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Self Shielded Linearity Coil

IP.com Disclosure Number: IPCOM000122745D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 48K

Publishing Venue

IBM

Related People

Kohlrausch, W: AUTHOR

Abstract

A linearity coil, as used in deflection circuits of Video Display Terminals (VDTs), corrects a non-linearity of the image that is caused by the unavoidable resistance of the deflection coils. It does so by introducing an opposing non-linear inductance into the yoke current path, and it is customized for each deflection system.

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Self Shielded Linearity Coil

      A linearity coil, as used in deflection circuits of Video
Display Terminals (VDTs), corrects a non-linearity of the image that
is caused by the unavoidable resistance of the deflection coils.  It
does so by introducing an opposing non-linear inductance into the
yoke current path, and it is customized for each deflection system.

      It is commonly built on a rod inductor, topped by a permanent
magnet, because that structure has been least costly for achieving
the desired characteristic of L = f(i yoke).  Because DC and AC
magnetic fields close through the surrounds, this coil is the source
of convergence aberrations as field lines interfere with beam
deflection. Furthermore, it is a troublesome source of VLF fields
(Very Low Frequency fields) that can clearly be measured outside of
VDTs, and for which suppression is required per Swedish VLF
Standards.

      This disclosure describes a structure that contains the DC and
AC fields within itself and thereby will not cause convergence and
VLF problems (Fig. 1).  The flux concentrating return path through
ferrite can be made from U-cores, E-I cores, pot cores, or other
shapes.

      The important property of such structure is that a
nonsaturating path (A), a saturating section (B), a permanent magnet
(C), an air gap (D), and a coil (E) are arranged in such way that
the flux (o) generated in coil (E) by deflection yoke current (Iy)
always has non-saturating section (A) as...