Optical disc apparatus having automatic gain control circuit of open loop type

摘要

An optical disc apparatus generates a tracking error signal and a focusing error signal for an objective lens. In addition, the apparatus generates a tracking sum signal or a focusing sum signal for the objective lens. The apparatus multiplies the sum signal by the tracking error signal and the sum signal by the forcing error signal. Corresponding to the results of multiplications, the apparatus moves the objective lens in the tracking direction and focusing direction.