Display tube with magnetic correction elements
AssigneeU.S. Philips Corporation
InventorOtto Mensies
Life of this patent
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Abstract
Display tube such as a projection television display tube or a DGD tube (DGD=Data Graphic Display), including an electron gun (5) in an evacuated envelope (1) for generating an electron beam (6) which is focussed to a spot (8) on a display screen (7) with the aid of an electrostatic focussing lens (27, 30) and which is deflected across the display screen (7) in two mutually perpendicular directions (x, y). If a correction structure (37) consisting of magnetic half-hard material is provided in such a tube in the proximity of the focussing lens (27, 30) and coaxially of the gun axis (20) in which at least one magnetic 2N pole (N.gtoreq.2) is induced for correcting spot shape errors, a high spot quality can be realized with low-cost deep-drawn lens electrodes (27, 30).
Claims5
In a display tube comprising an envelope containing a luminescent screen and an electron gun having a central axis for producing an electron beam directed at said screen, said electron gun including, successively-centered along said axis;
- (a) a cathode for emitting electrons;
- (b) means for forming the emitted electrons into the electron beam;
- and
- (c) first and second cylindrical focusing electrodes for producing therebetween an electric focusing lens field for focusing the electron beam into a spot on said screen, each of said electrodes having a front end closer to said screen then the rear end thereof, the first electrode extending partially within the second electrode so as to leave a space between the front ends of said electrodes within which said electric field extends;
- the improvement comprising first permanent magnet means disposed in said space between the front ends of said electrodes and producing a 2N pole magnetic field, N being an integer, which acts on said beam so as to compensate for asymmetries of said electric focusing lens field which adversely affect circularity of said beam.
Dependencies are inferred from the claim text.