9.2iSP3 Timing - Changes in the calculation of Discrete Jitter for the uncertainty equations for PLL2DCM and DCM2PLL

疑问描述

When I do timing analysis, I noticed that the calculation of Discrete Jitter (DJ) for the PLL2DCM and DCM2PLL situations has changed. When did this happen?

解决方案

From DCM to PLL 

Currently Dj is calculated by {Dj(pll) + Dj(dcm)}. However, PLL is very good at filtering out the DCM jitter, so we will change the Dj equation to only include the Dj from the PLL and to ignore the Dj from the DCM. The "Ref Jitter" input will be inputted to the PLL jitter equation. 

From PLL to DCM 

DCM will pass any PLL jitter and then add in its own jitter. So we will calculate Dj as Dj(pll)+Dj(dcm). The"Ref Jitter" input will used as an input to the PLL jitter equation. 

This problem has been fixed in the latest 9.2i Service Pack available at: 

http://www.xilinx.com/xlnx/xil_sw_updates_home.jsp
 

The first service pack containing the fix is 9.2i Service Pack 4.