HORIZONTAL PARALLELOGRAM CORRECTION COMBINED WITH HORIZONTAL CENTERING

摘要

An electron beam tends to slope downwardly as it is deflected horizontally to form a raster in a video display apparatus. The sloping of the beam can cause geometric errors in the raster, for example orthogonality and parallelogram errors. A raster correction circuit substantially offsets the downward slop of the electron beam by modulating a vertical deflection current (IV) with an induced horizontal-rate raster correction current, thereby substantially eliminating orthogonality and parallelogram errors in the raster. A raster correction transformer (41) utilizes a raster centering inductor (LC) for a primary winding, and a horizontal-rate centering current (IC) is magnetically coupled into the vertical deflection coils (LV1, LV2) to modulate the vertical deflection current.