Patent ID: 6556087
Filing Date: 2003-04-29
Classification: H03L

Abstract:
A frequency synthesizer comprising an oscillator that controls the frequency of an oscillation signal in accordance with a control signal, a fractional frequency division type frequency divider coupled to the oscillator that frequency-divides said oscillation signal and generates a comparison signal, a standard clock signal generator that generates a standard clock signal, a phase comparator coupled to the frequency divider and the standard clock signal generator that compares the phase of said comparison signal and the phase of said standard clock signal and outputs a phase difference signal, a rounding circuit that determines if the phase difference signal and a compensation signal are within a predetermined range and revises a frequency division value if the phase difference signal or compensation signal are outside the predetermined range, a charge pump circuit that outputs a current in accordance with the phase difference signal, a low-pass filter that eliminates the higher harmonics of the current that is output from said charge pump circuit and supplies it to said oscillator as said control signal, a compensation circuit that supplies to the output terminal of said charge pump circuit, the compensation signal for compensating the ripple current included in said control signal, and a frequency division value setting circuit that nonperiodically alters the frequency division value of the frequency divider.