Answers Database Virtex: How does signal grouping affect the number of SSO a device can support before ground bounce becomes a problem? Record #8390 Product Family: Hardware Product Line: Virtex Product Part: Virtex General Hardware Problem Title: Virtex: How does signal grouping affect the number of SSO a device can support before ground bounce becomes a problem? Problem Description: Urgency: Standard General Description: As far as ground bounce goes, does it make any difference which bank the signals are in? For example, say I have 8 signals: either 4 in bank1 and 4 in bank2, or 8 in bank1. Is ground bounce more likely to occur in the setup where all signals are in bank1? It seems that the problem is with disturbances in the ground plane, and there's only one ground plane, so it seems signal placement shouldn't matter. Solution 1: Signal placement matters because at these frequencies, every distance you traverse with a signal really counts. So the number of VCC/GND pairs in close proximity to your IO is what determines how much SSO you can handle before gnd bounce becomes a problem. It's always better to spread signals out, because effectively you increase the ratio of VCC/GND pairs per IO. That may not make sense if you think of the VCC and GND planes as ideal conductors. The thing is, they're not. Up around 200MHz and above, opposite sides of the chip (bank 0 vs bank 4), are invisible to each other. End of Record #8390 - Last Modified: 01/14/00 09:36

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