Browse Prior Art Database

Linearity Correction for CRT Horizontal Scan

IP.com Disclosure Number: IPCOM000047279D
Original Publication Date: 1983-Oct-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Ainscow, F: AUTHOR

Abstract

Non-linearity is inherent in line-scan circuits because of resistance and semiconductor voltage drops. Most methods of correction are inaccurate or costly. Two sources of non-linearity exist in a horizontal scan circuit: yoke resistance and voltage drops (exponential effect) and phase error in the S-correction waveform. Normally these effects both act in the same direction. By placing the active picture area to the left of the raster, and offsetting the raster to the right to bring the picture to the screen center, the two effects can be made to cancel out. In CRT displays which already have a raster shift control, this can be accomplished simply by changing the timing of the video vs. horizontal synchronization signals.

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Linearity Correction for CRT Horizontal Scan

Non-linearity is inherent in line-scan circuits because of resistance and semiconductor voltage drops. Most methods of correction are inaccurate or costly. Two sources of non-linearity exist in a horizontal scan circuit: yoke resistance and voltage drops (exponential effect) and phase error in the S- correction waveform. Normally these effects both act in the same direction. By placing the active picture area to the left of the raster, and offsetting the raster to the right to bring the picture to the screen center, the two effects can be made to cancel out. In CRT displays which already have a raster shift control, this can be accomplished simply by changing the timing of the video vs. horizontal synchronization signals. Non-linearity, g, is defined as the difference in width between the widest and narrowest character columns, expressed as a percentage of the average character width. In order to eliminate screen curvature effects, it has been assumed that the left-most and right-most character columns are widest and narrowest, respectively,

(Image Omitted)

The above expression for g is based on the assumption that the picture is centered in the raster. If this is not true, then a further component of non-linearity arises as a result of the deviation from center. Centering error, k, is defined as half the difference between the positive and negative peaks of deflection current, expressed as a percentage of the peak-to-...