Composite-VGA encoder/decoder eases display upgrade

摘要

An older computer system fed RGB video and composite-synchronization signals through four 75Ω coaxial cables to an RGB color monitor 150 feet away. To upgrade it, the replacement VGA video cards could directly drive the 75Ω loads that the VGA monitors' internal terminations presented. However, the VGA standard uses separate horizontal and vertical positive-going synchronization signals. Adding an extra coaxial cable to the original cables to carry the separate synchronization signals presented a difficult and expensive proposition. An obvious solution would be to combine the separate synchronization signals into a composite format.