Patent ID: 6518697
Filing Date: 2003-02-11
Classification: H01J

Abstract:
A colour display device (1) comprising a cathode ray tube having a display screen (3), a means for generating at least one electron beam (6) and a deflection unit (11) for generating deflection fields for deflecting electron beam(s) (7, 8, 9) across the display screen (3) in two perpendicular directions (x, y), and having magnetic field-generating means (26, 25) at or near a display screen-facing end of the deflection unit for generating an electromagnetic field to reduce raster distortions, characterized in that the magnetic field-generating means (25, 26) comprise correction electromagnets (25, 26), said correction electromagnets extending along an arc portion between angles &agr;1 and &agr;2, said angles obeying the following rules:|cos(3&agr;1)âˆ’cos(3&agr;2)|&gE;1.33 and|cos(5&agr;1)âˆ’cos(5&agr;2)|&lE;0.5, &agr;1 and &agr;2 being taken with respect to the line (horizontal, x-z) deflection plane, andthe display device comprising means (27) for driving the electromagnets (25, 26), the electromagnets (25, 26) and the means (27) being arranged to generate a correction field that is substantially mirror-symmetrical with respect to the line (horizontal, x-z) deflection plane, and substantially anti-mirror-symmetrical with respect to the field (vertical, y-z) deflection plane.