PROCEDURES AND COUNCIL FOR FOCUSSIONAL REGULATION.

摘要

A photodetector generates a focusing error signal (FE), a tracking error signal (TE) and an RF signal (RF), and a closed loop focusing servo circuit (10) is responsive to the focusing error signal applied thereto for focusing a light spot in position on an optical disc. The focusing error signal (FE) is detected synchronously with the tracking error signal (TE) in circuit blocks (22a,26a,26b) to produce a first periodic function signal. The focusing error signal (FE) is also detected synchronously with the RF signal (RF) in circuit blocks (22b,26c,26d) to produce a second periodic function signal. The tracking error signal (TE) is converted into a sine-wave signal having a predetermined amplitude in an AGC circuit (29a). The RF signal (RF) is converted into a cosine-wave signal having a predetermined amplitude in an AGC circuit (29b). The first periodic function signal is multiplied by the cosine-wave signal in a multiplier (28a) to produce a first component signal. The second periodic function signal is multiplied by the sine-wave signal in a multiplier (28b) to produce a second component signal. The first and second component signals are added in an adder (30) to produce a composed disturbance (W min (S)). The composed disturbance signal (W min (S)) is subtracted from the focusing error signal (FE) applied to the focusing servo circuit (10), thereby cancelling a disturbance (W(S)) superimposed on the focusing error signal (FE) applied to the focusing servo circuit (10).