| abstract |
A broadband modulation PLL having an excellent modulation accuracy is provided at a low cost. A PLL includes a VCO (21), a frequency divider (22), a phase comparator (23), a charge pump (24) and a loop filter (25). The frequency division ratio of the frequency divider (22) and the VCO (21) are controlled for adjustment. The VCO (21) has two control terminals for PLL and for modulation. A control signal producing part (28) produces, based on an input voltage (Vt1) to be applied to the PLL control terminal and a phase modulation data, a control voltage (Vtm) to be applied to the VCO (21). During a modulation factor adjustment, the control voltage (Vtm) to be applied to the modulation control terminal of the VCO (21) is controlled, and the input voltage (Vt1) is measured to calculate the frequency modulation sensitivity of the VCO (21) to the control voltage (Vtm). Then, the modulation factor of the phase modulation data is adjusted based on the modulation sensitivity as calculated. |