That is true since 1 ground reference cannot be shared with more than one internal or single port. You can have multiple ground references for 1 internal port, though (e.g., CPW with two finite grounds on each side of a signal line). Ground references should also be electrically close to the associated ports. Further, ground references can be placed on edges of metal planes (as is done when using them with Single ports which results in long calibration line extensions on BOTH the ground reference edge and the single port edge). However, if such metal edges are electrically large, then you may start to see numerical problems as the ground/return currents are distributed along the entire edge. In such a case, you would have to place the ground references on the inside of the ground metal, close to an internal port, but not too close to the metal edge either (to avoid slivery mesh cells).
Yes, the Ground References are all tied together to the global analog ground in a circuit simulation. You can change the wiring using differential setups by using Layout Components. If you want to add SMT devices to a model, then you would need two internal ports on the broken strip and place ground references on the other side.
I'm not sure of any examples right now other than one of the lectures/labs in the Momentum training class. However, defining multiple ground references for an internal (or single) port is pretty easy - you just associate as many as you want with the same internal/single port. Typically, you have two for CPW (GSG) type feeds. If the ground refs are not spaced symmetrically, they will not carry the same return current I/N (I=signal current, N=number of ground refs). For example, if one is very far away, and one is close, then the close ground ref will carry most of the return current.
Are the GND Reference Ports of several Internal Ports connected after Simulation?
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SinglePort InternalPort SMT GNDPort SingleP.
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GND Port GND P.
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IS this CPS Line "ported" correct? I have no GND layer?