Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Patent
1992-04-27
1994-07-05
O'Shea, Sandra L.
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
313413, 313414, 313440, 313458, 313448, H01J 2970
Patent
active
053270444
ABSTRACT:
An electron gun for a 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 yoke for simultaneous focusing and deflection of the electron beam on the CRT's display screen. The deflection lens includes a first 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 electrode disposed either on or immediately adjacent to the inner surface of the CRT's frusto-conical funnel portion intermediate the magnetic deflection yoke and the CRT's display screen. By positioning the CRT's focus lens within the deflection field, the deflection center of the beam 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. The coincidence of the beam focus and deflection regions reduces beam "throw distance" (field-free zone) resulting in a corresponding reduction in beam magnification and space charge effect and improved beam spot on the CRT's display screen. Positioning a focus electrode on the CRT's neck or funnel portion increases the equivalent diameter of the main focus lens which reduces the lens spherical aberration effect on the beam, while co-locating the beam focus and deflection regions also allows for shorter CRT length.
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A Wide-Deflection Angle (114.degree.) Trintron Color Picture Tube, Yoshida et al., IEEE Chicago Spring Conference on BTR, Jun. 12, 1973.
Chunghwa Picture Tubes Ltd.
O'Shea Sandra L.
Patel Ashok
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