| 摘要 |
PROBLEM TO BE SOLVED: To provide a digital Costas loop circuit that can decide a required frequency with high accuracy. SOLUTION: The digital Costas loop circuit 22 includes a phase difference detection circuit 22, which detects a phase difference on the basis of signals I', Q'. This digital Costas loop circuit first tentatively decides the frequency in the 8 PSK mode. That is, a synchronization detection circuit 30 detects presence of synchronization on the basis of a synchronous word signal included in a synchronizing signal part. When detecting the presence of synchornization, the synchronization detection detection circuit 30 sets a PBSK mode and decides the frequency on the basis of a TMCC signal included in the synchronizing signal part. That is, even when the presence of the synchronization is detected, the frequency is a little deviated from the accurate frequency, the deviation is corrected in the BPSK mode. Since the frequency is tentatively decided in the 8 PSK mode and then the frequency is decided in the BPSK mode, the frequency can accurately be decided. |
