Astigmatic electron lens for a cathode-ray tube
AssigneeU.S. Philips Corporation
InventorPiet G. J. Barten
Life of this patent
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Abstract
A focusing electron lens having a controllable astigmatism. An auxiliary electrode affects the non-rotationally symmetrical field defined by two tubular electrodes to vary the convergence in one main direction while maintaining it constant in the other main direction. In an in-line electron gun system in a color television display tube, such a lens corrects for the effect of parastigmatic, self-converging deflection coil systems on the focusing of the electron beams.
Claims5
In an electron gun assembly including a cathode, first and second axially arranged tubular electrodes extending in that order from said cathode, at least one of said electrodes being non-rotationally symmetrical, and means for applying a substantially fixed potential between said first and second tubular electrodes whereby an electric field is produced which defines an astigmatic lens for focusing an electron beam emitted from the cathode and passing through said field,
- the improvement comprising a further electrode means positioned to influence said electric field, and means for applying a time varying voltage between said further electrode means and said first tubular electrode, whereby said further electrode means simultaneously varies the astigmatism and strength of said lens.
In a cathode ray tube a system having a display screen and an electrode system for generating at least one electron beam directed onto said screen, said electrode system including an electron gun assembly comprising a cathode, first and second axially-arranged tubular electrodes extending in that order from said cathode, at least one of said electrodes being nonrotationally symmetrical, and means for applying a substantially fixed potential between said first and second tubular electrodes whereby an electric field is produced which defines an astigmatic lens for focusing an electron beam emitted from the cathode and passing through said field,
- the improvement comprising a further electrode positioned to influence said electric field, and means for applying a time-varying voltage between said further electrode and said first tubular electrode, whereby said further electrode simultaneously varies the astigmatism and strength of said lens.
Dependencies are inferred from the claim text.