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Design Notes

EM Extraction Example

This example consists of two schematics:

"Circuit Model" - a regular microstrip simulation of a TEE junction on GaAs.  The microstrip elements in this schematic use the MSUB in the Global Definitions window.

"Extract Model' - the same geometry as "Circuit Model", except the structure is automatically extracted and analyzed with AXIEM.  Because all elements in this schematic are associated with the EM_Extract block, they use the STACKUP in the Global Definitions window.

This discussion will focus on a simple extraction first and then how to use extraction as well as swept variables.  


Once the EXTRACT block is placed (under Simulation Control in the elements tree), its parameters are set up as follows:

EM_Doc - This is the name of the EM document that is created at run time.  Note that the value in this example is "EM_Extract_Model", which will correspond to the name of the EM document in the project tree (after you run the analysis).  If the document does not exist, it is created based on the other parameters in the EXTRACT block.

Name - This is the name that links the desired schematic elements to the EXTRACT block.  Select any element in the "Extract Model" schematic.  Right click, select Properties, and click on the Model Options tab.  Note that the Enable block is checked and the Group Name is set to, "EM_Extract", which corresponds to the "Name" parameter in the EXTRACT block.  Note also that you can select all of the schematic elements and view the same settings, because they are all included in the group.  Finally, note that you can select the EXTRACT block itself and see highlights on the elements that are associated with it through the "Name" parameter.

Simulator - AXIEM is selected for this project but you can select the simulator of your choice

X_Cell_Size - size of each drawing cell in the x direction - will affect the mesh of the structure. 

Y_Cell_Size - size of each drawing cell in the y direction - will affect the mesh of the structure. 

STACKUP - the EXTRACT block requires a STACKUP for the substrate definition.  STACKUP is a general multi-layer substrate definition that is configured dynamically.  Double-click the STACKUP element in the Global Definitions window to see its setup dialog. It is set up to mimic the construction of the MSUB.  Also, note that if "Extract Model" was the only schematic, both MSUB and STACKUP would still be required - this is to cover the possibility that you would want to disable the EXTRACT block and still run the regular circuit analysis.  (That's the real way to run this comparison - the second schematic is not necessary but it makes this example easier to read.)

The remaining parameters are set to their defaults, please see the help for this element to see further help on these parameters. 

Meshing the EM Structure Before Simulating

We always recommend viewing the EM structures mesh before simulating.  For extraction, the EM structure is typically created when you hit simulate.  To view the mesh before simulating, right click on the extract block and select Add Extraction. This will create the EM document without simulating.  Now you can view the mesh, you can use the toolbar command Show 2D mesh if the 2D layout is the active window or Show 3D mesh if the 3D layout is active.  Typically, meshes will look better in the 3D view.

Running the Project

Before you run the project, note that there is no EM structure defined.  It will be automatically created when the analysis is performed.  Note that the circuit dimensions are contrived, as is the frequency.  The purpose is to show something with a resonance for easy comparison.

When the analysis is run, you will see that the EM structure called "EM_Extract_Model" is created and AXIEM runs its analysis on this structure.  The results show very good agreement, but there is a slight difference which may be important in a final design.

Extraction and Swept Variables

You can configure most element parameters to be swept over a range of values using a SWPVAR block in a schematic (the details of this are beyond the scope of this example, please see the documentation for details on swept variables).    Both of the schematics have SWPVAR blocks setup,  right click on each and select Toggle Enable.

Now simulate and view the graphs.  Notice the circuit model simulation shows the three results while the extract only shows one result.   You must configure the EXTRACT block to know which swept variables to use.  On the EXTRACT block in the “Extract_Model” schematic, for the parameter “SweepVar_Names”, type in the variable “L”, it must be between the quotes.   Now simulate again to see that three EM simulations will happen.   

Schematic - Circuit_Model

Schematic - Extract_Model

EM Structure - EM_Extract_Model

Graph - S21

Graph - S11