PLL circuit and radio communication terminal apparatus using the same

A PLL circuit, comprising:

• a phase comparator outputting a signal proportional to a phase difference between a first input signal and a second input signal;
• a low-pass filter connected to an output terminal of the phase comparator;
• a frequency generator to generate a plurality of frequencies, the frequency generator being connected to an output terminal of the low-pass filter and provided with at least one VCO;
• a plurality of coupling nodes connected to an output terminal of the frequency generator;
• and
• a frequency converter connected to each output terminal of the plurality of coupling nodes, and converting a frequency of an output signal from the plurality of coupling nodes so as to generate the second input signal, and
• wherein in said phase comparator a phase difference conversion gain changes based on an amplitude of the second input signal, and a variable gain amplifier capable of varying a gain is interposed between the phase comparator and the frequency converter.

A radio communication terminal apparatus, comprising:

• a transmitter system including a quadrature modulator, to which I and Q signals are inputted, a PLL circuit connected to an output terminal of the quadrature modulator, and a power amplifier connected to an output terminal of the PLL circuit;
• a receiver system outputting I and Q signals;
• an antenna;
• and
• an antenna switch interconnecting the antenna, the transmitter system and the receiver system;
• wherein the PLL circuit comprises:
• a variable-bandwidth phase comparator outputting a signal proportional to a phase difference between a first input signal and a second input signal;
• a low-pass filter connected to an output terminal of the variable-bandwidth phase comparator;
• a frequency generator to generate a plurality of frequencies, the frequency generator being connected to an output terminal of the low-pas filter and provided with at least one VCO;
• a plurality of coupling nodes connected to an output terminal of the frequency generator;
• and
• a frequency converter connected to each output terminal of the plurality of coupling nodes, and converting a frequency of an output signal from the plurality of coupling nodes so as to generate the second input signal.