Digital System for Convergence of Three-Beam High-Resolution Color Data Displays

This paper describes a new method of generating and adjusting convergence waveforms required by a delta-gun cathode-ray tube for digital color data display applications to ensure that the primary color images produced by three guns are correctly registered with respect to each other. The display is divided into 480 zones, and a number of correction values are associated with each zone. Digital values are converted into convergence currents using special smoothing techniques to ensure that quantizing effects do not cause unacceptable image distortion. A microprogram is described which enables the total of 2016 digital correction values to be adjusted rapidly from the keyboard by a simple procedure using a crosshair adjustment pattern which is displayed sequentially at 13 positions on the screen. Special attention is paid to rounding errors which can occur during adjustment. Also accounted for in the waveform generation is the effect of phase delay between convergence coil current and its effect on the electron beams. Improvements necessary to the design of the radial and lateral convergence coil assemblies, normally found in the television industry, to reduce spot distortion and to improve sensitivity and temperature stability, are also presented. The design is realized in the IBM 3279 Color Display Station.