Automatic convergence adjustment system with the capacity to modify test

Abstract

Apparatus and method for performing convergence calibration in a system that uses multiple beams to generate a video display on a screen. A photosensor is exposed to first and second distinct convergence test patterns which have illuminated areas that cover approximately first and second halves of the photosensor, respectively. For each beam, first and second output signals are generated by the photosensor when the first and second test patterns are generated, respectively, and alignment is determined on the basis of the output signals. The test patterns are selected in such a manner as to reduce the dynamic range requirement for the A/D converter(s) that digitize photosensor output signals. Optionally, measurement resolution is enhanced by varying test pattern density in accordance with the A/D converter input signal level so as to maintain a generally constant A/D converter input level. This approach optimizes A/D converter resolution, thereby enhancing measurement resolution even when CRT and photosensor characteristics vary. Test pattern density may be reduced by generating a segregated test pattern.