| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a PLL circuit capable of performing switching VCO characteristics in such a way that a control voltage falls within a predetermined allowable range, in accordance with a change of target frequency, and executing such switching at early timing as much as possible. <P>SOLUTION: The PLL circuit comprises: a voltage controlled oscillation section that can be switched to a plurality of VCO characteristics, a phase comparator; and a VCO switching section that switches VCO characteristics in accordance with a result of comparison between a control voltage and a predetermined allowable range, wherein a clock of a frequency set to that target frequency at a present time point is outputted, wherein the VCO switching section detects whether a sampled voltage is settled within the allowable range or not and switches the VCO characteristics in accordance with a result of the detection, and timing of the sampling is after the lapse of a first time that is a predetermined time, from a time point of switching the target frequency. <P>COPYRIGHT: (C)2009,JPO&INPIT |
