Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2001-01-11
2001-11-13
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S414000, C313S479000, C313S47700R, C313S425000, C313S437000, C313S4770HC, C315S382000
Reexamination Certificate
active
06316871
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a compensation device for convergence drift used in a cathode ray tube, and more particularly, to a device capable of reducing an occurrence of convergence drift due to electric charges accumulated on an inner surface of a neck portion thereof.
(b) Description of the Related Art
A cathode ray tube (CRT) is a device for displaying images on a screen by emitting electron beams from an electron gun assembly and landing the electron beams onto a phosphor screen. The electron gun assembly is mounted in a neck portion, and includes three cathodes for emitting electrons and a plurality of grid electrodes for generating electric lenses therebetween to control the focusing and accelerating degree of the electron beams.
After three electron beams are emitted, they are horizontally and vertically deflected by magnetic fields generated by a deflection yoke, and divided onto corresponding red, green and blue phosphor layers respectively through a shadow mask. Thus, the electron beams strike all pixels on the phosphor screen.
In such a CRT, a voltage supplied to a vacuum bulb when the CRT starts operation leaks to the neck portion with time because of a high potential difference between the grid electrodes and the neck portion. Consequently, electric charges in the bulb are continuously accumulated on an inner surface of the neck portion.
Because the accumulated charges generate new electric fields, they change the path of electron beams passing on the grid electrodes and vary the convergence degree of the beams. Thus, the charges cause “convergence drift” that allows deterioration of image quality.
To reduce the convergence drift, U.S. Pat. No. 4,868,454, 4,564,786 and 4,503,357 provide the use of conductive tape attached on an outer surface of the neck portion for early stabilization of the convergence drift.
However, the conductive tape that is simply attached on the neck portion is under a floating condition that makes a uniform potential state unattainable. Thus, the conductive tape is sensitive to outer influences, for example approach of charged materials and variation of humidity, so that it is difficult to operate in a stable fashion.
In particular, when the conductive tape is placed opposite to intervals between the grid electrodes, minute potential variation of the conductive tape has a great deal of influence on the electric lenses generated in the intervals. Such variation of the electric lenses impedes accurate control of the electron beams.
Also, when the conductive tape is grounded, it easily increases potential differences and intensity of electric fields between the grid electrodes and the neck portion. Thus, the grounded conductive tape has a tendency to increase the convergence drift as the electric fields increase the accumulated charges on the neck portion.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a compensation device capable of reducing the convergence drift by weakening electric fields formed between the grid electrodes and the neck portion, the electric fields causing the charges to be accumulated on the neck portion.
In order to achieve this object, the compensation device includes a convergence electrode provided on an outer surface of the neck portion, an inducement means for inducing high potential from voltage to be supplied to an inner graphite layer, and a connecting member formed between the convergence electrode and the inducement means to supply the potential from the inducement means to the convergence electrode.
The inducement means can be provided on an outer surface of a cone portion to induce high potential from voltage supplied to the inner graphite layer. Alternatively, the inducement can be provided on a voltage supply line, for transmitting voltage to the inner graphite layer to induce high potential from voltage passing on the line.
As the inducement means provides high potential to the neck portion through the convergence electrodes, it can decrease the potential difference between the grid electrodes and the neck portion. Thus, the compensation device makes the electric fields, which cause the charges to be accumulated, to weaken so that it can effectively reduce the convergence drift.
REFERENCES:
patent: 4503357 (1985-03-01), Ouhata et al.
patent: 4564786 (1986-01-01), Baum et al.
patent: 4868454 (1989-09-01), Paridaens
patent: 5015925 (1991-05-01), Spanjer et al.
patent: 9201839 (1992-03-01), None
Christie Parker & Hale LLP
Patel Nimeshkumar D.
Roy Sikha
Samsung SDI Co., LTD
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