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A Technique for Eliminating Jitter on CRT Displays

IP.com Disclosure Number: IPCOM000110483D
Original Publication Date: 1992-Nov-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 1 page(s) / 50K

Publishing Venue

IBM

Related People

Howard, WE: AUTHOR

Abstract

One problem affecting the image quality of cathode ray tube (CRT) displays is jitter, the movement of the image about its intended positions. This caused disturbances of the eye at low frequency and blurring of the image at high frequency. While this is sometimes caused by power supply problems, such jitter can be corrected by good design. A more difficult problem is the jitter caused by stray magnetic fields from other equipment. This cannot always be accommodated in the design of a CRT terminal. For instance, high quality monitors incorporate magnetic shields in the vicinity of the gun and yoke, but the shielding may not be adequate, and shielding the region of vacuum near the faceplate is impractical.

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A Technique for Eliminating Jitter on CRT Displays

      One problem affecting the image quality of cathode ray tube
(CRT) displays is jitter, the movement of the image about its
intended positions.  This caused disturbances of the eye at low
frequency and blurring of the image at high frequency.  While this is
sometimes caused by power supply problems, such jitter can be
corrected by good design.  A more difficult problem is the jitter
caused by stray magnetic fields from other equipment.  This cannot
always be accommodated in the design of a CRT terminal.  For
instance, high quality monitors incorporate magnetic shields in the
vicinity of the gun and yoke, but the shielding may not be adequate,
and shielding the region of vacuum near the faceplate is impractical.

      What is proposed here is a system of active compensation for
stray magnetic fields.  By having one or more sensors of magnetic
field, each of which detects independently the vertical and
horizontal components of the fields, one can generate correction
signals to be fed to the horizontal and vertical deflection coils
such that the effect will be to cancel the influence of the stray
external field and eliminate or reduce the jitter.

      Magnetic field detectors, for example, coils wound on high
permeability material, could be placed so as to detect both vertical
and horizontal components perpendicular to the beam direction.
Multiple sets of detectors might be used to better estimate the
...