Apparatus for writing digital information in a disc-shaped optically readable record carrier.

摘要

An apparatus for recording optically detectable information in a record carrier (1) provided with information areas (9) arranged in accordance with a spiral or concentric track pattern, which areas (9) alternate with synchronization areas (8) in each of which the address of the associated information area is recorded in an optically detectable manner. Recording is effected with the aid of first modulated laser beam (16a), whilst a second beam (16b) is projected after the first beam for reading the recording. The track pattern has previously been provided with a periodic track modulation of a frequency at which the power spectrum of the information to be recorded substantially exhibits a zero point. The apparatus comprises a first and a second filter for filtering a signal corresponding to the track modulation out of the first or second laser beam reflected or transmitted by the record carrier, whilst in series with the second filter there is included a delay network (51), from which a synchronization signal is available. Furthermore, there is provided a phase comparator (52) which during reading of the synchronization areas determines the phase difference between the signals obtained by means of the first and the second filter and which controls the delay network (51) in such a way that the output signal of said delay network is in phase with the output signal of the first filter.