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

摘要

A phase-locked loop circuit includes a current output type phase comparator (1) for converting a phase difference of a first signal (fIN) and a second signal (fREF) into a current signal to be produced, a low pass filter (4) for filtering the current signal of the current output type phase comparator (1) to produce an output signal, a voltage controlled oscillator (5) for producing a signal having a frequency (fRF) corresponding to the output signal of the low pass filter (4) and a frequency converter (7) for frequency-converting the output signal of the voltage controlled oscillator (5) to produce a second signal. A current source (2) is provided for supplying a current which is added to the current signal produced by the phase comparator (1), and the resulting sum current is supplied to an input of the low-pass filter (4). Furthermore a reset switch (3) applies a reset voltage to the voltage controlled oscillator (5) for cancelling a phase-locked state of the phase-lock loop circuit. The phase-locked loop may be used in a transmittor section of a radio communication apparatus, such as a portable terminal of a mobile communication system, to provide for a short frequency settling time and low output noise without broadening of the band of the PLL.