Cross-talk Shielding Net

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kumar_eee

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When we face cross-talk violation, we can shield the net to avoid the cross-talk effects. While shielding, we always shield the net with VSS, why not with VDD?

What are the pros and cons of connecting it to VDD?
 

my guess is that we want any noise or interferance to "go" or to be transfered into the ground (vss) which is usually a plane (high coductivity and low inductance) or the chassis .
donot you think that if the noise transfers to the VDD line , it could "couple" or become a problem in the power section !!??
 

From my experience, a net can be shielded with VDD (usually we shield a net with both VSS and VDD).
 

VDD being a always high net can inturn affect the shielded net if there are glitches in power supply. So the shielding is preferred in VSS to couple the caps to ground.
 

the issue is not with glitches in the power supply to signaling, because there is ground bounce which plagues vss. VSS is the base of the design as in the substrate. It is like the global earth. You can treat glitches as extra current dumped on the nets, it is much easier to dump the extra charge into the ground.

From basic electrical engg, the electric conductor installed on the roofs of houses is always properly earthed to the GND as it is treated 0 potential. it is always a better practice to shield using VSS but people have been using VDD too. The use VDD is due to routing and connectivity issues.
 

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