Abstract:
Methods and apparatuses for dynamically adjusting sync windows are described. A default sync window is set; a data signal is input; detecting if parts of the data signal within the sync window form a sync pattern; accumulating a count of the sync pattern within and without the sync window; and reducing the sync window when the count of sync pattern within the sync window achieves a first threshold value, and increasing the sync window when the count of the sync pattern outside the sync window achieves a second threshold value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Taiwanese Application Ser. No. 093101443, filed on Jan. 20, 2004, and entitled “APPARATUS AND METHOD OF DYNAMIC ADJUSTING THE SYNC WINDOW,” which is hereby incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an apparatus and method for optical drive searching, and more particularly to an apparatus and method for an optical drive searching sync pattern. 
     2. Description of the Prior Art 
     As optical storing media is further introduced, storing a large amount of data is not as difficult. And since storing data within an optical media in a digital form is better than that in traditional magnetic media recorded in analog form, the data signal can keep longer and will not distort over time. 
     Philips and Sony set up the earliest standard of the optical media in 1980 (RED BOOK). In order to store different data content, a lot of different standards (such as: YELLOW BOOK, ORANGE BOOK . . . etc.) are established. However, the optical media data formats are almost all the same and most of them are extended based on the earliest standard, the RED BOOK. 
     Taking a compact disc (CD) as an example of: at first, data signal is modulated by non-return to zero, NRZ (also called eight to fourteen modulations, EFM). Then the data is stored into a compact disc (CD). For 24 bytes data signal, the data is in form of 588 channel bits after EFM. Since EFM is based on clock, T, the data can be rewritten in 588T. Every 588T includes:
         Sync pattern: 24+3 unit: channel bits   Control byte: 14+3   Data byte:12*(14+3)   Error correction: 4*(14+3)   Data byte: 12*(14+3)   Error correction: 4*(14+3)
 
Every 588T forms a frame. In a compact disc, every sector has 98 frames and every 75 sector forms a second data signal (as shown in  FIG. 1A ).
       

     Similarly, for digital versatile disc (DVD), the data signal is modulated by EFM plus. The data signal is in form of 1488T of a frame, and then the data signal is stored into a digital versatile disc (DVD). 
     After modulated by EFM, data signal forms different pits long from 3T to 11T. And these nine different length pits (known as pit and land) forms a spiral groove. The optical drive determines and reads the data signal according to the reflection of pits of the spiral groove. 
     According to the previous said, the data format of an optical disc, it is understood that every frame has a group of 24 bits sync pattern for separating every frame. By the sync pattern, the optical drive determines every frame range and finds and reads data the signal quickly and correctly. For the compact disc (CD), the sync pattern is formed in 11T/11T and exists in every 588T data signal (as shown in  FIG. 1B ). And for the digital versatile disc (DVD), the sync pattern is formed in 14T/4T and exists in every 1488T data signal. 
     Referring to  FIG. 2 , the symbol  2 A is shown as the frame signals in the optical disc. When an optical drive reads a disc, it produces the sync found  2 B. When the sync found  2 B and the sync pattern of the frame signal occurs at the same time, the optical drive generates the sync flag  2 C for highlighting the position of the sync pattern. However, the rotational speed of the optical drive is different when reading the outer circle and the inner circle of the disc. Therefore, the timing of the actual sync found (such as:  2 D) and the timing of the sync pattern occurs at different timing and a jitter is generated, so as the optical drive generating the sync flag for labeling the sync pattern is inaccuracy. (As shown in  FIG. 3 ) In order to solve this problem, setting a W width sync window  3 C (about 30T) tolerates the error between the sync found  3 B and the sync pattern  3 A. So if the optical drive can detect the sync pattern within the sync window, it can generate the sync flag  3 D and read the data signal correctly. 
     As the sync window is fixed, when the optical disc has been scraped, the optical drive cannot detect the sync pattern correctly and it can be a problem for reading the data signal. 
     For example: the optical drive reads a disc as shown in  FIG. 4 . When the disc is scraped or stained, it generates an 11T signal before the position of the sync pattern occurs. Therefore, the signal includes the sync pattern as 11T/11T/11T (as shown in  4 A_ 4 ). If the sync window has a large window range, the optical drive can misjudge the first half 11T/11T of the 11T/11T/11T as the sync pattern. It generates the wrong sync flag  4 C. As the result, It cannot read the correct data signal and cannot detect the following sync pattern. Furthermore, if the sync window has a small window range, the frequency of the phase lock loop, PLL will be floating and tolerates the error between the sync pattern and the sync flag will be decreased. As a consequence, it cannot lock the sync pattern correctly. 
     SUMMARY OF THE INVENTION 
     The invention provides a method and a system of dynamic adjusting for the sync window. The method and system according to the condition adjusts the sync window range for the optical drive correctly detecting the sync pattern. 
     The apparatus of dynamically adjusting the sync window of the present invention includes: a buffer for storing an input data; a sync window generator for generating a sync window; a sync pattern detection circuit for detecting if the input data having any sync pattern showing in the sync window; a first counter for accumulating times of the sync pattern found within the sync window; a second counter for accumulating times of the sync pattern found outside the sync window; and an adjusting circuit for adjusting the range of the sync window when the accumulative values of the first or the second counter achieves the threshold. 
     The method of dynamic adjusting the sync window in the present invention including: setting a default sync window; inputting the data signal one at a time; detecting if parts of the data signal within the sync window is a sync pattern; accumulating times of the sync pattern within and without the sync window; and reducing the sync window when times of the sync pattern within the sync window achieve one threshold value, and increasing the sync window when times of the sync pattern outside the sync window achieve another threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a schematic diagram illustrating the data signal of the optical disc; 
         FIG. 1B  shows a schematic diagram illustrating the sync pattern of the optical disc; 
         FIG. 2  shows a schematic diagram illustrating the timing sequence when optical drive reads disc data signal; 
         FIG. 3  shows a schematic diagram illustrating the timing sequence when optical drive generates sync window for detecting the sync pattern; 
         FIG. 4  shows a schematic diagram illustrating that the optical drive detects the wrong sync pattern. 
         FIG. 5  shows a schematic block diagram illustrating the apparatus of dynamic adjusting the sync window; 
         FIG. 6  shows a schematic diagram illustrating the method flow chart of dynamic adjusting the sync window; and 
         FIG. 7  shows a schematic diagram illustrating the timing sequence of dynamic adjusting the sync window. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention provides a method and an apparatus of dynamically adjusting the sync window. For the optical drive detecting the sync pattern, the scraped disc or stained disc does not affect the optical drive and furthermore it does not read the wrong data signal. Some of the embodiments of the invention will describe in detail and clearly as follows. However, except for the detailed description, the invention can widely apply in others. And the true scope of the invention is not limited here but the claims. 
       FIG. 5  shows the apparatus for dynamic adjusting sync window  500  of the invention. It includes: a buffer  510  for storing the inputting data signal; a sync window generator  520  for generating a sync window; a sync pattern detection circuit  530  connecting to the sync window generator  520  for detecting the sync pattern when the data signal occurs in the sync window; a first counter  540  connecting to the sync pattern detection circuit  530  for accumulating the numbers of the sync pattern occurring in the sync window; a second counter  550  connecting to the sync pattern detection circuit  530  for accumulating the numbers of the sync pattern occurring out of the sync window; and an adjusting circuit  560  separately inputting from the first counter  540  and the second counter  550  and outputting to the sync window generator  520  for adjusting the sync window range when the first counter  540  and the second counter  550  achieving the threshold. 
     As shown in  FIG. 5 , the buffer  510 , the sync window generator  520 , and the sync pattern detection circuit  530  are the apparatus, which is used to search the sync pattern in a general optical drive. However, the invention uses the first counter  540  and the second counter  550  for counting the numbers of the sync pattern occurring in the predefined sync window and the numbers of the sync pattern occurring out of the predefined sync window. And then using an adjusting circuit  560  dynamically adjusts the sync window range, wherein the adjusting circuit  560  may include a multiplexer with different range sync windows, which are separate according to the calculating result of the first counter  540  and the second counter  550  for choosing one of the sync windows. In other words, the adjusting circuit  560  can be called a calculating circuit. It is according to the calculating result of the first counter  540  and the second counter  550  to reduce or enlarge the predefined sync window. 
     The method for the dynamic adjusting sync window of the invention is disclosed herein. The sync window generator  520  predefines a sync window with length W; wherein the sync window has the range W which is bigger than the sync pattern. At the same time, when a data signal input to the buffer  510  and the pulse of the sync found is triggered, the sync pattern detection circuit  530  detects if there has sync pattern occurred within the detecting range W of the sync window. If yes, the first counter  540  accumulates the numbers of the sync pattern occurring in the sync window (the first accumulating number CNT 1 ); if no, the second counter  550  accumulates the numbers of the sync pattern occurring out of the sync window (the second accumulating number CNT 2 ). Herein, when the CNT 1  achieves the first threshold, the system reduces the range W of the sync window for detecting the next inputting data signal and resets the CNT 1  of the first counter to zero. Otherwise, when the CNT 2  achieves the second threshold, the system increases the range W of the sync window for detecting the next inputting data signal and resets the CNT 2  of the second counter to zero. 
     The flow chart shows one of the methods of the invention in  FIG. 6 
       610 : Setting a default sync window range W     620 : Inputting data signal     630 : Detecting the data signal part in the sync window whether it exists the sync pattern or not.   

     If yes, executing the step  640 ; if no, executing the step  650 .
       640 : Accumulating the numbers of the sync pattern happened in the sync window     642 : Determining the first accumulating value CNT 1  whether it achieves the first threshold or not.   

     If yes, executing the step  644 ; if no, executing the step  620 .
       644 : The sync window range W=W−(W− is smaller than the predefined sync window)     646 : Reset the first accumulating value CNT 1  to zero and return to step  610       650 : Accumulating the numbers CNT 2  of the sync pattern happened out of the sync window/     652 : Determining the second accumulating value CNT 2  whether it achieves the second threshold or not.   

     If yes, executing step  654 ; if no, executing step  620 .
       654 : the sync window range W=W+(W+ is bigger than the predefined sync window)     656 : Reset the second accumulating value CNT 2  to zero and return to step  610     

       FIG. 7  shows an example for an optical drive searching the sync pattern of an optical disk. The symbol  7 A shows some frames signal of an optical disc and  7 B is the sync found generated by the optical drive. For a compact disc (CD), the sync pattern should be formed as 11T/11T However, when the CD has scraped or stained, it generates 11T/11T/11T signal (as shown in  7 A_ 4 ). In the predefined sync window range, the sync pattern occurs twice and the threshold is achieved (suppose the threshold is 2). Therefore reducing the sync window range (as shown in  7 C_ 4 ) and the system can determine the correct sync pattern (as shown in  7 D_ 4 ). As the result, the optical drive can find every sync pattern of the frame and it further can read the correct data signal on the disc. 
     By comparing the method of detecting the sync pattern in a normal optical drive, the invention provides a method and apparatus for a dynamic adjusting sync window. When a disc error signal occurs, the optical drive can still find the correct sync pattern of every frame. 
     As previous said, the invention, depending on the conditions adjusts the sync window range of the optical drive. When analogy sync pattern continuously occurs, the optical drive adaptively reduces the sync window so as to find the correct sync pattern. Otherwise, when the optical drive cannot find the sync pattern in the sync window, it can adaptively increase the sync window range so as to find the sync pattern. 
     Although the invention discloses the example as optical drive herein, it is not limit the spirit of the invention. The invention also covers that other embodiments disclose storing media with sync pattern detecting. It is intended that the specification and examples to be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.