Automatic gain and offset control of a video decoder analog front end

摘要

A digital control technique for automatically obtaining lock on an analog video signal, and identifying the sync tip and back porch levels, by adjusting gain and offset. Pixel samples for each scan line are obtained from the output of an analog-to-digital converter (112) and fed back to a microprocessor (120) running a control program which provides digital control of gain and offset. After gain and offset are adjusted to obtain lock, a fine adjustment mode is entered during which gain and offset are adjusted to obtain the desired sync tip height and back porch levels. <IMAGE>