US Patent 7352666 Focus-balance calibration method

Absolute time in pre-groove (ATIP) signals or gain amplification signals corresponding to the ATIP signals for auto gain control (AGC) are used for focus-balance calibration of a blank optical disc. The ATIP signals are obtained in response to the movement of an optical pickup head to different positions. The ATIP signals or gain amplification signals are referred to locate an optimal position of the optical pickup head relative to the blank optical disc, therby accomplishing the focus-balance calibration.