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Design Notes
Axiem Series Ports
This project demonstrates the use of series ports to simulate a gap in layout across which packaged components will be mounted. It also demonstrates how to connect up the EM subcircuit in a schematic with circuit models for packaged components. Comparisons are made with an equivalent differential port structure.
Description of Series Ports
A series port is basically a differential port that has been reformatted to allow access to the second port when the EM structure is utilized as an EM subcircuit. When simulating a series port, the port is actually converted to a differential port. Therefore, series ports are subject to the same guidelines and restrictions as differential ports. While series ports have two ports associated with it, it is imported to remember that the two ports represent 1 equivalent port across the two nodes.
EM Structures
The two EM Structures, "Diff_Ports" and "Series_Ports", simulate identical layouts. There are three gaps in the layout across which packaged components will be placed. The only difference between the two structures is the use of differential versus series ports to terminate the gaps.
In the "Series_Ports" EM structure, series ports are formed by selecting exactly 2 ports, and setting the Port Group property to have the same Name, and Type to "Series".
Schematics
This project also contains two equivalent schematics, "Schematic_Diff" and "Schematic_Series". Both contain an EM subcircuit that is connected to lumped element models.
In "Schematic_Diff", note that only one node is exposed for each differential port in the EM subcircuit symbol. That is because only 1 number is used to index the port (ex: "3" and "-3"). As a result, the lumped component that connects across the gap in layout is connected to ground in the schematic.
In "Schematic_Series", there are now two nodes exposed for each series port on the EM subcircuit symbol. That is because two port numbers are used to index the port (ex: "3" and "4"). As a result, the lumped component that connects across the gap in layout also connects across the two nodes in the schematic. This setup is more intuitive, although, simulation-wise, is identical to the differential port setup.
Simulation Results
The "Comparison" graph plots s-parameter results for the two schematics. As expected, results for both schematics are the same.
Schematic - Schematic_Series
Schematic - Schematic_Diff
EM Structure - Series_Ports
EM Structure - Diff_Ports