| 摘要 |
PURPOSE:To prevent the fluctuation of phase difference of an input/output signal with simple constitution by controlling an oscillation frequency of a local oscillator fed to a frequency converter at the pre-stage of a BPF so as to bring the phase difference between the input and output signals to the BPF into a prescribed value. CONSTITUTION:A recovered carrier fed to an input terminal IN is subject to frequency conversion by a down-converter 21 into a low frequency signal, which is filtered by the BPF 11. When the input signal frequency is lowered to the BPF 11 and the phase difference between the input and output signal is increased than a prescribed value, the DC voltage fed from a phase comparator 12 to a sample holding circuit 16 via an LPF 14, a sample holding circuit 15 and an adder 17 is larger than zero V. As a result, the control voltage fed to a local oscillator 23 is increased, the oscillation frequency of an oscillator 23 is lowered and the input signal frequency to the BPF 11 is increased. The phase difference between the input and output signal approaches a prescribed value attended with it. When the input signal frequency to the BPF 11 is increased and the phase difference between the input and output signals is decreased than the prescribed value conversely, the input signal frequency to the BPF 11 is increased.
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