Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Patent
1996-12-05
1999-05-04
Patel, Vip
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
335310, H01J 2970
Patent
active
059006935
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a color picture tube (CRT) display system.
A CRT with a large screen size such as 89 cm diagonal that is substantially flat is more susceptible to geometry distortions than a CRT with a faceplate that is not flat. To attain a high performance, a saddle-saddle (S-S) deflection yoke has been utilized. An S-S deflection yoke has the advantage of providing design flexibility not available in a saddle-toroid (S-T) construction.
North-South pin (NS-pin) distortion is a geometrical distortion that distorts straight horizontal lines into parabolas. NS-pin distortion is more difficult to correct in a CRT having a 4:3 aspect ratio than in a CRT having a 16:9 aspect ratio. Permanent magnets have been used for correcting NS-pin distortion in a CRT having a 4:3 aspect ratio. This is accomplished by mounting two small bar magnets horizontally at top and bottom, respectively, of the front end of the vertical deflection coil, referred to as pin-magnets. It may be desirable to reduce the NS-pin distortion in a CRT having a 4:3 aspect ratio without using permanent magnets. This is so because the tolerance in permanent magnets tend to vary over a wide range. Furthermore, when the screen of the CRT is large such as 89 cm diagonal, the magnets may not provide adequate correction. Additionally, magnets may have an undesirable effect on, for example, convergence or color purity.
SUMMARY OF THE INVENTION
A deflection yoke embodying an aspect of the invention includes a vertical deflection winding disposed adjacent a core for producing a vertical deflection field. The vertical deflection winding includes a pair of saddle shaped coils, each having a plurality of winding turns that form first and second side sections extending in a longitudinal direction of the yoke. The vertical deflection winding includes a front endturn section, disposed adjacent a screen end of the yoke between the first and second side sections and a rear endturn section disposed remote from the screen end and between the side sections. The rear endturn section are constructed in a manner to concentrate the majority of its winding turns close to the gun end. A ratio less than 0.15 is maintained between a length of a region of the rear endturn section that includes 50% of all the winding turns in the rear endturn section, including the winding turn closest to the gun end, and the effective length of the vertical magnetic field. The result is that a vertical deflection center is shifted toward a gun side of said yoke relative to a horizontal deflection center. A ratio between a first length separating the deflection centers and an effective length of the vertical deflection field is greater than 0.09 so as to significantly reduce raster distortion.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cross section of a deflection yoke, embodying an aspect of the invention, mounted on a cathode ray tube;
FIG. 2 illustrates a more detailed side cross section of the yoke of FIG. 1;
FIG. 3 illustrates a side view of a vertical deflection coil that is included in the yoke of FIG. 1;
FIG. 4 illustrates a top view of the vertical deflection coil of FIG. 1;
FIG. 5 illustrates a shunt that is included in the yoke of FIG. 1;
FIG. 6 illustrates field distribution functions V.sub.0 (Z) and H.sub.0 (Z) of the yoke of FIG. 1; and
FIG. 7 illustrates field distribution functions V.sub.2 (Z) and H.sub.2 (Z) of the yoke of FIG. 1.
DETAILED DESCRIPTION
In FIG. 1, a CRT 10 includes a screen or faceplate 11 upon which are deposited repeating groups of red, green and blue phosphor trios. CRT 10 is of the type A89FDT with a Super-Flat faceplate size 35V or 89 centimeter along a diagonal. The maximum deflection angle is 108.degree.. The distance from the yoke reference line to the inside of the screen at the screen center, referred to as the throw distance, is 366 millimeter. The faceplate 11 has an aspect ratio of 4:3.
The contour of the inner surface of the faceplate 11 is defined by the following equation. ##EQU1## where: Z.sub.c is the distance fr
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Azzi Nacerdine
Masson Olivier
Henig Sammy S.
Laks Joseph J.
Patel Vip
Thomson Tubes & Displays S.A.
Tripoli Joseph S.
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