Dynamic Interpolated Fine Phase Shift in MMCM and XPLL (variable phase shift)

Versal ACAP Clocking Resources Architecture Manual (AM003)

Document ID
AM003
Release Date
2022-05-24
Revision
1.4 English

Interpolated fine phase shift mode has a linear shift behavior independent of the CLKOUT_DIVIDE/CLKFBOUT_MULT value. There is an individual phase interpolator (PI) for each of the O clock output counters and the M counter in the MMCM. The phase shift resolution only depends on the VCO frequency. The phase shift resolution is 1/32nd of the VCO frequency ((VCO period in ps)/32)) and is based on one of the eight phases out of the VCO selected. In this mode, the output clocks can be rotated 360° round robin. The phase interpolators can be controlled by either of the two deskew phase detectors (PDs) or by the phase shift interface.

If the VCO runs at 3 GHz, the phase resolution is approximately (rounded) 10 ps, and at 4 GHz it is approximately (rounded) 8 ps.

When using fine phase shift, the initial phase step value of every PI can be independently setup. The phase can be dynamically incremented or decremented. The dynamic phase shift is controlled by the PS interface of the MMCME5_ADV. This phase shift mode affects each individual CLKOUT output. In interpolated fine phase shift mode, a clock must always be connected to the PSCLK pin of the MMCM. Fixed or dynamic phase shifting of the feedback path results in a negative phase shift of all output clocks with respect to CLKIN.