Electron gun system with dynamic convergence control

A three-beam in-line electron gun for a color cathode ray tube, comprising:

• means for generating three beams of electrons aligned in a common plane--a center beam and two outer beams;
• beam bending means for producing asymmetrical fields in the paths of said outer beams for diverting said outer beams from respective straight line paths toward a common point of convergence, comprising at least two facing electrodes, a first electrode being adapted to receive a relatively higher excitation potential and a second electrode a relatively lower excitation potential, said second electrode having a center opening and two outer openings arranged in line along an electrode horizontal axis orthogonal to the gun axis, said outer openings having inwardly extending enlargements which are symmetrical about said electrode horizontal axis and a vertical axis through the center opening, but asymmetrical about respective vertical axes through the outer openings to thereby produce said asymmetrical fields for said outer beams;
• and
• means for modulating the strength of said asymmetric field components acting on said outer beams as a function of beam deflection angle.

In a three-beam in-line electron gun system for a color cathode ray tube having a screen and a self-converging yoke which imparts an undesirable astigmatism to the beams in off-center regions of the screen, apparatus comprising:

• an electron beam source for developing three electron beams;
• focusing means for focusing said three electron beams at the screen of the tube, said focusing means being so constructed and arranged that changes in focusing field strength undesirably alter beam convergence;
• correcting lens means located within or coupled to said focusing means for developing an astigmatic field component in the path of each of said beams when said lens means is appropriately excited;
• and
• means for modulating the strength of said astigmatic field component as a function of beam deflection angle to at least partially compensate for said yoke-induced astigmatism in said off-center regions of the screen, said modulating of said astigmatic field component also modulating said focusing field strength and undesirably creating errors in the convergence of said beams,
• said correcting lens means including electrode means having a beam passing opening pattern shaped to create asymmetrical outer beam fields effective to at least partially compensate for said deflection-related beam convergence errors.

For use in a color cathode ray tube system having a color tube with a cathodoluminescent screen, a system adapted for use with a deflection yoke having an asymmetrical yoke field for self-converging said beams which undesirably astigmatizes said beams in off-center regions of the screen, said system comprising:

• an in-line electron gun for developing three electron beams for exciting said screen, said gun including, for each of said beams, means including cathode means for developing said beam, focus lens means including focus electrode means for receiving said electron beam and forming a focused electron beam spot at the screen of the tube, said focus lens means having a plurality of electrode means spaced along a lens axis;
• beam correcting means incorporated in said focus electrode means for developing in the path of said beam when said beam correcting means is appropriately excited, an astigmatic field component;
• and
• system signal generating means for developing a signal having amplitude variations correlated with a scan of the beams across the screen and means for applying said signal to said beam correcting means to cause, as a function of beam deflection angle, the strength of said astigmatic field component to vary to produce a dynamic astigmatism-correction effect to at least partially compensate for the beam-astigmatizing effect of said yoke, said focus lens means being so constructed and arranged that operation of said beam correcting means causes undesired deflection-related misconvergence of said beams as they are swept;
• said beam correcting means including misconvergence compensation means for at least partially compensating for said undesired beam misconvergence, comprising at least two facing electrodes, a first electrode being adapted to receive a relatively higher excitation potential and a second electrode a relatively lower excitation potential, at least one of said electrodes having a center opening and two outer openings arranged in line along an electrode axis orthogonal to the gun axis, said outer openings having profile distortions which are symmetrical about said electrode axis and a vertical axis through the center opening, but asymmetrical about respective vertical axes through the outer openings.

For use in a color cathode ray tube system having a color tube with a cathodoluminescent screen, a system adapted for use with a deflection yoke having an asymmetrical yoke field for self-converging said beams which undesirably astigmatizes said beams in off-center regions of the screen, said system comprising:

• an in-line electron gun for developing three electron beams for exciting said screen, said gun including for each of said beams, means including cathode means for developing said beam, focus lens means including focus electrode means for receiving said electron beam and forming a focused electron beam spot at the screen of the tube, said focus lens means having a plurality of electrode means spaced along a lens axis;
• dynamic quadrupole beam correcting means incorporated in said focus electrode means for developing in the path of said beam when appropriately excited an astigmatic field component, comprising three spaced electrodes, a center electrode adapted to receive a relatively lower excitation potential and two outer electrodes adapted to receive relatively higher excitation potentials, said electrodes having openings effective when said electrodes are excited to create a quadrupolar field therebetween;
• system signal generating means for developing a signal having amplitude variations correlated with a scan of the beam across the screen and means for applying said signal to said gun to simultaneously cause, as a function of beam deflection angle, the strength of the focusing field and the strength of said astigmatic field component to vary to produce a dynamic astigmatism-correction effect to at least partially compensate for the beam-astigmatizing effect of said yoke,
• said focus lens means being so constructed and arranged such that operation of said beam correcting means causes undesired deflection-related misconvergence of said beams as they are swept;
• said beam correcting means including means for at least partially compensating for said undesired beam misconvergence, comprising at least two facing electrodes, a first electrode being adapted to receive a relatively higher excitation potential and a second electrode a relatively lower excitation potential, at least one of said electrodes having a center opening and two outer openings arranged in line along an electrode axis orthogonal to the gun axis, said outer openings having profile distortions which are symmetrical about said electrode axis and a vertical axis through the center opening, but asymmetrical about respective vertical axes through the outer openings.

For use in a color cathode ray tube (CRT) wherein first, second and third inline electron beams are directed onto a phosphorescing screen in the CRT, with said second beam disposed intermediate said first and third beams, an electron gun comprising:

• cathode means for generating electrons;
• crossover means for receiving electrons from said cathode means and for forming a beam crossover;
• first focusing means driven by a dynamic voltage for focusing the inline electron beams on the phosphorescing screen, wherein a misconvergence is present among the electron beams on the phosphorescing screen;
• and
• second focusing means disposed adjacent to said first focusing means for displacing the first and third electron beams horizontally toward the second beam for reducing said misconvergence and bringing said electron beams into convergence on the phosphorescing screen, wherein said second focusing means includes first and third outer apertures and a second middle aperture through which respective ones of the electron beams are directed, and wherein said first and third outer apertures each include an inwardly directed notch.

For use in focusing a plurality of electron beams on a phosphorescing screen of a color cathode ray tube (CRT), wherein said electron beams are aligned in an inline array and are focused on said phosphorescing screen by a dynamic focus voltage which causes misconvergence of said electron beams, an electron gun comprising:

• an electron beam source for generating and directing a plurality of electron beams in a common direction;
• a first dynamically charged electrode having at least one aperture therein through which the electron beams are directed;
• a second statically charged electrode having a plurality of apertures therein through each of which a respective one of the electron beams is directed, wherein said second electrode includes first and third outer apertures and a second aperture intermediate said first and third apertures, and wherein said first and third apertures include respective notched portions extending inward toward said second aperture for moving said first and third electron beams in a generally horizontal direction and eliminating misconvergence between the electron beams;
• and
• a third dynamically charged electrode having at least one aperture therein through which the electron beams are directed, wherein said second electrode is disposed intermediate said first and third electrodes.

In an electron gun for accelerating and focusing a plurality of inline electron beams on a cathode ray tube (CRT) screen and including a focusing electrode, the improvement comprising:

• a first dynamically charged electrode incorporated in a first portion of said focusing electrode and having at least one elongated aperture for passing one or more of the electron beams;
• a third dynamically charged electrode incorporated in a second portion of said focusing electrode and having at least one elongated aperture for passing one or more of the electron beams, wherein said first and third electrodes are arranged in spaced relation along the electron beams so as to divide the focusing electrode into first and second focusing electrode portions;
• and
• a second statically charged electrode disposed along the electron beams between said first and third electrodes so as to form first and second electrostatic quadrupole fields respectively therewith, wherein said second electrode includes a plurality of spaced elongated apertures each adapted for passing a respective one of the electron beams and wherein the apertures in said first and third electrodes are aligned generally transverse to the apertures in said second electrode, and wherein a pair of outer apertures in said second electrode each include a respective inner cut-out portion for horizontally deflecting a pair of outer electron beams toward a center electron beam and causing said electron beams to converge on a phosphorescing screen of the CRT.

For use in a color cathode ray tube system having a color tube with a cathodoluminescent screen, the system comprising:

• an inline electron gun for developing first and third outer electron beams and a second center electron beam for exciting said screen, said gun including, for each of said beams, means including cathode means for developing said beam, focus lens means for receiving said electron beam and forming a focused electron beam spot at the screen of the tube, said focus lens means having a plurality of electrode means spaced along a lens axis including focus electrode means;
• yoke means for deflecting said electron beams, said yoke means having an asymmetrical field for self-converging said beams which undesirably astigmatizes said beams in off-center regions of the screen;
• beam correcting means incorporated in said focus electrode means for developing in the path of said beam when appropriately excited a first astigmatic accelerating field component and a second astigmatic decelerating field component;
• system signal generating means for developing a signal having amplitude variations correlated with a scan of the beam across the screen and means for applying said signal to said beam correcting means to cause, as a function of beam deflection angle, the strength of said first and second astigmatic field components to vary to produce a dynamic astigmatism-correction effect to at least partially compensate for the beam-astigmatizing effect of said yoke;
• and
• convergence correcting means incorporated in said focus electrode means for horizontally deflecting said two outer electron beams toward said second center electron beam on the cathodoluminescent screen in correcting for misconvergence of the electron beams, said convergence correcting means including an electrode having first and second offset keyhole-shaped slots through which said first and third outer electron beams are directed for exerting an asymmetrical electrostatic field on said first and third outer electron beams.

For use in a color cathode ray tube system having a color tube with a phosphor screen, the system comprising:

• a three-beam, in-line gun for exciting said screen, said gun including;
• cathode means and focus lens means for developing a center beam and two outer beams and for forming three focused electron beam spots at the screen of the tube, and
• electrostatic quadrupole-developing means configured and arranged to develop a horizontally unbalanced quadrupole field in the path of each of said outer beams when appropriately excited;
• and
• system signal generating means for developing a signal having amplitude variations correlated with the scan of the beams across the screen and for applying said signal to said electrostatic quadrupole-developing means to cause said beams to converge and diverge as a function of the strength of said signal, said quadrupole-developing means including electrode means having outer beam apertures shaped to create field-strength-dependent asymmetrical outer beam fields whose strength varies as said signal varies.