| 摘要 |
PURPOSE:To easily and appropriately decide the characteristic of VCO in a phase locked loop circuit which is made into an integrated circuit by controlling two VCOs by means of the output voltage of a loop filter to which a reference clock is inputted amount three VCOs of the same characteristic. CONSTITUTION:When VCO 4, 6 and 10 have the same circuit constitution and the same characteristic and a voltage-frequency characteristic is linear, the output voltages 13 and 14 from the loop filters 3 and 9 of the reference clock 1 are mutually equal, and they oscillate at the same frequency. Then, the ocsillation frequency of VCO 6 follows the frequency twice as much as the reference clock. When the VCO characteristic is not linear, VCO 6 oscillates at the frequency shifted from the clock twice as much as the reference clock. Thus, a voltage change quantity comes to be equal to the change quantity of the voltage 13 and the oscillation output frequency of VCO 4 changes. Consequently, the characteristic of VCO can easily and appropriately be decided by measuring the frequency of the output 11 of VCO 4. |
