Patent ID: 8531217

Claim:
A fractional-N frequency synthesizer having reduced fractional switching noise and spurious signals, the synthesizer comprising: a voltage controlled oscillator for providing an output signal; a fractional-N divider responsive to the voltage controlled oscillator for providing a divided output signal having fractional switching noise; a band pass filter having a center frequency at approximately a frequency of a reference signal and responsive to the fractional-N divider for reducing the fractional switching noise and non-linearities of the fractional-N divider that result in spurious signals; a phase detector responsive to the reference signal and the band pass filter for providing a control signal representative of the phase difference between the reference signal and the signal from the band pass filter; and a loop filter responsive to the phase detector for filtering the control signal to control the voltage controlled oscillator, the output of the loop filter having reduced fractional switching noise and spurious signals.