Patent ID: 7973606
Filing Date: 2011-07-05
Classification: H03L

Abstract:
1. A fractional-N frequency synthesizer improving noise characteristics, comprising: a reference oscillator that generates a reference frequency signal; a sigma-delta modulator that generates a desired decimal value based on the reference frequency signal; a divider that divides a voltage controlled oscillation frequency signal; first to M phase/frequency detectors that detect a difference in phase and frequency between the reference frequency signal and the divided voltage controlled oscillation frequency signal; first to M charge pumps that are connected to each of the phase/frequency detectors in series and charge or pump charge amount according to output signals from each of the phase/frequency detectors; a loop filter that controls amount of supplied current based on output signals from the charge pumps to filter low-pass frequency components; a voltage controlled oscillator that is oscillated in response to an output signal from the loop filter and generates the voltage controlled oscillation frequency signal; and a phase controller that divides the divided voltage controlled oscillation frequency signal by 1/M times, controls each phase thereof, and then supplies them to each of the first to M phase/frequency detectors.