| 摘要 |
A PLL circuit includes a voltage controlled oscillator (VCO), a phase comparator detecting phase difference between a reference signal and a feedback signal provided from the VCO, an input voltage control unit controlling input voltage to be provided to the VCO according to the phase difference detected by the phase comparator, a switching unit switching a value of the input voltage to be provided to the VCO, and a switching timing control unit controlling a switching timing of the switching unit based on the given reference signal, wherein the VCO controls a frequency of the feedback signal according to the input voltage provided from the input voltage control unit. As a result, the VCO can rapidly make the feedback signal in phase with the reference signal and therefore it is possible to effectively reduce the required lock-up time.
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