Abstract:
An optical recording medium and a recording/reproducing method therefor to stably and accurately address a basic recording and/or reproducing unit (a sector or a frame) when a track pitch is decreased for recording of a large capacity of data. The general information (e.g., a variable frequency oscillator, a sector number, a sector type, and error detection information) of a corresponding sector is read from a header, which has physical pits between adjacent land and/or groove tracks, before recording or reproducing. The arrangement of the header is in the form of physical pits, with a sector structure where 2-kilobyte minimum recording units are included in a user area within a basic recording unit of 4 kilobytes, which thereby reduces overhead and facilitates the generation of a servo control signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims priority of Korean Application Nos. 99-14286 and 99-24296, Apr. 21, 1999 and Jun. 25, 1999 respectively, in the Korea Patent Office, the disclosures of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical recording medium, and more particularly, to an optical recording medium, and a recording/reproduction method therefor, in which a header, used for addressing, is disposed between adjacent land and/or groove tracks, a basic addressing unit having a first predetermined size is assigned, and a minimum recording unit having a second predetermined size is assigned. 
     2. Description of the Related Art 
     A mass recording capacity and high speed reproduction of optical discs is required for recording and/or reproducing high definition (HD) images. Accordingly, a multimedia technology of recording and/or reproducing a large quantity of information on and/or from a recording medium such as a rewritable or read only HD-digital versatile disc (DVD) is required. 
     Various methods have been suggested for satisfying the requirements of mass recording capacity and high speed reproduction. For example, the area of a disc or the rate of rotation may be increased. However, such methods are not practical since they require an increase in the sizes of a disc and a player and also result in increased production cost. Thus, it is preferable to increase the recording density per unit area of the disc, rather than increase the area of a disc at the rate of rotation. 
     The size of a recording laser spot is proportional to the laser wavelength and inversely proportional to the numerical aperture (NA) of an object lens. Accordingly, to increase the recording density per unit area of the disc, the laser wavelength should be decreased, or an object lens having a high numerical aperture should be used to decrease track pitch. 
     In such an optical disc, particularly, a recordable disc, a recording area for recording data in regular units is segmented into regular basic recording units (e.g., sectors or frames). In writing or reading data to or from an area which is a physically segmented basic recording unit, it is essential for an optical pick-up unit (hereinafter, referred to as a pickup) to move to the exact position of the corresponding area at high speed without error. 
     To allow a pickup to move to an exact position a header field in the optical disc is utilized. In a 2.6 gigabyte (GB) or 4.7 GB DVD-RAM, a header field for each sector is assigned 128 bytes. The information of the header field is written on the disc in the form of pre-pits during the manufacture of a substrate. The header field is composed of a variable frequency oscillator region for a phase locked loop (PLL), a physical identifier (PID) region to which a sector number is assigned, an ID error detection (IED) region for storing ID error detection information, and a postamble (PA) region for regulating modulation. A header field is appropriately disposed at the front portion of a sector. When a pickup accesses a desired position, a microcomputer (not shown), recognizing signals which are stored in the header field and picked up by the pickup, can detect the sector number and sector type of a sector corresponding to the accessed position and determine whether the sector is included in a land track or a groove track. Moreover, the microcomputer can perform servo control using the picked up signals. 
     Representative examples of the structures of conventional headers are shown in FIGS. 1A through 1D. “G” indicates a groove track, and “L” indicates a land track. In FIG. 1A, a header is located between adjacent land and groove tracks. In this structure, the track pitch is narrowed as the recording density increases, thus, crosstalk between adjacent tracks may occur. 
     In FIG. 1B, a single header is located at the boundary between a land track and a groove track. The single header can be used for a pair of land and groove tracks. This structure produces more advantageous signals than the structure of FIG. 1A since the width of a header of FIG. 1B is wider than the width of the header in the structure of FIG.  1 A. However, since the arrangement of headers is unbalanced, this structure is susceptible to a tracking offset (or margin). 
     In FIG. 1C, a header is located between adjacent groove and land tracks such that headers are not adjacent between the adjacent land and groove tracks. In this structure, crosstalk does not occur. However, servo control compensation cannot be achieved. Therefore, an additional servo control compensation method is required. 
     The structure of FIG. 1D is used in a DVD-RAM. Compared to the structure of FIG. 1C, a header is shifted by half of a track pitch. The structure of FIG. 1D compensates for the drawbacks of the structures of FIGS. 1A,  1 B and  1 C. However, since half of a header is offset from the other half of the header by one track pitch, the manufacture of this structure is more difficult compared to the other structures. For this reason, particularly in a 4.7 GB DVD-RAM having the structure of FIG. 1D, the signal characteristics (jitter) of first and second header fields may not be the same as those of third and fourth header fields. The content of the header field will later be described with reference to FIGS. 4A and 4B. 
     To provide mass storage capacity of HD image data, for example, 15-20 GB, a recordable area (user data area) needs to be increased by minimizing not only track pitch but also areas (overhead) other than a recording area. The size of header fields in a DVD-RAM is about 5% of the physical sectors of the DVD-RAM. To achieve high density recording, by decreasing the size of an overhead, a structure for decreasing header fields, that is, a structure in which a header field is located at the boundary between adjacent tracks as shown in FIGS. 1B and 1D, is necessary. However, as described above, in the structure of FIG. 1B, servo control compensation, including track offset, must be implemented. 
     FIGS. 2A through 2C show examples of a typical track structure. FIG. 2A shows a concentric circle track structure. FIG. 2B shows a double spiral track structure. FIG. 2C shows a single spiral track structure used in a DVD-RAM. Reference numeral  1  indicates a groove track, reference numeral  2  indicates a land track, and reference numeral  3  indicates a header assigned to each basic recording unit (here, a sector). 
     Particularly in the single spiral track structure of FIG. 2C, a land track can be distinguished from a groove track at a land/groove track transition position  4 , at which the land track transitions to the grove track or the groove track transitions to the land track, based on a detection of the land/groove track transition position signal and according to the arrangement of a header therein. 
     For discs having the single spiral track structure of FIG.  2 C and the header structures of FIGS. 1B,  1 C and  1 D, the header structures of the discs, at a position at which groove tracks are connected to land tracks, are shown in FIGS. 3A,  3 B, and  3 C. It can be determined whether a sector including a header belongs to a land track or a groove track using a header signal (for example, a two-divisional signal of a photodetector) at a position at which the groove track is connected to the land track. 
     Accordingly, in the header structure of FIG. 1A, it can be determined whether a sector including a header belongs to a land track or a groove track, at a position at which the land track is connected to the groove track, from pre-pit information within the header. In the header structure of FIG. 1B, it can be determined whether a sector including a header belongs to a land track or a groove track, at a position at which the land track is connected to the groove track as shown in FIG. 3A, from pre-pit information within the header or from a header signal. In the header structure of FIG. 1C, it can be determined whether a sector including a header belongs to a land track or a groove track at a position, at which the land track is connected to the groove track as shown in FIG. 3B, from pre-pit information within the header or from a time difference between header detections. In the header structure of FIG. 1D, since a header extends over a land track and a groove track and half of the header is offset from the other half of the header by one track pitch, it can be determined whether a sector including a header belongs to the land track or the groove track, at a position at which the land track is connected to the groove track, as shown in FIG. 3C, from pre-pit information within the header or from a header signal. 
     In FIG. 1B, the header can be commonly used for indicating the land and groove tracks since it extends over the land and groove tracks. However, when information for indicating whether the sector, including the header, belongs to the land track or the groove track is recorded in a header of the same length as headers in other header structures (FIGS.  1 C and  1 D), it is not advantageous to utilize the structure of FIG. 1B because the other structures include offsetting half of the header from the other half of the header by one track pitch. 
     FIGS. 4A and 4B show an example of the content of a conventional header. In the header of FIG. 4A, employed in a method of performing servo control at a constant angular velocity (CAV), the address of a sector is represented by a track number and a sector number. Alternatively, in the header of FIG. 4B, employed in a method of performing servo control at a zoned constant linear velocity (ZCLV) for use in a DVD-RAM, since the number of sectors in each track is different, addressing information is represented by only a sector number without using a track number. The sector number is embedded in a PID region of FIG.  4 B. 
     In a case in which a third header field and a fourth header field are offset from a first header field and a second header field by one track pitch (FIG.  1 D), the first and third header fields have a 36-byte VFO 1  which is longer than an 8-byte VFO 2  included in the second and fourth header fields as shown in FIG.  4 B. When the header is arranged without offset, the length of VFO 1  in the first and third header fields may be set to 8 bytes which is the same as assigned to VFO 2  in the second and fourth header fields. Further, the number of header fields can be decreased because the header fields have the same signal characteristics. 
     FIG. 5 shows a slice level and a PID signal provided through a first channel indicating a header detection signal corresponding to a change in a header, that is, a sum signal of two-divisional signals of a photodetector, when the header is arranged with offset. Referring to FIG. 5, fluctuation occurs at a position A at which the first and second header fields are connected to the third and fourth header fields and at the slice level, which is used for slicing, for a predetermined period of time. Accordingly, the magnitude of VFO 1  (represented by reference numeral  3 ) of the third header field is set to 36 bytes which is the same as that of VFO 1  (represented by reference numeral  1 ) of the first header field. A drive detects only the latter 8 bytes from each VFO 1  in the first and third header fields, not the first 28 bytes. 
     When a HD disc of 20 GB or more, which will be developed in the near future, uses a complementary allocated pit address (CAPA) structure (FIG.  1 D), used in a conventional 4.7 GB DVD-RAM or a structure in which headers are shifted by half of the track pitch (Tp/2), for common use by land and groove tracks as shown in FIG. 1B, base jitter problems do not occur. However, the margin characteristics become much worse compared to a conventional 4.7 GB disc or a HD disc having an on-track structure, that is, a structure in which headers are not shifted (off-track=0), as shown in FIG.  6 . 
     SUMMARY OF THE INVENTION 
     To solve the above problems, a first object of the present invention is to provide an optical recording medium having a sector structure in which a user area of a basic recording unit is physically divided into units of a first predetermined size (4 KB) and in which the user area is logically divided into a second predetermined size (2 KB) in order to reduce the amount of overhead. 
     A second object of the present invention is to provide an optical recording medium for improving the reliability of a system by disposing headers in the middle of land and groove tracks in the form of physical pits. 
     A third object of the present invention is to provide a method of recording and reproducing user data in and from an optical recording medium having headers between adjacent land and/or groove tracks, and having sectors which are basic recording units physically divided into units of a first predetermined size (4 KB) and where a user area within the basic recording units is logically divided into minimum recording units of a second predetermined size (2 KB). 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     To achieve the above objects and other objects, the present invention provides an optical recording medium including a header area, which indicates address information and is added to basic recording units of a first predetermined size, wherein a user area within the basic recording unit is divided into minimum recording units of a second predetermined size. 
     To achieve the above objects and other objects, the present invention provides a method of recording/reproducing information on/from an optical recording medium in an optical recording medium recording and reproducing apparatus. The method includes the steps of recording address information in a header area added to each basic recording unit of a first predetermined size, and dividing a user area within the basic recording unit into minimum recording units of a second predetermined size and recording information in the minimum recording units. 
     The method of the present invention also includes the steps of reading the address information in the header area from the optical recording medium and addressing the basic recording unit, and reproducing data in the user area in the minimum recording units within the addressed basic recording unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIGS. 1A through 1D illustrate examples of the structure of headers in a conventional optical disc; 
     FIGS. 2A through 2C illustrate examples of the structure of tracks in a typical optical disc; 
     FIGS. 3A through 3C illustrate examples of conventional header structures at positions at which a land track transitions to a groove track and a groove track transitions to a land track; 
     FIGS. 4A and 4B illustrate examples of the content of a conventional header; 
     FIG. 5 is a diagram illustrating the header signal of FIG. 4B and a slice level; 
     FIG. 6 is a table for comparing the signal characteristics of discs having off track headers with the signal characteristics of a disc having on-track headers; 
     FIG. 7 illustrates a structure of headers and sectors according to a first embodiment of the present invention; 
     FIG. 8 illustrates a structure of headers and sectors according to a second embodiment of the present invention; 
     FIG. 9 illustrates a structure of headers and sectors according to a third embodiment of the present invention; 
     FIG. 10 is a diagram illustrating mirrors included in a sector at a position where the land and groove tracks of FIG. 9 are connected; 
     FIG. 11 illustrates a structure of headers and sectors according to a fourth embodiment of the present invention; 
     FIG. 12 illustrates a structure of headers and sectors according to a fifth embodiment of the present invention; 
     FIG. 13 illustrates a structure of headers and sectors according to a sixth embodiment of the present invention; and 
     FIG. 14 illustrates a structure of pre-pits in a read only memory (ROM) disc including a header structure according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 7 shows a header structure and a position where a land track transitions to a groove track and a groove track transitions to a land track. Reference character G denotes a groove track, reference character L denotes a land track, reference character a denotes a header disposed in front of a basic recording unit, reference character b denotes a region for division of sectors, that is, a logical sector boundary portion, and reference character c denotes a user data area. A predetermined recording pattern e indicating the boundary between buffer fields d is recorded in the logical sector boundary portion b. 
     The header a stores an even or odd logical sector number, such that addressing is performed by skipping one conventional logical sector of 2 KB for compatibility with typical DVD RAMs. The buffer field d is a redundant region for complying with an accurate control requirement of a spindle motor in a digital versatile disc-random access memory (DVD-RAM). The buffer field d may be disposed at either one side or both sides of the logical sector boundary portion b. Alternatively, the buffer field d may not be used. A mirror f may be included in the header a and disposed immediately before a physical identifier (PID) to indicate the start of the PID. The mirror f may also be disposed immediately after the PID. 
     In the present invention, a header in the form of physical pits is disposed between adjacent groove and/or land tracks. Half of a header is offset from the other half of the header by one track pitch. Accordingly, headers are not adjacent between adjacent tracks. A header is physically added to each basic recording unit whose size is, for example, 4 KB, to reduce the amount of overhead. To logically divide a sector composed of a physical 4-KB unit into 2-KB units, the predetermined recording pattern e is recorded as shown in FIG.  7 . The predetermined recording pattern e may be, for example, pattern data having a fixed frequency like data stored in a variable frequency oscillator region VFO 1  of FIG.  4 B. The physical 4-KB unit is referred to as a basic recording unit, and the logical 2-KB unit is referred to as a minimum recording unit. 4 KB is referred to as a first predetermined size, and 2 KB is referred to as a second predetermined size. 
     Data in a header area and data in a user area may be modulated by different data modulation schemes. For example, pit position modulation (PPM), which does not require precise detection performance and has a characteristic of low recording density, may be used for the header a, and a mark edge recording (MER) method, which requires a precise detection performance and allows for a high recording density, may be used for the user area c. Alternatively, the same modulation scheme may be used for data in both header and user areas. 
     In a disc having such a header and sector structure, address information is stored in the header of each 4-KB basic recording unit. A user area in the basic recording unit is divided into 2-KB minimum recording units, and information is recorded in minimum recording units. When reproducing information from the disc, the address information in the header is read and data is addressed in basic recording units. Data in the user area is reproduced in minimum recording units included in the addressed basic recording unit. 
     FIG. 8 shows a header and sector structure according to a second embodiment of the present invention. The structure of FIG. 8 is different from that of FIG. 7 in that a wobble pit pattern is recorded in the logical sector boundary portion b. 
     FIG. 9 shows a header and sector structure according to a third embodiment of the present invention. The structure of FIG. 9 is different from that of FIG. 7 in that a wobble groove pattern of a predetermined frequency is recorded in the logical sector boundary portion b. The wobble frequency of the logical sector boundary portion b is a frequency high enough to lock data in the next user area to a phase locked loop (PLL). A predetermined pit pattern as shown in FIG. 10 may be recorded in the mirror f, included in the last sector of each track, to provide land/groove switching information. A pit pattern recorded in a land track may be different from that in a groove track. 
     When a mirror is provided in front of a PID to discriminate the PID from a track (a groove or land track) for recording, the length of the mirror of the last sector of a track may be set to be different to the length of the mirrors of the other sectors of the track. The position of the mirror of the last sector of a track may be different to the position of the mirrors of the other sectors of the track, or the number of mirrors of the last sector of a track may be set to be different to the number of mirrors of the other sectors of the track, in order to sort out land/groove switching information. The mirror described above can be adopted for use in all the embodiments of the present invention. 
     Although not shown in FIGS. 7 through 9 and  11  through  13 , which show the examples of a header and sector structure according to the present invention, a land track and/or a groove track usually have/has a wobble track of a predetermined frequency as shown in FIG.  10 . Accordingly, when the wobble frequency of a data area connected to a PID region is high enough to lock data to a PLL, a frequency different from a land/groove wobble frequency will be used as the wobble frequency of the logical sector boundary portion b of FIG.  9 . By doing this, a variable frequency oscillator (VFO) region for the PLL in the PID can be eliminated, so that overhead can be further reduced. When the VFO region is used, reliability can be increased. 
     FIG. 11 is a diagram showing a header and sector structure according to a fourth embodiment of the present invention. The structure of FIG. 11 is different from that of FIG. 7 in that the logical sector boundary portion b is formed by recording the predetermined recording pattern e in the form of pre-pits on a mirror between the buffer fields d. 
     FIG. 12 is a diagram showing a header and sector structure according to a fifth embodiment of the present invention. In FIG. 7, since headers are disposed in between adjacent groove and/or land tracks, and half of a header is offset from the other half of the header by one track pitch, headers of adjacent tracks are not adjacent. On the other hand, in FIG. 12, a header is disposed in each track in a similar pattern. As in FIG. 7, predetermined pattern data may be recorded in the logical sector boundary portion b. As in FIG. 8, a wobble pit pattern may be recorded in the logical sector boundary portion b. As in FIG. 9, a wobble groove pattern of a predetermined frequency may be recorded in the logical sector boundary portion b. And in FIG. 11, a predetermined pattern may be recorded in the logical sector boundary portion b in the form of pre-pits. 
     FIG. 13 is a diagram showing a header and sector structure according to a sixth embodiment of the present invention. Compared to the structure of FIG. 12, the starting points of header fields of adjacent tracks are different, such that fields of adjacent tracks that are in similar positions in the different header fields of FIG. 13 are not the same. In the structure of FIG. 13, the lengths of mirrors f immediately before each PID, in the headers of adjacent tracks, are different. The difference in the length of a mirror can be used to determine whether a sector belongs to a land track or a groove track. 
     The positioning of a PID in a sector structure in which a header is disposed in the middle of each of the groove and land tracks, as shown in the embodiments of the present invention illustrated in FIGS. 7 through 13, and in which a sector has a user area of a size exceeding PID+2 KB, can be applied to each of the header structures of FIGS. 1A through 1D. 
     Even if physical formats shown in FIGS. 7,  9 ,  11 ,  12  and  13  are applied to HD-ROMs, as shown in FIG. 14, a problem related to playback compatibility with DVD-RAMs and DVD-ROMs does not occur. 
     FIG. 14 shows a pre-pit structure of a ROM disc, which includes a header structure according to the present invention. The embodiments shown in FIGS. 7,  9 ,  11 ,  12  and  13  can be applied to ROM type discs such as DVD-ROMs and HDROMs. However, the header and sector structures of FIGS. 12 and 13, in which a logical sector boundary portion of a wobble pit pattern, as shown in FIG. 8, cannot be applied to ROM type discs. The embodiments shown in FIGS. 7 through 12 can be effectively applied to RAM type discs such as DVD-RAMs and HD-RAMs. 
     The present invention can also be applied to the track structures shown in FIGS. 2A through 2C (a concentric circle structure, a double spiral structure and a single spiral structure). In the embodiments of FIGS. 7 through 12, a header is disposed in the middle of each of the land and groove tracks in a single spiral track structure. Since the header is disposed between adjacent land and/or groove tracks in the present invention, headers are not shifted by half of a track pitch as in a complementary allocated pit address (CAPA) structure used in conventional DVD-RAMs, Thus, the present invention does not have a conventional crosstalk problem and simplifies manufacturing. In addition, the present invention reduces the time delay necessary for determining a slicing level using the 36-byte VFO 1  in each of the first and third header fields as shown in FIG.  5 . 
     In another functional aspect of a header, the present invention can compensate for a tracking offset using mirrors, and compensate for tilting and de-tracking of a disc using mirrors and a pit signal. According to the present invention, a land track can be discriminated from a groove track using a wobble pit. 
     As described above, the present invention disposes a header between adjacent land and/or groove tracks and has portions, each of which includes a recording mark of a predetermined pattern, a wobble pit, a wobble groove and a predetermined pre-pit pattern, at predetermined intervals to physically divide a 4-KB area into 2-KB areas, thereby reducing overhead compared to a conventional header structure. According to the present invention, the position of a beam for forming a groove is the same as that for forming a header during the manufacture of headers, thereby simplifying manufacture.