| 摘要 |
PURPOSE:To attain stable demodulation by setting a frequency drawing range added to a voltage controlled oscillator control signal larger in the case of the sweeping state and smaller in the case of the tracking state and changing the protection stage number. CONSTITUTION:When the synchronization is stepped-out, a sweeping control signal is inputted from a sweeping/tracking control signal generating section 7 to a loop filter 5. Thus, a voltage controlled oscillator 6 reaches the sweeping mode and the deviation of a phase difference sweeps from -45 deg. to 45 deg.. In this case, the F is set larger and the protection stage number reaches a value suitable for the sweeping state. When the phase difference reaches a range including 0, since a tracking control signal is outputted from the generating section 7, the oscillator 6 releases the sweeping mode and makes the phase difference completely 0 based on the phase difference signal from a phase detector 4. When the phase difference reaches 0 and the synchronization is finished, the F is revised into a smaller value than that used so far. In this case, the protection stage difference set by a protection circuit 9 is set to a different value from that in the sweeping state. |
