MIDPOINT SEARCHING METHOD FOR TRACK, TRACK SEARCHING METHOD AND APPARATUS

摘要

PURPOSE: To realize a jumping scanning method for shifting a light beam at a high speed to a target track on a high density disc, e.g. an L/G disc. ;CONSTITUTION: The midpoint detecting method 15 employed for a disc 3 provided with a track having alternating polarities for tracking control. The disc 3 is irradiated, at first, with a light beam from a disc/head block 33. A tracking control block 34 detects positional shift of the optical beam from a track based on a light reflected on the disc 3 and produces a tracking error signal S1 corresponding to the positional shift. Subsequently, a difference circuit 23 produces the difference signal S28 of the tracking error signal S1. Since the positional shift is nullified at the midpoint between tracks on such disc 3, arrival of the light beam at the midpoint between adjacent tracks can be detected based on the polarity change of the difference signal S28.;COPYRIGHT: (C)1995,JPO