| 摘要 |
PURPOSE:To attain high speed switching of the output frequency of the frequency synthesizer. CONSTITUTION:A variable frequency divider 12 whose frequency division ratio is set variable is provided between a reference oscillator 11 and a phase comparator 13 and a control section 17 controls the frequency division ratio so as to select a comparison frequency fed from the reference oscillator 11 stepwise from a higher frequency toward a lower frequency. Furthermore, the synthesizer has two phase locked loops and uses the frequency division output of the 2nd phase locked loop for the reference signal of the voltage controlled oscillator 15 of the 1st phase locked loop to set a phase comparison frequency to be higher than the reference frequency thereby attaining high speed pull-in operation and the band of a loop filter 14 is set to an optimum value thereby optimizing the loop characteristic. |
