1. Field of the Invention
The present invention relates to an overwrite type disk recording device which allows overwriting of data already recorded on a disk, and in particular to a disk recording device for data overwriting while ensuring synchronism between recorded data and overwritten recording data.
2. Description of the Related Art
A CD-RW (compact disk rewritable) drive is a known type of CD (compact disk) disk recording device for data overwriting onto a disk.
In a CD-RW drive, a recording position is detected with reference to a recorded address, referred to as ATIP (Absolute Time in Pre-groove), which has been FM-modulated into a wobble of 22.05 kHz of a pre-groove formed on a blank disk.
In a typical CD-RW, recording data to be recorded onto a disk and a sub-code contained in recording data are synchronism with a synchronous signal of an ATIP.
Synchronism between a synchronous signal of an ATIP and that of a sub-code, however, may be impaired due to irregular disk turning and so on, even though a resultant displacement between the synchronous signals is tolerable within a predetermined range.
In particular, with a CD-RW drive capable of high speed writing, such displacement is likely to occur as acceleration or deceleration torque of a spindle motor are more likely to be shorted.
In recording a signal onto a disk while referring to an ATIP, such a displacement in synchronism between synchronous signals of an ATIP and of a sub-code would hinder establishment of synchronism between already recorded data and overwriting recording data.
In general, overwriting in a packet-writing method does not require synchronism established between recorded data and overwriting recording data. However, as all CD-ROM drives may not be able to employ the packet-write method, a track-at-once method or a session-at-once method may be preferred for data recording in view of compatibility with a CD-ROM drive.
In addition, a packet-writing method requires as many as seven link blocks to be formed for packet connection, and thus may waste disk storage capacity.
In view of the above, for data overwriting onto a disk, a method for data writing without leaving a trace of rewriting would be preferred if that would be possible, in view of compatibility with a CD-ROM and effective utilization of disk storage capacity. Thus, a disk recording device capable of data overwriting while leaving no trace, or only a subtle trace, of rewriting is desired.
For data rewriting while leaving no or a subtle trace, overwriting of recording data must have precise synchronism with the data then recorded on the disk. Otherwise, the newly recorded data might be written beyond a defined recording region, which may cause problems of partial damaging of recorded data beyond the region, or incomplete writing of a prescribed amount of overwriting recording data with partly cut-off toward the end thereof.
The present invention is directed to achieving precise writing of recording data to overwrite corresponding recorded data on a disk within a defined recording region while ensuring synchronism between the recording and recorded data.
According to the present invention, in data overwriting, recorded data is read from a disk, and a bit clock is reproduced from the read recorded data in a clock reproduction circuit so that data is processed in an encoder in synchronism with the reproduced bit clock. Recording data is accordingly output from the encoder in synchronism with the data recorded in the disk thereby synchronizing the overwriting recording data with the recorded data.
With this arrangement, in which recording data is output from an encoder in synchronism with the recorded data in a disk and written for overwriting the disk in synchronism with the recorded data, the overwriting data can be written precisely within a defined recording region. This can prevent problems such as partial damaging of the recorded data due to overwriting beyond a defined recording region, or incomplete writing of a prescribed amount of overwriting data.
Consequently, overwriting recording data can be written onto a disk while leaving no trace, or only a subtle trace, of rewriting on the disk in a boundary, and the overwriting data written on the disk can be reproduced successive to the preceding recorded data to help ensure compatibility with a typical CD-ROM drive.
Further, a bit clock can be readily reproduced even during an overwriting operation, when the bit clock is reproduced from the recorded data read by a preceding beam prior to a main beam.
Still further, a constant output can be maintained with the preceding beam even during a recording operation using a main beam when the preceding beam is emitted from a second light source, which is different from a light source emitting the main beam. This ensures reliable reproduction of a bit clock.