FOCUSING METHOD AND SYSTEM FOR FOCUS CAPTURE AND FOCUS CONTROL IN OPTICAL DISC SYSTEM INCLUDING DETECTION OF QUAD SUM SIGNAL TO CLOSE FOCUS

摘要

ABSTRACT An optical disc system includes focusing and tracking mechanisms controlled byfeedback loops having electronic circuits for generating servo error signals. A digitallead/ag compensation circuit assembly includes a servo loop having a transfer functionand error signal. The circuit assembly includes a motor having a resonance frequency lessthan a predetermined sampling frequency and a compensation circuit for stabilizing theservo loop. The compensation circuit has a transfer function including a single lead andcomplex lag for producing a notch filter with a notch. This, function is formulated so thatthe notch occurs at approximately one half the predetermined sampling frequency therebyreducing amplitude of the resonance frequency in the servo loop transfer function, Alsoincluded are an isolator for vibration isolation and accommodation of thermal expansion,an oscillator with a tank circuit, an Improved focus capture system, and means foridentifying blank sectors in a storage medium.