| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a frequency synthesizer that can minimize a variation in an output frequency in the event of an input interruption of an external reference signal by implementing high speed switching to output a constant voltage as a control voltage to an oscillator. <P>SOLUTION: In the frequency synthesizer, a control circuit 11 receives a detection output from a detection circuit 10, outputs to a SW 3 a switching signal to output an output of a PLL-IC 1 to a loop filter 4 when an external reference input signal is "on," and outputs to the SW 3 a switching signal to output an output of a variable resistance 2 to the loop filter 4 if the external reference input signal is "off," and a high speed switching circuit 12 outputs to the SW 3 a switching signal to output the output of the variable resistance 2 to the loop filter 4 earlier than the control circuit 11 when detecting that the external reference input signal is "off." <P>COPYRIGHT: (C)2013,JPO&INPIT |
