Servo apparatus for error reduction for optical reproduction systems

摘要

The system, when for an optical disc (10), includes a first servo loop (42, 44, 46, 60, 52, 32) to maintain, in the presence of eccentricity in a rotating disc, a light beam on a selected data track on a surface (20) of the disc (10), and a second servo loop (40, 48, 50, 60, 54, 31) to maintain an objective lens (33) at the proper distance from the disc surface. Both servo loops share a common error reduction circuit (60). The error reduction circuit includes a tracking memory and a focus memory which store at locations thereof the expected (historical) error words whose values represent earlier-measured tracking and focus position errors, respectively, for a large number of locations around the disc. The values expressed in stored error words are combined using an arithmetic logic unit with currently-measured error values into words representing computed error values. The computed error values are used in the respective servo loops to reduce the measured errors. The memories are updated by storing in their locations the computed words containing values of tracking and focus corrections for respective locations around the disc during every disc revolution. IMAGE