Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-10-19
2004-02-03
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
Reexamination Certificate
active
06686686
ABSTRACT:
The present invention relates to a cathode ray tube and, in particular, to a cathode ray tube including a deflection aiding electrostatic field.
Conventional cathode ray tubes (CRTs) are widely utilized, for example, in television and computer displays. One or more electron guns positioned in a neck of a funnel-shaped glass bulb of a CRT direct a corresponding number of beams of electrons toward a glass faceplate biased at a high positive potential, e.g., 30 kilovolts (kV). The faceplate usually has a substantially rectangular shape and is generally planar or slightly curved. Together, the glass bulb and faceplate form a sealed enclosure that is evacuated. The electron gun(s) are positioned along an axis that extends through the center of the faceplate and is perpendicular thereto.
The electron beam(s) is (are) raster scanned across the faceplate so as to impinge upon a coating or pattern of phosphors on the faceplate that produces light responsive to the intensity of the electron beam, thereby to produce an image thereon. The raster scan is obtained by a deflection yoke including a plurality of electrical coils positioned on the exterior of the funnel-shaped CRT near the neck thereof. Electrical currents driven in first coils of the deflection yoke produce magnetic fields that cause the electron beam(s) to deflect or scan from side to side (i.e. horizontal scan) and currents driven in second coils of the deflection yoke produce magnetic fields that cause the electron beam(s) to scan from top to bottom (i.e. vertical scan). The magnetic deflection forces typically act on the electrons of the beam(s) only in the first few centimeters of their travel immediately after exiting the electron gun(s), and the electrons travel in a straight line trajectory thereafter, i.e through a substantially field-free drift region. Conventionally, the horizontal scan produces hundreds of horizontal lines in the time of each vertical scan to produce the raster-scanned image. U.S. Pat. No. 5,327,044 to Chen entitled “Electron Beam Deflection Lens for CRT” describes a single-electron-gun monochrome cathode ray tube in which a resistive coating 54 in the tube neck and funnel portion 62a, 62b is biased to a potential less than screen potential and contacts a second coating G4 on the interior of the tube funnel and the screen 48 that is biased at screen potential. Chen is not seen to provide any description or suggestion regarding any plural-beam or color CRT.
The depth of a CRT, i.e. the distance between the faceplate and the rear of the neck, is determined by the maximum angle over which the deflection yoke can bend or deflect the electron beam(s) and the length of the neck extending rearward to contain the electron gun. Greater deflection angles provide reduced CRT depth.
Modern magnetically-deflected color (i.e. plural beam) CRTs typically obtain a ±55° deflection angle, which is referred to as 110° deflection. However, such 110° CRTs for screen diagonal sizes of about 62 cm (about 25 inches) or more are so deep that they are almost always provided in a cabinet that either requires a special stand or must be placed on a floor. For example, a 110° CRT having a faceplate with an about 100 cm (about 40 inch) diagonal measurement and a 16:9 aspect ratio, is about 60-65 cm (about 24-26 inches) deep. Practical considerations of increasing power dissipation producing greater temperature rise in the magnetic deflection yoke and its drive circuits and of the higher cost of a larger, heavier, higher-power yoke and drive circuitry make increasing the maximum deflection angle so as to decrease the depth of the color CRT disadvantageous.
Accordingly, there is a need for a plural beam cathode ray tube having either a greater deflection angle without an excessive increase in deflection power or the same deflection angle at a reduced deflection power, i.e. as compared to a conventional color CRT having an equivalent screen-size.
To this end, the plural-beam tube of the present invention comprises a tube envelope having a faceplate and a screen electrode on the faceplate adapted to be biased at a screen potential, a source of at least two beams of electrons directed toward the faceplate and adapted for magnetic deflection of the beams of electrons, and phosphorescent material disposed on the faceplate for producing light in response to the beams of electrons impinging thereon. At least first and second electrostatic electrodes on an interior surface of the tube envelope define a non-Z-planar gap therebetween. The first electrode is proximate the source and adapted to be biased at a potential less than the screen potential, and the second electrode is between the first electrode and the screen electrode and is adapted to be biased at the screen potential.
According to another aspect of the invention, a display comprises a tube envelope having a faceplate and a screen electrode on the faceplate biased at a screen potential, a source within the tube envelope of a beam of electrons directed toward the faceplate, a deflection yoke proximate the source of a beam of electrons for magnetically deflecting the beam of electrons and defining a deflection plane, and phosphorescent material disposed on the faceplate for producing light in response to the beam of electrons impinging thereon. First and second electrostatic electrodes interior said tube envelope define a gap therebetween that intersects the deflection plane and is partly disposed on one side thereof and partly to the other side thereof. The first electrode is proximate the source of a beam of electrons and is biased at a potential less than the screen potential, and the second electrode is between the first electrode and the screen electrode and is biased at the screen potential.
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PCT Application, PCT/US00/28927, Written Opinion, Dated Apr. 1, 2002, 5 pages.
International Search Report, PCT/US00/28927, Feb. 6, 2001, (3 Pages).
Bechis Dennis John
Carpinelli Joseph Michael
Firester Arthur Herbert
Riddle George Herbert Needham
Burke William J.
Krishnan Sumati
O'Shea Sandra
Sarnoff Corporation
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