Browse Prior Art Database

Electron Beam Spot Size Control for Multimode Monitors

IP.com Disclosure Number: IPCOM000112381D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Grant, G: AUTHOR [+4]

Abstract

Disclosed for multimode CRT monitors is a compensation method of de-focussing the CRT spot size to reduce the visibility of inter-line gaps when line spacing increases with lower line frequency modes. Spot size is controlled to meet ISO VDU image parameters. The solution is applicable to all raster scan monochrome and colour displays in addition to multimedia types.

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Electron Beam Spot Size Control for Multimode Monitors

      Disclosed for multimode CRT monitors is a compensation method
of de-focussing the CRT spot size to reduce the visibility of
inter-line gaps when line spacing increases with lower line frequency
modes.  Spot size is controlled to meet ISO VDU image parameters.
The solution is applicable to all raster scan monochrome and colour
displays in addition to multimedia types.

      To meet the ISO 9241 requirements for displays, certain
conditions are placed on the displayed image in terms of character
contrast and raster modulation.  For monitors with a wide range of
display resolutions, these ISO requirements will place a limit on the
range of raster lines that can be displayed whilst still being ISO
compliant.  The reason is that 'character breakup' will occur on
large displays with a small electron beam spot size when displaying a
low number raster lines.  The effect will be analogous to the IBM
logo which comprises 8 horizontal lines - the gaps between
horizontally adjacent lines is quite visible.  This raster modulation
is unacceptable for ISO compliant displays.

      A solution is that use be made of the intrinsic display
operating conditions to control the spot size (focus) of the electron
beam.  For multimode displays, the horizontal and vertical scan rates
are variable.  As the number of displayed lines of data is increased,
so the horizontal scan rate must increase for a given frame rate. ...