WO2005057564A1

WO2005057564A1 - Method and apparatus for writing optical discs with optimal power calibration

Info

Publication number: WO2005057564A1
Application number: PCT/IB2004/052500
Authority: WO
Inventors: Gerard E. N. Schreurs
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-12-09
Filing date: 2004-11-22
Publication date: 2005-06-23
Also published as: TW200523898A

Abstract

A method of writing data to an optical disc (1) having a power calibration area (PCM) and a data recording area, the method comprising recording data in a plurality of discrete sections of the data recording area, the sections being separated by non-user data recording areas, the method further comprising testing, in the non-user data recording areas, write quality of data being written to said optical disc (1). A session of data may be written to each discrete section of the data recording area, in which case the non-user data recording areas comprise lead-in and lead-out areas respectively, and the write quality of data being written to the optical disc (1) is tested in a portion (2) of the lead-in areas prior to writing each session of data to the optical disc (1). Alternatively, a track (3) of data may be written to each discrete section of the data recording area, and the non-user data recording areas may each comprise a pre-gap (4). The write quality of data being written to the optical disc (1) is, in this case, tested in a portion (5) the pre-gap (4) prior to writing each track (3) of data to the optical disc (1).

Description

Method and Apparatus for Writing Optical Discs with Optimal Power Calibration

This invention relates to a method for recording data onto an optical disc comprising a power calibration area and one or more data recording areas, the method comprising performing optimum power control in said power calibration area of said optical disc prior to recording said data onto said optical disc. An optical disc such as a compact disc (CD) is known as one type of information recording media. According to a standard recording format of the CD, a recording area of the CD comprises a lead-in area, a program area, and a lead-out area. These areas are arranged in that order in a direction from an inner periphery to an outer periphery of the CD. Index information referred to as the table of contents (TOC) is recorded in the lead- in area. The TOC includes management information as a sub-code which is used for managing information recorded in the program area. For example, if main information recorded in the program area is information relating to a music tune, the management information may comprise the playing time of the tune. Information relating to the track number of the corresponding music tune may also be recorded in the program area. A lead- out code which indicates the end of the information area is recorded in the lead-out area. Before user data is recorded, a test write is performed on a small segment of the media. For optical discs, this segment is along the inner radius of the disc. The test write writes at various power levels and write pulse shapes. By reading back the test written pattern, the optimum power level and pulse shape are set, for recording the user data. This process is referred to as "optimum power control" or OPC. The OPC process is performed before each write operation. However, OPC can produce inaccurate results, because a test write whose length is a fraction of a full revolution of the disc is used to determine the optimum write power. As can be seen in Figure 1 of the drawings, the disc 1 includes a small area for test data, labelled Power Calibration Area (PCA) 2 toward the inner portion of the disc 1. The use of power calibration data from less than a full revolution of the disc may cause errors because of any of these issues: vertical and radial run out which cause focus and tracking errors, circumferential variations in the thickness of the recording layer or in the optical properties of the substrate, localised errors in the test write area, changes in temperature, etc. Additionally, the changes in optimum power for each write speed is predicted from a minimal sample. Because the test area and number of test writes is limited, traditional OPC predicts the optimum power for the entire range of write speeds by extrapolation based on one or two short test writes at the inner diameter of the disc. Therefore, traditional OPC has problems in setting the laser power and write format optimally. In addition, traditional OPC, which is performed at the inner diameter of the disc, cannot predict the optimum power over the entire disc surface. One prior art method of solving the above-mentioned problems associated with conventional OPC is by using running optimum power calibration (ROPC). During the recording of user data, the amplitude of light reflected from the media during the writing of the marks that encode the user data may be monitored. The signature of the data, as it is being written, is compared to the data recorded during the OPC process. If the signature has changed significantly, the power or write strategy is changed. However, ROPC also has some shortcomings. For example, ROPC adjusts the write power based on the read back data of the reflected write power. The predictive parameters are non-linear and have a low signal-to-noise ratio. They may also vary according to the manufacturer's process. This reduces the accuracy of the ROPC process. In addition, if it is required to write data directly onto a part of the disc without previous information, the first part of the disc can still be inaccurate, for example, in the event that it is required to write data after a reserved track (on which no data has yet been recorded). It is therefore an object of the present invention to provide a method and apparatus for writing an optical disc in which laser power calibration is improved relative to the prior art, and in which the first part of any portion of user data is correct, irrespective of what has occurred previously on the disc. In accordance with a first aspect of the present invention, there is provided a method of writing data to an optical disc having a power calibration area and a data recording area, the method comprising recording said data in a plurality of discrete sections of said data recording area, said sections being separated by non-user data recording areas, the method further comprising testing, in said non-user data recording areas, write quality of data being written to said optical disc. In a preferred embodiment of the first aspect of the present invention, the step of testing write quality of data being written to the optical disc comprises halting said data recordal, reading and evaluating data written to the optical disc, and then restarting data recordal. A link point is preferably provided between a location on the optical disc at which data recordal is halted and a location on the optical disc at which data recordal is restarted. The link point is beneficially provided substantially entirely within a non-user data recording area. As a result, all parts of the user data, including the first part, will be correct irrespective of what has occurred previously on the disc, and the overall format of the data recorded on the optical disc is maintained in the standard prescribed therefor. No special test data is required; just the normal data prescribed by the standard. In summary, in a preferred embodiment of the invention, the linking points provided as a result of stopping the writing process at the beginning of the writing and reading back the written signal to judge the quality, are always placed in the non-user relevant data area. As a result, if the combination of the linking process and the first writing decreases the write quality at the link point, the customer is not adversely affected. In one embodiment of the invention, a session of data may be written to each discrete section of said data recording area, and wherein said non-user data recording areas comprise lead-in and lead-out areas respectively. Preferably, the write quality of data being written to the optical disc is tested in the lead-in areas prior to writing each session of data to the optical disc. In another embodiment of the invention, a track of data is written to each discrete section of the data recording area, and the non-user data recording areas each comprise a pre-gap. The write quality of data being written to the optical disc is, in this case, preferably tested in the pre-gap prior to writing each track of data to the optical disc. Testing write quality of the data being written to the optical disc preferably comprises performing optimal power calibration, which is beneficially also performed in the power calibration area of the optical disc. Preferably, a substantially seamless link is provided between data written to each of the discrete sections of the optical disc. The first aspect of the present invention also extends to apparatus for writing data to an optical disc having a power calibration area and a data recording area, the apparatus comprising means for recording said data in a plurality of discrete sections of said data recording area, said sections being separated by non-user data recording areas, the apparatus further comprising means for testing, in said non-user data recording areas, write quality of data being written to said optical disc. In accordance with a second aspect of the present invention, there is provided a method of writing data to an optical disc having a power calibration area and a data recording area, the method comprising writing tracks of data to said optical disc as a sequence of packets of data, the method further comprising testing, in respect of one of said packets of data, write quality of data being written to the optical disc. Preferably, the write quality of data being written to the optical disc is tested in respect of the first packet of data of a sequence. Each packet of data beneficially comprises a link block, one or more run-in blocks, a plurality of data sectors, and one or more run-out blocks. Also in accordance with the second aspect of the present invention, there is provided apparatus for writing data to an optical disc having a power calibration area and a data recording area, the apparatus comprising means for writing tracks of data to said optical disc as a sequence of packets of data, and means for testing, in respect of one of said packets of data, write quality of data being written to the optical disc.

These and other aspects of the present invention will be apparent from, and elucidated with reference to, the embodiments described herein. Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-sectional illustration of the various sections of a conventional disc-at-once (DAO) recorded optical disc; Figure 2a is a schematic cross-sectional illustration of the various sections of a conventional multi-session optical disc; Figure 2b is a schematic cross-sectional illustration of the various sections of the optical disc of Figure 2a, recorded using a method according to an exemplary embodiment of the present invention; Figure 3a is a schematic cross-sectional illustration of the various sections of a conventional multi-session optical disc to which data has been written in a Track at Once (TAO) mode; Figure 3b is a schematic cross-sectional illustration of the various sections of the optical disc of Figure 3a, recorded using a method according to an exemplary embodiment of the present invention; and Figure 4 is a schematic block diagram of optical disc recording apparatus according to the prior art. By way of background information, US Patent No. 6,636,468 describes a method and apparatus for writing data to an optical storage medium in which the characteristics of the write laser are set in a power calibration area of the disc, using an optical power calibration technique such as that described above. In addition, data writing or recording is halted at various locations on the disc and data previously recorded on the disc is read. The read data is evaluated and, if necessary, the characteristics of the write laser are adjusted, and then data writing is restarted using the updated characteristics of the write laser. As explained above, optical disc media typically include a continuous spiral groove which extends across the entire data storage capacity of the disc. CD-based optical disc media architecture utilises the continuous spiral groove with sectors (also called "blocks") of equal length, which are accessed at a constant linear velocity (CLV). A recordable compact disc (CD-Recordable or CD-R) or a rewritable compact disc (CD-Rewritable or CF-RW) is a CD-based medium, and includes a continuous spiral CLV groove. Current CD-R and CD-RW devices have a buffer to accumulate the input data and organise that data into sectors for writing on a disc in a continuous sequence of sectors. When the current buffer of a CF-R or CF-RW device fails to receive input data from the host on a timely basis, the buffer may under-run and will become empty, causing the writing process to be halted. In prior art arrangements, in the event that the writing process was halted, either for data evaluation purposes or as a result of buffer under-run, a problem was encountered in restarting the writing process because the location on the disc at which recording should re-commence could not be located precisely. As a result, a writing method was developed whereby a linking point or link block is provided between the point at which the write process is interrupted and the point at which it is restarted. This link block is intended to provide a substantially seamless link across the resultant data gap so as to keep the data frame length constant (such that is conforms to the standard data format prescribed for the optical storage medium). The link block can, therefore, be treated as a non-interrupted recording area and will not result in the occurrence of a decoding error during a subsequent reading process. However, the link block will still be perceived during the reading process as user data and will be read back as such, which will result in a reduced quality of the reproduced user data. It is therefore a further preferred object of the present invention to provide a method and apparatus for writing an optical disc, including means for evaluating data written to the disc during the write process by stopping the wring process, evaluating data written to the disc, and restoring the writing process, wherein link points are provided between locations at which the writing process is stopped and restarted respectively for the purposes of data evaluation, such link points being provided in non-user data sections of the data recording area of the disc. Referring to Figure 4 of the drawings, optical information recording apparatus according to the prior art comprises an optical disc drive unit using an optical disc 8 such as a CD-R(W). In the optical disc drive unit, an optical pick-up 9 is provided to record information on or reproduce information from the optical disc 8. The optical pick-up is connected to a motor 10 so as to be moved between an inner side and an outer side of the optical disc 8 to perform a seek operation. The motor 10 is connected to a controller 12 via a motor control system 11. The controller 12 is connected to a rotation control system 13, a signal processing system 14 and a pick-up control system 15. The rotation control system 13 is connected to a spindle motor 16 so as to rotate the optical disc 8. The signal processing system 14 and the pick-up control system 15 are connected to the optical pick-up 9 so as to perform a recording or reproducing operation and a servo control operation (focusing, tracking) of the optical pick-up 9. There are several different methods by means of which data can be written to an optical disc, such as a CD-R(W) disc. The first of these is known as Disc at Once (DAO) which is a writing mode in which a whole disc is copied in a single write event, and is also known as single session recording. Disc at Once is a writing mode that requires lead-in, program data and lead -out to be written in one write event, such that all of the necessary information required to be recorded on the disc needs to be on the hard disc prior to recording in the DAO mode. This mode is usually necessary for discs that are sent to a CD replication facility for CD-ROM replication where the CD-R is the original source. Recording in the DAO mode, eliminates the linking, run-in and run-out blocks associated with multisession and packet recording modes, which are often interpreted as uncorrectable errors during the glass mastering process. Referring once again to Figure 1 of the drawings, the data format of an optical disc which has been written in DAO mode is illustrated. It can be seen that, because, when the write process starts, there is always previous information available (from the PCA section), the above-described problems do not occur, and the present invention is therefore not required. Another writing mode is known as multi-session, the principle of which is to allow additional data to be appended to a previously recorded disc. A session is defined as a data section including lead-in, program data and lead-out, as illustrated in Figure 2a of the drawings. The lead-in and lead-out information is written to the disc during a process known as "fixation". A CD-R recorder that supports multi-session can write a disc that will have multiple sessions linked together so that any multisession supported CD reader can access the data, whether it was written in the first session or a subsequent session. The benefit of multisession CD writing is that all of the available space on the CD can be used. When the first session is written, the above-mentioned problems do not arise, because the data relating to Session 1 is written to an area which is relatively close to the PCA containing the initially-obtained OPC information. However, when Session 2 is recorded, the area to which it is written is rather further away from the OPC information held in the PCA, and as such, the above-mentioned problems may arise. In accordance with this exemplary embodiment of the present invention, this problem can be overcome by using part 2 of the lead-in to Session 2 (and all subsequent sessions) to test the write quality and record OPC information, as illustrated schematically in Figure 2b of the drawings. This is achieved by starting and then stopping the writing process, recoding the data written to the disc, and evaluating its quality, adjusting the OPC information if necessary, and then restarting the writing process. A link point (spawning part 2 of the lead-in to Session 2) is provided to maintain the standard data format. In a conventional multisession disc, the table of contents (TOC) relating to each session is held in the lead-in area for each session. However, the TOC is repeated many times in the lead-in area and the CD writer is arranged to read the lead-in until the entire TOC has been reconstructed, so there is no disadvantage if a small part of the lead-in has a reduced write quality. It will be appreciated that the term OPC or "optimal power calibration" is used herein in its conventional sense, i.e. it is a technique for determining an optimum power for an optical disc media and optical driving apparatus combination before data recording is executed. In one specific embodiment, this technique may comprise first reading a value of a recommended recording power which is recorded on the optical disc, then executing a test recording wherein data is recorded utilising several levels of recording power based on the recommended recording power. These test recordings are performed in a power calibration area (PCA) of the disc, as referred to above. Based on the reproduction of the test data thus recorded, an optimum recording power for the optical disc is determined. More specifically, the recommended recording laser power is encoded in the Absolute Time In Pre-groove (ATIP) of the disc and is read by the recorder's firmware. The recorder then performs a test write of 6 sectors in the PCA of the CD-R disc with several different laser power values based on the recommended power, then reads the sectors back and selects the laser power that produced the sector with the best reflectivity. With CD-RW media, in addition to the recommended write power being encoded in ATIP, the recommended erase power and bias powers are also encoded and read by the recorder. It will be further appreciated that the term "fixation", as stated above, is the process of writing the lead-in and lead-out information to the disc. This process finishes a writing session and creates a table of contents (TOC). Fixation is required for a CD-ROM or CD Audio player to play the disc. Discs which are fixated for append can have additional sessions recorded, with their own session lead-in and lead-out, thus creating a multisession disc. When the disc is finalised, the absolute lead-in and lead-out for the entire disc is written, along with information which tells the reader not to look for subsequent sessions. This final table of contents (TOC) conforms to the ISO 9660 standard. CD-R writers support incremental packet writing (to be described in more detail below). Using this mode, data can be saved to a CD without finalising a session or the CD so more data can be added to the CD at a later time, although the CD cannot be read in a CD-ROM player until it has been finalised. Another mode of writing to an optical disc is known as Track at Once (TAO) in which a session can be written in a number of discrete write events. The disc may be removed from the writer and read in another writer before the session is fixated, and the sessions written contain complete tracks of information. This mode of writing to an optical disc 1 is illustrated schematically in Figure 3a of the drawings. As shown, each track 3 starts with a so-called pre-gap 4 of 2 seconds and 150 frames, and in this pre-gap 4 there is no relevant user data. Thus, in accordance with an exemplary embodiment of the present invention, a small portion 5 (say around 20 frames) of the pre-gap 4 of each track 3 can be used to test write quality, as described above and as illustrated schematically in Figure 3b, with the link point spanning the small portion 5 of the pre-gap 4. In all of the above write modes, and as explained above, the ROPC is required to be provided with a substantially seamless link to maintain the standard data format prescribed for the optical storage disc, because data which was supposed to be consecutive is interrupted using the techniques described above. This seamless link in itself can degrade the write quality a little, but because this occurs within non-user data, it is not a significant disadvantage. Yet another mode of writing to an optical disc is known as incremental or packet writing. A TAO written track has 150 blocks of overhead for run-in, run-out, pre-gap and linking. Packet writing is a method whereby several write events are allowed within a track, thus reducing the overhead. Here, the data is written in packets with a first link block, four run-in blocks, 32 data sectors, and two run-out blocks. In this case, the write quality of the first packet of each track can be tested. Of course, this packet can contain user data, but only the first packet may have a reduced quality, which is acceptable. In this case, however, we do not need a seamless link because the link block can be used. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A method of writing data to an optical disc (1) having a power calibration area and a data recording area, the method comprising recording said data in a plurality of discrete sections of said data recording area, said sections being separated by non-user data recording areas, the method further comprising testing in said non-user data recording areas, write quality of data being written to said optical disc (1).

2. A method according to claim 1, wherein the step of testing write quality of data being written to the optical disc (1) comprises halting said data recordal, reading and evaluating data written to the optical disc (1) and then restarting data recordal.

3. A method according to claim 2, wherein a link point (2,5) is provided between a location on the optical disc (1) at which data recordal is halted and a location on the optical disc (1) at which data recordal is restarted, said link point (2,5) being provided substantially within a respective non-user data area (4).

4. A method according to any one of claims 1 to 3, wherein a session of data is written to each discrete section of said data recording area, and wherein said non-user recording areas comprising lead-in and lead-out areas respectively.

5. A method according to claim 4, wherein write quality is tested in a portion (2) of the lead-in area prior to writing each session of data to said optical disc (1).

6. A method according to any one of claims 1 to 3, wherein a track (3) of data is written to each discrete section of said data recording area, and wherein said non-user data recording areas each comprise pre-gap (4).

7. A method according to claim 6, wherein write quality is tested in a portion (5) of the pre-gap area (4) prior to writing each track (3) of data to said optical disc (1).

8. A method according to any one of claims 1 to 7, wherein testing said write quality comprises performing optimal power calibration (OPC).

9. A method according to any one of claims 1 to 8, wherein optimal power calibration is performed in said power calibration area (PCA) of said optical disc (1).

10. A method according to any one of claims 1 to 9, wherein a substantially seamless link is provided between said data written to each of said discrete sections of said optical disc (1).

11. A method of writing data to an optical disc (1) having a power calibration area (PCA) and a data recording area, the method comprising writing tracks of data to said optical disc (1) as a sequence of packets of data, the method further comprising testing, in respect of one of at least one of said packets of data, write quality of data being written to said optical disc (1).

12. A method according to claim 11, comprising testing write quality in respect of a first packet of data of each sequence.

13. A method according to claim 11 or claim 12, wherein each packet of data comprises a link block, one or more run-in blocks, a plurality of data sectors and one or more run-out blocks.

14. Apparatus for writing data to an optical disc (1) having a power calibration area and a data recording area, the apparatus comprising means for recording said data in a plurality of discrete sections of said data recording area, said sections being separated by non-user data recording areas, the apparatus further comprising means for testing, in respect of one of said packets of data, write quality of said data being written to said optical disc (1).

15. Apparatus for writing data to an optical disc (1) having a power calibration area and a data recording area, the apparatus comprising means for writing tracks of data to said optical disc (1) as a sequence of packets of data, and means for testing, in respect of at least one of said packets of data, write quality of data being written to said optical disc (1).