FREQUENCY SYNTHESIZER, AND CONTROL METHOD THEREFOR

摘要

PROBLEM TO BE SOLVED: To make it possible to return a voltage control signal in a specified voltage range while keeping a frequency synthesizer in locking status, when the frequency synthesizer remains in locking status and the voltage control signal of a voltage controlled oscillator is out of the specified voltage range.

SOLUTION: The frequency synthesizer includes: a monitor circuit 8 wherein compensation variable capacitance diodes 53 and 54 are provided in a voltage controlled oscillator 5 in addition to a variable capacitance diode 52 wherein a DC bias voltage is controlled by a control voltage signal 11 generated by a low-pass filter 3, and which monitors the control voltage signal 11 and changes the level of control signals 16 and 17 when the voltage of the control voltage signal 11 becomes out of a voltage range enough to easily change a capacitance of the variable capacitance diode 52; and a time constant circuit 72 which weakens a change of the level of the control signals 16 and 17 into a slow voltage change with which the locking state is not released and gives the DC bias voltage to the compensation variable capacitance diode.

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