| 摘要 |
PROBLEM TO BE SOLVED: To make a reference frequency high and to shorten a frequency switching time in a frequency synthesizer having a fraction frequency divider. SOLUTION: In this frequency synthesizer by a phase locked loop provided with a phase frequency comparator 16, a voltage-controlled oscillator 12 and a frequency divider 14, the voltage-controlled oscillator 12 is provided with varactor lines 82 capable of selecting an oscillation frequency band and a voltage source 90 for selecting varactors of the varactor lines 82. An optimum varactor is selected on the basis of a control voltage from the voltage source 90 in accordance with the setting of the integer part of a frequency division ratio N, and the oscillation frequency bands of the voltage-controlled oscillator 12 are switched. |
