Focus capture for optical disc system including detection of quad sum signal to close focus

摘要

A system for focus capture wherein a lens is initially retracted to the bottom of its stroke, moved up to the top of its stroke while looking for the maximum Quad Sum signal, then moved back away from the disc while the system looks for the total light coming back from the disc to be above one-half of the peak value it measured, searching for the first zero crossing and, after the Quad Sum is over one-half amplitude, closing focus.