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What's Good About PCB SI AutoSolving Models in SigXplorer? You’ll Need the 16.6 Release to See!

Comments(0)Filed under: SPB, Allegro, SI, SigWave, PCB, SigXP UI, PCB SI, IBIS, "PCB design", SI analysis and modeling, design, "PCB SI", High Speed, Allegro PCB SI, signal integrity, Allegro GUI, Grzenia, Allegro 16.6, 16.6

In previous releases, when you extract a net into SigXplorer, all the structures are automatically solved in Allegro PCB SI and then passed to SigXplorer. At times, the layerstack of the extracted structure might differ from the real layerstack in terms of the voids in a plane layer or shapes on the conducting layer. In such cases, the structure needs to be re-solved in SigXplorer. At other times, a field solution in SigXplorer takes a long time to run and often runs when not needed.
The 16.6 release of Allegro PCB SI provides support for on-demand solving of models using Bem2D, Ems2D, and FSVia. However, unlike previous releases, now compulsory model solving during extraction from PCB SI is eliminated. The vias and trace models are unsolved when extracted from PCB SI and no impedance values are reported for trace models after extraction if no matched models are found in the existing working IML library.

Read on for more details …



The autoSolve parameter, when set to On, automatically calls the field solver when you make changes in the parameters of a trace in the spreadsheet, for example. By default, the autoSolve parameter at the circuit level is set to Off. As a result, during extraction, no solving is triggered except for FSVia. FSVia models are always solved during extraction:

For the commands which require a field solution, such as Simulate, Generate S-Parameters, and Transform to Constraint Manager, the default status of the autoSolve parameter is overridden and models are produced.

Solving Models

Models can only be solved using one of the following methods if the autoSolve parameter is set to Off by default -

  • Running a simulation
  • Using the Manage Unsolved Parts command
  • Using the Solve Batch Mode command

The Manage Unsolved Parts command helps you manage all the unsolved parts including vias and traces. This command can be accessed through the Analyze menu or by right clicking in the SigXp canvas -     

Analyze menu:

RMB menu:

The command launches the Unsolved Part dialog which lists all the parts that have not been solved:


The Part Name column lists unsolved parts, while the Type column shows the type of the part, such as via or trace. The currently selected solver for vias and traces are also displayed. For example, in the figure above, FSvia will be used to solve the Vias, while Bem2D is used to solve the traces.

Note: All of the parts in the design appear in this dialog if there are no solved models associated with the extracted geometry found in the interconnect model library. If you run the Solver for one of the vias or traces, it is possible that the geometry matches one or more of the other elements. If so, the next time you launch this dialog, it may show fewer parts than expected.

Solving in Batch Mode

You can also solve traces and all vias using the Solve Batch command. Use this command to solve a single part in order to see the impedance, for example, or to create a model in the library with the current parameters.

Right-click on an unsolved part and choose Solve Batch Mode (FSvia):


Please feel free to share your feedback on this new PCB SI capability.

Jerry “GenPart” Grzenia


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