The MMCM feedback can be internal to the MMCM when the MMCM is used as a synthesizer or jitter filter, and there is no required phase relationship between the MMCM input clock and the MMCM output clock. The MMCM performance increases because the feedback clock is not subjected to noise on the core supply since it never passes through a block powered by this supply. However, noise introduced on the CLKIN signal and the BUFG are still present ( This Figure ).
