DVR-7000
3.2 OUTLINE OF THE PRODUCT
3.2.1 DVD-RW Standard
The DVD-RW disc is a phase-change type, rewritable disc, as are
CD-RW and DVD-RAM discs. In playback of a phase-change type
disc, signals that are obtained through the change in reflectivity
between crystalline and amorphous states of the recording layer can
be read by the optical system employed in playback-only players.
Fig. 1 shows the structure of a DVD-RW disc. On a 0.6-mm-thick
polycarbonate molded substrate, an Ag-In-Sb-Te-alloy recording
layer, a protective layer, and a reflective layer are deposited.
DVD-RW uses CLV-type groove-recording format, and employs
the wobble groove & land pre-pit system, as does DVD-R, for
rotation control and address information during recording.
For this, so-called LPPs (Land Pre-Pits) are provided on certain
locations in the land areas, and the groove has a minutely undulating
structure called "wobble." The wobble is mainly used for rotation
control of the disc, and the frequency of the wobble signal is 8 times
that of the sync frame (8 cycles in one sync frame). LPPs are located
from the first to the third bits of the sync frame at the maximum
oscillation of the wobble, and these three bits and one ECC (error
correction code) comprise preaddress information.
Table 1 shows the basic specifications of DVD-RW. The
specifications, such as the form of the disc, 4.7 GB/side recording
capacity, 0.4
µ
m minimum pit length, 0.74
µ
m track pitch,
modulation method, and error-correcting code, are the same as those
of DVD-ROM. The recording and playback wavelengths are both
635/650 nm.
Protective layer (ZnS-SiO
2
)
Polycarbonate
Polycarbonate
2P Resin
Reflective layer(AL alloy)
Protective layer (ZnS-SiO
2
)
Recording layer (Ag-In-Sb-Te)
0.74
µ
m
Land Pre-Pit
Wobble
Groove
Land
Laser Beam
Fig. 1 Structure of DVD-RW disc
I t em
Specifications
of DVD-RW
Specifications
of DVD-ROM
Media Type
Phase Change
Re -writable
Read On
←
←
←
←
←
←
←
ly
Diameter
120/ 80mm
Pre- format
Wobble & LPP
Spindle Control
CLV
User Data Capacity
4.7G/1.46Gbytes
8.54Gbytes *
*
Recording Rate
1 1.08M bps
Record Wave
Length
6
6
35/650 nm
--------
--------
--------
--------
Playback
Wave
Length
35/650
nm
Write Power
15 mW
Track Pitch
0.74
µ
m
µ
m
Minimum Pit Length
0. 4
Data Modulation
8-16 Modulation
Reflectivity
18 – 30 %
45-85%*
18-30%**
Case or Cartridge
O ption
* Single Layer Disc
**
Du al Layer Disc
Table 1 Basic Specifications of DVD-RW
–
As to the characteristics after recording, the reflectivity is within
the standard value of a dual-type DVD-ROM, and the specifications
for modulation and jitter are the same as those of DVD-ROM format.
Moreover, as the tracking system during playback, phase-difference
tracking is employed, analogous to DVD-ROM.
