Abstract:
An apparatus for detecting burst cutting areas on optical discs includes an optical pickup head, a front-end processing unit, a sync pattern detector, a channel clock recovery device, and a data demodulator. The front-end processing unit generates a BCA signal in response to a radio frequency signal. The sync pattern detector counts the BCA signal according to a reference clock, detects a sync pattern of the BCA signal and outputs a channel bit length counting value. The channel clock recovery device generates a channel clock according to the reference clock and the channel bit length counting value. The data demodulator transfers the BCA signal into a BCA data according to the channel clock. The sync pattern detector continuously counts the B CA signal and continuously outputs a plurality of counting values, so that the sync pattern of the BCA signal can be determined according to at least three sequential counting values.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method and a related apparatus for detecting optical discs, and more particularly, to a method and a related apparatus for detecting burst cutting areas on optical discs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Please refer to  FIG. 1A .  FIG. 1A  is a diagram illustrating a burst cutting area (which is called as BCA in the following descriptions) on an optical disc. The BCA is a circular and is near to a center hole of the optical disc, wherein the pattern of the BCA is similar to a bar code and alternates bright with dark. Generally speaking, The BCA is an area used for recording copyright-related information on the optical disc, which records essential messages capable of decoding contents of the optical disc. As a result, the BCA is widely applied to an optical disc having copyright protection. For a latest blue-ray disc, the BCA is more than an essential protection mechanism. Hence, how to quickly and accurately decode the data in the BCA has become an important problem that needs be solved by disc drive manufactures. 
         [0003]    Please refer to  FIG. 1B .  FIG. 1B  is a diagram illustrating the structure of a BCA defined in the blue-ray disc specification. Each row has five bytes, wherein a first byte of each row is a sync byte SB BCA  and the sync byte SB BCA  of each row has the same sync pattern. Based on the blue-ray disc specification, the first sync byte (SB BCA,−1 ) is the beginning of the whole BCA, so that the whole BCA can be decoded only when the first sync byte (SB BCA,−1 ) is first detected. In addition, based on the blue-ray disc specification, a BCA signal with 5 T, 3 T, 2 T, and 4 T is generated when the laser beam emitted from the optical pickup head is projected on the sync pattern. In other words, when a pattern with 5 T, 3 T, 2 T, and 4 T is appeared in the BCA signal, it represents that the sync pattern is detected in the BCA signal. 
         [0004]    Since the BCA signal is affected by the rotating speed of the spindle motor, the conventional methods usually find out an accurate sampling clock first and then utilize the sampling clock to perform the follow-up sync pattern detection in the BCA signal and the decoding of the BCA signal in order to accurately sample the BCA signal and the sync pattern of the BCA signal. 
         [0005]    A sampling clock generator for BCA data decoding has been disclosed in the U.S. Pat. No. 7,006,415. As shown in  FIG. 2 , the sampling clock generator  41  receives a spindle-motor-speed indicating signal FG and a BCA reproducing signal, and then generates a sampling clock in response to the spindle-motor-speed indicating signal FG and the BCA reproducing signal. After that, the sampling clock is inputted to a BCA channel bit generator  42  and a BCA decoder  43 . As a result, the BCA channel bit generator  42  is capable of finding out the sync pattern of the BCA signal according to the sampling clock and accurately generating a BCA channel bit to the BCA decoder  43 . The BCA decoder  43  is capable of generating a BCA data bit according to the sampling clock and the BCA channel bit. 
         [0006]    Obviously, the spindle motor must be fixed at a designated rotating speed in the above-mentioned conventional method, and thus the sampling clock can be calculated according to a relationship between the BCA reproducing signal and the rotating speed. However, the frequency variations of the sampling clock are very small and will be easily affected by the optical disc or the spindle motor. 
         [0007]    A method and apparatus for generating a sampling clock for a burst cutting area of an optical disc has been disclosed in the US Publication No. 20060181998. As shown in  FIG. 3 , the sampling clock generating device  400  includes a BCA signal reproduction device  410 , a detecting device  420 , a computing unit  430 , a clock generator  440 , and a control unit  450 . 
         [0008]    After a radio frequency signal passes through the BCA signal reproduction device  410 , a BCA reproducing signal BRS can be generated to the detecting device  420 . A counter  422  of the detecting device  420  then continuously counts the BCA reproducing signal BRS according to a reference clock REFCLK to obtain a counting value, and the counting value is stored in a register  424  of the detecting device  420 . In addition, when the counting value of the counter  422  is greater than the counting value stored in the register  424 , the counting value stored in the register  424  will be updated. That is, the counting value stored in the register  424  is the largest value. Moreover, based on the blue-ray disc specification, the maximum channel bit length of the BCA reproducing signal BRS is 5 T. 
         [0009]    For example, assume that the counting value stored in the register  424  is 100. The counting value is divided by 5 by using the computing unit  430  (i.e., 100/5=20), so as to output a value equaling 20 to the clock generator  440 . The clock generator  440  obtains a period of the channel bit length with 1 T equaling twenty periods of the reference clock REFCLK, and generates the sampling clock. Only after the sampling clock is obtained, the sync pattern detection can be performed according to the sampling clock. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an apparatus and method for detecting burst cutting areas on optical discs. The apparatus is capable of detecting a sync pattern of a BCA signal and simultaneously generating a channel clock when the sync pattern is detected. After that, the apparatus is capable of demodulating the BCA signal to generate a BCA data according to the channel clock. 
         [0011]    According to an exemplary embodiment of the present invention, an apparatus for detecting a burst cutting area on an optical disc is provided. The apparatus consists of an optical pickup head, a front-end processing unit, a sync pattern detector, a channel clock recovery device, and a data demodulator. The optical pickup head is capable of emitting a laser beam to the burst cutting area of the optical disc and obtaining a radio frequency signal. The front-end processing unit receives the radio frequency signal and generates a BCA signal in response to the radio frequency signal. The sync pattern detector counts the BCA signal according to a reference clock and is capable of detecting a sync pattern of the BCA signal and outputting a channel bit length counting value. The channel clock recovery device receives the reference clock and the channel bit length counting value, and generates a channel clock according to the reference clock and the channel bit length counting value. The data demodulator receives the channel clock and the BCA signal, and transfers the BCA signal into a BCA data according to the channel clock. The sync pattern detector is capable of continuously counting the BCA signal and continuously outputting a plurality of counting values, so that the sync pattern of the BCA signal is able to be determined according to at least three sequential counting values. 
         [0012]    In addition, according to another exemplary embodiment of the present invention, a method for detecting a burst cutting area on an optical disc is provided. The method includes the following steps: continuously sampling a BCA signal according to a reference clock, and continuously outputting a first counting value, a second counting value and a third counting value; and determining a sync pattern of the BCA signal according to a relationship between the first counting value, the second counting value and the third counting value. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
           [0014]      FIG. 1A  is a diagram illustrating a burst cutting area on an optical disc; 
           [0015]      FIG. 1B  is a diagram illustrating a structure of a BCA defined in the blue-ray disc specification; 
           [0016]      FIG. 2  is a diagram illustrating a conventional sampling clock generator for decoding the data of a BAC according to prior art; 
           [0017]      FIG. 3  is a diagram illustrating a conventional sampling clock generating device of a BCA on an optical disc according to prior art; 
           [0018]      FIG. 4  is a diagram illustrating an apparatus for detecting a sync pattern of a BCA on an optical disc according to an embodiment of the present invention; 
           [0019]      FIG. 5  is a diagram showing an embodiment of a sync pattern detector applicable to the apparatus of  FIG. 4 ; and 
           [0020]      FIG. 6  is a diagram showing an embodiment of the BCA signal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Since the conventional methods usually find out the sampling clock of the BCA signal and then detect the sync pattern of the BCA signal according to the sampling clock, they have a lower efficiency and complicated circuits are required. On the other hand, the method and apparatus for detecting a sync pattern of a BCA on an optical disc disclosed in the present invention detects the sync pattern of the BCA signal and simultaneously generates a channel clock when the sync pattern is detected. Therefore, some complicated circuits can be saved, which can effectively reduce the circuit size. In addition, a spindle motor provided with rotating speed information is not required if the mechanism disclosed in the present invention is applied to optical storage devices, which can reduce the manufacturing cost. 
         [0022]    Please refer to  FIG. 4 .  FIG. 4  is a diagram illustrating an apparatus for detecting a sync pattern in a BCA on an optical disc according to an embodiment of the present invention. The apparatus  500  consists of an optical pickup head  510 , a front-end processing unit  520 , a sync pattern detector  530 , a channel clock recovery device  540 , and a data demodulator  550 . The optical pickup head  510  is capable of emitting a laser beam to a BCA of an optical disc and obtaining a radio frequency (RF) signal. The front-end processing unit  520  then receives the radio frequency signal and generates a BCA signal in response to the radio frequency signal. In the meanwhile, the BCA signal is inputted to the sync pattern detector  530  and the data demodulator  550 . The sync pattern detector  530  can find out the sync pattern according to the BCA signal and a reference clock CLK ref . When the sync pattern is detected, the sync pattern detector  530  outputs a channel bit length counting value to the channel clock recovery device  540 . The channel clock recovery device  540  generates a channel clock to the data demodulator  550  according to the channel bit length counting value and the reference clock CLK ref , so that the data demodulator  550  can immediately transfer the BCA signal into a BCA data. 
         [0023]    Based on the blue-ray disc specification, the radio frequency signal is generated when the laser beam emitted from the optical pickup head  510  is radiated on the sync pattern. After that, the BCA signal with 5 T, 3 T, 2 T, and 4 T can be generated by processing the radio signal via the front-end processing unit  520 . In other words, when a pattern with 5 T, 3 T, 2 T, and 4 T is appeared in the BCA signal, it represents that the sync pattern is detected. For further analysis, a signal having a continuous pattern with 5 T, 3 T, 2 T, and 4 T is impossible to be appeared in the BCA signal except for the sync pattern of the BCA signal. Hence, such feature is adopted in the present invention. When the continuous pattern with 5 T, 3 T, 2 T, and 4 T is appeared in the BCA signal, it is determined as the sync pattern. 
         [0024]    Please refer to  FIG. 5 .  FIG. 5  is a diagram showing an embodiment of a sync pattern detector applicable to the apparatus  400  of  FIG. 4 . The sync pattern detector  530  consists of a counter  532  and a determining unit  538 . The counter  532  continuously counts the BCA signal according to the reference clock CLK ref , and outputs the corresponding counting values to the determining unit  538 . The determining unit  538  determines whether the sync pattern is appeared in the BCA signal according to three sequential counting values. When the sync pattern is detected, the determining unit  538  outputs the channel bit length counting value to the channel clock recovery device  540 . 
         [0025]    Please refer to  FIG. 6 .  FIG. 6  is a diagram showing an embodiment of the BCA signal, wherein high logic levels and low logic levels with different timing lengths are appeared in the BCA signal. According to an embodiment of the present invention, the counter  532  continuously samples the high logic levels and low logic levels in the BCA signal according to the reference clock CLK ref . In other words, when the BCA signal changes from the high logic level to the low logic level, the counter  532  outputs the counting values of the high logic level and re-counts the low logic level. Similarly, when the BCA signal changes from the low logic level to the high logic level, the counter  532  outputs the counting values of the low logic level and re-counts the high logic level. That is, the counter  532  continuously outputs the counting values to the determining unit  538  during a transformation between high/low logic levels of the BCA signal. After three sequential counting values are received by the determining unit  538 , it immediately performs the sync pattern detection. 
         [0026]    For example, the determining unit  538  can determine whether the BCA signal has the sync pattern by reference to a ratio of the three sequential counting values, e.g. Cnt1, Cnt2, and Cnt3, equaling 5:3:2 or not. When the ratio of the three sequential counting values Cnt1, Cnt2, and Cnt3 is equal to 5:3:2, the BCA signal is determined to have the sync pattern. Otherwise, the BCA signal is determined to have no sync pattern. 
         [0027]    The determining unit  538  can set more judgment conditions to make the judgments of the sync pattern more accurate. For example, when a condition of Cnt1&gt;Cnt2&gt;Cnt3 is true and an absolute value of (Cnt1−Cnt2−Cnt3) is smaller than a threshold, it represents that the sync pattern of the BCA signal is detected. 
         [0028]    Take  FIG. 6  as an example, after the three sequential counting values Cnt1, Cnt2, and Cnt3 respectively equaling 40, 19, and 51, are received by the determining unit  538 , a first judgment (I) can be performed. Since the ratio of the three sequential counting values Cnt1, Cnt2, and Cnt3 is approximately 4:2:5, the BCA signal is determined to have no sync pattern. Otherwise, since the condition that Cnt1&gt;Cnt2&gt;Cnt3 is not true, the BCA signal is determined to have no sync pattern. 
         [0029]    After that, when a next counting value is received by the determining unit  538 , the determining unit  538  discards the old Cnt1 by reference to a first-in-first-out manner. At this time, the three sequential counting values Cnt1, Cnt2, and Cnt3 are respectively equal to 19, 51, and 28, and a second judgment (II) can be performed. Since the ratio of the three sequential counting values Cnt1, Cnt2, and Cnt3 is approximately 2:5:3, the BCA signal is determined to have no sync pattern. Otherwise, since the condition that Cnt1&gt;Cnt2&gt;Cnt3 is not true, the BCA signal is determined to have no sync pattern. 
         [0030]    Afterwards, when a next counting value is received by the determining unit  538  again, the determining unit  538  discards the old Cnt1 by reference to a first-in-first-out manner. At this time, the three sequential counting values Cnt1, Cnt2, and Cnt3 are respectively equal to 51, 28, and 21, and a third judgment (III) can be performed. Since the ratio of the three sequential counting values Cnt1, Cnt2, and Cnt3 is approximately 5:3:2, the BCA signal is determined to have the sync pattern. Assume that the threshold is set as 5. Since the condition that Cnt1&gt;Cnt2&gt;Cnt3 is true and the absolute value of (Cnt1−Cnt2−Cnt3) is smaller than the threshold (i.e., Cnt1−Cnt2−Cnt3=51−28−21=2&lt;5), the BCA signal is determined to have the sync pattern. 
         [0031]    Similarly, the sync pattern is not detected in the BCA signal during a fourth judgment (IV) and a fifth judgment (V). 
         [0032]    As can be known from the above-mentioned descriptions, the BCA signal is determined to have the sync pattern when the third judgment (III) is performed by the determining unit  538 . After that, the determining unit  538  is capable of outputting the channel bit length counting value according to the received counting values. For example, a calculating result equaling 10.5 can be obtained from dividing the third counting value Cnt3 representative of 2 T by 2 via the determining unit  538 , and then the calculating result equaling 10.5 is set as the channel bit length counting value to be outputted. Or another calculating result equaling 9.875 can be obtained from dividing a sum of the first counting value Cnt1 and the second counting value Cnt2 representative of 8 T by 8 (i.e., [51+28]/8=9.875), and then the calculating result equaling 9.875 is set as the channel bit length counting value to be outputted. Or another calculating result equaling 10 can be obtained from dividing a sum of the first counting value Cnt1, the second counting value Cnt2, and the third counting value Cnt3 representative of 10 T by 10 (i.e., [51+28+21]/10=10), and then the calculating result equaling 10 is set as the channel bit length counting value to be outputted. Similarly, by reference to the calculating result obtained from dividing a sum of the second counting value Cnt2 and the third counting value Cnt3 representative of 5 T by 5, by reference to the calculating result obtained from dividing a sum of the first counting value Cnt1 and the third counting value Cnt3 representative of 7 T by 7, by reference to the calculating result obtained from dividing the first counting value Cnt1 representative of 5 T by 5, or by reference to the calculating result obtained from dividing the second counting value Cnt2 representative of 3 T by 3, the channel bit length counting value can be obtained. In other words, the manner for obtaining the channel bit length counting value is not limited in the present invention. 
         [0033]    Therefore, when the clock cycle of the reference clock CLK ref  is multiplied by the channel bit length counting value by using the channel clock recovery device  540 , a period of the channel bit representative of 1 T can be obtained and the channel clock can be recovered. After that, the data demodulator  550  is capable of transferring the BCA signal into the BCA data according to the channel clock. 
         [0034]    That is, the mechanism disclosed in the present invention can detect the sync pattern of the BCA signal and can simultaneously generate the channel clock when the sync pattern is detected, so that the data demodulator is capable of immediately demodulating the BCA signal to generate the BCA data. 
         [0035]    While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not to be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.