Electric lamp and discharge devices: systems – Cathode ray tube circuits – Plural concentrating – accelerating – and/or de-accelerating...
Patent
1992-04-27
1993-04-20
Blum, Theodore M.
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Plural concentrating, accelerating, and/or de-accelerating...
315382, H01J 2946, H01J 2956
Patent
active
052045854
ABSTRACT:
An electron gun for a color cathode ray tube (CRT) includes a cathode, a low voltage beam forming region (BFR), and a high voltage deflection focus lens disposed in the beam deflection region of the CRT's magnetic deflection yoke for simultaneous and coincident focusing and deflection of the electron beams on the CRT's display screen. The deflection lens includes a first focus electrode either in the form of a cylindrical metal grid or a conductive coating disposed on the inner surface of the CRT's neck portion and extending into the magnetic deflection field. The deflection lens further includes a second focus electrode either in the form of a conductive coating or a frusto-conical metallic grid disposed on or immediately adjacent to the inner surface of the CRT's funnel portion intermediate the magnetic deflection yoke and the CRT's display screen. By positioning the electron gun's deflection focus lens within the deflection field, the deflection center of the electron beams is disposed within the focal point of the focus lens permitting the focus lens to operate as a deflection lens to not only focus the beam, but also increase beam deflection sensitivity. By reducing beam "throw distance" (fieldfree zone) and realizing a corresponding reduction in beam magnification and space charge effect, improved electron beam spot on the display screen is also provided. The focus lens increases the equivalent diameter of the main focus lens which reduces lens spherical aberration effect on the beams, while co-locating the beam focus and deflection regions also allows for shorter CRT length.
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