| 摘要 |
PURPOSE:To attain the oscillation close to an oscillation signal of a reference signal by comparing and switching the free run oscillation of plural VCOs with a reference frequency. CONSTITUTION:An output of a voltage controlled oscillator (VCO) is inputted to a switch 10. The switch selects and outputs a specific VCO among the VCO group through a control line 6. A comparison/controller 7 applies the frequency comparison between the oscillation signal inputted from the switch with a reference signal inputted from the reference input 8 (or phase comparison) and holds the result. Since the comparison controller applies the operation onto n-set of VCOs, the switch sends a control signal through the control line 6 so as to select sequentially from the 1st-n-th VCOs. Then at which number of VCO applying oscillation close to the reference frequency most is decided depending on the result of comparison held after the comparison is finished up to the n-th VCO and a control signal is fed to the switch to switch the output to the said VCO. Through the operation above, the output of the VCO whose free run frequency is closest to the reference oscillation frequency is obtained at the output 9.
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