| 摘要 |
PROBLEM TO BE SOLVED: To provide a digital demodulator that prevents a frequency from being deviated when a received electric field strength level is low and conducts AFC correction at a high-speed when the received electric field strength level is normal and when a received signal is switched. SOLUTION: The digital demodulator comprises a phase error calculation section 18 that calculates a phase error from I and Q signals detected by a digital orthogonal detection section 2, an AFC calculation section 16 that calculates frequency fluctuations on the basis of phase error data, an AFC correction section 4 that automatically corrects the frequency, and an AFC filter section 17 including a level detection section 22 that detects a level of the received signal, a level discrimination section 23 that discriminates a difference between the level of the received signal and a prescribed level threshold, a phase error discrimination means 25 that discriminates whether or not a phase error calculated by the phase error calculation section 18 exceeds a prescribed angular threshold, and a selector means 26 that selects passing or interruption of phase error data to the AFC calculation section 16 on the basis of the result of discrimination by the level discrimination section 23 and the phase error discrimination means 25. |
