| 摘要 |
PROBLEM TO BE SOLVED: To provide a PLL circuit having a loop filter having the same lockup time in bidirectional channel switching and capable of preventing the reduction of a CN ratio. SOLUTION: The PLL circuit is provided with a reference oscillation circuit 2, a fixed frequency divider 3, a voltage controlled oscillator 7, a variable frequency divider 9, a phase comparator 4 and a charge pump circuit 5 for outputting a phase difference signal between an output signal from the divider 3 and an output signal from the divider 9 and a lock detection signal, a loop filter 6, and a lock detection circuit 10 for outputting a lock detection signal detecting signal. A switch circuit having plural capacitors and capable of switching a time constant by switching the connection state of these capacitors in accordance with a detection signal is connected to the loop filter 6. Thus lockup time can be set up to the same value independently of a channel switching direction without reducing a CN ratio. |
