SNAS722A December 2017 – October 2018 LMK61E07
These spurs occur at multiples of fPD/DEN and are not the integer boundary spur. For instance, if the phase detector frequency is 100 MHz and the fraction is 3/100, the primary fractional spurs would be at 1 MHz, 2 MHz, 4 MHz, 5 MHz, 6 MHz, and so forth. These are impacted by the loop filter bandwidth and modulator order. If a small frequency error is acceptable, then a larger equivalent fraction may improve these spurs. This larger unequivalent fraction pushes the fractional spur energy to much lower frequencies that where they are not impactful to the system performance.