Patent ID: 6034364
Filing Date: 2000-03-07
Classification: G11B,H02K

Abstract:
In an optical disc system of the type having a focusing mechanism, a tracking mechanism, and a lens, the improvement comprising:means for impinging light upon a disc to be read;means for initially retracting the lens to the bottom of its stroke, for subsequently scanning up to the top of the lens stroke while searching for a maximum of a Quad Sum signal associated with light returning from the disc and for moving said lens away from the disc;means for monitoring light returning from said disc, and for determining, during said monitoring, when said Quad sum signal is above a predetermined value;digital processing means for processing a focus error signal, said digital processing means having a transfer function providing a frequency notch at the mechanical resonance of said means for moving said lens, said digital processing means further producing zero crossings corresponding to focus conditions;means for searching for a first of said zero crossing after said Quad sum signal exceeds said one-half of said maximum; andmeans for closing focus when said first zero crossing is detected.