Browse Prior Art Database

Electronic Technique for Reducing Magnetic Interference in CRT Displays

IP.com Disclosure Number: IPCOM000121561D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Eagle, DJ: AUTHOR [+2]

Abstract

This disclosure describes circuits able to reduce the effect of magnetic interference on a CRT-based display product. They represent an alternative to the costly solution of mumetal shielding.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Electronic Technique for Reducing Magnetic Interference in CRT Displays

      This disclosure describes circuits able to reduce the
effect of magnetic interference on a CRT-based display product. They
represent an alternative to the costly solution of mumetal shielding.

      Stray AC magnetic fields on CRT-based displays produce jitter
which in extreme cases causes displays to become unusable, or less
severe cases cause stress and fatigue for the user.  This effect is
particularly noticeable in interlaced displays.  In a typical
environment, the most significant stray magnetic fields are caused by
the scan magnetic fields of adjacent displays or else by stray fields
from mains wiring in the building.  Fields from the latter source can
be very large.

      Stray scan fields are important when displays are placed in
close proximity to each other.  Where magnetic susceptibility is a
problem, mumetal shielding is used to screen the display from
external magnetic fields.  Mumetal is a material with magnetic
properties that make it suitable for screening.

      The disclosed electronic solution is to detect the AC magnetic
field in the area of the CRT and then to add a correcting signal to
the centering circuits (both horizontal and vertical) of the CRT.
Fig. 1 shows how this may be achieved.  In practice, there would be
two separate circuits, one to provide correction for vertical AC
fields and another to provide correction for horizontal AC fields.
The magnetic sensor may be a simple coil, or a semiconduc...