Inline electron gun with negative astigmatism beam forming and dynamic quadrupole main lens

For use in a color cathode ray tube (CRT) including three inline cathodes for providing three groups of energetic electrons and having a display screen and a self-converging magnetic deflection yoke for deflecting a plurality of electron beams across said display screen in a raster-like manner, wherein said deflection yoke imparts a negative astigmatism in a beam deflection zone to the beams incident on the screen, giving rise to beam horizontal under-focusing, said CRT further including a high voltage lens portion including a dynamic electrostatic quadrupole for focusing the beams on the screen, a low voltage electron beam forming arrangement comprising:

• a first charged electrode having a first plurality of inline through-hole circular apertures each aligned with a respective one of said cathodes and having an associated aligned rectangular indentation;
• and
• a second charged electrode having a second plurality of inline through-hole circular apertures each aligned with a respective one of said first plurality of apertures in said first charged electrode, wherein each of said aligned first and second pluralities of through-hole circular apertures and said aligned rectangular indentation receives one of said three groups of energetic electrons and forms said energetic electrons into an electron beam and provides said electron beam to the high voltage lens portion of the CRT, wherein said first charged electrode is a G.sub.1 control electrode maintained at a first voltage V.sub.F1 and said second charged electrode is a G.sub.2 control electrode maintained at a second voltage V.sub.F2, and wherein V.sub.F2 >V.sub.F1 and said G.sub.1 control electrode and said G.sub.2 screen electrode comprise a static electrostatic quadrupole;
• wherein said electrodes apply a fixed negative astigmatism to each of the electron beams in a horizontal overfocusing of the electron beams to reduce the horizontal beam size in the deflection zone and improve the deflected electron beam's horizontal resolution.

For use in a color cathode ray tube (CRT) including three inline cathodes for providing three groups of energetic electrons and having a display screen and a self-converging magnetic deflection yoke for deflecting a plurality of electron beams across said display screen in a raster-like manner, wherein said deflection yoke imparts a negative astigmatism in a beam deflection zone to the beams incident on the screen, giving rise to beam horizontal under-focusing, said CRT further including a high voltage lens portion including a dynamic electrostatic quadrupole for focusing the beams on the screen, a low voltage electron beam forming arrangement comprising:

• a first charged electrode having a first plurality of inline through-hole circular apertures each aligned with a respective one of said cathodes and having an associated aligned rectangular indentation, wherein each of said rectangular indentations has a longitudinal axis oriented generally vertically, or transverse to the three inline cathodes;
• and
• a second charged electrode having a second plurality of inline through-hole circular apertures each aligned with a respective one of said first plurality of apertures in said first charged electrode, wherein each of said aligned first and second pluralities of through-hole circular apertures and said aligned rectangular indentation receives one of said three groups of energetic electrons and forms said energetic electrons into an electron beam and provides said electron beam to the high voltage lens portion of the CRT, wherein said rectangular indentations are disposed toward a first surface side of said first charged electrode, and wherein said first surface side is in facing relation to said second charged electrode;
• wherein said electrodes apply a fixed negative astigmatism to each of the electron beams in a horizontal overfocusing of the electron beams to reduce the horizontal beam size in the deflection zone and improve the deflected electron beam's horizontal resolution, and wherein said first charged electrode is a G.sub.2 screen electrode maintained at a first voltage V.sub.F2 and said second charged electrode is a G.sub.1 control electrode maintained at a second voltage V.sub.F1.

For use in a color cathode ray tube having a display screen and a self-converging magnetic deflection yoke for deflecting a plurality of electron beams across said display screen, wherein said deflection yoke imposes a negative astigmatism on said electron beams resulting in horizontal under-focusing and vertical over-focusing of said electron beams when deflected toward a lateral edge of said display screen, an electron gun comprising:

• a plurality of cathodes for providing a plurality of groups of energetic electrons;
• low voltage beam forming means disposed adjacent said cathodes for receiving and forming each of said groups of electrons into a respective beam directed toward the display screen;
• static electrostatic quadrupole means disposed in said beam forming means for applying a fixed negative astigmatism to each of the electron beams for over-focusing horizontally, thereby reducing a spot size of said each electron beam in a horizontal cross-section;
• high voltage beam focusing means disposed intermediate said beam forming means and the display screen for focusing each of the electron beams on the display screen;
• and
• dynamic electrostatic quadrupole means disposed in said beam focusing means for applying a deflection dependent positive astigmatism to said each of the horizontally over-focusing electron beams when said electron beams are deflected toward a lateral edge of said display screen for compensating for the negative astigmatism of said self-converging magnetic deflection yoke and of said static electrostatic quadrupole means thereby reducing said electron beam horizontal spot size.

For use in a color cathode ray tube (CRT) including a plurality of cathodes for providing a plurality of groups of energetic electrons, low voltage beam forming means for receiving and forming each of said groups of energetic electrons into a respective electron beam, high voltage beam focusing means for receiving and focusing each of said electron beams, and a screen for receiving each of said electron beams and forming a spot image of each of said electron beams, wherein a self-converging magnetic deflection yoke deflects said electron beams across said display screen in a synchronous, raster-like manner and wherein said deflection yoke imposes a negative astigmatism on said electron beams resulting in a horizontal under-focusing, or elongation, and vertical over-focusing, or compression, of said electron beams when deflected toward a lateral edge of said display screen, an arrangement for improving an electron beam spot size on said display screen comprising:

• static electrostatic quadrupole means disposed in said low voltage beam forming means for applying a fixed negative astigmatism to each of the electron beams thereby reducing a spot size of said each electron beam in a horizontal cross-section;
• and
• dynamic electrostatic quadrupole means disposed in said high voltage beam focusing means for applying a positive astigmatism to said each of the electron beams, wherein said positive astigmatism increases as said beams are deflected toward a lateral edge of said display screen with essentially no positive astigmatism applied when said electron beams are horizontally undeflected and wherein said positive astigmatism compensates for the negative astigmatism of said self-converging magnetic deflection yoke and of said static electrostatic quadrupole means for reducing said electron beam spot size on said display screen.