| 摘要 |
PURPOSE:To ruduce the fluctuation of an oscillation frequency arising the moment a power source is cut off by inserting an isolator between a voltage controlled oscillator constituting a phase locked loop oscillator and a frequency divider dividing the frequency of a clock signal from the oscillator. CONSTITUTION:An intermittent control signal inputted from a terminal 17 opens and closes a switch 9 through a drive circuit 11, whereby the supply of a voltage and current to a prescaler 6 from the power source 8 is disconnected. Since the bias point of an active element for a transistor constituting the prescaler 6 fluctuates due to the disconnection of a voltage and a current, the input impedance of the prescaler 6 changes. However, since the isolator 20 is inserted between terminals 21 and 22, a load impedance when the isolator side is viewed from the terminal 21 hardly changes. If the VCO 5 runs freely when the power source is intermittently disconnected, a change in an oscillation frequency, which is caused by the fluctuation of the load, is minimized, and the intention comes true.
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