Electron beam shaping aperture in low voltage, field-free region of electron gun

An electron gun for a color cathode ray tube wherein a plurality of inline electron beams are deflected in a raster-like manner across a display screen to produce an image thereon, said electron gun comprising:

• cathode means for generating energetic electrons;
• low voltage beam forming means disposed adjacent said cathode mans for receiving said energetic electrons and forming each of the electron beams along a respective axis and directing the electron beams toward the display screen, said beam forming means including a charged electrode having a thickness t along said axes for forming a relatively electrostatic field-free region on the respective axes of each of said electron beams;
• high voltage asymmetric focusing means disposed intermediate said beam forming means and the display screen for receiving the electron beams and forming an electron beam crossover on each electron beam axis in focusing said electron beam on the display screen, wherein said high voltage asymmetric focusing means imposes an asymmetric electrostatic field on said electron beam giving rise to electron beam spot distortion on the display screen;
• and
• means for defining a plurality of beam shaping apertures each disposed on a respective electron beam axis in the relatively field-free region of said low voltage beam forming means for intercepting an outer lateral portion of a respective electron beam and removing electrons from a peripheral portion of said electron beam in compensating for said asymmetric electrostatic field and reducing electron beam spot distortion on the display screen, wherein each beam shaping aperture has a curvilinear, non-circular shape and a horizontal width d, where t>d.

The electron gun for directing a focused electron beam on a display screen of a cathode ray tube (CRT), said electron gun comprising:

• a cathode for providing energetic electrons;
• low voltage beam forming means for receiving said energetic electrons, forming said energetic electrons into a beam along an axis, and directing said electron beam toward the display screen of the CRT, said beam forming means including a charged electrode having a thickness t along said axis for defining a substantially electrostatic field-free region on said axis;
• high voltage asymmetric focus means for receiving said electron beam and applying an asymmetric electrostatic field to the beam in focusing the beam in the form of a spot on the display screen of the CRT, wherein said asymmetric electrostatic field gives rise to over-focusing of a peripheral portion of the beam resulting in beam spot spherical aberration;
• and
• means for defining a beam intercepting aperture on said axis and in said substantially electrostatic field-free region of said charged electrode for receiving and passing the electron beam to said asymmetric focus means, said beam intercepting aperture having an asymmetric shape with a horizontal width d for removing said peripheral portion of the beam and providing a beam cross section which compensates for the over-focusing of said asymmetric focus means to provide a rotationally symmetric, focused beam spot on the CRT display screen, where t>d.