Television – Video display – Cathode-ray tube
Reexamination Certificate
1997-09-12
2001-06-12
Lee, Michael (Department: 2614)
Television
Video display
Cathode-ray tube
C315S370000, C315S008000
Reexamination Certificate
active
06246448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a purity adjustment device for a video display appliance such as a television receiver or a color monitor. In particular, the present invention relates to a purity adjustment device for a video display appliance which can automatically compensate for the purity of the picture that is varied due to the influence of the earth magnetism by electromagnetic deflection using a purity coil.
2. Description of the Related Art
Generally, in order to clearly display RGB (red, green, blue) color signals on a CRT (cathode ray tube) screen of a video display appliance, a purity adjustment is essentially required. Such a purity adjustment is performed in such a manner that the RGB color signals are scanned on one point of the screen, i.e., on a pixel of the screen and then the purity is adjusted until the color of the point becomes white.
A conventional purity adjustment device for a video display appliance, as shown in
FIG. 1
, includes a CRT
71
having electron guns
70
for emitting electron beams for the RGB color signals and displaying a color image on its screen, a centering permanent magnet
72
, mounted on the neck portion of the CRT
71
, for positioning the electron beam spot on the center of the fluorescent screen of the CRT
71
by its electromagnetic force, and a deflection coil
73
, mounted on the neck portion of the CRT
71
, for deflecting the electron beams emitted from the electron guns
70
in horizontal and vertical directions.
The operation of the conventional purity adjustment device as constructed above will be explained.
First, when an experimental image signal is inputted to the CRT
71
for the purity adjustment of the CRT
71
, electron beams for the RGB color signals corresponding to the input video signal are emitted from the electron guns
70
to the fluorescent screen of the CRT
71
. At the same time, the electron beams emitted from the electron guns
70
pass through the region of the centering magnet
72
, and thus the spot of the electron beams is positioned on the center of the fluorescent screen by the magnetic field produced from the centering magnet
72
. Also, the spot of the electron beams is deflected in the vertical and horizontal directions by the deflection coil
73
to scan the fluorescent screen of the CRT
71
, resulting in that the fluorescent screen of the CRT
71
produces a color which corresponds to the electron beams for the RGB color signals being scanned on the fluorescent screen. At this time, an examiner may observe the color displayed on the screen of the CRT
71
, and adjust the purity by adjusting the position of the deflection coil
73
and the centering magnet
72
so that the color displayed on the screen presents white.
However, according to the conventional purity adjustment device as described above, since the purity is adjusted so that the electron beam spot is positioned on the center of fluorescent screen of the CRT
71
by the centering magnet
72
mounted on the neck portion of the CRT
71
, the purity should be newly adjusted if the direction of the earth magnetic field is changed. Specifically, if the use environment of the video display appliance is changed, for instance, if the video display appliance whose purity adjustment has been made in the Southern Hemisphere is to be used in the Northern Hemisphere, the position of the electron beam spot scanned on the CRT screen will be changed due to the change of the earth magnetic field, whose direction in the Southern Hemisphere is opposite to that in the Northern Hemisphere, thereby deteriorating the purity of the picture displayed on the CRT screen.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems involved in the related art, and to provide a purity adjustment device for a video display appliance which can keep the purity of the picture displayed on the CRT screen uniform regardless of the change of the use environment of the video display appliance by automatically compensating for the purity that is varied due to the influence of the earth magnetic field by electromagnetic deflection using a purity coil.
In order to achieve the above object, there is provided a purity adjustment device for a video display appliance having a cathode ray tube (CRT), comprising:
an initial value determining section for determining a first voltage corresponding to an earth magnetic field of a specified place where a purity of a picture displayed on the CRT presents white;
an earth magnetic field detecting section for detecting the earth magnetic field of a present place where the video display appliance is located and producing a second voltage corresponding to a detected earth magnetic field;
a comparison-amplifying section for comparison-amplifying a third voltage, in which the first voltage from the initial value determining section and the second voltage from the earth magnetic field detecting section are superimposed together, with reference to an input reference voltage;
an amplifying section for amplifying an output of the comparison-amplifying section and producing a purity compensation voltage; and
a purity coil for producing a magnetic field for controlling a position of electron beams scanned on a screen of the CRT in accordance with the purity compensation voltage provided from the amplifying section.
REFERENCES:
patent: 4950955 (1990-08-01), Hoover et al.
patent: 5604403 (1997-02-01), Levy et al.
patent: 95201774 (1991-04-01), None
patent: 91201364 (1991-04-01), None
patent: 02227392 (1990-08-01), None
L.G. Electronics Inc.
Lee Michael
Oppenheimer Wolff & Donnelly
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