Phase-locked loop circuit and radio communication apparatus using the same

A radio communication apparatus comprising:

• an antenna;
• a transmitter having an output;
• a receiver having an input;
• and
• a duplexer which selectively couples either of the input of the receiver and the output of the transmitter to the antenna;
• wherein the transmitter includes:
• a phase-locked loop circuit which receives a first signal having a frequency and converts the first signal into an output signal having a transmission frequency;
• and
• an output amplifier which amplifies the output signal of the phase-locked loop circuit to produce an output signal of the transmitter and supplies the output signal of the transmitter to the output of the transmitter;
• and
• wherein the phase-locked loop circuit includes:
• a current output type phase comparator which converts a phase difference between the first signal and a second signal into a current signal;
• a low pass filter which filters the current signal of the current output type phase comparator to produce an output signal;
• a voltage controlled oscillator which produces an output signal having a transmission frequency corresponding to the output signal of the low pass filter, the output signal of the voltage controlled oscillator constituting the output signal of the phase-locked loop circuit;
• and
• a frequency converter which frequency-converts the output signal of the voltage controlled oscillator to produce the second signal.