PLL circuit and radio communication terminal apparatus using the same

摘要

A PLL circuit and a radio communication terminal apparatus using the PLL circuit is provided. In the PLL circuit, the number of n pieces of LPFs which have been required is reduced to only one LPF, so that the PLL circuit can reduce a mounting area and the number of pins, and can simplify its design. The PLL circuit according to the present invention comprises a variable-gain phase comparator 1, a mixer 2, an LPF 3, n pieces of VCOs 4-1 to 4n, n pieces of couplers 5-1 to 5-n, and a control circuit 6 for controlling the on/off of the operation of the VCOs. The variable-gain phase comparator 1 is a phase comparator capable of varying a phase difference gain. By the control circuit 6, the on/off of the operation of the VCOs 4-1 to 4n and one of the VCOs 4-1 to 4-n is operated in accordance with a desired operation frequency band; other VCOs are controlled to an off state. The phase difference conversion gain is varied in accordance with the sensitivity of the VCOs 4-1 to 4-n, and thereby, the number of LPF required for the PLL circuit can be reduced to only one.