| 摘要 |
A frequency synthesizer includes a digitally-controlled oscillator and an oscillation frequency control unit. The digitally-controlled oscillator includes a loop-shaped transmission line path having an odd number of parallel portions in each of which two conductors are arranged in parallel to each other with a space therebetween, and an odd number of intersection portions in each of which two conductors intersect spatially, an active circuit coupled between the two conductors, and a first variable capacitance unit and a second variable capacitance unit. The oscillation frequency control unit includes a &Sgr;&Dgr; modulation circuit for subjecting to &Sgr;&Dgr; modulation a first control signal for switching a high capacitance state and a low capacitance state of a first variable capacitance element included in the first variable capacitance unit.
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