Dynamic Phase Shift Interface in the MMCM

Versal ACAP Clocking Resources Architecture Manual (AM003)

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

The MMCME5_ADV primitive provides three inputs and one output for dynamic fine phase shifting. Each CLKOUT and the CLKFBOUT divider can be individually selected for phase shifting. The dynamic phase shift amount is common to all the output clocks selected.

The variable phase shift is controlled by the PSEN, PSINCDEC, PSCLK, and PSDONE ports (see the following figure). The phase of the MMCM output clock(s) increments/decrements according to the interaction of PSEN, PSINCDEC, PSCLK, and PSDONE from the initial or previously performed dynamic phase shift. PSEN, PSINCDEC, and PSDONE are synchronous to PSCLK. When PSEN is asserted for one PSCLK clock period, a phase shift increment/decrement is initiated. When PSINCDEC is High, an increment is initiated and when PSINCDEC is Low, a decrement is initiated. Each increment adds to the phase shift of the MMCM clock outputs by 1/32nd of the VCO period. Similarly, each decrement decreases the phase shift by 1/32nd of the VCO period. PSEN must be active for one PSCLK period. PSDONE is High for exactly one-clock period when the phase shift is complete. The number of PSCLK cycles (12) is deterministic. After initiating the phase shift by asserting PSEN and the completion of the phase shift signaled by PSDONE, the MMCM output clocks gradually drift from their original phase shift to an increment/decrement phase shift in a linear fashion. The completion of the increment or decrement is signaled when PSDONE asserts High. After PSDONE has pulsed High, another increment/decrement can be initiated. There is no maximum phase shift or phase shift overflow. An entire clock period (360°) can always be phase shifted regardless of frequency. When the end of the period is reached, the phase shift wraps around round-robin style. In the case where there is no additional phase shift initiated (PSEN stays Low), PSDONE continues to repeat a one-cycle High pulse every 32 PSCLK cycles.

Figure 1. Phase Shift Timing Diagram