To provide a PLL circuit which is hardly affected by external noises and the variation of its power-supply voltage, where the control sensibility of its VCO is not increased, even when the oscillation frequency range of its VCO is widened to make its VCO responsive to a plurality of bands.
A VCO 10, constituting the PLL circuit, is configured to enable it to operate in a plurality of bands. In the state wherein the controlling voltage of the oscillation circuit of the VCO 10 is fastened to a predetermined value, the oscillation frequencies of the oscillation circuit are measured in the respective bands to store them in a memory circuit 18. Then, by comparing the stored frequency measurement values with the set value for assigning the band given, when operating the PLL circuit, the band used actually in the oscillation circuit is determined from the comparison result thereof.
OSAWA HIROTAKA
HENSHAW ROBERT ASTLE
TTP COMMUNICATIONS LTD
Next Patent: SEMICONDUCTOR-DEVICE INSPECTING METHOD, AND SEMICONDUCTOR DEVICE