BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a digital television system, and more particularly, to a synchronization signal detector and related method of the digital television system.  
         [0003]     2. Description of the Prior Art  
         [0004]     Due to the need for decoding a digital TV signal, the digital TV signal is designed to contain a fixed pattern, which appears repeatedly, to allow a digital TV receiver to synchronize the digital TV signal accordingly. Taking a digital TV signal used in the U.S.A. as an example, the digital TV signal complies with a specification defined by an Advanced Television Systems Committee (ATSC). According to the specification, each data field contains 313 segments, and the beginning of each segment corresponds to a four-symbol fixed pattern which is commonly called segment SYNC or data segment SYNC. For convenience, these four symbols will hereafter be called sync symbols.  
         [0005]     The synchronization of the digital TV signal is achieved by identifying the sync symbol in the received digital TV signal through the aid of a reference signal containing the same sync symbol. Because of the interference caused by the noise or transmission path variations, however, the sync symbol in the received signal may in actuality differ from the sync pattern in the reference signal, which causes synchronization errors to occur due to the failure of identifying the sync symbol in the digital TV signal.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore one of the objectives of the present invention to provide a synchronization signal detector and related method for detecting a synchronization signal of a digital TV signal according to synchronization symbols of the digital TV signal, to solve the above-mentioned problem.  
         [0007]     According to an exemplary embodiment of the claimed invention, an apparatus for detecting a synchronization signal of a data signal is disclosed. The apparatus includes: a first circuit configured to delay the data signal by a predetermined period to generate a delayed signal; a second circuit configured to produce a plurality of similarity signals according to the data signal and the delayed signal, each of the similarity signals representing the similarity between the data signal and the delayed signal; and a third circuit configured to determine the synchronization signal of the data signal according to the similarity signals.  
         [0008]     The claimed invention provides a method of detecting a synchronization signal for a data signal. The method includes: delaying the data signal by a predetermined period to generate a delayed signal; comparing the data signal and the delayed signal to output a plurality of comparison values; outputting a plurality of similarity signals according to the comparison values, each of the similarity signals representing the similarity between the data signal and the delayed signal; and determining the synchronization signal of the data signal according to the similarity signals.  
         [0009]     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  
       [0010]      FIG. 1  is a diagram of a signal detector according to a first embodiment of the present invention.  
         [0011]      FIG. 2  is a diagram illustrating a signal format of a digital signal processed by the signal detector shown in  FIG. 1 .  
         [0012]      FIG. 3  is a diagram of a signal detector according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0013]     Please refer to  FIG. 1  and  FIG. 2 .  FIG. 1  is a diagram of the signal detector  100  according to a first embodiment of the present invention, and  FIG. 2  is a diagram illustrating a signal format of an input signal D 1  processed by the signal detector  100  shown in  FIG. 1 . The digital signal D 1 , in this embodiment, is a digital TV signal D 1  used in the U.S.A, which complies with the ATSC specification and is further called ATSC signal D 1 . The signal format of the ATSC signal D 1  is well known, and further description is omitted here for brevity. Please note that the present invention also can be applied to digital signals defined by other specifications, or other kinds of digital signals.  
         [0014]     According to a first embodiment of the present invention, the signal detector  100  is used to detect a synchronization signal S 1  according to the digital signal D 1 . The digital signal D 1  has a plurality of symbols and can be sorted into a plurality of segments as the “data segment” shown in  FIG. 2 . There are four sync symbols (segment SYNC) in each segment of the digital signal D 1 . As shown in  FIG. 1 , the signal detector  100  comprises a slicer  110 , a buffering module  120 , a symbol comparator  130 , a symbol detector  140 , and a decision unit  150 . The buffering module  120  comprises a plurality of registers  120 - 1  to  120 - 832 , cascaded orderly. Additionally, the decision unit  150  comprises an adder  152 , a buffering module  154 , a minimum identification unit  156 , a comparator  158 , and a slice level generator  159 . The buffering module  154  comprises a plurality of registers  154 - 1  to  154 - 832  orderly cascaded in a series.  
         [0015]     The operation of the signal detector  100  in this embodiment is detailed as follows. As shown in  FIG. 1 , after the digital signal D 1  is inputted into the symbol comparison circuit  101 , the slicer  110  converts the digital signal D 1  into a binary signal S_SL according to a slice level. Every symbol in the binary signal S_SL has either a first logic value or a second logic value. In this embodiment, assume that the slice level is zero, the value of the digital signal D 1  is represented by Y[n], and the value of the binary signal S_SL is represented by X[n]. Therefore, X[n] is expressed as follows. 
 
 X[n]= 0, if  Y[n]&gt; 0; or 
 
 X[n]= 1, otherwise. 
 
         [0016]     Each symbol of the binary signal S_SL at the output of the slicer  110  corresponds to a bit. As shown in  FIG. 2 , the output of the slicer  110  corresponds to a high level when an incoming sync symbol corresponds to a high level, and the output of the slicer  110  corresponds to a low level when an incoming sync symbol corresponds to a low level. Therefore, the fixed pattern carried by the four sync symbols in the digital signal D 1  is preserved in the binary signal S_SL, which can simplify the following operation and save the memory capacity needed in post-end buffers. In other words, the storage capacity allocated to the buffering modules  120 ,  154  can be reduced accordingly. The above-mentioned slicer  110  can be omitted here and still the functionality of the signal detector  100  can be achieved.  
         [0017]     The segment delay circuit  120  delays the binary signal S_SL to generate a delayed signal whose value is represented by Xbuffer[n]. Here, the buffering module  120  is called the segment delay circuit  120  because the delay amount of the delay signal corresponds to at least one segment. In this embodiment, the segment delay circuit  120  can be viewed as an 832-bit shift register so that the value Xbuffer[n] of the delay signal is delayed by 832 symbols (one segment) relative to the value X[n] of the binary signal S_SL. The symbol comparator  130  compares the delayed signal with the binary signal S_SL to output the signal S_XOR, wherein the symbol comparison circuit  130  can be implemented by an XOR logic gate. When the output signal S_XOR is “0”, it means that the values X[n], Xbuffer[n] of the binary signal S_SL and the delayed signal are the same. According to the signal format shown in  FIG. 2 , if there are four continuous “0”s in the output signal S_XOR, the value X[n] of the binary signal S_SL corresponds to the sync symbol. Therefore, the symbol detector  140  is used to detect if there are four continuous “0”s in the output signal S_XOR.  
         [0018]     The symbol detector  140  comprises a plurality of registers  142 - 1  to  142 - 4  and an adder  144 . The registers  142 - 1  to  142 - 4  buffer four continuous logic values while the adder  144  adds these buffered logic values for outputting a calculation result  146 . When the calculation result  146  is equal to a minimum value (i.e., 0), it means that these four continuous logic values are “0”s. The symbol detector  140  outputs  832  successive calculation results to the registers  154 - 1  to  154 - 832  of the decision unit  150 .  
         [0019]     Due to the periodic appearance of the fixed pattern represented by the four sync symbols in every segment, there should be two minimum values spaced by an interval of one segment among calculation results  146  outputted from the symbol detector  140 . When each of the registers  154 - 1  to  154 - 832  buffers a specific calculation result  146 , the adder  152  starts accumulating every two calculation results  146  spaced by a segment, and generates 832 summation results corresponding to a specific segment. These 832 summation results are buffered in the buffering module  154 . Among these 832 summation results, there is a minimum value which is exactly an accumulated result of minimum values of the plurality of calculation result values  146 .  
         [0020]     The minimum identification unit  156  in the decision unit  150  reads the buffered content of each of the registers  154 - 1  to  154 - 832  to identify a minimum value, and then outputs a signal S_MIN capable of acting as a synchronization signal. The combination of the adder  152 , the register  154  and the minimum identification unit  156  can be viewed as a filter.  
         [0021]     In a preferred embodiment, the minimum value output signal S_MIN is further inputted into a comparator  158 . The comparator  158  compares the output signal S_MIN with a threshold S_TH provided by the threshold value generator  159 , wherein if the signal S_MIN is less than the threshold S_TH, the comparator  158  will trigger a synchronization signal S 1 . The comparator  158  and the threshold value S_TH are used to lower the probability of error detection. Therefore, the decision unit  150  can generate the synchronization signal S 1  through identifying the minimum of the plurality of calculation results  146  to acknowledge the starting point of each segment.  
         [0022]     In another embodiment, these 832 registers  154 - 1  to  154 - 832  can also record the counts of the appearances of a minimum calculation result  146 . Therefore, a count having the largest value is utilized to identify the starting point of each segment for generating the synchronization signal S 1 .  
         [0023]     Please refer to  FIG. 1  in conjunction with  FIG. 3 .  FIG. 3  is a diagram of a signal detector  200  according to a second embodiment of the present invention. The signal detector  200  is further equipped with a front stage processing module  160  used to update the digital signal D 1  by accumulating every two symbols in the digital signal D 1  spaced by a segment. In the second embodiment, the digital signal D 1  is pre-processed by the front stage processing module  160 . The front stage processing module  160  then outputs the pre-processed result Yavg[n] to the slicer  110 . The front stage processing module  160  comprises a buffering module  164  to buffer a plurality of accumulated values, an adder  162  coupled to the buffering module  164  for accumulating two symbols spaced by a segment to generate one of a plurality of accumulated values, a switch  166 - 1  used for selectively coupling the adder  162  to either the buffering module  164  or an initial signal S_INT, a switch  166 - 2  used for selectively coupling the adder  162  and an input port of the slicer  110 , and a controller  168  coupled to the switch  166 - 1  and switch  166 - 2  for controlling the on/off status of both switches  166 - 1  and  166 - 2 .  
         [0024]     Accordingly, the pre-processed result Yavg[n] of the front stage processing module  160  is equivalent to an accumulated value related to a sector within the original data Y[n] of the digital signal D 1 . Utilizing this additional data processing process, not only is the integrity of the fixed pattern strengthened, but also the noise interference affecting the digital signal D 1  is alleviated.  
         [0025]     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. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
A synchronization signal detector includes: a first circuit configured to delay the data signal by a period of at least one data segment of the data signal to generate a delayed signal; a second circuit configured to produce a plurality of similarity signals according to the data signal and the delayed signal, each of the similarity signals representing the similarity between the data signal and the delayed signal, and a third circuit configured to determine the synchronization signal of the data signal according to the similarity signals. The present invention further provides a method corresponding to the signal detector.