Optical scanning device comprising a focus control system and integrated circuit for use in the focus control system.

摘要

An optical scanning device is disclosed which comprises a focus control system comprising an actuator (13) for moving the focus (P) of a scanning beam (8) relative to a recording layer (4) of a record carrier (2), a focus-error detection system (9, 14, 15, 16, 17) for generating a focus-error signal (FE), and a control circuit (26) for generating a first control signal (AS sec ) for the actuator (13). In order to ensure that the focus-control system locks in to the recording layer (4), the scanning device comprises a lock-in circuit (20). The lock-in circuit (20) comprises a signal generator (21, 23) for generating an additional control signal (AS min ) during locking-in of the focus-control system. An auxiliary circuit (21) then generates a first signal (AH) for an integrator (23) and the additional control signal (AS min ) is taken from the output of the integrator (23). A detection circuit (25) generates a detection signal (INFOCUS), which indicates that the actuator has reached the operating range (B) in which the focus-error signal is indicative of the focus error. The control circuit (26) is rendered operative in response to the detection signal (INFOCUS). Moreover, the integrator (23) is disconnected from the auxiliary circuit (21) and is connected to the output of the focus-error detection system (9, 14, 15, 16, 17) by means of a switch (22). After locking-in the integrator (23) and the control circuit (26) constitute a controller with an integrating action.