Patent ID: 7526055
Filing Date: 2009-04-28
Classification: H03L,H03M

Abstract:
1. A fractional-N frequency synthesizer, comprising: a phase detector for detecting a phase difference between a reference signal and a feedback signal; a voltage controlled oscillator for receiving a phase difference control signal based on the detected phase difference, and for oscillating a signal with a frequency based on the detected phase difference; a divider for selecting a value from at least three integers according to a predetermined selection signal, for dividing the frequency of the oscillated signal output from the voltage controlled oscillator by the selected value, and for outputting a divided signal as a feedback signal to the phase detector; and a sigma-delta modulator for adding a predetermined input value to an internal feedback value, for successively accumulating added values, for quantizing an accumulated value to at least three levels, and for converting a quantized value into the predetermined selection signal, wherein the sigma-delta modulator comprises: