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AR# 20948

Virtex-II Pro X RocketIO - What is the unit interval (UI) that is referred to in the Tgjtt specification in the data sheet?


General Description: 

In the Virtex-II Pro Data Sheet, (ds083.pdf) version 4.1 from November 04, page 14, Table 22: "RocketIO X Reference Clock Switching Characteristics," the reference clock total jitter pk-pk is stated as 0.012 UI at the different serial speeds. 


What is the unit interval (UI) referring to? 




The Tgjtt number refers to REFCLK. 


The unit interval (UI) is based on one clock period NOT the serial bit period. 


For Example: 


If the application is running at 2.5Gb/s, and REFCLK = 125 MHz, 


UI = 1/125 MHz = 8 ns 

Tgjtt = 0.012 x 8 ns = 96 ps

AR# 20948
Date Created 09/04/2007
Last Updated 05/19/2014
Status Archive
Type General Article