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Vias to ground in EM simulations

Question asked by SRPENNEY on Jun 16, 2006
Latest reply on Jun 20, 2006 by ALEPEREZ
Hey folks,

I've been working on a microstrip board layout in ADS for a relatively
simple PA.  As part of the design I have a stabilization resistor that
shunts the gate of the active device to ground.  My problem lies in
performing a momentum simulation of the input matching network with
this shunt branch.  When I perform the simulation on the schematic
level in ADS I get one response, upon trying to verify the same
response in the EM simulation I find it behaves completely differently.

After some investigation, I've found that the same behaviour that
results in the EM simulator can be duplicated in the schematic
simulator by deleting the ground symbol that is at the bottom of the
shunt stabilizing resistor.  What this boils down to is that the EM
simulator will not recognize my shorts to ground and is leaving one end
of the shunt resistor floating.

I've tried a few things to get a working short to ground: Short-circuit
stubs and vias to ground.

My question to you all is:  To use the VIAGND element in layout for a
microstrip design in ADS what layers should I be using for conductor
(I've tried cond) and hole (I've tried cond and hole)?  If one of the
things I mentioned above was actually right, is there something else
that I'm missing?

Thanks in advance,