Patent ID: 8258835

Claim:
A fractional-N frequency synthesizer having a cancellation system for a phase discontinuity due to loop gain changes which is accompanied with a change of a charge-pump current value, comprising: a phase detector; a current-changeable charge-pump; a loop filter for providing a tuning signal; a voltage-controlled oscillator (VCO) controlled by the tuning signal for providing a VCO output signal; a divider for providing a divided signal; and a modulator for generating a modulating signal for fractional-N functionality; wherein the phase detector comprises: a first input for receiving a reference signal oscillating at a reference frequency; and a second input for receiving the divided signal from a voltage-controlled oscillator after the second input passes through a divider, wherein the phase detector and current-changeable charge-pump is configured to compare a phase of the first input and a phase of the second input and to generate a charge-pump current on and off, and wherein the cancellation system for a phase discontinuity is implemented inside the modulator, the modulator having an additional input defined by the current-changeable charge-pump current values.