| 摘要 |
PURPOSE:To obtain an output frequency of high accuracy in a sweep period and at the same time to attain the sweep of frequency with high stability, by actuating a PLL circuit in a hold-off period to obtain a reference output frequency and holding the control voltage based on the PLL circuit in that state to supply the control voltage to a VCO. CONSTITUTION:The 1st switch 16 provided in a PLL circuit is controlled to be turned on in hold-off periods t1-t2 and forms a PLL circuit. The 1st control voltage corresponding to the voltage Vs decided by a D/A converter 18 is supplied to the 1st terminal (a) of a VCO5 in the periods t1-t2. At the same time, the 2nd control voltage based on the PLL circuit is applied to the 2nd terminal (b). As a result, an output frequency fO has high accuracy and high stability. While the voltage charged to a capacitor 12 is held by OFF of the switch 16 in the periods t1-t2. Thus the voltage obtained immediately before the switch 16 is turned off is continuously supplied to the VCO5 as the 2nd control voltage, and the frequency fO has high accuracy. |
