Synchronization detecting method and synchronization detecting circuit

A synchronization detecting circuit, comprising:

• a window generator that generates a window;
• a synchronization detector that sequentially detects synchronous signals that repeatedly appear in a reproduced signal of a recording medium where a method is employed of randomly shifting a recording start position within a certain width with respect to a predetermined recording reference position every time one or more data blocks formed of a header area, a data area, and a footer area are recorded using the window, and obtains synchronization positional information included in the synchronous signal and a data signal following the synchronous signal;
• a predicted coordinate generator that generates a first coordinate indicating a predicted phase of each synchronous signal to be subsequently appeared based on periodicity of the synchronous signal every time the synchronous signal is detected;
• and
• a controller that makes the window generator generate a first window having as a central phase each predicted phase in the first coordinate when it is determined that a synchronous signal to be detected next is not a leading synchronous signal included in a data area of one data block based on the synchronization positional information and the data signal, and makes the predicted coordinate generator generate a second coordinate obtained by replicating the first coordinate and makes the window generator generate a second window having as a central phase a first predicted phase selected from predicted phases in the second coordinate based on area length of the footer area and the header area and having a phase width equivalent to twice the certain width when it is determined that the synchronous signal to be detected next is the leading synchronous signal,
• wherein the window generator generates a third window having as a central phase one predicted phase in the second coordinate and having a phase width equivalent to twice the certain width when the synchronous signal is not detected using the first window after the synchronous signal is detected using the second window by the synchronization detector.