Dynamic electrostatic and magnetic focusing apparatus for a cathode ray tube
AssigneeDavid Sarnoff Research Center, Inc.
InventorRoger C. Alig
Life of this patent
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Abstract
Apparatus, associated with a cathode ray tube (CRT), containing both a electrostatic focusing lens and a magnetic focusing lens for maintaining the focus of an electron beam within the CRT at any location on a CRT screen. The apparatus applies a dynamic focusing voltage to an electrostatic focus grid of an electron gun and applies a dynamic focusing current to a magnetic focus coil. The focusing voltage and current vary in accordance with the position of the electron beam on the screen. As such, the electron beam remains focused upon the screen for all beam positions.
Claims11
Apparatus for focusing an electron beam in a cathode ray tube, said apparatus comprising:
- an electrostatic focus lens, circumscribing the electron beam, for generating an electric field having a magnitude that is responsive to a position of said beam on a screen of said cathode ray tube;
- a magnetic focus lens, circumscribing said electron beam, for generating a magnetic field having a magnitude that is responsive to a position of said beam on a screen of said cathode ray tube;
- and
- wherein, operating simultaneously, said magnetic and electrostatic lenses focus the electron beam at any location on the screen.
Apparatus for focusing an electron beam in a cathode ray tube, said apparatus comprising:
- an electrostatic focus lens, circumscribing the electron beam, for generating an electric field having a magnitude that is responsive to a position of said beam on a screen of said cathode ray tube;
- a parabolic waveform generator for producing a first parabolic voltage waveform for each scanline of the electron beam and for producing a second parabolic voltage waveform for each frame of scanlines, and a waveform combiner for combining said first and second parabolic waveforms to produce a composite waveform that is applied to said electrostatic lens to generate said electric field;
- a magnetic focus lens, circumscribing said electron beam, for generating a magnetic field having a magnitude that is responsive to a position of said beam on a screen of said cathode ray tube;
- a parabolic current waveform generator, connected to said magnetic lens, for producing a parabolic current waveform having an amplitude that varies in response to the vertical position of the beam on the screen;
- and
- wherein, operating simultaneously, said magnetic and electrostatic lenses focus the electron beam at any location on the screen.
Dependencies are inferred from the claim text.