Browse Prior Art Database

Screen Corner Convergence Correction

IP.com Disclosure Number: IPCOM000044670D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

Beeteson, JS: AUTHOR

Abstract

In-line color CRTs used in display systems require only low precision convergence correction. Parabolic convergence would be required for accurate correction over a whole screen but here a straight line approximation can be used to give correction only at the corners of the screen. The circuits disclosed may be added during manufacture without disturbing components such as neck hardware and without impact on yoke parameters such as purity and sensitivity. This disclosure makes use of the fact that precision yokes from suppliers give the required precision over most of the screen area, needing extra convergence (for certain applications) only in the screen corners. For example, a worst-case convergence error of less than 0.

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Screen Corner Convergence Correction

In-line color CRTs used in display systems require only low precision convergence correction. Parabolic convergence would be required for accurate correction over a whole screen but here a straight line approximation can be used to give correction only at the corners of the screen. The circuits disclosed may be added during manufacture without disturbing components such as neck hardware and without impact on yoke parameters such as purity and sensitivity. This disclosure makes use of the fact that precision yokes from suppliers give the required precision over most of the screen area, needing extra convergence (for certain applications) only in the screen corners. For example, a worst-case convergence error of less than 0.3 mm is easily obtainable over 90% of the screen area, while the corner convergence error may go out to less than 0.5 mm. With this kind of performance it is only necessary to add a maximum of 0.25 mm corner correction to achieve a final error of less than 0.3 mm all over the screen. This essentially is a 1-bit corner convergence requirement, i.e., a system that provides a single increment of Å 0.25 mm in the corner. Because the correction is so low, and because it is provided only in a small part of the screen, relatively inefficient convergers can be used. The inefficiency of these designs is not important, because the low convergence requirement still keeps total powers low. The advantage is that these types of converger can be designed to "bolt-on" without requiring any existing neck hardware to be removed, and without requiring any yoke redesign - because yoke fields are not disturbed. With only a 1-bit corner correction needed, the parabolic waveform can be provided by a coarse linear approximation, so simplifying the waveform generation. Also, a 1-bit correction system can be implemented using switches rather than potentiometers. The correction can be extended to digital control, but in view of the small correction needed, this hardly seems wo...