| 摘要 |
A frequency synthesizer includes an AND circuit ( 17 ) for detecting whether a frequency synthesizer is in a lock state according to a signal outputted from an Up terminal and a Down terminal of a phase comparator and switching circuits ( 18, 19 ) for switching between presence and absence of connections of constant current circuits ( 14, 15 ) constituting a charge pump circuit ( 4 ) according to the output signal of the AND circuit ( 17 ). When the AND circuit ( 17 ) has detected a high impedance state of the charge pump circuit ( 4 ), the switching circuits ( 18, 19 ) disconnects the constant current circuits ( 14, 15 ) by the switching circuits ( 18, 19 ). Thus, it is possible to eliminate current flowing into the charge pump circuit ( 4 ) without using a control signal from outside such as a power cut signal and an intermittent signal.
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