| 摘要 |
PURPOSE: A digital down converter is provided to obtain a low spurious level and a high frequency accuracy without increasing power consumption of a local oscillator. CONSTITUTION: An antenna(201) is used for receiving a signal(fa(t)). The received signal(fa(t)) is converted to an intermediate frequency signal by a radio frequency(202), a mixer(203), and a local oscillator(204). The intermediate frequency signal is restricted by a band pass filter(205) and the remaining signals except for a receiving band is restricted thereby. An analog/digital converter(206) receives and samples an output of a band pass filter(205) and inputs the first digital intermediate frequency signal(f1(t)) to a digital down converter(207). The digital down converter(207) is formed with the first mixer for converting the digital intermediate frequency signal(f1(t)) to the second intermediate frequency signal, a digital filter for restricting a band, and the second mixer for converting an output of the digital filter to a processing frequency of a detector.
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