Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1999-03-15
2001-07-31
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S044130, C369S047100
Reexamination Certificate
active
06269071
ABSTRACT:
The invention relates to an optical record carrier comprising a recording layer having substantially parallel tracks for recording user information in a pattern of optically detectable marks, the tracks being provided with control information.
The invention also relates to an apparatus for scanning such a record carrier.
When writing user information on a record carrier by means of a scanning radiation spot, it is in general desirable to know the position of the radiation spot on the record carrier. Since user information is not available on a virgin recordable record carrier, the position may be determined by reading control information stored comprising position information and stored on the record carrier, for instance in the form of embossed wobbled grooves or embossed pits of the record carrier. The control information may also comprise recording information, such as write or erase powers, which may be give as a function of the wavelength of the radiation spot and/or the write speed.
In general, a track is a line on the record carrier to be followed by a scanning device and which has a length of the order of a characteristic dimension of the record carrier. A track on a rectangular record carrier has a length substantially equal to the length or width of the record carrier. A track on a disc-shaped record carrier is a 360° turn of a continuous spiral line or a circular line on the disc.
A track may be a series of marks arranged along a line. A track may also be a groove and/or a land portion between grooves. A groove is a trench-like feature in a land portion of the recording layer, the bottom of the trench being nearer to or further away from the light-incident side of the record carrier. User information may be recorded on the lands or in the grooves. The embossed pits may be located on the lands or in the grooves.
A record carrier according to the preamble is known from U.S. Pat. No. 5,023,856, which has tracks provided with grooves. The position of the centre of the grooves is modulated in a direction transverse to the length direction of the groove. The wobble of the groove represents control information in the form of addresses indicating the position on the record carrier. A disadvantage of this known modulation scheme is the increase in crosstalk of control information between neighbouring tracks when the track pitch is reduced.
It is an object of the invention to provide a record carrier having a reduced crosstalk of the control information between neighbouring tracks.
This object is met if, according to the invention, the tracks of the record carrier are grouped in pairs of neighbouring tracks, the control information in both tracks of a pair being identical and the control information in tracks of different pairs being different. When scanning a track on the record carrier, the crosstalk of only one neighbouring track, i.e. the one having different control information, will affect the reading of the control information of the track being scanned. The crosstalk of the other neighbouring track, having identical control information preferably over its entire length, will hardly affect or even enhance the reading of the control information of the track currently being scanned. Preferably, at least 90% of the pairs on the record carrier have identical control information in the two tracks. Also, preferably at most 10% of the tracks of the record carrier comprise identical information.
The lower crosstalk improves the quality of the read signal that can be obtained from the control data on the record carrier. Hence, the amount of overhead of error-detection data and error-correction data added to the control data can be reduced on a record carrier according to the invention. The invention also allows a reduction of the track period, thereby increasing the user information storage capacity of the record carrier.
The tracks of the record carrier are preferably provided with wobbled longitudinal grooves, the control information being encoded in the wobbles of the grooves. The reading of user information and control information can now be separated.
The wobble is preferably a transverse displacement of the groove centre line. This allows the user information to be derived from the so-called central-aperture signal and the control information from the so-called push-pull signal. The pairing of the tracks according to the invention reduces the crosstalk of neighbouring tracks on the push-pull signal.
The wobbles of both tracks in a pair are preferably in antiphase. The amplitude of the push-pull signal obtained when reading a track is enhanced by the antiphase of the modulation of the groove of the neighbouring track.
The control information of substantially each track comprises preferably a marker pattern, allowing a determination of the position of the radiation spot along a track. In combination with the antiphase groove wobble, the marker may be used to determine which one of the two tracks in a pair is currently being scanned.
Another object of the invention is to provide an apparatus for scanning the optical record carrier according to the invention. The apparatus comprises an optical system for scanning the tracks by a radiation beam, a detector for detecting a radiation beam coming from the record carrier and a first circuit for deriving the user information from an output signal of the detector and a second circuit for deriving the control information from an output signal of the detector, and is characterized in that the apparatus comprises a third circuit for identifying the track of a pair being currently scanned from the control information. Since the control information in the two tracks of a pair is identical, the determination of the addresses from the control information does not suffice to identify the track currently being scanned. The apparatus according to the invention uses the control information to allow the identification of the correct track from the pair of tracks.
In a preferred embodiment the apparatus identifies the track by means of the track wobble, the phase of which is suitable for identification purposes, or from a comparison of control information stored in the track being currently scanned and a neighbouring track.
REFERENCES:
patent: 5023856 (1991-06-01), Raaymakers et al.
patent: 5235576 (1993-08-01), Shigemori
patent: 5321675 (1994-06-01), Ito et al.
patent: 6088307 (2000-07-01), Fushimi et al.
Drenten Ronald R.
Spruit Johannes H. M.
Van Den Enden Gijsbert J.
Van Vlerken Johannes J. L. M.
Belk Michael E.
Edun Muhammad
U.S. Philips Corporation
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