公开(公告)号：MY107468A

公开(公告)日：1995-12-31

申请号：MYPI19911799

申请日：1991-09-19

Applicant: IBM

Inventor： ALAN AUGUST FENNEMA ,  ROBERT ALAN KLEM

IPC: G11B7/00 ,  G11B7/09 ,  G11B7/095

Abstract: A FOCUS ACQUISITION SYSTEM (46-49, 56-58, 65-66, 70-76) INCLUDES PROVIDING A FOCUS OFFSET AND CHANGING THE OFFSET SYMMETRICALLY FOR EACH MEASUREMENT CYCLE. THE AMPLITUDES OF THE READBACK OR TRACKING ERROR SIGNAL ARE SENSED AND COMPARED. WHEN THE AMPLITUDES OF THE TRACKING ERROR OR READBACK SIGNAL IS DIFFERENT AT EACH OF THE OFFSETS, THEN A NEW MEASURMENT CYCLE IS PERFORMED AFTER CALCULATING A NEW OFFSET VALUE. THE PROCESS IS REPEATED UNTIL THE TEMPORARY MEASUREMENT OFFSETS RESULT IN READBACK AMPLITUDES THAT ARE SUBSTANTIALLY EQUAL. A BEST FOCUS IS THEN INDICATED AS BEING A POSITION IN WHICH SMALL DEFOCUSSING WILL NOT SUBSTANTIALLY DEGRADE THE QUALITY OF THE READBACK SIGNAL.