Patent ID: 6873213
Filing Date: 2005-03-29
Classification: H03L

Abstract:
1. A fractional N frequency synthesizer controlling an oscillation frequency of a voltage controlled oscillator output of a voltage controlled oscillator essentially based on a phase difference between a comparison signal and a modulated reference signal, comprising: a first frequency dividing circuit coupled to receive the voltage controlled oscillator output and providing the comparison signal by dividing the voltage controlled oscillator output by a first frequency dividing number; a frequency dividing number control circuit for controlling the first frequency dividing number of the first frequency dividing circuit to a non-integer value to provide the comparison signal; a modulating circuit coupled to receive a reference signal and providing the modulated reference signal having a first predetermined modulation width every T periods where T is an integer greater than or equal to 2; a phase comparison circuit coupled to receive the modulated reference signal and the comparison signal and providing a phase difference signal based on a phase difference between the modulated reference signal and the comparison signal; and a low pass filter coupled to receive the phase error signal and providing a low frequency component of the phase difference signal to the voltage controlled oscillator.