| 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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