US 5,204,585 A · Electron beam deflection lens for color CRT

Abstract

An electron gun for a color cathode ray tube (CRT) includes a cathode, a low voltage beam forming region (BFR), and a high voltage deflection focus lens disposed in the beam deflection region of the CRT's magnetic deflection yoke for simultaneous and coincident focusing and deflection of the electron beams on the CRT's display screen. The deflection lens includes a first focus electrode either in the form of a cylindrical metal grid or a conductive coating disposed on the inner surface of the CRT's neck portion and extending into the magnetic deflection field. The deflection lens further includes a second focus electrode either in the form of a conductive coating or a frusto-conical metallic grid disposed on or immediately adjacent to the inner surface of the CRT's funnel portion intermediate the magnetic deflection yoke and the CRT's display screen. By positioning the electron gun's deflection focus lens within the deflection field, the deflection center of the electron beams is disposed within the focal point of the focus lens permitting the focus lens to operate as a deflection lens to not only focus the beam, but also increase beam deflection sensitivity. By reducing beam "throw distance" (fieldfree zone) and realizing a corresponding reduction in beam magnification and space charge effect, improved electron beam spot on the display screen is also provided. The focus lens increases the equivalent diameter of the main focus lens which reduces lens spherical aberration effect on the beams, while co-locating the beam focus and deflection regions also allows for shorter CRT length.

Claims45

Dependent claims

An inline electron gun for directing a plurality of electron beams along an axis onto a display screen in a color cathode ray tube (CRT) having a neck portion and a frusto-conical funnel portion disposed intermediate said neck portion and said display screen, said CRT further including a magnetic deflection yoke disposed generally intermediate said neck and funnel portions for providing a magnetic deflection region for deflecting said electron beams across said display screen in a raster-like manner, said electron gun comprising:

a source of energetic electrons;
low voltage beam forming means disposed adjacent said source of energetic electrons and within the neck portion of the CRT for forming the energetic electrons into a plurality of electron beams directed along said axis;
and
high voltage focus means disposed in the magnetic deflection region and intermediate said beam forming means and the display screen for providing a common aperture electrostatic focus region for the plurality of electron beams for focusing the electron beams on the display screen, wherein said magnetic deflection region and said electrostatic focus region overlap and are coincident, wherein said focus means includes a first charged electrode defining a first common aperture aligned with said axis through which the electron beams are directed and disposed intermediate said magnetic deflection yoke and said display screen and adjacent to an inner surface of the funnel portion of the CRT.

1 more element

For use with a color cathode ray tube (CRT) wherein a plurality of electron beams are directed onto phosphor elements disposed on an inner surface of a display screen for providing a video image, said CRT including an apertured color selection electrode disposed adjacent said display screen for passing each of said electron beams onto selected phosphor elements, said CRT further including coincident beam magnetic deflection and beam focus regions wherein said electron beams are simultaneously deflected across said display screen in a raster-like manner and focused on said display screen to provide a dynamic deflection center effect on said electron beams, wherein a deflection center of sid electron beams moves along a centerline axis generally transverse to said display screen and extending through the center of said display screen giving rise to misfocusing of the electron beams on the display screen, an arrangement for activating said phosphor elements whereupon said phosphor elements are responsive to an electron beam incident thereon for emitting phosphorescent light, said arrangement comprising:

a source of light disposed on the centerline axis of the display screen;
displacement means coupled to said source of light for moving said source of light along said axis whereupon light transmitting the apertures in the color selection electrode illuminates phosphor elements on the inner surface of the display screen in activating said phosphor elements;
and
ray blocking means disposed intermediate said light source and the display screen for blocking light from selected ones of said phosphor elements disposed within first designated area on the display screen while permitting light to illuminate and activate selected others of said phosphor elements disposed within second designated areas on the display screen as said light source is displaced along said axis to accommodate the dynamic deflection center effect on said electron beams and improve electron beam focusing on the display screen.

1 more element

Dependencies are inferred from the claim text.

Electron beam deflection lens for color CRT

Life of this patent

Electron beam deflection lens for color CRT

Life of this patent

Abstract

Claims45