Patent Publication Number: US-2006018218-A1

Title: Method and apparatus for increasing the ability of decoding a land pre-pit

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a method for increasing the ability of decoding a land pre-pit, and more particularly to the method for increasing the ability of decoding a land pre-pit by means of adjusting the pre-pit slicing level.  
      2. Description of the Prior Art  
      A DVD (Digital Versatile Disc) has energetically been researched and developed because the DVD is a recording medium which is capable of recording information in a greater quantity than that recorded on a typical CD.  
      Referring to  FIG. 1 , a cross-sectional perspective view of a typical DVD of minus format (for example, DVD Recordable, DVD-R) is shown. The DVD-R2 includes lands  4  and pre-grooves  6 . The pre-grooves  6  are regions on which information, such as video data and audio data, must be recorded as recording pits. Moreover, DVD-R has land pre-pits (hereinafter called LPP, not shown) formed on lands  4  which are regions formed among the pre-grooves. The LPP contain address information of the DVD-R. In other words, an absolute address of the DVD-R is recorded on the LPP. An optical pickup should decode the LPP in order to know the position where the optical pickup is located above the DVD-R. Because of deviation in the process of manufacturing the DVD-R, the amplitudes of the LPP for all kinds of the DVD-R are not identically. Especially for rewritable discs, such as the DVD-RW, the amplitudes of the LPP on some positions of the rewritable discs are smaller due to the manufacturing process, or become smaller due to erode by the recording power and rewritable times. Accordingly, a pre-pit slicer with fixed slicing level may not be able to slice a correct LPP. Thus, a decoder may not decode a pre-pit information correctly so as to cause a failure of the recording action.  
      Presently, disc drives are without functions for solving these questions about different amplitudes of the LPP between different kinds of discs. The cost and time are too much of a waste for customers to use these disc drives. The present invention supplies a method and apparatus for increasing the ability of decoding a land pre-pit to solve above-mentioned questions.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is one objective of the present invention to provide a method for increasing the ability of decoding a land pre-pit to solve the question of different kinds of discs with different amplitudes of land pre-pits. A characteristic of the method is to adjust the pre-pit slicing level to slice to correctly decode the land pre-pit. Decoding correct land pre-pit information could avoid the wrong message and the failure of the recording action.  
      It is another objective of the present invention to supply an apparatus for increasing the ability of decoding a land pre-pit to solve the question of wasting the cost and time for recording information on the discs. The invention could decode the correct land pre-pit information by way of adjusting the pre-pit slicer without changing the design of the hardware.  
      In order to achieve above-mentioned purposes, a method for increasing the ability of decoding a land pre-pit is disclosed. The method includes providing a host for executing an interface seek command. A seeking servo action is generated by the interface seek command. A first pre-pit slicing level is regulated to make the seeking servo action decode an absolute position. A tracking servo action starts from the absolute position. A second pre-pit slicing level is regulated to make the tracking servo action decode a target position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention can be best understood through the following description and accompanying drawings wherein:  
       FIG. 1  is a cross-sectional perspective view of a typical DVD-R.  
       FIG. 2  is a flow chart of the embodiment of the present invention.  
       FIG. 3  is a schematic diagram of the embodiment of the present invention.  
       FIG. 4  is a block diagram of the embodiment of the present invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Some embodiments of the present invention have detailed descriptions below. However, except for the detailed descriptions, the present invention can have a broad use in other embodiments, and the scope of the present invention can not be defined by this preferred embodiment, but by the appended claims.  
      In the preferred embodiment, a method for increasing the ability of decoding a land pre-pit is disclosed. The method includes providing a host for executing an interface seek command. A seeking servo action is generated by the interface seek command. A first pre-pit slicing level is regulated to make the seeking servo action decode an absolute position. A tracking servo action starts from the absolute position. A second pre-pit slicing level is regulated to make the tracking servo action decode a target position.  
      Referring to  FIG. 2 , the preferred embodiment of the present invention is a flow chart of increasing the ability of decoding a land pre-pit by adjusting a pre-pit slicing level. The steps of the flow chart include providing a host (step  100 ). An interface seek command is executed by the host (step  120 ). A seeking servo action is generated by the interface seek command (step  140 ). The seeking servo action is checked to decide whether the optical pickup is located on an absolute position or not (step  160 ). If not, a pre-pit slicing level is adjusted (step  180 ). The steps  140  and  160  are repeated again. If the optical pickup is located on the absolute position, the seeking servo action is checked to decide whether the optical pickup is located on a target position or not (step  200 ). If not, another pre-pit slicing level is adjusted (step  220 ). The steps  120 ,  140 ,  160  and  180  are repeated again. If the seeking servo action decodes the target position, i.e. the optical pickup is located on the target position, the recording action is executed (step  240 ). Herein the flow path from step  180  through step  140  to step  160  is not limited by the number of times but limited by a predetermined time. In other words, the flow path proceeds to decode the absolute position in the predetermined time. In the same way, the flow path from step  220  through steps  120 ,  140 ,  160  to step  200  also is not limited by the number of times but limited by the time. In other words, the flow path proceeds to decode the target position in the limited time. Besides, the absolute position in step  160  means that a position of the LPP is located on the disc before the target position. The absolute position generally has a distance from about one to three tracks before the target position, thus a tracking servo action is generally executed so as to locate the optical pickup on the target position (at the same time the optical pickup can decode the LPP of the target positions. The target position is a starting position for the host to read or record the information on the disc. In addition, the method of adjusting the pre-pit slicing level in the step  180  and step  220  could be set in many ways, such as that the range of the slicing level is preset to divide into 30 levels. One of the 30 levels could be selected in each time of adjusting the pre-pit slicing level. The present invention is not limited in this embodiment. Besides, the pre-pit slicing level in the step  180  may be the same or may be different with one in the step  220 .  
      Referring to  FIG. 3 , the preferred embodiment of the present invention is a schematic diagram for increasing the ability of decoding a land pre-pit by adjusting a pre-pit slicing level.  FIG. 3A  is a waveform diagram of a normal signal of the LPP and  FIG. 3B  is a waveform diagram of an abnormal signal of the LPP. The amplitude of a land pre-pit signal  300  in  FIG. 3B  is smaller than one in  FIG. 3A . The reason which causes the amplitude of a land pre-pit signal  300  to be smaller may be that the amplitude of the land pre-pit formed during manufacturing is smaller or severe temperature variation during the recording action so as to erode the amplitude of the land pre-pit. The smaller amplitude of the land pre-pit would reduce the amount of light reflection and then the light detector receives a smaller light signal so as to produce a smaller land pre-pit signal  300 . The amplitude of the land pre-pit signal  300  in  FIG. 3A  is a larger difference than one of the noise  310 , so as to slice the land pre-pit signal  300  easily by the slicing level  320  with a fixed position. If the above-mentioned reason makes the land pre-pit signal  300  smaller as depicted in  FIG. 3B , the slicing level  320  with fixed position could not slice the land pre-pit signal  300  correctly. At this moment, the method of the present invention is used to adjust the slicing level  320  to lower the slicing level  330  so as to easily slice the land pre-pit signal  300 .  
      During the seeking of the target position of the disc, if LPP could not be decoded, the seeking action of the absolute position or the target position fails. In this situation, the optical drive would return to seek the absolute position of the disc again. One characteristic of the present invention is to adjust the slicing level of the pre-pit slicer in this moment to check whether the next seeking process succeeds or not. If not, the slicing level is adjusted again and then the absolute position of the disc is sought until success.  
       FIG. 4  is a block diagram showing the general structure of an optical drive apparatus according to the embodiment. The apparatus includes a host  500 , a servo system device  510 , a pre-pit detecting device  520 , and an optical reading/recording device  530 , herein the pre-pit detecting device  520  contains a pre-pit slicer  540 , a amplifier, a comparator, and a decoder. When the host  500  sends a seek command to the servo system device  510 , the servo system device  510  would drive the DVD-RW disc  550  and the optical reading/recording device  530 . The optical reading/recording device  530  would collect the reflective light from the DVD-RW disc  550  and transform the reflective light to electrical signal. Then, the pre-pit detecting device  520  detects the electrical signal. After amplifying and comparing the electrical signal, the absolute position of the LPP on the DVD-RW disc  550  is decoded. When the pre-pit detecting device  520  could not decode the absolute position of the LPP on the DVD-RW disc  550 , the slicing level of the pre-pit slicer  540  is adjusted by means of the method of the present invention to decode the absolute position of the LPP.  
      Above said preferred embodiment is only used to illustrate the present invention, not intended to limit the scope thereof. Many modifications of the preferred embodiment can be made without departing from the spirit of the present invention.