In which case vdd shielding

[rojalin]

can I know In which scenario Vdd is used as shield instead of VSS?

thanks

 

[erikl]

can I know In which scenario Vdd is used as shield instead of VSS?

It doesn't matter if you shield by VSS or Vdd: In terms of ac shielding they are identical. Use that one which is more simple (shorter) to connect with.

 

[nitishn5]

If you have a supply referred node. it would be useful to have shielding using VDD lines. This would improve PSRR.

For example, a PMOS gate bias for a current mirror. It is a supply referred node. and and needs to be tightly coupled to supply in order to reject supply noise and hence improve PSRR.