to the structure of the CRT. With the induced electromotive force, as shown in
FIG. 6
, the G beam should be deflected toward the left side S
1
of the screen with a smaller size than the R and B beams. On the contrary, the G beam is deflected toward the right side S
2
with a larger size than the R and B beams. This divergence, called “a horizontal center raster (HCR) phenomenon”, causes the resolution at the peripheral portion of the screen to seriously deteriorate.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electron gun for a CRT for preventing divergence of the electron beam at the peripheral portion of the screen while maintaining the horizontal deflection frequency of the deflection yoke at a high degree.
In order to achieve this object and others, the CRT electron gun includes three cathodes arranged in a horizontal line to emit thermal electrons. A plurality of grid electrodes are sequentially placed along a common axis from the cathodes to focus and accelerate the thermal electrons into beam shapes. Each of the grid electrodes has three beam-guide holes for producing three primary colors of red, green and blue. A shield cup is attached to the outermost grid electrode. The shield cup includes a bottom side having red, green and blue beam-guide holes arranged in a row, and a side wall drawn from the circumference of the bottom side with a cylindrical shape. The shield cup includes an induced electromotive force increasing unit for increasing the electromotive force operating in the vicinity of the red and blue beam-guide holes, and an induced electromotive force decreasing unit for decreasing the electromotive force operating in the vicinity of the green beam-guide hole.
The induced electromotive force increasing unit is formed with burrs formed along the circumferences of the red and blue beam-guide holes of the shield cup each with a predetermined diameter and a predetermined height. The induced electromotive force decreasing unit is formed with slits opposite to each other and centered around the green beam-guide hole, formed along the side wall of the shield cup with a predetermined width and a predetermined depth.
REFERENCES:
patent: 4659961 (1987-04-01), Naiki
patent: 4877993 (1989-10-01), Ogasa
patent: 5703430 (1997-12-01), Dekker
patent: 5736812 (1998-04-01), Park et al.
patent: 6028392 (2000-02-01), Miyazawa et al.
Inkyu Park
Seon Kim Yoo
Christie Parker & Hale LLP
Guharay Karrabi
Patel Nimeshkumar D.
Samsung Display Devices Co. Ltd.
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