Abstract:
A data signal includes a master signal generated by a master part of an optical pickup head in response to a light beam reflected from the optical recording medium and a side signal generated by a side part of the optical pickup head in response to the light beam reflected from the optical recording medium. A discriminating signal is obtained by subtracting the master signal from the side signal. Then, whether a data defect is existent in a data storage region of the optical recording medium can be determined according to the discriminating signal and optionally the side signal. When the data defect is determined existent, a servo tracking operation in the reading procedure is suspended.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for detecting a data defect, and more particularly to a method for detecting a data defect existing in an optical recording medium.  
       BACKGROUND OF THE INVENTION  
       [0002]     Data defects may exist in optical recording medium such as compact discs, video compact discs or digital video discs due to imperfect recording quality, inadequate preserving condition or incorrectly operating the discs. The poor conditions of discs themselves, for example suffering from scratches or contaminants, are also likely to result in undesired data defects. The data defects could be rendered in various aspects. For example, a slicer in an optical reading system is used for converting the read analog signals into digital signals according to a default central level signal. The default central level signal is a predetermined voltage value stored in the optical reading system. When the read analog signal is higher than the default central level signal, the sliced digital signal will be a high level signal. When the read analog signal is lower than the default central level signal, the sliced digital signal will be a low level signal. If there is any data defect existing in the optical disc, the read analog signal will be affected by the data defect, so that the sliced digital signal will be obtained with errors. If the error-sliced digital signal is operated by the following data processing circuit and then is processed by the continuing servo tracking operation, it causes errors of the data processing or a crash of the optical reading system. For preventing the data-reading procedure from being affected by data defects, it is preferred to detect these data defects existing in the discs and take adequate measures in advance.  
         [0003]     Please refer to  FIG. 1  which is a schematic diagram showing the light-receiving portions of an optical pickup head. The optical pickup head  1  includes a master part  11  having four receiving portions A˜D, a first side part  12  having two receiving portions E and G, and a second side part  13  having two receiving portions F and H. The laser light emitted from the optical pickup head  1  is reflected by the optical disc. The reflected laser signal carries certain data stored in the focused spot of the optical disc. Then, the reflected laser signal is received by the eight receiving portions A˜H to be processed into useful signals. One of the useful signals is a sub-beam addition signal (SBAD) signal. The SBAD signal is substantially the summation of the sub-beam signals generated by the light-receiving portions E, F, G and H in response to the received light intensities. Conventionally, the optical reading system monitors the SBAD signal to realize the data-storage quality of an optical disc. If the level of the SBAD signal is lower than a predetermined level, it is determined that data defects occur. In the meantime, the subsequent servo tracking operation of the optical reading system is suspended to prevent from incorrect data processing of the data stored in the optical disc.  
         [0004]     An example that there are serious and small scratches existing in the data storage region of a disc is given with reference to  FIG. 2 ( a ) in which the relationships among SBAD, data and defect-indicating signals are shown. Due to a serious scratch in the data storage region of the disc, a data signal drop E 11  of the data signal E 1  is rendered, and a signal drop S 11  occurs in the SBAD signal S 1  correspondingly. Since the signal drop S 11  has been down lower than a preset threshold level L 1 , the defect-indicating signal D 1  is switched to a high level D 11  to suspend the servo tracking operation of the optical reading system, thereby protecting the optical reading system from errors or hanging. After the scratch has been passed and the defect-indicating signal D 1  is switched back to a low level, the servo tracking operation of the optical reading system is restored. The preset threshold level L 1  can be a voltage value stored in the optical reading system.  
         [0005]     Afterwards, another scratch that is less serious in the data storage region of the disc is encountered, so a less data signal drop E 12  of the data signal E 1  is rendered. Correspondingly, a less signal drop S 12  occurs in the SBAD signal S 1 . Since the signal drop S 12  has not been down to the preset threshold level L 1 , the defect-indicating signal D 1  will not be switched to a high level D 11  to suspend the servo tracking operation of the optical reading system. Instead, the defect-indicating signal D 1  stays low as indicated by the reference D 12 .  
         [0006]     Unfortunately, in a case that the SBAD signal S 1  cannot reflect the real defect situation, e.g. data interruption E 21  and E 22  occurring in the data signal E 2  as exemplified in  FIG. 2 ( b ), errors may happen. Since the signal drops S 21  and S 22  of the SBAD signal S 2  corresponding to the data interruption E 21  and E 22  are insignificant, i.e. not lower than the preset threshold level L 1 , there will be no high-level peaks occurring in the defect-indicating signal D 2 , neither in the corresponding section D 21  nor in the corresponding section D 22 . Accordingly, the subsequent data processing circuit and the servo tracking operation keeps on processing the sliced digital data. Therefore, the signal drops S 21  and S 22  of the SBAD signal S 2  corresponding to the data interruption E 21  and E 22  will affect the optical reading system and causes the incorrect data processing of the data stored in the optical disc or a crash of the optical reading system.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, the present invention provides a method capable of detecting a data defect that cannot be located with the SBAD signal.  
         [0008]     The present invention provides a method for detecting a data defect. The method includes steps of: detecting a data signal including a master signal generated by a master part of an optical pickup head and a side signal generated by a side part of the optical pickup head; subtracting the master signal from the side signal to obtain a discriminating signal; and detecting whether a data defect is existent according to the discriminating signal.  
         [0009]     In an embodiment, the master part of the optical pickup head has four light-receiving portions A, B, C and D, the side part has two light-receiving portions E and G at a first side of the master part and two light-receiving portions F and H at a second side of the master part opposite to the first side, the master signal is the summation of the main-beam signals generated by the light-receiving portions A, B, C and D in response to the received light intensities, and the side signal is the summation of the sub-beam signals generated by the light-receiving portions E, F, G and H in response to the received light intensities.  
         [0010]     In an embodiment, the data defect is determined existent when a signal drop is down lower than a threshold value in the discriminating signal.  
         [0011]     For example, the data defect results from a scratch or data interruption.  
         [0012]     In an embodiment, the method further includes a step of switching a level of a defect-indicating signal to locate the data defect when the data defect is determined existent. For example, the defect-indicating signal is switched from a low level to a high level when the data defect is determined existent.  
         [0013]     The present invention further provides a method for detecting a data defect in an optical recording medium. The method includes steps of receiving a master signal generated by a master part of an optical pickup head in response to a light beam reflected from the optical recording medium and a side signal generated by a side part of the optical pickup head in response to the light beam reflected from the optical recording medium; subtracting the master signal from the side signal to obtain a discriminating signal; and detecting whether a data defect is existent in a data storage region of the optical recording medium according to the discriminating signal and the side signal.  
         [0014]     In an embodiment, the data defect is determined existent when a signal drop of the discriminating signal is down lower than a first threshold value, and simultaneously a signal drop of the side signal is down lower than a second threshold value. In this case, the data defect might result from a serious scratch.  
         [0015]     In an embodiment, the data defect is determined existent when a signal drop of the discriminating signal is down lower than a first threshold value, and simultaneously the side signal has a little variation but higher than a second threshold value. In this case, the data defect might result from data interruption.  
         [0016]     The present invention further provides a method for discriminating a data defect in an optical recording medium, which includes steps of: receiving a discriminating signal and a side signal; comparing the discriminating signal with a first threshold value to obtain a first comparing result; comparing the side signal with a second threshold value to obtain a second comparing result; and discriminating the data defect by the first and second comparing results; wherein the discriminating signal is obtained by subtracting a master signal generated by a master part of an optical pickup head from the side signal generated by a side part of the optical pickup head.  
         [0017]     In an embodiment, the data defect is determined to be a serious scratch when the discriminating signal is down lower than the first threshold value and the side signal is down lower than the second threshold value simultaneously.  
         [0018]     In an embodiment, the data defect is determined to be a small scratch when the discriminating signal is down lower than the first threshold value and the side signal is down but higher than the second threshold value simultaneously.  
         [0019]     In an embodiment, the data defect is determined to be data interruption when the discriminating signal is down lower than the first threshold value and the side signal has a little variation which is higher than the second threshold value simultaneously. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     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:  
         [0021]      FIG. 1  is a schematic diagram showing the light-receiving portions of an optical pickup head;  
         [0022]      FIG. 2 ( a ) is a schematic diagram showing the relationship among SBAD, data and defect-indicating signals when there are scratches existing in the read optical disc;  
         [0023]      FIG. 2 ( b ) is a schematic diagram showing the relationship among SBAD, data and defect-indicating signals when there are data interruptions occurring in the read optical disc;  
         [0024]      FIG. 3 ( a ) is a schematic diagram showing the relationship among RFRP 1 , data and defect-indicating signals when there are scratches existing in the read optical disc;  
         [0025]      FIG. 3 ( b ) is a schematic diagram showing the relationship among RFRP 1 , data and defect-indicating signals when there are data interruptions occurring in the read optical disc;  
         [0026]      FIG. 4 ( a ) is a schematic diagram showing the relationship among SBAD, RFRP 1 , data and defect-indicating signals when there are scratches existing in the read optical disc;  
         [0027]      FIG. 4 ( b ) is a schematic diagram showing the relationship among SBAD, RFRP 1 , data and defect-indicating signals when there are data interruptions occurring in the read optical disc; and  
         [0028]      FIG. 5  is a table illustrating a data-defect discriminating algorithm according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     In order to detect a data defect that cannot be located with the SBAD signal, the present invention introduces a RFRP 1  signal to dominate or facilitate defect detection. The RFRP 1  signal is obtained by subtracting a master signal, which is the summation of the main-beam signals generated by the light-receiving portions A, B, C and D in response to the received light intensities (see  FIG. 1 ), from a side signal, which is the SBAD signal, the summation of the sub-beam signals generated by the light-receiving portions E, F, G and H in response to the received light intensities (see  FIG. 1 ). The RFRP 1  signal is a discriminating signal used for discriminating the data defect detection.  
         [0030]     In a first embodiment, a RFRP 1  signal F 1  is used to determine whether there is any data defect existent in the data signal. An example that there are serious and small scratches existing in the data storage region of a disc is given with reference to  FIG. 3 ( a ) in which the relationships among RFRP 1 , data and defect-indicating signals are shown. Due to a serious scratch in the data storage region of the disc, a data signal drop E 11  of the data signal E 1  is rendered, and a signal drop F 11  occurs in the RFRP 1  signal F 1  correspondingly. Since the signal drop F 11  has been down lower than a preset threshold level L 3 , a peak D 31  will occur in the defect-indicating signal D 3  to suspend the servo tracking operation of the optical reading system, thereby protecting the optical reading system from errors or hanging. After the scratch has been passed and the defect-indicating signal D 3  is switched back to a low level, the servo tracking operation of the optical reading system is restored. The preset threshold level L 3  can be a voltage value stored in the optical reading system.  
         [0031]     Afterwards, another scratch that is less serious in the data storage region of the disc is encountered, so a less data signal drop E 12  of the data signal E 1  is rendered. Correspondingly, a less signal drop F 12  occurs in the RFRP 1  signal F 1 . Since the signal drops F 12  are also down lower than the preset threshold level L 3 , peaks D 32  will occur in the defect-indicating signal D 3  to suspend the servo tracking operation of the optical reading system. After the scratch has been passed and the defect-indicating signal D 3  is switched back to a low level, the servo tracking operation of the optical reading system is restored.  
         [0032]     The RFRP 1  signal can also be applied to detect data defect resulting from data interruption. For example, data interruptions E 21  and E 22  occur in the data signal E 2  as illustrated in  FIG. 3 ( b ). As shown, signal drops F 21  and F 22  of the RFRP 1  signal F 2  occur corresponding to the data interruption E 21  and E 22  and become lower than the preset threshold level L 3 . Therefore, peaks D 41  and D 42  occur in the defect-indicating signal D 4  to indicate the data defects E 21  and E 22 . Accordingly, the servo tracking operation of the optical reading system is suspended when encountering with these areas.  
         [0033]     The above embodiment of data-defect detection method is sensitive enough to respond to a small scratch. In other words, the servo tracking operation of the optical reading system in the small-scratch area will be suspended. As known to those skilled in the art, however, the data defect resulting from a small scratch is usually recoverable. Thus, it may sometimes be disadvantageous to skip the data within the scratch area instead of recovering it. Therefore, in a second embodiment of the present invention, both of the RFRP 1  signal and the SBAD signal are referred to determine whether there is any data defect existent in the data signal.  
         [0034]     In a case that there are serious and small scratches existing in the data storage region of a disc, the relationships among SBAD, RFRP 1 , data and defect-indicating signals are shown in  FIG. 4 ( a ). Due to a serious scratch in the data storage region of the disc, a data signal drop E 11  of the data signal E 1  is rendered. Thus, a signal drop S 11  occurs in the SBAD signal S 1  and a signal drop F 11  occurs in the RFRP 1  signal F 1  correspondingly. Afterwards, another scratch that is less serious in the data storage region of the disc is encountered, so a less data signal drop E 12  of the data signal E 1  is rendered. Correspondingly, a less signal drop S 12  occurs in the SBAD signal S 1  and a less signal drop F 12  occurs in the RFRP 1  signal F 1 .  
         [0035]     In another case that there are data interruptions existing in the data storage region of a disc, the relationships among SBAD, RFRP 1 , data and defect-indicating signals are shown in  FIG. 4 ( b ). As shown, signal drops F 21  and F 22  of the RFRP 1  signal F 2  occur corresponding to the data interruption E 21  and E 22  and become lower than the preset threshold level L 3 . On the other hand, the SBAD signal S 2  has little variation but higher than the preset threshold level L 1  at S 21  and S 22  corresponding to the data interruption E 21  and E 22 .  
         [0036]     Therefore, the second embodiment of the data-defect detecting method according to the present invention utilizes the combination states of the SBAD and RFRP 1  signals to determine the data-defect type, and then determines whether the servo tracking operation should be suspended or not.  
         [0037]     Please refer to  FIG. 5  which is a table summarizing the discriminating algorithm of the second embodiment of data-defect detecting method according to the present invention. When there are signal drops simultaneously occurring in both the RFRP 1  and SBAD signals to levels lower than respective preset threshold levels L 3  and L 1 , it is determined that there is a serious scratch existing in the data storage region of the disc. Therefore, a high level D 51  is rendered in the defect-indicating signal D 5  as illustrated in  FIG. 4 ( a ) and the servo tracking operation is suspended. If there are signal drops simultaneously occurring in both the RFRP 1  and SBAD signals but only the signal drop of the RFRP 1  signal is down lower than the preset threshold level L 3 , and the SBAD signal is down but higher than the preset threshold level L 1 , it will be determined that there is a small scratch existing in the data storage region of the disc. In this case, no peak is rendered in the corresponding portion D 52  of the defect-indicating signal D 5  as illustrated in  FIG. 4 ( a ). It means that the scratch can be omitted and the servo tracking operation will continue to be performed normally. Further, if the RFRP 1  signal is down lower than the preset threshold level L 3  but there is little variation which is higher than the preset threshold level L 3  in the SBAD signal correspondingly, it will be determined that data interruption occurs. Therefore, peaks D 61  and D 62  are rendered in the defect-indicating signal D 6  as illustrated in  FIG. 4 ( b ), and the servo tracking operation is preferably suspended to avoid reading errors.  
         [0038]     According to the present method, the data defect resulting from data interruption can be located by referring to the RFRP 1  signal. Moreover, by referring to both the RFRP 1  signal and the SBAD signal, the data defect resulting from data interruption can be located while omitting the small scratch. Accordingly, the servo tracking operation of the optical reading system can be adequately suspended to prevent from reading errors without losing too much data.  
         [0039]     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 be limited to the disclosed embodiments. 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.