| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a frequency synthesizer capable of switching oscillation frequency into target frequency without causing any overshoot. SOLUTION: The output frequency of a frequency synthesizer is switched according to a set value switching signal of a frequency division ratio switching part 6. First and second VCO 8 and 9 input an error signal from a phase comparator 3, and generates an oscillation output proportional thereto. At the time of switching the output frequency due to the change of the set value, the first VCO 8 obtains the holding voltage of a first voltage holding circuit 12, by the operation of switches 10 and 13, then the number of the oscillation outputs before switching is kept and selected by a selector 7 to obtain a clock output 16. The oscillation output of the second VCO 9 is supplied to a second program divider 4 by the selector 7 so that a loop can be formed of the second VCO 9, and the oscillation output of the second VCO 9 can be changed. When it is judged that the output frequency of the second VCO 9 is stabilized by a lock detector 17, the output of the second VCO 9 is obtained as the clock output 16 by the selector 7.</p> |
