Abstract:
A system includes an encoding module and a laser driver module. The encoding module is configured to encode a data stream. The laser driver module is configured to convert the encoded data stream into a write signal including one or more edges. The write signal is output to an optical writer. The laser driver module is configured to adjust an actual position at which the optical writer writes a first edge of the one or more edges on an optical storage medium away from a desired position for the first edge. The adjustment is made based on (i) a first preceding edge position, (ii) a first following edge position, (iii) a second preceding edge position or a second following edge position, and (iv) a third preceding edge position or a third following edge position. The first edge corresponds to a beginning of a mark edge of the write signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Nos. 61/022,635, filed on Jan. 22, 2008 and 61/036,268 filed on Mar. 13, 2008. The disclosures of the above applications are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The subject matter of the present disclosure relates generally to optical data storage, and more particularly to systems and methods for storing data on an optical storage medium. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Optical recording devices are used to record information, such as music, movies, pictures, data, etc., on recordable media. Examples of recordable media are compact discs (CDs), digital versatile discs (DVDs), high density/high definition DVDs and Blu-ray Discs (BDs). In order to record information onto recordable media, a recording device typically tracks the location of a laser beam on the recordable media. 
       FIGS. 1A-1B  respectively illustrate partial cross-sectional views of examples of recordable mediums  10 -A,  10 -B. The recordable mediums  10 -A,  10 -B have lands  12  and grooves  14 , which are formed on one or more recording layers  16  of one or more main substrates  18 . The main substrates  18  may be adhered via an adhesive layer  20  to dummy substrates  22 , as shown. 
     The lands  12  and grooves  14  refer to physical structures of the recording layer  16  that are adjacent each other but that have different associated depths. For example, the grooves  14  have a greater associated depth than the lands  12 . Sample land depths D 1  and sample groove depths D 2  are shown. The depths may be measured relative to a disk outer surface  24  and are equal to a fraction of an optical wavelength of a laser beam. The lands  12  and grooves  14  provide servo information for positioning of a laser beam spot on a disc. The lands  12  and grooves  14  also provide reflected beam signal modulation that is detected and used for tracking. 
     Standards, such as DVD+/−R and DVD+/−RW, require recording only over grooves. An alternative standard, referred to as DVD-RAM, requires recording over both land and groove structures. In DVD+/−R and DVD+/−RW recording, the lands  12  and grooves  14  typically form a continuous spiral. In DVD-RAM recording, the lands  12  alternate with the grooves  14  to form a continuous spiral. 
       FIG. 2  illustrates a conventional optical DVD drive system  50 . The optical DVD drive system  50  includes a laser source  52 , such as a laser diode, that emits a laser beam  54 . The laser source  52  may be part of an optical read/write assembly (ORW)  56 . The ORW  56  includes a collimator lens  58 , a polarizing beam splitter  60 , a quarter wave plate  62 , and an objective lens  64 . The laser beam  54  is collimated by the collimator lens  58  and passed through the polarizing beam splitter  60 . The laser beam  54  is received by the quarter wave plate  62  from the beam splitter  60  and is focused via the objective lens  64 . The laser beam  54  may be radially displaced across tracks of the optical storage medium  68  through movement of the ORW  56  via a sled motor  66 . The laser beam  54  is moved while the optical storage medium  68  is rotated about a spindle axis  69 . The laser beam  54  is shaped and focused to form a spot over the land/groove structures of an optical storage medium  68  via lens actuators  70 . 
     The light from the laser beam  54  reflects off the optical storage medium  68  and is thus directed back into the ORW  56 . The reflected light, represented by dashed line  72 , is redirected by the beam splitter  60 . An astigmatic focus lens  76  focuses the reflected light into a spot over a photo-detector integrated circuit (PDIC)  74 . Although not shown, additional photo-detectors may be used to detect other diffracted light beams, which are also not shown. 
     Referring now to  FIG. 3 , an exemplary bit-stream of write channel data is presented. Data that is to be written to optical storage media may first be encoded using techniques such as cyclic redundancy check (CRC), error-correcting code (ECC), Reed-Solomon coding, and/or interleaving. Alternatively, 8-to-14 modulation (EFM) may be used to encode the data to be stored on an optical storage medium. The encoded data stream may then be sent to a laser driver unit, which converts the data stream into a series of electrical pulses that are used to record the data onto the optical storage medium. 
     An exemplary channel bit-stream is represented as waveform  80 . The waveform  80  contains one bit for every time period (T). The interval where the waveform  80  is high may be referred to as a space  82   a ,  82   b . The intervals where the waveform  80  is low may be referred to as marks  84   a - 84   c . Marks may be represented on the optical storage media as areas of low reflectivity (pits), amorphous domains, or any other type of form that can be sensed by the optical system. Spaces may be represented as areas of high reflectivity between marks. These reflectivities may be created by a laser beam, as is known in the art. 
     A typical optical reader, for example a DVD player, has a light spot that is approximately 9T wide. In other words, a typical optical reader detects the reflectivity of an area on the optical storage medium that is nine time periods long. Thus, marks or spaces of a length less than 9T may be difficult to distinguish from adjacent spaces or marks. In most encoding schemes, optical readers are generally designed to detect edges of a waveform (e.g., edges  85  of waveform  80 ) in order to decode the data therein. 
     Depending on the parameters of the optical storage media, and the binary encoding scheme employed, the length of marks and spaces may be constrained. For example, in the EFM encoding technique, the smallest length of a mark or space is 3T and the longest length of a mark or space is 11T. A laser driver, based on the information in the data stream, determines the correct power and time duration for operating a laser to create marks (e.g., marks  84   a - 84   c ). These marks  84   a - 84   c , in combination with spaces  82   a ,  82   b , are then detected or read by an optical reader. The goal of the laser driver is to create marks and spaces such that the optical reader will detect the stored data correctly. In accordance with this goal, a laser driver typically includes a translation module, such as a laser table, that dictates how data is to be stored on an optical storage medium. 
     Among other functions, a laser table will direct the laser driver to position a mark based on the immediately preceding space length and the length of the mark to be written. Thus, the actual physical beginning of a mark edge  85  may need to be adjusted from a desired position (that is, the position corresponding substantially to the intended data stream) in order for the position that is detected to correspond with the desired position of the signal to be stored. In other words, the optical reader will detect an edge  85  in a position that may not correspond to the actual physical position of the edge as written on the optical storage medium. This phenomenon is referred to as inter-symbol interference or ISI and causes the waveform that is output from the optical reader to differ from the physical marks and spaces that are stored on the optical storage medium. ISI contributes to jitter and other causes of error in data retrieval. 
     SUMMARY 
     In various embodiments, the present disclosure is directed to a driver for an optical storage medium. The driver comprises a converting module and an adjustment module. The converting module converts an encoded data stream into a write signal including one or more edges. The write signal is output to an optical writer. The adjustment module adjusts an actual position that the optical writer writes a first edge of the one or more edges on the optical storage medium away from a desired position for the first edge. The adjustment is based on a first preceding edge position, a first following edge position, and at least one of a second preceding edge position and a second following edge position. The adjustment is made such that a sensed position of the first edge on the optical storage medium as sensed by an optical reader corresponds to the desired position for the first edge. 
     In various embodiments, the adjustment module comprises a look-up table that stores one or more adjustment values and the adjustment module adjusts the actual position using an adjustment value stored in the look-up table. 
     In various embodiments, the adjustment module further adjusts the actual position that the optical writer writes the first edge on the optical storage medium based on inter-symbol interference of adjacent spaces and marks of the encoded data stream. 
     In various embodiments, the desired position for the first edge corresponds to a transition point in the encoded data stream. 
     In various embodiments of the disclosure, the present disclosure is directed to a method for writing to an optical storage medium. The method comprises converting an encoded data stream into a write signal including one or more edges, the write signal being output to an optical writer. The method further comprises adjusting an actual position that the optical writer writes a first edge of the one or more edges on the optical storage medium away from a desired position for the first edge. In some embodiments, the adjustment is made based on a first preceding edge position, a first following edge position, and at least one of a second preceding edge position and a second following edge position. In some embodiments, a sensed position of the first edge on the optical storage medium as sensed by an optical reader corresponds to the desired position for the first edge. 
     In various embodiments, the adjustment of the actual position that the optical writer writes the first edge on the optical storage medium is based on an adjustment value stored in a look-up table. 
     In various embodiments, the adjustment of the actual position that the optical writer writes the first edge on the optical storage medium is based on inter-symbol interference of adjacent spaces and marks of the encoded data stream. 
     In various embodiments, the desired position for the first edge corresponds to a transition point in the encoded data stream. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. The detailed description and specific examples, while indicating various embodiments of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIGS. 1A-1B  are partial cross-sectional views of recording mediums according to the prior art; 
         FIG. 2  is a functional block diagram of an optical drive system according to the prior art; 
         FIG. 3  is an exemplary bit-stream of write channel data; 
         FIG. 4  is an exemplary bit-stream of write channel data, adjusted write channel data and read channel data; 
         FIG. 5  is an exemplary bit-stream of write channel data; 
         FIG. 6  is an exemplary depiction of the contents of a look-up table according to various embodiments of the present disclosure; 
         FIG. 7  is a functional block diagram of an optical drive system and write control module according to various embodiments of the present disclosure; 
         FIG. 8  is a functional block diagram of a write control module according to various embodiments of the present disclosure; 
         FIG. 9  is a functional block diagram of a write control module according to various embodiments of the present disclosure; and 
         FIG. 10  is a flowchart describing a method of writing to an optical disk according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. A software module or module that is software based may refer to a set or series of software code, which are used to perform one or more tasks. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     The present disclosure is directed to a system and method of writing to an optical disk that compensates for inter-symbol interference by adjusting the position of an edge between spaces and marks of an optical storage medium. An optical read/write system detects (or “reads”) the data stored on the optical storage medium by detecting light (e.g., from a laser beam) that is reflected from the spaces and marks of the optical storage medium. The light that is reflected from the optical storage medium may comprise a compilation of the reflections from a number of periods, or T&#39;s, of the signal and ISI may cause the detected edges to “shift” from the true physical position of the edges on the medium. Thus, it is desirable to store the data on the optical storage medium such that the optical read/write system will detect the transition points or edges of the signal at appropriate points, even if the actual stored position differs from the position that the data dictates. In other words, the optical storage medium will be written such that the optical reader will detect edges or transition points of the signal at the desired position, even if this means that the actual physical location of an edge of a mark or space differs from the desired physical position of the edge as detected. 
       FIG. 4  illustrates exemplary waveforms  90   a - 90   c . Waveform  90   a  corresponds to a signal to be stored on an optical storage medium. For example in an EFM scheme, transition points (from high to low or low to high) or edges  91  are indicative of a one in a binary data stream while periods in which there is no transition are indicative of a zero. Thus, signal  90   a  corresponds to a binary data stream  92 . The binary data stream  92  is the information that the optical read/write system is to write on the optical storage medium. The limitations of the optical read/write system, such as ISI, may require that the marks  93   a - 93   c  and spaces  94   a - 94   c  be stored on the optical storage medium in positions other than dictated by edges  91   a - 91   e  in order for the data to be detected correctly. 
     Waveform  90   b  comprises the actual spaces and marks to be written on the optical storage medium. Waveforms  90   a  and  90   b  differ from each other by adjustments d 1 -d 3 . Adjustments d 1 -d 3  comprise variations in the actual physical position of the edges or transition points  91   a - 91   e  to be written on the optical storage medium. Adjustments d 1 -d 3  are determined such that the optical read/write system will detect the edges  91   a ′ through  91   e ′ to be at the position dictated by edges  91   a - 91   e  of the desired waveform  90   a.    
     Waveform  190   c  comprises the actual reflected light signal detected from the optical storage medium based on the stored waveform  90   b , while waveform  90   c  comprises the square waveform corresponding to waveform  190   c . Waveforms  90   c  and  190   c  are related in that whenever a zero crossing  95   a - 95   e  of waveform  190   c  is detected by the optical read/write system, a transition of square waveform  90   c  is determined. Adjustments d 1 -d 3  are designed such that the zero crossings  95   a - 95   e  of waveform  190   c  correspond to the location of edges  91   a - 91   e  of waveform  90   a . In this manner, the optical read/write system is able to reconstruct waveform  90   a  in waveform  90   c  more accurately. Thus, even though the actual edges of spaces and marks of waveform  90   b  are stored on the optical storage medium in physical locations  91   a ′- 91   e ′ that differ from the position of edges  91   a - 91   e  of waveform  90   a , the detected waveform  90   c  corresponds to the binary data stream  92 . 
     The adjustments between the data signal to be stored on the optical storage medium and the actual data stream stored thereon may be determined as follows. Referring now to  FIG. 5 , the position of edge  100  of waveform  110  when detected by an optical reader may be dependent on adjacent spaces and marks. As described above, marks  112   a - 112   d  are formed by forming a pit within the optical storage medium. The length of the spaces  114   a - 114   c  and marks  112   a - 112   d  are determined by the placement of the edges or transition points between the spaces  114   a - 114   c  and marks  112   a - 112   d.    
     The sense position of edge  100  may be dependent upon the length of adjacent space  114   b  and adjacent mark  112   c , as well as adjacent mark  112   b  and adjacent space  114   c . The transition between adjacent mark  112   b  and adjacent space  114   b  is referred to as edge  116   a , which may also be referred to as the first preceding edge of edge  100 . The edge between space  114   a  and mark  112   b  may be referred to as the second preceding edge  116   b . Similarly, the edge between mark  112   c  and space  114   c  is first following edge  118   a , while the edge  118   b  between space  114   c  and mark  112   d  may be referred to as second following edge  118   b . The length of marks  112   b  and  112   c  and spaces  114   b  and  114   c  will affect the detection of edge  100  by the optical read/write system. Thus, the position of edges  116   a ,  116   b ,  118   a  and  118   b  will affect the position of edge  100  when detected by the optical read/write system. 
     As stated above, the laser beam utilized by the optical read/write system in a standard DVD reader is typically 9T long, where T refers to the period or bit length described above. Thus, an optical read/write system that is attempting to detect edge  100  may also detect a partial reflection from symbols adjacent thereto. This phenomenon becomes more pronounced for marks and spaces of short length. Thus, edges  116   b  and  116   a  may need more adjustment than edges  118   a  and  118   b  of  FIG. 5 . 
     Referring now to  FIG. 6 , an exemplary laser table  200  is illustrated. Laser table  200  corresponds to and includes adjustments necessary for writing an edge SαMβ in column  202 , which is the edge between a space “S” of a periods and mark “M” of β periods. Column  204  of laser table  200  comprises the length of the mark preceding the edge SαMβ at issue. Column  206  comprises the list of potential space lengths following the edge SαMβ. Column  208  comprises adjustment values Δ 1  to Δ n  corresponding to each of the entries in laser table  200 . As an example only, laser table  200  dictates that the edge SαMβ will be adjusted by Δ 3  in the event that the preceding mark is three periods long and the space following SαMβ is five periods long, seen at row  210 . 
     It should be noted that laser table  200  may contain rows or adjustments Δ 1  to Δ n  in the event that the edge to be written indicated in column  202  actually needs to be adjusted. In the event that a preceding mark of a certain length in conjunction with a following space of a sufficient length will not require an adjustment to edge SαMβ, laser table  200  may not include an entry corresponding thereto. 
     Laser table  200  may be replicated for each edge that is expected to be written. In the event that the edge to be written is a transition from a mark to a space, in contrast to the edge in laser table  200  that corresponds to a transition from a space to a mark, column  204  will correspond to the preceding space length and column  206  will correspond to the following mark length. The adjustment factors may be determined, for example, by laboratory testing or simulation or other process. It should be noted that laser table  200  corresponds to a data signal that has been encoded using EFM, which dictates that the minimum length of a space or a mark is three periods long and the maximum length of a space or mark is eleven periods long. In the event that another modulation method is used, the laser table may include more or less entries. Furthermore, laser table  200  includes adjustments relating for an edge only based on the two preceding and two following edges. In some implementations, a more comprehensive laser table may be constructed in which additional adjacent edges are considered and adjustments provided. 
       FIG. 7  illustrates an optical DVD drive system  300  according to various embodiments of the present disclosure. The system  300  includes a laser source  302 , such as a laser diode, that emits a laser beam  304 . The laser source  302  may be part of an optical read/write assembly (ORW)  306 . The ORW  306  includes a collimator lens  308 , a polarizing beam splitter  310 , a quarter wave plate  312 , and an objective lens  314 . The laser beam  304  is collimated by the collimator lens  308  and passed through the polarizing beam splitter  310 . The laser beam  304  is received by the quarter wave plate  312  from the beam splitter  310  and is focused via the objective lens  314 . The laser beam  304  may be radially displaced across tracks of the optical storage medium  318  through movement of the ORW  306  via a sled motor  316 . The laser beam  304  is moved while the optical storage medium  318  is rotated about a spindle axis  319 . The laser beam  304  is shaped and focused to form a spot over the land/groove structures of an optical storage medium  318  via lens actuators  320 . 
     The light from the laser beam  304  reflects off the optical storage medium  318  and is thus directed back into the ORW  306 . The reflected light, represented by dashed line  322 , is redirected by the beam splitter  310 . An astigmatic focus lens  326  focuses the reflected light into a spot over a photo-detector integrated circuit (PDIC)  324 . Although not shown, additional photo-detectors may be used to detect other diffracted light beams, which are also not shown. 
     DVD system  300  further comprises a write control module  350  coupled to ORW  306 . In the illustrated embodiment, write control module  350  comprises a separate module from the ORW  300 , but one can appreciate that the write control module  350  and ORW  300  may be combined into one module (not illustrated). Write control module  350  may include a laser table  360 . Laser table  360  may be similar to laser table  200  described above and illustrated in  FIG. 6 . The write control module  300  directs the ORW  306  to record the appropriate spaces and marks on optical storage medium  318 . 
       FIG. 8  illustrates an exemplary write control module  350   a  according to some embodiments of the present disclosure. Write control module  350   a  comprises encoding module  352   a , laser driver module  354   a  and laser table  360   a , and is coupled to ORW  306 . Encoding module  352   a  receives a data stream  351   a  to be encoded, e.g., by cyclic redundancy check (CRC), error-correcting code (ECC), Reed-Solomon coding, 8-to-14 modulation (EFM), and/or interleaving. Encoding module  352   a  outputs an encoded data stream  353   a  to laser driver module  354   a , which converts the encoded data stream into a write signal comprising a series of electrical pulses  355   a  that are used by ORW  306  to record the data onto the optical storage medium. Laser driver module  354   a  may utilize laser table  360   a  to adjust the position of the edges of the spaces and marks to be written, as described above. According to some embodiments of the present invention, the laser driver module  354   a  adjusts the position of an edge to be written based on the two preceding and two following edge positions. In these embodiments, therefore, the laser driver module  354   a  must store the preceding edge positions, as well as wait until receiving the following edge positions, before determining the adjustment of the edge to be written. 
       FIG. 9  illustrates an exemplary write control module  350   b  according to some embodiments of the present disclosure. Write control module  350   b  comprises encoding module  352   b  and laser table  360   b . Encoding module  352   b  receives a data stream  351   b  to be encoded and outputs a series of electrical pulses  355   b  that are used by ORW  306  to record the data onto the optical storage medium. Instead of splitting the functions of the write control module between an encoding module and laser driver, write control module  350   b  utilizes one module, i.e., encoding module  352   b , to perform both the encoding and conversion functions. Encoding module  352   b  may utilize a laser table  360   b  to adjust the position of the edges of the spaces and marks to be written, as described above. Because encoding module  352   b  generates the encoded data stream, the position of the edges to be written is known and the adjustment of the edge positions, e.g., from laser table  360   b , can be determined more easily than laser driver module  354   a.    
     A flowchart describing a method  400  of writing to an optical disk according to some embodiments of the present disclosure is shown in  FIG. 10 . The method  400  begins at block  401 . At block  402 , the desired position of the edge to be written is determined. As described more fully above, the desired position of an edge comprises the physical position of the transition between a space and a mark and may correspond to a high or “1” value in the data stream. The position of the edge immediately preceding the edge to be written, otherwise known as the first preceding edge position, is determined at block  403 . At block  404 , the position of the edge immediately preceding the first preceding edge position, which is otherwise known as the second preceding edge position, is determined. At block  405 , the position of the edge in the data stream immediately following the edge to be written, known as the first following edge position, is determined. The position of the edge in the data stream immediately following the first following edge position, known as the second following edge position, is determined at block  406 . 
     An adjustment of the position of the edge to be written, for example, based on the first and second preceding and following edge positions, is determined at block  407 . At block  408 , the edge to be written is recorded onto the optical storage medium at the desired position adjusted by the adjustment determined at block  407 . The method ends at block  409 . 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications may be applied to the various embodiments upon a study of the drawings, the specification and the following claims. For example, one or more steps of the methods described above can be performed in a different order and still achieve desirable results.