| 摘要 |
PROBLEM TO BE SOLVED: To expand a pull-in range (pull-in frequency bandwidth) in the case of AFC control in a narrow-band digital mobile communication system. SOLUTION: The AFC circuit stores, as move information, whether control is performed in a (+) direction (to increase an output frequency of a reference oscillator) or control is performed in a (-) direction (to decrease the frequency) (step 210) when AFC control is performed (steps 206-209). If synchronization is not detected within a fixed period of time (step 211), the AFC circuit then determines that the deviation of the reference oscillator exceeds a pull-in range, and switches an initial value to be set as a center value of a control voltage to be outputted to the reference oscillator based on the move information (steps 201, 203, 204, 205). Therefore, the deviation of a reception frequency that may be out of the pull-in range in a conventional AFC control method, can be pulled in and the pull-in range can be expanded. COPYRIGHT: (C)2007,JPO&INPIT
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