EP2S130F1020I4 Datasheet, PDF (751/768 Pages) List of Unclassifed Manufacturers – Stratix II Device Handbook, Volume 1

High-Speed Board Layout Guidelines
1 If possible, you should avoid using stubs in your PCB design.
For high-speed designs, even very short stubs can create signal
integrity problems.
Figure 11–14. Daisy Chain Routing with Stubs
Main Bus
Stub
Clock
Source
Termination
Resistor
Device 1
Device 2
Device Pin
(BGA Ball)
Figures 11–15 through 11–17 show the SPICE simulation with different
stub length. As the stub length decreases, there is less reflection noise,
which causes the eye opening to increase.
Figure 11–15. Stub Length = 0.5 Inch
Figure 11–16. Stub Length = 0.25 Inch
Altera Corporation
May 2007
11–15
Stratix II Device Handbook, Volume 2