| 摘要 |
PROBLEM TO BE SOLVED: To provide the frequency synthesizer whose frequency can be switched at a high speed. SOLUTION: The synthesizer is provided with a voltage controlled oscillator 1 and a phase comparator 4 that compares a signal, frequency-dividing a frequency of an output of the voltage controlled oscillator 1 with an output of a frequency divider 3 and provides an output of the phase difference to the voltage controlled oscillator 1 via a low-pass filter 5. In the case of changing a frequency of the output of the voltage controlled oscillator 1, at first a comparison frequency is set higher and the comparison frequency is set lower, when the synchronization is nearly locked. Furthermore, the synthesizer is provided with a frequency division ratio control circuit 9 that controls a frequency division ratio of a 1st variable frequency divider 2 frequency-dividing the frequency of the output of the voltage controlled oscillator 1 to include the value below a decimal point. Since the setting frequency division ratio step of the variable frequency divider is divided to be very small, the frequency error of the output of the voltage controlled oscillator 1, before and after the changeover of the comparison frequency, is reduced and high speed locking is attained. |
