RFICDUDE wrote on Apr 28th, 2009, 7:25am:Hmm, do you have a reference or a data point that supports the assertion that the floating shield reduces losses by preventing eddy current losses in the substrate?
The shield would have to somehow terminate the inductive field lines with less loss than currents induced in the substrate.
I am just curious how much benefit there is versus the modeling and layout effort to shield the inductor.
Thanks
Hi RFICDUDE,
The PGS cuts the plate into strips so the eddy current can hardly flow. Floating PGS would reduce the electrically coupled capacitance to substrate (how effective depends on technologies). On the other hand, rf current can penetrate into substrate with PGS floating. So you see some trade-offs here. And whether it is useful depends on lots of factors.
For RF circuits, every dB counts. So if the PGS is helpful, surely it worths the work of modelling. PGS as I saw from this year's ISSCC, is still used for applications around 1-2GHz. But for higer frequencies (>=4G), it is almost never used. And it works better for LNA than VCO since PGS harms the tunability.
pancho_hidebo, since you have practical experiences on floating PGS, I hope you can add your comments to RFICGUIDE's questions, and correct me if I was wrong.