Title: AFC circuit, carrier reproducing circuit, and receiver
Application Number: 98801365 Application Date: 1998.09.18
Publication Number: 1239622 Publication Date: 1999.12.22
Approval Pub. Date: 2004.07.14 Granted Pub. Date: 2004.07.14
International Classifi-cation: H04L27/22;H04N5/455
Applicant(s) Name: Nippon Hoso Kyokai Address:
Inventor(s) Name: Shibuya Kazuhiko;KUmada Junji;Iwadate Yuichi
Attorney & Agent: ni xiaoling
Abstract:
    Stabilized carrier recovery is acheived even at the time of a low C/N ratio by measuring the phase of a signal and controlling VCO or NCO (Numerical Controlled Oscillator) using only a period having few constellation points. At this time, false lock phenomenon is avoided as follows. That is, relatively short SYNC modulated by an already-known pattern is entered into a modulation wave, VCO or NCO oscillation frequency is swept in a wide range and sweep is stopped at a frequency in which the SYNC can be received, thereby carrying out coarse control AFC. Further, a period having long to some extent, having few constellation points is provided in the modulation wave and then, a difference between the frequency of a received modulated signal and a local oscillation signal of VCO or NCO is obtained in this period. This frequency difference is analyzed according to the phase differential function method, self-correlation function method or count method, and the VCO or NCO is controlled based on this result of analysis.
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