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

Claim 1

An apparatus for writing information in a disc-shaped optically readable recording medium which comprises a substrate provided with a radiation-sensitive information layer and with information areas arranged in accordance with a spiral or concentric track pattern, which areas alternate with synchronization areas in each of which the address of the associated information area is recorded in an optically detectable manner, which apparatus comprises a light source, a first optical system for directing a first light beam to the information areas, a write circuit with modulation means for modulating the first light beam in order to record digitally coded information of fixed bit frequency in the information areas, a first detector for the detection of the radiation of the first light beam which is reflected or transmitted by the record carrier, and a read circuit for decoding the radiation detected by the first detector in order to read the information recorded in the synchronization areas, characterized in that the apparatus is adapted to write information in a record carrier whose synchronization areas and information areas exhibit an optically detectable periodic track modulation, of a frequency at which the power spectrum of the information to be recorded substantially exhibits a zero point, for generating a clock signal at least during recording, and that the apparatus comprises a second optical system for projecting a second light beam onto the track pattern on the record carrier behind the first light beam, a second detector for detecting the radiation of the second light beam which is reflected or transmitted by the record carrier, a first and a second band-pass filter tuned to the frequency corresponding to the periodic track modulation, the first and the second band-pass filter being connected in series with the first and the second detector respectively, a first adjustable delay network with a control input, an input and an output, of which the input is coupled to an output of the second band-pass filter, and on the output of which a clock signal is available for synchronization of the write circuit, a phase comparison circuit having a first and a second input and an output, of which the first input is connected to an output of the first band-pass filter, of which the second input is connected to the output of the delay network and of which the output is ccnnected to the control input of the delay network via switching means for adjusting the time delay of said delay network in such a way that the signal on the output thereof is in phase with the signal on the output of the first band-pass filter, and control means for closing the said switching means when the first beam scans synchronization areas and for opening said switching means when the first beam scans information areas.

Claim 2

An apparatus for writing information in a disc-shaped optically readable recording medium which comprises a substrate provided with a radiation-sensitive information layer and with information areas arranged in accordance with a spiral or concentric track pattern, which areas alternate with synchronization areas in each of which the address of the associated information area is recorded in an optically detectable manner, which apparatus comprises a light source, a first optical system for directing a first light beam to the information areas, a write circuit with modulation means for modulating the first light beam in order to record digitally coded information of fixed bit frequency in the information areas, a first detector for the detection of the radiation of the first light beam which is reflected or transmitted by the record carrier, and a read circuit for decoding the radiation detected by the first detector in order to read the information recorded in the synchronization areas, characterized in that the apparatus is adapted to write information in a record carrier whose synchronization areas and information areas exhibit an optically detectable periodic track modulation, of a frequency at which the power spectrum of the information to be recorded substantially exhibits a zero point, for generating a clock signal at least during recording, and that the apparatus comprises a second optical system for projecting a second light beam onto the track pattern on the record carrier behind the first light beam, a second detector for detecting the radiation of the second light beam which is reflected or transmitted by the record carrier, a first and a second band-pass filter tuned to the frequency corresponding to the periodic track modulation, the first and the second band-pass filter being connected in series with the first and the second detector respectively, a first adjustable delay network with a control input, an input and an output, of which the input is coupled to an output of the second band-pass filter, and on the output of which a clock signal is available for synchronization of the write circuit, a phase comparison circuit having a first and a second input and an output, of which the first input is connected to an output of the first band-pass filter, of which the second input is connected to the output of the delay network and of which the output is ccnnected to the control input of the delay network via switching means for adjusting the time delay of said delay network in such a way that the signal on the output thereof is in phase with the signal on the output of the first band-pass filter, and control means for closing the said switching means when the first beam scans synchronization areas and for opening said switching means when the first beam scans information areas.