Hi, All
The fractional-spur is a main disadvantage of fractional-N PLL. Although the Delta-Sigma modulation is used to dithering the fractional number, the Spur still remain in the PLL output spectrum. It is easy to predict the offset frequency of the Spur, but how to estimate the amplitude (dBc) of the Spur? If it is assumed that nonlinearity of the PLL can be ignored.

Thanks and best regards.

Leon