| 摘要 |
PURPOSE:To reduce cost with the simplification of the entire circuitry, by determining the frequency of a reference signal to let a phase difference detected with a phase difference detection circuit be down to zero after a phase adjusting time passes. CONSTITUTION:A phase difference detection circuit 3 detects a phase difference between a reference signal outputted from a voltage control oscillation circuit 2 and a modulation signal at each fixed time. A correction frequency calculation means 8 determines the frequency of a reference signal to let the phase difference be down to zero after a phase adjusting time passes from the detection of the phase difference while an oscillation frequency of the voltage control oscillation circuit 2 is controlled to the frequency thus obtained only for the phase adjusting time. A phase difference change rate detection circuit 4 and an averaging circuit 5 as reference frequency adjusting means determine speed of changes in the phase difference detected with the phase difference detection circuit 3 while the oscillation frequency of the oscillation circuit 2 is adjusted by a deviation of the frequency corresponding to the speed of changes in the phase difference. Thus, the frequency of the reference signal to be outputted from the oscillation circuit 2 follows the frequency of a modulation signal with respect to displacement of the frequency of the modulation signal due to a Doppler shift or the like.
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