| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem of a conventional direct digital synthesizer(DDS) that is excellent as a stable variable frequency oscillating source but has caused spurious radiation in very many frequencies when the DDS is used for a reference signal source to configure a frequency synthesizer. SOLUTION: An output of the direct digital synthesizer(DDS) 1 passes through a narrow band variable frequency filter 12 before the output is given to a phase synchronous loop 10. In the case of changing the frequency of the DDS 1 to change an output frequency of a frequency synthesizer 80, a center frequency of the narrow band variable frequency filter 12 is changed in matching it. The narrow band variable frequency filter 12 eliminates spurious radiation from the DDS 1 to reduce spurious radiation included in the output of the frequency synthesizer 80. |
