| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a PLL circuit wherein a charge pump receives a noise comprising a high frequency component and converts the noise into a noise with a frequency component lower than a cut-off frequency of a loop filter so that it is prevented that the loop filter cannot eliminate the noise, resulting in causing a phase noise to an FSK modulation signal. <P>SOLUTION: The PLL circuit includes: a phase comparator 13 for detecting a phase difference between a reference frequency signal fr and a comparison frequency signal fp and providing an output of a phase comparison signal PD; a low pass filter 31 for eliminating the noise comprising a high frequency component included in the phase comparison signal PD; the charge pump 14 for increasing / decreasing a control current IC in response to the phase comparison signal PD to provide an output; the loop filter 15 for eliminating the high frequency component of the control current IC, converting the control current IC into a control voltage VC and providing an output; and a voltage-controlled oscillator 1 for increasing / decreasing the comparison frequency signal fp in response to the control voltage VC and providing an output. <P>COPYRIGHT: (C)2006,JPO&NCIPI |
