Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-02-15
2004-06-29
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S059230, C369S124070, C375S368000, C360S051000
Reexamination Certificate
active
06757231
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for identifying erroneous detection of a pre-pit synchronization bit at the time of detecting pre-pits from readout signals of an optical disc (disk) having the pre-pits formed therein in a given signal format and a method for identifying stability/instability of pre-pit synchronization bit detection by use of the identified result of the erroneous detection identifying method, as well as electric circuits for implementing these methods. In particular, the present invention concerns a technique for identifying the erroneous detection of a pre-pit synchronization bit and identifying the stability/instability of pre-pit synchronization bit detection with high accuracy.
Recordable optical discs, such as recordable CDs like CD-R and CD-RW discs and recordable DVDs like DVD-R, DVD+RW, DVD-RAM and DVD-RW, have recording tracks wobbling in predetermined cycles. Generally, during recording, a wobble signal is extracted out of a push-pull signal generated by receiving a reflection of a recording laser light beam off the optical discspecifically, the push-pull signal is indicative of a difference between outputs from light-receiving elements positioned symmetrically about the longitudinal axis of the recording track. Spindle motor control, reproduction of address information, generation of reference clock pulses for a recording signal, etc. are performed on the basis of the extracted wobble signal. Where the optical disc has pre-pits, i.e. marks previously formed intermittently along the recording track in a laterally displaced relation to the centerline of the track, pre-pit signals (i.e., signals indicative of detected pre-pits) are extracted out of the push-pull signal, and the generation of reference clock pulses for a recording signal, reproduction of address information, spindle motor control, etc. are performed on the basis of the extracted pre-pit signals.
Examples of the known pre-pit signal formats include one in which synchronization bits are placed at predetermined locations in every other one of a plurality of track-constituting unit sections arranged in the longitudinal direction of the track, and in which in each regions of the track where the synchronization bit substantially overlaps with the synchronization bit of an adjacent track in a radial direction of the optical disc, the recorded location of the synchronization bit is displaced by one track-constituting unit section in the longitudinal direction of the track. As a good example of such a pre-pit signal format, the pre-pit signal format of a DVD-R disc is explained below with reference to FIG.
2
. As shown, the recording track (groove track) of the DVD-R disc wobbles at a predetermined frequency 140 kHz, and each length equal to eight waves of the wobbling recording track is set as a track-constituting unit section (sync frame) for recording information. 26 such sync frames constitute a sector and 16 sectors constitute an ECC block, so that information is recorded onto the optical disc ECC block by ECC block. The 26 sync frames constituting a sector consist of even-numbered frames (frame
0
, frame
2
, . . . , frame
24
) and odd-numbered frames (frame
1
, frame
3
, . . . , frame
25
). In a land track adjacent to the outer edge of the groove track, there are formed land pre-pits in such a manner that the land pre-pits occur once for every two sync frames in correspondence with the groove track. The land pre-pits are normally recorded in the even-numbered sync frames; however, in each region where the land pre-pits in the outer land track substantially overlap radially with similar land pre-pits in another land track adjacent to the inner edge of the groove track, the land pre-pits of the outer land track are formed in the odd-numbered sync frame immediately following the even-numbered sync frame in question (i.e., at a location displaced by one sync frame in the longitudinal direction of the track). so as to avoid undesired interference between the radially overlapping land pre-pits of the inner and outer land tracks (i.e., between radially adjoining land tracks). Each set of the land pre-pits thus formed on the land track consists of a total three bits (i.e., “b2”, “b1” and “b0” bits in the head-to-rear direction), each formed at one of predetermined phase angle locations of the leading wobble wave within the sync frame. In TABLE 1 below, there are shown pre-pit codes constituted by various combinations of logical values at the “b2”, “b1” and “b0” bits and pre-pit information represented by the pre-pit codes. Note that a logical value “1” of the bit indicates that a land pre-pit is formed at the corresponding location on the disc while a logical value “0” of the bit indicates that no land pre-pit is formed at the corresponding location on the disc.
TABLE 1
Information
b2
b1
b0
sector sync. code (location in
1
1
1
even-numbered frame)
sector sync. code (location in
1
1
0
odd-numbered frame)
data “1”
1
0
1
data “0”
1
0
0
The leading “b2” bit in the pre-pit code is a synchronization signal of the corresponding sync frame, which is invariably present at the head of each sync frame having pre-pits formed therein. The “b1” bit is a signal indicating whether the corresponding pre-pit information is a sector synchronization code or data (information such as position information), and this b1 bit takes the value “1” if the corresponding pre-pit information is a sector synchronization code but takes the value “0” if the corresponding pre-pit information is data. Further, in the case of the sector synchronization code, the “b0” bit is a bit signal indicating whether the recorded location of the pre-pits is in an even-numbered sync frame or in an odd-numbered sync frame. In the case of the data, the “b0” bit represents contents of the data, i.e. data of one bit constituting information such as position information. Where the sector synchronization code is recorded in an even-numbered sync frame, it is formed in the leading (i.e., 0th) sync frame of the sector, while the sector synchronization code is recorded in an odd-numbered sync frame, it is formed in the second-from-head (i.e., 1st) sync frame of the sector. Namely, in every sector on the track of the optical discsuch a sector synchronization code is formed in either the leading (0th) sync frame or the second-from-head (i.e., 1st) sync frame.
During recording or reproduction on the optical disc, pre-pit signal components can be determined as projecting beyond peak points of wobble signal components contained in a push-pull tracking error signal, as shown in FIG.
3
. Thus, the pre-pit signal can be detected, for example, by comparing a tracking error signal with an appropriate threshold value, as also shown in FIG.
3
. By decoding the thus-detected pre-pit signal, there can be obtained information, such as address information, sync frame synchronization information (b
2
=“1”) and sector synchronization information (b
2
, b
1
, b
0
=“1, 1, 1” or “1, 1, 0”).
As noted earlier, the synchronization bit of the pre-pit code is normally placed in every other track-constituting unit section appearing along the longitudinal direction of the track, it is recorded in a track-constituting unit section immediately following the normal track-constituting unit section in such a region of the track where the synchronization bit in the land track substantially overlap radially with the synchronization bit in an inner adjacent track. Thus, the synchronization bit sometimes occurs in two successive track-constituting unit sections or no synchronization bit sometimes occurs in two successive track-constituting unit sections. As a consequence, when the synchronization bit has been detected in two successive track-constituting unit sections, it is very difficult to determine whether the successive synchronization bits are correctly-detected synchronization bits, or erroneously-detected synchronization bits despite loss of the predetermined synchronization. Similarly, when no synchronization bit has
Pillsbury & Winthrop LLP
Tran Thang V.
Yamaha Corporation
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