Patent Publication Number: US-2012044794-A1

Title: Discrimination method of optical disc

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a discrimination method of an optical disc, and more particularly, to a method for identifying whether an optical disc is a Digital Versatile Disc-Random Access Memory (DVD-RAM) disc or a Digital Versatile Disc-ReWritable (DVD-RW) disc when the optical disc is accessed (i.e., read or written) by an optical disc drive. 
     2. Description of the Prior Art 
     Optical discs can be divided into different specifications, such as Compact Disc (CD), Video Compact Disc (VCD), Digital Versatile Disc (DVD), and Blu-ray Disc (BD), according to their storage capacities. Besides, the optical discs can be categorized into Read Only Memory (ROM) discs, Write-once (R) discs, ReWritable (RW) discs, and Random Access Memory (RAM) discs according to the reading/writing requirements. However, the optical characteristics of the optical discs vary with their storage capacities and disc types. Thus, the optical disc drive has to identify the type of the optical disc for properly adjusting the servo parameters to ensure valid reading/writing operations applied to the optical disc. 
     Among all the optical discs, the rewritable optical discs, such as DVD-RAM discs, are more complex than other types of optical discs. Please refer to  FIG. 1 , which is a diagram illustrating a data structure of a DVD-RAM disc. As shown in  FIG. 1 , the surface of a DVD-RAM disc  10  is divided into an embossed zone  11  and a rewritable zone  12 . The embossed zone  11  is located at the inner-most part of the DVD-RAM disc  10 , and used for providing the disc information, such as a storage capacity and type if the DVD-RAM disc  10 . The embossed zone  11  is surrounded by the rewritable zone  12 . The rewritable zone  12  is utilized for recording the user data. The major difference between the DVD-RAM disc  10  and other optical discs is that the rewritable zone  12  is divided into a plurality of sectors by a header  13 , thereby allowing recording of the user data in sectors. The header  13  with a higher reflection rate is utilized for storing physical addresses respectively corresponding to data stored in the sectors, thereby allowing the DVD-RAM disc  10  to randomly delete data and/or write data as a hard disk does. In this manner, the optical disc drive can identify the type of the optical disc by detecting the high reflection signal of the header  13  to check if the optical disc is a DVD-RAM disc  10 . 
     However, regarding a blank DVD-RAM disc, the reflection rate of its user data area is close to the reflection rate of its header. As a result, it is difficult to identify the reflection signal of the header of a blank DVD-RAM disc. Hence, a blank DVD-RAM disc would probably be erroneously identified as a DVD-RW disc, which leads to incorrect read/write operations of the optical disc. It is therefore, a demand for solving the problem of discriminating between a DVD-RAM disc and a DVD-RW disc that is encountered by the prior art. 
     SUMMARY OF THE INVENTION 
     It is therefore one of the objectives of the present invention to provide a discrimination method of an optical disc. The present invention first determines whether the optical disc is a data disc or a blank disc, and then selects a sub-beam added (SBAD) signal or a differential phase detection (DPD) signal according the characteristics of the optical disc for identifying the type of the optical disc correctly. 
     To achieve the aforementioned objective, the disclosed discrimination method of an optical disc includes following steps: focusing on a rewritable zone of the optical disc; checking whether the optical disc is a data disc or a blank disc by checking the existence of an Eight-to-Fourteen Modulation (EFM) signal (the data mark signal of the optical disc); utilizing the SBAD signal to identify the type of the optical disc when the optical disc is a data disc; and utilizing the DPD signal to identify the type of the optical disc when the optical disc is a blank disc; checking the existence of the header signals; identifying the optical disc as a DVD-RAM disc when the header signals exist; and identifying the optical disc as a DVD-RW disc when there is no header signal, wherein the step of utilizing the SBAD signal to identify the type of the optical disc comprises checking an SBAD signal of the header in the rewritable zone and an SBAD signal of the user data area in the rewritable zone; and the step of utilizing the DPD signal to identify the type of the optical disc comprises executing a track-on operation first, and then checking a DPD signal of the header in the rewritable zone and a DPD signal of the user data area in the rewritable area. When checking if the header signals exist or not, a predetermined threshold is set, and the length of a checking period is longer than the length of accessing one or more sectors. The existence of the header signals is checked by counting the number of header signals exceeding the predetermined threshold. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a data structure of a conventional DVD-RAM disc. 
         FIG. 2  is a diagram illustrating an optical disc drive generating an SBAD signal according to an exemplary embodiment of the present invention. 
         FIG. 3  is a diagram illustrating an SBAD signal generated by an optical disc drive that accesses a DVD-RAM data disc according to an exemplary embodiment of the present invention. 
         FIG. 4  is a diagram illustrating an SBAD signal generated by an optical disc drive that accesses the DVD-RAM blank disc according to an exemplary embodiment of the present invention. 
         FIG. 5(   a ) is a diagram illustrating the optical disc drive that generates a DPD signal according to an exemplary embodiment of the present invention. 
         FIG. 5(   b ) is a diagram illustrating the formation of the DPD signal according to an exemplary embodiment of the present invention. 
         FIG. 6  is a diagram illustrating a partial structure of the data track of a DVD-RAM data disc according to an exemplary embodiment of the present invention. 
         FIG. 7  is a diagram illustrating a DPD signal that is generated when a DVD-RAM data disc is being accessed according to an exemplary embodiment of the present invention 
         FIG. 8  is a diagram illustrating the DPD signal that is generated when there is an offset during the track-on operation. 
         FIG. 9  is a diagram illustrating a partial structure of the data track of a DVD-RAM blank disc according to an exemplary embodiment of the present invention. 
         FIG. 10  is a flowchart illustrating a discrimination method of an optical disc according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The technical features of the present invention will be described in detail hereinafter by way of preferred embodiments with reference to the drawings. 
     Please refer to  FIG. 2 , which is a diagram illustrating an optical disc drive generating a sub-beam added signal according to an exemplary embodiment of the present invention. The optical disc drive  20  is an apparatus utilized for accessing an optical disc  21 , and includes an optical pickup head  22 , a photo detector  23 , a first adder  24 , a second adder  25 , and a third adder  26 . When the optical disc drive  20  is accessing the optical disc  21 , the optical pickup head  22  emits a laser beam upon the optical disc  21  and then receives a reflected beam from the optical disc  21 , where the reflected beam is projected to the photo detector  23 . The photo detector  23  has four sensing areas A, B, C, and D used for generating signals A, B, C, and D by converting the respective received luminous flux into electrical signals, respectively. Next, a signal (A+C) is generated from summing up two of the four signals A-D through the first adder  24 , and a signal (B+D) is generated from summing up the other two of the four signals A-D through the second adder  25 . When the signal (A+C) and the signal (B+D) are added together through the third adder  26 , a sub-beam added (SBAD) signal is generated accordingly. 
     Please refer to  FIG. 3  and  FIG. 4 .  FIG. 3  is a diagram illustrating an SBAD signal generated by an optical disc drive that accesses a DVD-RAM data disc according to an exemplary embodiment of the present invention.  FIG. 4  is a diagram illustrating an SBAD signal generated by an optical disc drive that accesses a DVD-RAM blank disc according to an exemplary embodiment of the present invention. As shown in  FIG. 3 , when the optical disc drive accesses an optical disc, the optical pickup head needs to emit a laser beam focused on the optical disc. If the optical disc is a DVD-RAM data disc with the rewritable zone having user data recorded therein, the reflection rate of the optical disc is decreased. At this time, the reflection rate of the header is obviously higher than the reflection rate of the user data area. Thus, the detected SBAD signal includes user data area signals  31  with lower peak values and header signals  32  with higher peak values exceeding a predetermined threshold  33  of the SBAD signal. In this way, by utilizing the obvious difference between the user data area signals  31  and the header signals  32 , the header signals can be found easily for identifying the optical disc as a DVD-RAM data disc. 
     However, as shown in  FIG. 4 , if the optical disc is a DVD-RAM blank disc with a data area that is not used for recording user data yet, the blank rewritable zone also has a higher reflection rate. At this time, the reflection rate of the header is close to the reflection rate of the user data area. That is, the user data area signals  31  included in the SBAD signal derived from a blank optical disc are similar to the header signals  32  included in the SBAD signal derived from the blank optical disc. As a result, as the optical disc drive has difficulty in correctly identifying the header signals by using the predetermined threshold  33  of the SBAD signal, it is difficult to precisely identify the optical disc as a DVD-RAM blank disc by referring to the SBAD signal. That is, the SBAD signal is more suitable for discrimination of a DVD-RAM data disc. 
     Please refer to  FIG. 5(   a ) in conjunction with  FIG. 5(   b ).  FIG. 5(   a ) is a diagram illustrating the optical disc drive that generates a differential phase detection (DPD) signal according to an exemplary embodiment of the present invention.  FIG. 5(   b ) is a diagram illustrating the formation of the DPD signal according to an exemplary embodiment of the present invention. Similarly, the optical disc drive  50  utilizes four sensing areas A, B, C, and D of a photo detector  53  for obtaining four signals. The signal A and the signal C generated from sensing areas located at diagonal locations are compared by a first comparator  54 , and the signal B and the signal D generated from sensing areas located at other diagonal locations are compared by the second comparator  55 . Accordingly, phase signals S 1  and S 2  are generated from the first comparator  54  and the second comparator  55 , respectively. When the phase of the phase signal S 2  is subtracted from the phase of the phase signal S 1  through a phase detector (PD)  56 , a phase difference signal (S 1 -S 2 ) is thereby generated. The phase difference signal (S 1 -S 2 ) is a differential phase detection (DPD) signal. 
     Please refer to  FIG. 6  in conjunction with  FIG. 7 .  FIG. 6  is a diagram illustrating a partial structure of the data track of a DVD-RAM data disc according to an exemplary embodiment of the present invention.  FIG. 7  is a diagram illustrating a DPD signal that is generated when a DVD-RAM data disc is being accessed according to an exemplary embodiment of the present invention. As shown in  FIG. 6 , the data track  60  of the DVD-RAM disc is constructed by grooves  61  and lands  62 , and each of the recording sectors has a user data area immediately follows the header. When data is recorded onto the DVD-RAM disc, marks  63  will be formed at grooves  61  and lands  62 . Besides, there are a plurality of pre-embossed pits  64  for providing the physical address information of to the recording sectors. 
     When the DVD-RAM data disc is being accessed, a light spot  65  projected by the optical pickup head is locked to the data track  60  correctly, and moves along a midline  66  of the data track  60  to access the DVD-RAM disc. Since the pits  64  of the header are merely located at one side of the midline  66  of the data track  60  (e.g., located at the upper side of the midline  66 ), the sensing areas (B+D) detect the pits  64  of the header earlier than the sensing areas (A+C), and the phase signal S 2  is a phase leading signal, thereby making the phase signal S 2  have larger amplitude and the phase signal  51  have amplitude equal to zero. As a result, the DPD signal is a phase difference signal with an upper part reaching the heist level. On the other hand, if the pits  64  are located at the lower side of the midline  66 , the sensing areas (A+C) detect the pits of the header earlier than the sensing areas (B+D), and the phase signal  51  is a phase leading signal. At this time, the phase signal  51  has larger amplitude and the phase signal S 2  has amplitude equal to zero. As a result, the DPD signal is a phase difference signal with a lower part reaching a lowest level. By the above operations, the header signals  67  having larger amplitude in the DPD signal shown in  FIG. 7  are generated. When the light spot  65  keeps moving along the midline  66  of the data track  60  and enters the groove  61  or land  62  of the user data area for accessing the DVD-RAM data disc, the light spot  65  exactly moves along the midline  66  of the mark  63  with two symmetrical sides. Hence, the phase signal  51  corresponding to the sensing areas (A+C) is almost the same as the phase signal S 2  corresponding to the sensing areas (B+D), resulting in a phase difference close to zero. As a result, user data area signals  68  with smaller amplitude in the DPD signal are generated. That is, by utilizing the predetermined threshold  70  of the DPD signal, the existence of the header signals can be easily checked. 
     Please refer to  FIG. 8  in conjunction with  FIG. 6 .  FIG. 8  is a diagram illustrating the DPD signal that is generated when there is an offset during the track-on operation. As shown in  FIG. 6 , when the optical disc is eccentric or when the servo system of the optical disc drive is abnormal, the optical pickup head fail to move along the normal midline  66  of the track and is locked to an offset on-track path  69 . Hence, the pits  64  of the header are allocated at two sides of the offset on-track path  69 , resulting in a reduced phase difference between the phase signal S 1  corresponding to the sensing areas (A+C) and the phase signal S 2  corresponding to the sensing areas (B+D). Thus, as shown in  FIG. 7 , the header signals  67  with reduced amplitude in the DPD signal are generated. However, due to the fact that the offset on-track path  69  is shifted to one side of the data track  60 , when the mark  63  of the user data area is accessed, the phase difference between the phase signal S 1  corresponding to the sensing areas (A+C) and the phase signal S 2  corresponding to the sensing areas (B+D) is increased and similar to that generated from accessing the header. As a result, user data area signals with increased amplitude in the DPD signal are generated. Therefore, it is difficult to identify header signals by utilizing the predetermined threshold  70  of the DPD signal. That is, in a case where a normal DVD-RAM data disc and a normal optical disc drive are present, the header signals  67  and the user data area signals  68  can be easily discriminated by referring to the DPD signal generated from subtracting the phase signal S 2  corresponding to the sensing areas (B+D) from the phase signal S 1  corresponding to the sensing areas (A+C). However, in another case where an abnormal DVD-RAM data disc and/or an abnormal optical disc drive are present, the DPD signal generated by subtracting the phase signal S 2  from the phase signal S 2  is easily to be affected by the abnormal DVD-RAM disc and/or the abnormal optical disc drive. As the header signals  67  and the user data area signals  68  of the DPD signal are quite similar to each other, the probability of erroneously identifying the type of the optical disc is high. 
     Please refer to  FIG. 9 , which is a diagram illustrating a partial structure of the data track of a DVD-RAM blank disc according to an exemplary embodiment of the present invention. For a DVD-RAM blank disc, no matter whether the optical disc and/or the optical disc drive are normal or not, the pits  64  located one side of the data track still make the DPD signal generated from subtracting the phase signal S 2  corresponding to the sensing areas (B+D) from the phase signal S 1  corresponding to the sensing areas (A+C) maintain at larger amplitude, regardless of the optical pickup head moving along the midlines  66  or the offset on-track path  69 . When the optical pickup head moves to the user data area, the reflection rates of two sides of the offset on-track path  69  are identical to each other since there are no marks. That is, the phase difference between the phase signal S 1  corresponding to the sensing areas (A+C) and the phase signal S 2  corresponding to the sensing areas (B+D) is almost zero, which makes the user data area signals of the DPD signal have amplitude almost equal to zero. The waveform of the DPD signal generated from accessing a DVD-RAM blank disc is similar to that of the DPD signal shown in  FIG. 7 , and the difference therebetween is that the DPD signal now has smaller amplitude. However, though the DPD signal has smaller amplitude, the header signals and the user data area signals can be easily discriminated by referring to the DPD signal. By utilizing the predetermined threshold  70  of the DPD signal, the existence of header signals can be efficiently checked. Therefore, the DPD signal is more appropriate for discrimination of the DVD-RAM blank disc. 
     The discrimination method of the type of the optical disc according to the present invention utilizes the aforementioned SBAD signal which can be used to identify the DVD-RAM data disc correctly and the aforementioned DPD signal which can be used to identify the DVD-RAM blank disc correctly. Before the optical disc discrimination is performed, the optical disc drive accesses the optical disc to check existence of data mark signals for determining whether the optical disc is a data disc or a blank disc. The existence of a signal of data marks of the optical disc may be checked by checking an Eight-to-Fourteen Modulation (EFM) signal. If the EFM signal exists, meaning that there are recorded marks on the optical disc, the optical disc at this time is a data disc with data recorded thereon. If the EFM signal does not exist, meaning that there are no recorded marks on the optical disc, the optical disc at this time is a blank disc. After the operation of checking if the optical disc is a data disc or a blank disc is completed, an SBAD-based discrimination method which utilizes a predetermined threshold of an SBAD signal to check existence of the header signals is employed if the optical disc is a data disc, and a DPD-based discrimination method which utilizes a predetermined threshold of a DPD signal to check existence of header signals is employed if the optical disc is a blank disc. If the optical disc has header signals, it is identified as a DVD-RAM disc; otherwise, it is identified as a DVD-RW disc. In the end, the type of the optical disc can be identified correctly. 
     Because the rewritable zone is divided into sectors by the header and each sector has a fixed length, the operation of checking the header signals is allowed to check at least one sector instead of checking all of the sectors, thereby shortening the processing time of identifying the type of the optical disc. That is, the length of a checking period of checking the existence of header signals is required to be not shorter than the length of accessing one sector. However, for enhancing the accuracy of the discrimination of the optical disc type, the length of the checking period of checking the existence of header signals is preferably to encompass the length of accessing a plurality of sectors. Besides, only when the number of the header signals exceeding the predetermined threshold is greater than a predetermined value, the existence of header signals is confirmed. 
       FIG. 10  is a flowchart illustrating the discrimination method of the optical disc according to an exemplary embodiment of the present invention. The detailed steps of the discrimination method of the present invention which utilizes the SBAD signal or the DPD signal is described in the following. Step S 1  is executed to start the discrimination process of the optical disc. Next, in Step S 2 , the optical pickup head is moved to the rewritable zone of the optical disc. In Step S 3 , the optical pickup head focuses a light spot on the optical disc. In Step S 4 , it is checked to see if the optical disc is a data disc or a blank disc by checking the existence of a data mark signal of the optical disc. If the optical disc is a data disc, the flow proceeds with Step S 5 . If the optical disc is a blank disc, the flow proceeds with Step S 6 . In Step S 5 , the SBAD signal is utilized for discrimination of the optical disc; next, the flow proceeds with Step S 7 . In Step S 6 , the track-on operation is first executed, and then the DPD signal is utilized for discrimination of the optical disc. In Step S 7 , the SBAD/DPD signal is checked to see if the header signals exist or not. If the header signals exist, the flow proceeds with Step S 8  to identify the optical disc as a DVD-RAM disc. If there is no header signal in the SBAD/DPD signal, the flow proceeds with Step S 9  to identify the optical disc as a DVD-RW disc. 
     In conclusion, the discrimination method of the optical disc provided in this invention firstly checks if the optical disc is a data disc or a blank disc. When the optical disc is a blank disc, the track-on operation is executed, and the existence of header signals is checked by using the DPD signal. When the optical is a data disc, the SBAD signal is utilized to check if the header signals exist. Therefore, the discrimination of the optical disc is accomplished based on the checking result of the existence of header signals. In this way, the objective of identifying the DVD-RAM disc correctly is achieved. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.