| 摘要 |
<P>PROBLEM TO BE SOLVED: To shorten the lockup time of a frequency synthesizer by using simple structure. <P>SOLUTION: A phase difference signal to be outputted from an exclusive logical type phase comparator 3' is inputted into a loop filter 12 via a main buffer circuit 4, a sub-buffer circuit 7 and a sub-buffer circuit 21 which restricts an output current by the gate size of a MOS transistor. In a process of shifting from a transient state to a stationary state of phase drawing, variation of average voltage output of the loop filter 12 which occurs in switching loop bands is reduced and the lockup time is shortened by performing control of stopping the sub-buffer circuit 21 after stopping the sub-buffer circuit 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
