Focus control device, and optical disc device

An optical disc device comprising:

• a rotation unit for rotating an optical disc having a thin film of a phase-change type recording material on which tracks are radially or concentrically formed at prescribed intervals, at a predetermined linear velocity;
• a focus actuator for varying the distance between the optical disc and an objective lens of an optical pickup;
• an objective lens driving unit having a tracking actuator for moving the objective lens in a direction perpendicular to the direction of tracks on the optical disc;
• abroad-band reproduction signal generator for generating, from a reflected light from the optical disc, a broad-band reproduction signal which is used for generating an RF signal, an address signal, and a wobble signal;
• a low-band reproduction signal generator for generating, from the reflected light from the optical disc, a low-band reproduction signal which is used for generating a servo signal;
• an RF envelope detector for, provided with a peak detector and a bottom detector, generating an RF envelope signal from the broad-band reproduction signal;
• a jitter detector for detecting a reproduction signal jitter from the broad-band reproduction signal;
• a wobble signal generator for detecting a wobble of a tracking groove of the optical disc from the broad-band reproduction signal, and binarizing the same to output a binary signal;
• an address detector for detecting the address information of the optical disc from the broad-band reproduction signal;
• a tracking controller for controlling the tracking actuator in accordance with the low-band reproduction signal;
• a land area focus learning unit for determining a first focus position in the land area of the optical disc in accordance with the RF envelope signal and the reproduction signal jitter;
• a groove area focus learning unit for determining a second focus position in the groove area of the optical disc in accordance with the RF envelope signal and the reproduction signal jitter;
• a switching area focus position calculation unit for determining a third focus position in an area where the land area and the groove area are switched;
• a switching signal generator for generating a switching signal whose polarity is inverted when a switching between the land area and the groove area is detected from the address information;
• a focus position controller for adjusting the focus of the optical pickup to the first focus position when the switching signal indicates the land area, while adjusting the focus of the optical pickup to the second focus position when the switching signal indicates the groove area, in accordance with the output signal of the wobble signal generator, the first focus position, the second focus position, the third focus position, and the switching signal;
• a focus controller for controlling the focus actuator of the optical disc on the basis of the low-band reproduction signal and the output signal of the focus position controller;
• and
• said focus position controller moving the focus position of the optical pickup so that it is located at the third focus position when the switching signal is inverted according to the switching between the land area and the groove area.