| 摘要 |
PROBLEM TO BE SOLVED: To obtain a frequency signal generating circuit that employs conventional components with a simple circuit configuration. SOLUTION: The frequency signal generating circuit is provided with a reference frequency generating source 11, a plurality of voltage controlled oscillators 18, 19, a switch 20 that selects either of the voltage controlled oscillators, frequency divider circuits 21, 22 that convert an output of the voltage controlled oscillators, a phase comparator 13 that receives an output of the frequency divider circuits and a reference signal from a reference signal generating source to compare phases of them, a low pass filter 14 that extracts a DC component from the phase comparator, voltage holding circuits 16, 17 that hold an output of the low pass filter for each voltage controlled oscillator, and a changeover circuit 15 that controls the changeover of the switch, the frequency divider circuits and the voltage holding circuits. Then the switch is switched in response to an output of the changeover circuit 15, a frequency division ratio of the frequency divider circuits is changed into a required frequency division ratio to take either of a plurality of the voltage controlled oscillators into a loop in time division and the voltage holding circuits added to the voltage controlled oscillators hold a control voltage so as to maintain the oscillated frequency in response to the frequency division ratio at that time.
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