| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a frequency synthesizer which exhibits a high responsiveness and is hardly affected by jitter noise. <P>SOLUTION: The frequency synthesizer is provided with a voltage-controlled oscillator 1 which generates an output signal at a frequency according to the control voltage, a frequency divider 2 which divides the output signal from the voltage-controlled oscillator 1, a phase comparator 3 which detects the phase difference between the output signal from the frequency divider 2 and a reference signal from the outside and outputs a lock signal according to the detected phase difference, a loop filter 4 which can be switched between at least two time constants and smooths the output signal from the phase comparator 3 and a time constant circuit 5 which switches the time constant of the loop filter 4 according to the lock signal and increases the time constant of the loop filter 4 at least when the frequency of the output signal of the voltage-controlled oscillator 1 is stable. <P>COPYRIGHT: (C)2004,JPO&NCIPI |
