Hello All,
In my opinion , let us say the net1 needs to shield. let us go to basics- usually we guide any unwanted signal to the ground not to the power. so we if we want to to shield the net1 we will place grounds nets, it will add a decoupling cap which is connected to ground. i forgot what we say the name of cap generated by neighbor net.
Contrary to it, if we shield the net by VDD, it will by pass only the disturbance from the VDD to the net itself by the cap formed by the vdd net and net1.
As we know charge flow from more charge to less charge, sheilding by ground is adopted over sheild by power.
I think , i didnt put in good words, can some one reshuffle my words to make it more clear..
thank you..