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 provided with information areas arranged in accordance with a spiral or concentric track pattern, which areas alternate with synchronization areas each containing the address of the associated information area. Recording is effected with a first modulated laser beam, while a second beam is projected after the first beam for reading the recorded information. 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 has a substantially zero value. The apparatus comprises a first and a second filter for filtering a signal corresponding to the track modulation out of the signal derived by detecting the first or second laser beam reflected or transmitted by the record carrier. In series with the second filter there is included a delay network from which a synchronization signal is available. Furthermore, there is provided a phase comparator which, during reading of the synchronization areas, determines the phase difference between the signals obtained from the first and the second filter and which controls the delay network in such a way that the output signal of the delay network is in phase with the output signal of the first filter.