SNAS669E September 2015 – April 2018 LMK03318
PRODUCTION DATA.
These spurs occur at multiples of fPD/DEN and are not integer boundary spurs. 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 etc. 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 where they do not significantly impact the system peformance.