Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
2000-04-11
2001-07-24
Dinh, Tan (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S275400
Reexamination Certificate
active
06266318
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to CLV (Constant Linear Velocity)-type recordable optical disks having track wobbles and apparatus for recording desired information onto such optical disks, and more particularly to a technique of minimizing unwanted cross-talk between wobble signals from adjoining tracks.
In recordable optical disks based on CD standards, such as CD-R (CD-Recordable) and CD-RW (CD-Rewritable) media, a plurality of tracks are previously formed as guide grooves, each of which wobbles typically at a fixed frequency of 22.05 kHz and has recorded thereon address (ATIP: Absolute Time In-Pregroove) information, indicative of absolute positions in the track, in FM-modulated form. The track wobbles are used as detection signals for disk rotation control at the time of recording on the optical disk, and are also used to generate reference clock pulses for the recording. Further, wobble signals detected from the optical disk during the recording are FM-demodulated to acquire the address information.
Further, in DVD-R (Digital Versatile Disk-Recordable) media, tracks are previously formed as grooves each wobbling typically at a fixed frequency of 140 kHz without modulation. Address information is recorded as pre-pits in lands (between the grooves). In this case too, the track wobbles are used as detection signals for disk rotation control at the time of recording on the disk.
In recording desired information onto such optical disks with the track wobbles, however, wobble signals from adjoining tracks tend to be detected as cross-talk signals. Particularly, with high-density optical disks, the cross-talk would occur in a considerably great amount because the track pitch is reduced relative to the size of a light spot irradiated onto the disk. With the CLV (Constant Linear Velocity)-type disks, the wobble signals, detected by the push-pull scheme, would be greatly modulated in both amplitude and phase by the cross-talk signals, resulting in beat signals. Thus, in the case where the address information is recorded in the track wobbles, the phase modulation by the cross-talk causes the address information to jitter, which would prevent accurate data-write linking. These jitters also lead to jitters in the recording reference clock pulses generated from the wobble signals, which would also prevent accurate data-write linking and degrade the quality of recording signals.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a recordable optical disk and apparatus for recording information onto the optical disk which can minimize influences of cross-talk between wobble signals from adjoining tracks to thereby substantially eliminate phase modulation of the wobble signals.
Explanation is given below about influences of cross-talk between wobble signals from adjoining tracks in recording/reproduction to/or a CLV (Constant Linear Velocity)—type optical disk having track wobbles.
(1) Definition of Variables and Constants:
Principal variables and Constants are defined as follows:
Tp: track pitch;
&lgr;: wavelength of track wobbles;
&ohgr;o: angular frequency of the track wobbles (wobble frequency fo=2&pgr;&ohgr;o)
Tc: time required to trace one round of an nth track;
rn: radial distance of the nth track from the center of the disk when
t=Tc/2; w=2&pgr;Tp/&lgr;,
namely, a difference in the number of wobble waves between adjoining tracks (fraction); and
&agr;=w&lgr;/ 2&pgr;rn=Tp/rn
(2) Calculation of Relative Angular Frequency of Wobble Waves:
Here, relative angular frequencies of the wobble waves in two tracks adjoining a particular track (nth track) on both sides of the particular track are calculated. First, let's consider a difference in the number of the wobble waves in one complete round between the tracks. Using the number of the wobble waves in one complete round of the nth track, Wn=2&pgr;rn/&lgr;,
the numbers of the wobble waves in the two adjoining (n+1)th and (n−1)th tracks can be expressed as follows:
(n+1)th track: Wn+w (n−1)th track: Wn−w
Then, respective periods of the wobble waves in the two adjoining (n+1)th and (n−1)th tracks relative to that of the nth track is determined. Because the period of the wobble waves in the nth track can be evaluated by dividing the time required for tracing one complete round of the nth track by the number of the wobble waves, the periods of the wobble waves in the adjoining (n+1)th and (n−1)th tracks can be computed as follows:
(n+1)th track: Tc/(Wn+w) (n−1)th track: Tc/(Wn−w)
Thus, the angular frequencies of the wobble waves in the two adjoining (n+1)th and (n−1)th tracks relative to that of the nth track can be determined as follows, using &ohgr;o:
(
n
+1)th track: 2&pgr;(
Wn+w
)/
Tc =
2&pgr;{1+(
Tp/rn
)}
fo=
(1+&agr;) &ohgr;o
(n−1)th track: 2&pgr; (
Wn−w
)/
Tc =
2&pgr;{1+(
Tp/rn
)}
fo=
(1−&agr;) &ohgr;o
(3) Calculation of Wobble Waves:
Now that the relative angular frequencies of the wobble waves in the two tracks adjoining the particular track (nth track) on both sides of the particular track have been calculated in the manner mentioned at item (2) above, mathematical expressions indicative of the individual wobble waves are evaluated in the following manner.
If the wobble waves in the nth track (actual wobble waves) is expressed by
Yn=
cos (&ohgr;
o t
)
,then the wobble waves in the (n+1)th and (n−1)th tracks can be expressed as follows:
(n+1)th track: cos {(1+&agr;) &ohgr;o t+&phgr;n+1}(n−1)th track: cos {(1−&agr;) &ohgr;o t+&phgr;n−1}
Note that some relationships based on the following boundary conditions exist between the wobble waves of the nth track and the wobble waves of the (n+1) and (n−1) tracks:
(a) The wobble waves in the nth track and (n+1)th track connect with each other continuously at a time point t (=Tc) of the former, i.e., at a zero time point t (=0) of the latter.
(b) The wobble waves in the nth track and (n−1)th track connect with each other continuously at a zero time point t (=0) of the former, i.e., at a time point t (=Tc) of the latter.
Thus, the following can be given:
from item (a) above, cos {(
1+&agr;) &ohgr;o
·0+&phgr;n+1
)=cos (&ohgr;o Tc),
and
from item (
b
) above, cos {(1−&agr;) &ohgr;o
Tc+&phgr;n
−1)=cos (&ohgr;o•0)
Solving these give
&phgr;n
+1=4&pgr;
2
rn/&lgr;,
and
&phgr;n
−1=−(1−&agr;) 4&pgr;
2
rn/&lgr;
If &phgr;=4&pgr;
2
rn/&lgr;, then &phgr;n+1 and &phgr;n−1 can be expressed as follows:
&phgr;n
+1=&phgr;
&phgr;n
−1=−(1−&agr;) &phgr;
From the foregoing, the wobble waves in the (n+1)th and (n−1)th tracks can be expressed as follows:
(n+1)th track: cos {(1+&agr;) &ohgr;o t+&phgr;}(n−1)th track: cos {(1−&agr;) &ohgr;o t−(1−&agr;)}
(4) Push-pull Detection Signal:
If one detection signal output from a four-quadrant photodetector is represented by “A+D” and the other detection signal is represented by “B+C”, a tracking error signal can be determined by “(A+D)−(B+C)”. Now that the mathematical expressions representing the wobbles of the adjoining tracks relative to those of the nth track have been determined at item (3) above, the push-pull detection signal “(A+D)−(B+C)” relative to the nth track can be determined as follows while taking into account influences of the adjoining tracks:
(
A
+D)−(
B
+C)=cos (&ohgr;
o t
)
−
K
cos {(1+&agr;)
&ohgr;o t+&phgr;}
−K′cos {(1−&agr;)
&ohgr;o t−
(1−&agr;) &phgr;}
&e
Honda Kazuhiko
Saito Minoru
Uchiyama Toshihito
Dinh Tan
Pillsbury & Winthrop LLP
Yamaha Corporation
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