Abstract:
A method for demodulating a WAP of an optical disc that ensures the read rate of address information while improving the reading accuracy. The method includes detecting in full bits a head invert phase wobble of each wobble data unit in an address field, and correcting generation timing of a demodulation signal based on the detection result so that the head invert phase wobble is properly detected.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-047535, filed on Feb. 23, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an optical disc record/reproduction apparatus, and more particularly, to a method for demodulating a wobble address in a periodic position (WAP) that is used to read address information recorded as a wobbling pattern on an HD-DVD disc.  
         [0003]     The demand for larger-capacity optical discs has-been increasing in recent years. To meet this demand, HD-DVD discs have been developed as next-generation optical discs. An HD-DVD-rewritable disc has a disc surface on which grooves and lands are formed. The disc has wobble signals, recorded on the side walls of the grooves in a wobbling manner. Each wobble signal is modulated and recorded as preformat data, such as address information. This recording technique enables efficient use of the data recording area of the disc, and increases the recording capacity of the disc.  
         [0004]      FIG. 1  is a schematic block diagram showing an optical disc record/reproduction apparatus  100 . The optical disc record/reproduction apparatus  100  reproduces the WAP before performing a data write operation. The operation of the apparatus  100  for reproducing a WAP will now be described.  
         [0005]     In a WAP reproduction mode, a read channel unit  3  reads a wobble signal from a disc  1  with a pickup  2  and generates a binary wobble signal, which is provided to a controller  4  with a clock signal CLK. The controller  4  is controlled by a CPU  5 . The read channel unit  3  is controlled by the controller  4 .  
         [0006]     The controller  4  includes a WAP reproduction unit  6 . The WAP reproduction unit  6  reproduces a WAP using a wobble signal normal phase wobble (NPW) and a wobble signal invert phase wobble (IPW), which are provided from the read channel unit  3  in accordance with the clock signal CLK, to specify a recording position using the WAP.  
         [0007]     Record tracks are spirally formed on the disc  1 . The record tracks are divided into a plurality of physical segments having predetermined lengths. Each physical segment has a WAP, which is written as preformat data. One record track includes ten to several tens of physical segments.  
         [0008]     To ensure the recording capacity of the disc, the preformat data is recorded as wobble signals in accordance with the wobbling of the grooves. The wobble signal IPW has a phase opposite to the phase of the wobble signal NPW.  
         [0009]      FIG. 5  shows the layout of a WAP, which is used to specify the recording position of each physical segment. The WAP is configured by  17  wobble data units (WDUs) that are divided into a SYNC field  8 , an address field  9 , and a unity field  10 .  
         [0010]     One WDU is assigned to the SYNC field  8 . Thirteen WDUs are assigned to the address field  9 . Three WDUs are assigned to the unity field  10 .  
         [0011]      FIG. 6  shows information recorded in the address field  9 . The address field  9  includes three bits of segment information, six bits of a segment address, five bits of a zone address, one bit of an address parity, twelve bits of a group track address, and twelve bits of a land track address.  
         [0012]     Japanese Laid-Open Patent Publication No. 2004-303395 describes information stored in the address field  9 .  
         [0013]      FIG. 7 ( a ) shows the layout of WDU  0 , which configures the SYNC field  8 . One WDU includes  84  wobbles. The SYNC field  8  includes six wobbles of IPW, four wobbles of NPW, six wobbles of IPW, and sixty-eight wobbles of NPW. IPW represents “1 b”, and NPW represents “0 b”. Bits are modulated incompliance with a rule. At the outer and inner circumferential sides of the disc, NPW is defined if reading is started at the point indicated in  FIG. 8 ( a ) and the wobble signals shift, and IPW is defined if reading is started at the point indicated in  FIG. 8 ( b ) and wobble signals shift.  
         [0014]      FIG. 7 ( b ) shows the layout of one of WDUs  1  to  13  that configure the address field  9 . Four wobbles of IPW, four wobbles of bit  2 , four wobbles of bit  1 , four wobbles of bit  0 , and sixty-eight wobbles of NPW are included at the head of the address field  9 . In other words, one WDU stores address information of three bits, which are bits  2 ,  1 , and  0 . As shown in  FIG. 7 ( c ), one WDU of the unity field  10  is configured by 84 wobbles of NPW.  
         [0015]     WDU  1  stores three bits of address information as segment information, and WDUs  2  and  3  store six bits of address information as segment addresses. Accordingly, in WDUs  1  to  13 , 39 bits of address information are stored from the segment information shown in  FIG. 6  as land track address.  
         [0016]      FIG. 2  is a schematic block diagram showing the WAP reproduction unit  6  of the prior art.  FIG. 3  is a time chart showing a basic operation of the WAP reproduction unit  6 . The WDUs of the WAP are sequentially provided to a shift register  11 . Each WDU is obtained by reading the wobble signals NPW and IPW from the disc  1  with the pickup  2  and generating binary wobble signals NPW and IPW. The wobble signals (WDUs) are provided to a SYNC detector  12  and to a data converter  13  in units of a predetermined number of bits.  
         [0017]     The SYNC detector  12  detects the SYNC field  8 , to which the first WDU of the WAP is assigned. In detail, the SYNC detector  12  detects a SYNC pattern of “1111 1100 0011 1111” by dividing the six wobbles of IPW, four wobbles of NPW, and six wobbles of IPW included in WDU  0  of the SYNC field  8  into sections of four bits. Upon detection of the pattern, the SYNC detector  12  provides a WDU/WAP counter  14  and a non-detection counter  17  with a detection signal X 1 .  
         [0018]     The WDU/WAP counter  14  counts  17  WDUs of one WAP in response to the detection signal X 1  and counts 84 wobble signals of each WDU. Based on the count values resulting from the count operations, the WDU/WAP counter  14  provides the data converter  13  and a data latch circuit  15  with a demodulation signal Y 1  at a predetermined timing.  
         [0019]     As shown in  FIG. 3 , the WDU/WAP counter  14  generates the demodulation signal Y 1  when counting the sixteenth wobble signal of each of WDUs  1  to  13  included in the address field  9  (i.e., when wobble signals, each having four wobbles, corresponding to bits  2 ,  1 , and  0  are provided to the data converter  13  after four wobbles of IPW). The demodulation signal Y 1  is generated in a locked state at the same timing as the 84 wobble signals of each WDU.  
         [0020]     In response to the demodulation signal Y 1 , the data converter  13  recognizes the wobble signal provided from the shift register  11  as the first IPW of each of WDUs  1  to  13 , and recognizes the wobble signal following the first IPW as address information stored in bits  2  to  0 . The data converter  13  then demodulates the wobble signals. In the demodulation process, the data converter  13  performs majority determination on each of the wobble signals read from bits  2  to  0  to generate three bits of address information.  
         [0021]     In accordance with the demodulation signal Y 1 , the data latch circuit  15  sequentially latches address information of each of the WDUs  1  to  13  provided from the data converter  13 . When completing the reading of one WAP, the data latch circuit  15  provides a parity check circuit  16  with the segment information, the segment address, the zone address, and the track address.  
         [0022]     The parity check circuit  16  performs a parity check on the address information stored in the data latch circuit  15 . When detecting an error in the address information, the parity check circuit  16  generates an error signal.  
         [0023]     The data converter  13  provides the non-detection counter  17  with a non-detection signal Z 1  when the IPW of the first four wobbles of each of the WDUs  1  to  13  included in the address field  9  is not detectable.  
         [0024]     The non-detection counter  17  counts the non-detection signal Z 1 . When the count value reaches a predetermined value, the non-detection counter  17  recognizes that the read operation of each of the WDUs  1  to  13  is anomalous, and generates an error signal. An address at which data is written is determined using the segment information, the segment address, the zone address, and the track address, which are read in the WAP read operation.  
         [0025]     When the SYNC detector  12  detects the SYNC pattern of the WDU  0 , the SYNC detector  12  usually reads the wobble signal “0000” prior to the SYNC pattern. It is preferable that the SYNC detector  12  detect in full bits the pattern “1111 1100 0011 1111 0000” following the wobble signal “0000”. However, this decreases the read rate. As a result, it is highly likely that the address information stored in the address field  9  cannot be properly demodulated.  
         [0026]     Therefore, as shown in  FIG. 4 ( a ), the SYNC detector  12  is set to generate the detection signal X 1  even when two or less of the four bits located at x in the pattern “0000 x111 1x00 00x1 111x 0000” are not detected.  
         [0027]     The data converter  13  detects the first IPW “1111” of each of the WDUs  1  to  13 . Before doing so, it is preferable that the data converter  13  reads the wobble signal “0000” and then detects in full bits the signals “0000 1111”. However, this would lower the read rate, and the count value of the non-detection counter  17  would increase quickly. Thus, it may become impossible to read the WDUs  1  to  13 .  
         [0028]     Therefore, as shown in  FIG. 4 ( b ), the SYNC detector  12  is set not to generate the non-detection signal Z 1  even if “1” cannot be detected at one of the two bits located to the positions of x in pattern “0000 x11x”.  
         [0029]     Japanese Laid-Open Patent Publication No. 2004-303395 describes an information recording method that sets the start position of a data segment, which is set based on address information, at the position of an NPW in the SYNC field.  
         [0030]     Japanese Laid-Open Patent Publication No. 2004-213870 describes an address reproduction circuit that improves the reliability of the read address information, which is obtained by performing A/D conversion on a wobble signal and performing a maximum likelihood decoding process.  
       SUMMARY OF THE INVENTION  
       [0031]     The SYNC detector  12  and the data converter  13  perform the read operation on the SYNC field  8  and the address field  9  with lowered detection accuracy to ensure the read rate. To ensure the read rate, the data converter  13  performs the read operation of the WDUs  1  to  13  included in the address field  9 . More specifically, the data converter  13  lowers the detection accuracy of the IPW for the first four wobbles. Further, when reading each of the wobble signals of bits  2  to  0 , the data converter  13  performs majority determination for every four bits of the wobble signal, and demodulates an address signal of one bit. In this case, when reading the WDUs  1  to  13  in the address field  9 , reading is enabled even when data is read at a timing deviated from the clock signal CLK. As a result, correct address information cannot be obtained.  
         [0032]     As one such example, referring to  FIG. 9 , when demodulating IPW and bits  2  to  0 , even if demodulation is performed in a state in which a deviation corresponding to one wobble occurs, the data converter  13  determines that the IPW has been properly read, performs majority determination on bits  2  to  0 , and demodulates the address information. However, this demodulation operation does not detect an error contained in the demodulated address information. As a result, the address used to write data is not properly demodulated.  
         [0033]     The present invention provides a method for demodulating a WAP of an optical disc that ensures the read rate of address information and improves the reading accuracy.  
         [0034]     One aspect of the present invention is a method for demodulating an address from a wobble signal recorded on a disc. The disc records a SYNC field and an address field that are configured by a plurality of wobble data units including a first wobble data unit of the SYNC field and a second wobble data unit of the address field. The firs wobble data unit includes a synchronization signal. The second wobble data unit includes a head invert phase wobble, having a plurality of bits, and an address. The method includes generating a plurality of wobble data units using the wobble signal recorded on the disc, detecting the synchronization signal from the first wobble data unit of the SYNC field, counting the plurality of wobble data units based on the detection of the synchronization signal, generating a demodulation signal for setting a timing at which the address in the second wobble data unit of the address field is demodulated based on a count value of the plurality of wobble data units, detecting the head invert phase wobble from the second wobble data unit of the address field in response to the demodulation signal and checking whether the plurality of wobble data units are properly readable, and demodulating the address in the second wobble data unit of the address field in response to the demodulation signal. Detection accuracy of the synchronization signal and the head invert phase wobble is set relatively low to improve read rate of the address. The method further includes detecting in full bit the head invert phase wobble in the second wobble data unit of the address field in parallel with the detection of the head invert phase wobble, and correcting generation timing of the demodulation signal based on the full bit detection result so that the head invert phase wobble is properly detected.  
         [0035]     Another aspect of the present invention is a method for demodulating an address from a wobble signal recorded on a disc. The disc records a SYNC field and an address field that are configured by a plurality of wobble data units including a first wobble data unit of the SYNC field and a second wobble data unit of the address field. The firs wobble data unit includes a synchronization signal. The second wobble data unit includes a head invert phase wobble, having a plurality of bits, and an address. The method includes generating a plurality of wobble data units using wobble signal recorded on the disc, detecting the synchronization signal from the firs wobble data unit of the SYNC field, counting the plurality of wobble data units based on the detection of the synchronization signal, continuously generating a plurality of demodulation signals for setting a timing at which the address in the second wobble data unit of the address field is demodulated based on a count value of the plurality of wobble data units, detecting the head invert phase wobble from the second wobble data unit of the address field and checking whether the plurality of wobble data units are properly readable, demodulating a plurality of addresses in the second wobble data unit of the address field in response to each of the plurality of demodulation signals, wherein detection accuracy of the synchronization signal and the head invert phase wobble is set relatively low to improve read rate of the plurality of addresses, detecting whether the plurality of addresses that are demodulated in response to the demodulation signals are proper, and correcting, when detecting that the plurality of addresses are proper, generation timing of one of the plurality of demodulation signals so as to be synchronized with generation timings of the demodulation signal that demodulates the proper plurality of addresses.  
         [0036]     A further aspect of the present invention is an apparatus for demodulating an address from a wobble signal recorded on a disc. The disc records a SYNC field and an address field that are configured by a plurality of wobble data units including a first wobble data unit of the SYNC field and a second wobble data unit of the address field. The first wobble data unit includes a synchronization signal. The second wobble data unit includes a head invert phase wobble, having a plurality of bits, and an address. The apparatus includes a SYNC detector for detecting the synchronization signal from the first wobble data unit of the SYNC field and generating a first detection signal. A counter counts the plurality of wobble data units in response to the first detection signal from the SYNC detector and generates a demodulation signal for setting a timing at which the address in the second wobble data unit of the address field is demodulated based on a count value of the plurality of wobble data units. An address demodulator detects the head invert phase wobble in the second wobble data unit of the address field in response to the demodulation signal and demodulates the address in the second wobble data unit of the address field. An IPW monitor detects in full bit the head invert phase wobble of the second wobble data unit of the address field in parallel with the detection of the head invert phase wobble and generates a second detection signal when properly detecting the head invert phase wobble. The counter corrects the count value in response to the second detection signal so that the demodulation signal is generated at a timing in which the head invert phase wobble is properly detectable in full bits.  
         [0037]     Another aspect of the present invention is an apparatus for demodulating an address from a wobble signal recorded on a disc. The disc records a SYNC field and an address field that are configured by a plurality of wobble data units including a first wobble data unit of the SYNC field and a second wobble data unit of the address field. The first wobble data unit includes a synchronization signal. The second wobble data unit includes a head invert phase wobble, having a plurality of bits, and an address. The apparatus includes a SYNC detector for detecting the synchronization signal from the first wobble data unit of the SYNC field and generating a first detection signal. A counter counts the plurality of wobble data units in response to the detection signal from the SYNC detector and continuously generates a plurality of demodulation signals for setting a timing at which the address in the second wobble data unit of the address field is demodulated based on a count value of the plurality of wobble data units. An address demodulator detects the head invert phase wobble from the second wobble data unit of the address field in response to each of the plurality of demodulation signals and demodulates a plurality of addresses in the second wobble data unit of the address field. An address comparator detects whether the plurality of addresses are proper, and when detecting that the plurality of addresses are proper, provides the counter with a correction signal for correcting generation timing of one of the plurality of demodulation signals so as to be synchronized with generation timings of the demodulation signal that demodulates the proper plurality of normal addresses.  
         [0038]     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0039]     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:  
         [0040]      FIG. 1  is a schematic block diagram showing an optical disc record/reproduction apparatus of the prior art;  
         [0041]      FIG. 2  is a schematic block diagram showing a WAP reproduction unit included in the optical disc record/reproduction apparatus of  FIG. 1 ;  
         [0042]      FIG. 3  is a time chart showing the operation of the WAP reproduction unit of  FIG. 2 ;  
         [0043]     FIGS.  4 ( a ) and  4 ( b ) are diagrams showing an operation for lowering the detection accuracy of wobble signals;  
         [0044]      FIG. 5  is a diagram showing the configuration of a WAP;  
         [0045]      FIG. 6  is a diagram showing the configuration of an address field in the WAP of  FIG. 5 ;  
         [0046]      FIG. 7 ( a ) is a diagram showing the configuration of a SYNC field in the WAP of  FIG. 5 ;  
         [0047]      FIG. 7 ( b ) is a diagram showing the configuration of one WDU in the address field of the WAP of  FIG. 5 ;  
         [0048]      FIG. 7 ( c ) is a diagram showing the configuration of one WDU in a unity field of the WAP of  FIG. 5 ;  
         [0049]     FIGS.  8 ( a ) and  8 ( b ) are diagrams showing the demodulating rule for wobble signals;  
         [0050]      FIG. 9  is a diagram showing an erroneous demodulation operation;  
         [0051]      FIG. 10  is a schematic block diagram showing a WAP reproduction unit of an optical disc record/reproduction apparatus according to a first embodiment of the present invention;  
         [0052]      FIG. 11  is a time chart showing the operation of the WAP reproduction unit of  FIG. 10 ;  
         [0053]      FIG. 12  is a schematic block diagram showing a WAP reproduction unit of an optical disc record/reproduction apparatus according to a second embodiment of the present invention; and  
         [0054]      FIG. 13  is a time chart showing the operation of the WAP reproduction unit of  FIG. 12 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0055]     In the drawings, like numerals are used for like elements throughout.  
         [0056]      FIG. 10  is a schematic block diagram of a WAP reproduction unit  50  in an optical disc record/reproduction apparatus according to a first embodiment of the present invention. The WAP reproduction unit  50  is incorporated in the controller  4  of the optical disc record/reproduction apparatus  100  shown in  FIG. 1 . The optical disc record/reproduction apparatus of the first embodiment is configured in the same manner as the optical disc record/reproduction apparatus  100  of  FIG. 1  except for the WAP reproduction unit  50  and is thus not shown in the drawings. A WAP (wobble address in a periodic position) having the same configuration as the WAP described in the prior art is recorded on a disc  1  as preformat information.  
         [0057]     The WAP reproduction unit  50  includes a shift register  11 , a SYNC detector  12 , a data converter  13 , a data latch circuit  15 , a parity check circuit  16 , a non-detection counter  17 , an IPW monitor  21 , and a WDU/WAP counter  22 . The WDU/WAP counter  22  operates in cooperation with the IPW monitor  21 .  
         [0058]     The WDUs of the WAP are sequentially provided to the shift register  11 . Further, wobble signals are provided to the SYNC detector  12  and to the data converter  13  in units of predetermined number of bits.  
         [0059]     The SYNC detector  12  detects a SYNC field  8  (i.e., six wobbles of IPW, four wobbles of NPW, and six wobbles of IPW configuring the SYNC field  8 ) as a synchronization signal. Upon detection of the SYNC field  8 , the SYNC detector  12  provides the WDU/WAP counter  22  and the non-detection counter  17  with a detection signal X 1 . The SYNC detector  12  is designed to generate the detection signal X 1  when detecting the SYNC pattern of “1111 1100 0011 1111” or when “1” cannot be detected at locations indicated by x in two or less of the four bits in the pattern “x111 1x00 00x1 111x 0000”.  
         [0060]     The WDU/WAP counter  22  counts seventeen WDUs  0  to  16  of one WAP in response to the detection signal X 1  and counts eighty-four wobble signals (binary signals) of each WDU. Based on the count values resulting from the count operations, the WDU/WAP counter  22  provides the data converter  13  and the data latch circuit  15  with a demodulation signal Y 2  at a predetermined timing.  
         [0061]     As shown in  FIG. 11 , the WDU/WAP counter  22  generates the demodulation signal Y 2  when counting the sixteenth wobble signal of each of the WDUs  1  to  13  in the address field  9  (i.e., when the four wobbles of the wobble signals corresponding to bits  2  to  0  are input into the data converter  13  after the four wobbles of the IPW). The demodulation signal Y 2  is generated in a locked state at the same timing as the 84 wobble signals of each of the WDUs  1  to  13 .  
         [0062]     In response to the demodulation signal Y 2 , the data converter  13  recognizes the wobble signal provided from the shift register  11  as the first IPW of each of the WDUs  1  to  13  and recognizes the wobble signal following the first IPW as address information stored in bits  2  to  0 . The data converter  13  then demodulates the wobble signals. In the demodulation process, the data converter  13  performs majority determination on each of the wobble signals read from bits  2  to  0  to generate address information. The address information is provided to the data latch circuit  15 . The data converter  13  provides the non-detection counter  17  with a non-detection signal Z 1  when the IPW of “0000 x11x” cannot be detected.  
         [0063]     In accordance with the demodulation signal Y 2 , the data latch circuit  15  sequentially latches the address information of each of WDUs  1  to  13 . Upon completion of the read operation of one WAP, the data latch circuit  15  provides the parity check circuit  16  with segment information, a segment address, a zone address, and a track address.  
         [0064]     The parity check circuit  16  performs a parity check on the address information stored in the data latch circuit  15 . When detecting an error in the address information, the parity check circuit  16  generates an error signal.  
         [0065]     The non-detection counter  17  counts the non-detection signal Z 1 . When the count value reaches a predetermined value, the non-detection counter  17  recognizes that the read operation of each of the WDUs  1  to  13  is anomalous and generates an error signal.  
         [0066]     The IPW monitor  21  receives the count value of the wobble signals of each of the WDUs  1  to  84 , which is provided from the WDU/WAP counter  22 , and the wobble signals of each WDU, which are provided from the data converter  13 . As shown in  FIG. 11 , the IPW monitor  21  sets an IPW monitoring window CW for a period from a first timing, which is one clock pulse before the timing the demodulation signal Y 2  is generated, to a second timing, which is one clock pulse after the timing the demodulation signal Y 2  is generated. The IPW monitor  21  detects full bits of the head IPW with the IPW monitoring window CW. In other words, the IPW monitor  21  sets the IPW monitoring window CW for a period expanded around the generation timing of the demodulation signal Y 2 , and detects full bits of the head IPW using the IPW monitoring window CW.  
         [0067]     For example, when the count value of the counter  14  is “15”, the IPW monitor  21  checks in full bits whether the head IPW “1111” can be detected for the wobble signal corresponding to count values “84” to “3”. When the count value of the counter  14  is “16”, the IPW monitor  21  checks in full bits whether the head IPW “1111” can be detected for the wobble signal corresponding to count values “1” to “4”. When the count value of the counter  14  is “17”, the IPW monitor  21  checks in full bits whether the head IPW “1111” can be detected for the wobble signal corresponding to count values “2” to “5”. When detecting the head IPW “1111” in full bits, the IPW monitor  21  provides the WDU/WAP counter  22  with a detection signal W 1 .  
         [0068]     When performing such a check, the wobble signal preceding the head IPW must be zero, and the wobble signal of bit  2  following the head IPW must all be zero. The wobble signal preceding the head IPW is an NPW for over 68 wobbles, that is, zero, and thus does not cause any problems. Although the chances of bit  2  being detected may increase or decrease depending on the values of the segment address, the zone address, etc., such increase and decrease in average do not cause any problems.  
         [0069]     The WDU/WAP counter  22  counts a plurality of detection signals W 1 . When the count value reaches a predetermined value, the WDU/WAP counter  22  corrects the count value of the wobble signal. As shown in  FIG. 11 , the WDU/WAP counter  22  receives a detection signal W 1  when the count value reaches “17”. When receiving the detection signal W 1  over a predetermined number of WDUs, the WDU/WAP counter  22  suspends counting for a period of one clock pulse and decreases the count value by a value corresponding to one clock pulse. With this operation, the count value of the WDU/WAP counter  22  is corrected based on the assumption that the timing at which the head IPW “1111” can be detected in full bits is normal.  
         [0070]     In the operation shown in  FIG. 11 , the timing for generating the demodulation signal Y 2  is corrected to the timing for generating the detection signal W 1 . In other words, for subsequent WDUs, the generation timing of the demodulation signal Y 2  is delayed by one clock pulse. For subsequent WDUs, demodulation is performed on the address information of bits  2  to  0  based on the demodulation signal Y 2  delayed by one clock pulse. As a result, address information A is generated based on the demodulation signal Y 2  prior to correction, and address information Aaj is generated based on the demodulation signal Y 2  subsequent to correction.  
         [0071]     The WAP reproduction unit  50  of the optical disc record/reproduction apparatus of the first embodiment has the advantages described below.  
         [0072]     (1) The SYNC detector  12  and the data converter  13  perform the read operation of the IPW in each of the SYNC field  8  and the address field  9  with lowered detection accuracy. This ensures the read rate of address information.  
         [0073]     (2) The IPW monitor  21  sets the IPW monitoring window CW for a period from the first timing, which is before the generation timing of the demodulation signal Y 2 , to the second timing, which is after the generation timing of the demodulation signal Y 2 . The IPW monitor  21  detects in full bits the head IPW of the address field  9  during the IPW monitoring window CW. Thus, even when the generation timing of the demodulation signal Y 2  is deviated due to the lowered detection accuracy of the SYNC detector  12  and the data converter  13 , the generation timing of the demodulation signal Y 2  is corrected to the timing at which the full bits of the head IPW are detectable. Further, accurate address information is demodulated based on the demodulation signal Y 2  of which generation timing has been corrected.  
         [0074]     (3) The WDU/WAP counter  22  corrects the count value when receiving a plurality of detection signals W 1 . Thus, even when the IPW monitor  21  erroneously detects the head IPW and generates one detection signal W 1 , the count value is prevented from being corrected in an unnecessary manner as long as erroneous detection does not occur a number of times in succession.  
         [0075]     (4) The read rate of the SYNC field  8  and the address field  9  is ensured, and the accuracy of the demodulated address information is improved.  
         [0076]      FIG. 12  is a schematic block diagram showing a WAP reproduction unit  60  according to a second embodiment of the present invention. The WAP reproduction unit  60  is incorporated in the controller  4  shown in  FIG. 1 . The optical disc record/reproduction apparatus of the second embodiment is configured in the same manner as the optical disc record/reproduction apparatus  100  shown in  FIG. 1  except for the WAP reproduction unit  60  and is thus not shown in the drawings. A WAP having the same configuration as the WAP described in the prior art is recorded on a disc  1  as preformat information.  
         [0077]     The WAP reproduction unit  60  includes a shift register  11 , a SYNC detector  12 , a data converter  13 , a data latch circuit  15 , a parity check circuit  16 , a non-detection counter  17 , an address comparator  23 , and a WDU/WAP counter  24 . The WDU/WAP counter  24  operates in cooperation with the address comparator  23 .  
         [0078]     The WDUs of the WAP are sequentially provided to the shift register  11 . The wobble signals are provided to the SYNC detector  12  and to the data converter  13  in units of predetermined number of bits.  
         [0079]     The operations of the SYNC detector  12 , the data converter  13 , the data latch circuit  15 , the parity check circuit  16 , and the non-detection counter  17  are the same as the operations described in the first embodiment.  
         [0080]     The WDU/WAP counter  24  counts seventeen WDUs  0  to  16  of one WAP in response to the detection signal X 1  and counts eighty-four wobble signals of each WDU. Based on the count values resulting from the count operations, the WDU/WAP counter  24  provides the data converter  13  and the data latch circuit  15  with demodulation signals Ya, Yb, and Yc at predetermined timings.  
         [0081]     As shown in  FIG. 13 , the WDU/WAP counter  24  generates demodulation signals Ya, Yb, and Yc over three clock pulses at timings when respectively counting the fifteenth, sixteenth, and seventeenth wobble signals of each of the WDUs  1  to  13  included in the address field  9  (i.e., the timing when the four wobbles of wobble signals corresponding to bits  2  to  0  are provided to the data converter  13  after four wobbles of an IPW is provided). The demodulation signals Ya to Yc are generated in a locked state at the same timing for the 84 wobble signals of each of the WDUs  1  to  13 .  
         [0082]     In response to the demodulation signals Ya to Yc, the data converter  13  recognizes the wobble signal output from the shift register  11  as the first IPW of each of the WDUs  1  to  13 , and recognizes the wobble signal following the first IPW as address information stored in bits  2  to  0 . The data converter  13  then demodulates the wobble signals. In the demodulation process, the data converter  13  performs majority determination on each of the signals read from bits  2  to  0  to generate three sets of address information. The three sets of address information are provided to the data latch circuit  15 . The data converter  13  provides the non-detection counter  17  with a non-detection signal Z 1  when the IPW of “0000 x11x” cannot be detected at any one of the generation timings of the demodulation signals Ya to Yc.  
         [0083]     According to the demodulation signals Ya to Yc, the data latch circuit  15  sequentially latches address information of each of the WDUs  1  to  13 . At the timing when completing the read operation of one WAP, the data latch circuit  15  provides the parity check circuit  16  with three sets of segment information, segment address, zone address, and track address, as addresses A, B, and C.  
         [0084]     The parity check circuit  16  performs parity check of the address information stored in the data latch circuit  15 . When detecting an error, the parity check circuit  16  generates an error signal.  
         [0085]     The non-detection counter  17  counts the non-detection signal Z 1 . When the count value reaches a predetermined value, the non-detection counter  17  recognizes that the read operation of each of the WDUs  1  to  13  is anomalous and generates an error signal.  
         [0086]     The WDU/WAP counter  24  provides the address comparator  23  with an address comparison window ACW following the demodulation signals Ya to Yc. The address comparator  23  retrieves the addresses A to C in accordance with the address comparison window ACW. The address comparator  23  determines the continuity between the address values (na, nb, and nc) of the three addresses A, B, and C, which are demodulated respectively at the generation timings of the demodulation signals Ya, Yb, and Yc in the read operation of the present WAP, and the address values (na- 1 , nb- 1 , and nc- 1 ) of the three addresses A, B, and C, which are demodulated respectively at the generation timings of the demodulation signals Ya, Yb, and Yc in the read operation of the immediately preceding WAP.  
         [0087]     The address comparator  23  determines that the demodulation timing of the address having the highest continuity of the addresses A, B, and C is normal, and provides the WDU/WAP counter  24  with a timing correction signal Q.  
         [0088]      FIG. 13  shows the case in which the address value na demodulated at the generation timing of the demodulation signal Ya has the highest continuity. In this case, the WDU/WAP counter  24  increases the count value by a value corresponding to one clock pulse. For subsequent WAPs, the demodulation signals Ya to Yc are generated based on the corrected count value. The demodulation operation and the address comparing operation described above are repeated.  
         [0089]     When the address value nb demodulated at the generation timing of the demodulation signal Yb has the highest continuity in the address comparing operation, the count value of the WDU/WAP counter  24  is not corrected. When the address value nc demodulated at the generation timing of the demodulation signal Yc has the highest continuity in the address comparing operation, the count value of the WDU/WAP counter  24  is decreased by a value corresponding to one clock pulse.  
         [0090]     In this way, the demodulation signal Yb is generated based on the uncorrected or corrected count value, and an address at which data is written is specified based on an address demodulated at the generation timing of the demodulation signal Yb.  
         [0091]     The WAP reproduction unit  60  of the optical disc record/reproduction apparatus of the second embodiment has the advantages described below.  
         [0092]     (1) The SYNC detector  12  and the data converter  13  perform the read operation of the IPW in each of the SYNC field  8  and the address field  9  with lowered detection accuracy. This ensures the read rate of address information.  
         [0093]     (2) The WDU/WAP counter  24  continuously outputs the demodulation signals Ya, Yb, and Yc. Based on the demodulation signals Ya, Yb, and Yc, three sets of address information respectively corresponding to the generation timings of the demodulation signals Ya, Yb, and Yc are demodulated in each of the WDUs  1  to  13  of the address field  9 , and three address values are demodulated in one WAP. For the three address values demodulated in each WAP, the address comparator  23  determines the continuity of the address values corresponding to the demodulation signals Ya to Yc. The address comparator  23  corrects the count value of the WDU/WAP counter  24  in a manner that the demodulation signal Yb is set as a signal that demodulates the address value having the highest continuity. This operation enables accurate address information to be demodulated based on the demodulation signal of which output timing has been corrected.  
         [0094]     (3) The read rate of the SYNC field  8  and the address field  9  is ensured and the accuracy of the demodulated address information is improved.  
         [0095]     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.  
         [0096]     In the first embodiment, the IPW monitoring window CW may be set for a period from a first timing that is one or more clock pulses before the generation timing of the demodulation signal Y 2  to a second timing that is one or more clock pulses after the generation timing of the demodulation signal Y 2  as indicated by the broken line in  FIG. 11 .  
         [0097]     The application of the present invention should not be limited to a rewritable disc. The present invention may be applied to other types of disc having WDUs, such as a HD-DVD-recordable disc.  
         [0098]     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.