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What's Good About Simplifying the Use of Third-Party SI Models? It's in SPB16.3!

Comments(1)Filed under: PCB Signal and power integrity, PCB design, IBIS-AMI, SI, Signal Intregrity, SPB 16.3, SigXP UI, PCB SI, IBIS, HSpice

Today, many users receive SI models that are not in DML format. They are given IBIS models, HSpice models, Spectre models as well as other generic SPICE models. We currently provide methods for translating these model formats into DML, but it's often not straightforward. It usually requires running a batch command with options that are not familiar to the non-expert user.

This translation process has been simplified. The idea is to allow users to select third party models from a browser, much like they currently select DML models.

Common Model Browser

The DML Model Browser that is available in PCB SI [http://www.cadence.com/products/pcb/pcb_si/pages/default.aspx] currently allows you to browse the models in the DML libraries that have been loaded. This browser has a number of different uses. For example, if you are doing model assignment, this browser is used to select a model to be assigned to a specific component. It is also used to select a model that is to be edited or viewed.

In 16.3, this model browser has been enhanced to also handle IBIS, HSpice, Spectre and generic SPICE models. The dialog displayed by this browser is shown below:

This is basically your one-stop-shop to translate various models!

More details are provided below...

Finding Third Party Model Files

There are two new environment variables that are used to find third party model files. The variable SI_MODEL_PATH defines the directories that are searched for these files and the variable SI_MODEL_FILE_EXT defines the file extensions of the files to be found.

A new button labeled Set Search Path has been added to the Model Browser dialog that allows you to set these two environment variables. This button opens the following form:

The list at the top of this dialog shows the directories in the SI_MODEL_PATH search path. The Add Directory button opens a directory browser that allows you to select another directory to be added to this list. A right-mouse-button popup over any entry in the list allows you to delete the entry or to move it up or down in the list.

The bottom fields in this form allows you to specify a list of file extensions that will be used to identify IBIS files, Spice files, HSpice files and Spectre files. As stated on the form, multiple file extensions should be separated by commas.


Browsing IBIS Models

The IBIS Models tab on the Model Browser is shown below:

The entries in the list displayed by this tab show the IBIS files that are found in the IBIS search path. The entries that have sub-items (such as y86a.ibs) are models that have already been translated into DML format. The sub-items are the DML models that were created from the IBIS file.

IBIS models can be translated by selecting an IBIS file and selecting the Translate button. The standard ibis2signoise batch utility is used to perform this translation. The only option that is used for this translation is the one that controls whether or not the buffer model names created by the translation are to be made unique to this IBIS file. You will be asked whether or not you wish for this to happen. If you answer yes, then the IBIS file name will be appended to each translated DML buffer model. If you answer no, then each translated buffer model will simply be given the name as specified in the IBIS file.

If any translation errors are found, the error messages are displayed in a text window and you are given the option to open the IBIS file in an editor.

The File Name Filter field contains a value that can be used to limit the IBIS files that are displayed in the list. This value can contain standard wildcard formats and defaults to “*”.

The Delete Derived Models button will delete any DML models that have been translated from the selected IBIS file. This button is grayed out if there is no selected IBIS file. This button does not delete the actual IBIS file.

The Model Editor button allows you to edit the selected model. The selected IBIS model file is opened in the new Model Editor. If the IBIS file is changed by the editor, then it is re-translated when the editor closes. If there is no selected IBIS file, then the Model Editor button is grayed out.

If a DML model that was translated from an IBIS file is edited from the DML Models tab, this model might no longer be consistent with the data in the IBIS file. Therefore, after a warning is issued, it will be removed from the list of DML files that are shown in the IBIS tab of this dialog. It will, however, continue to be in the list of models shown by the DML Models tab.

Browsing SPICE Models

The SPICE Models tab of the Model Browser dialog is shown below:

This tab operates much like the IBIS Models tab. The entries displayed in the list show generic SPICE files that are found in the SI_MODEL_PATH search path. The entries that have sub-items show DML models that have been translated from the owner SPICE file.

You can translate the SPICE file to a DML ESpice model using the Translate button. Translation errors are shown in a text window with an option of not saving the translated models.

The File Name Filter field allows you to filter the list of SPICE files. Standard wildcards are accepted in this field.

The Delete Derived Models and Model Editor buttons operate the same as described for the IBIS Models tab.


Browsing HSpice Models

The HSPICE Models tab of the Model Browser dialog is shown below:

This tab lists the HSpice files that are found in the search path. It operates the same as described for the IBIS Models and SPICE Models tabs.

You can translate an HSpice file to a DML model using the Translate button. Since HSpice model translation is not straightforward, a wizard is invoked that leads you through the translation process. The first step of the wizard is shown below:

This step allows you to provide a name for the DML model that is to be created. By default this name will be the same as the name of the HSpice file. If multiple models are created by the wizard, they will all have names that start with this given name. There are several more steps that you follow using the wizard, but I'm not including them.

Browsing Spectre Models

The SPECTRE Models tab looks and operates just like the HSPICE tab. It lists the Spectre files that are found in the search list. If an untranslated file is selected, a wizard is used to lead you through the translation. This wizard has the same options as the HSpice translation wizard described above.

Storing Translated DML Models

Each DML model that is translated from a third party format contains the following information as part of the model data:

(Type HSPICE )
(InputFile "max3801_out.sp" ) ) )

This identifies the name and type of file that was translated. This is what allows the model browser to maintain a connection between a third party model file and the DML models that were created from the file.

Browsing Models From PCB SI Model Assignment

One of the common uses of the Model Browser in PCB SI is during model assignment. The Model Assignment command has the following dialog:

To assign an existing model to a component, the component is first selected from the list. The Find Model button opens the Model Browser. In 16.3 you can now select a tab for a third party model, such as the IBIS Models tab.

You would then select the IBIS file that they want to assign to the component. If the IBIS file hasn't already been translated, it is translated at this time. By default the first IBISDevice model that was created from the translation is assigned to the component that was selected in the Model Assignment dialog. If the IBIS file contained several IbisDevice models, you can select a specific IbisDevice model from the sub-list of DML models that is associated with the IBIS file.

Browsing Models From SigXplorer

From SigXplorer, the Add Element command opens the following dialog:

The Browse All Models button is a new button that opens the same Model Browser as described above. This allows you to select any DML model or a third party model. Selecting a third party model causes it to be translated, if not already translated, and the translated model is shown on the SigXplorer canvas.

Using IBIS Models in HSpice or Spectre Simulations

IBIS models can be easily translated into DML, allowing the models to be used in a tlsim simulation. Using this same model in an HSpice or Spectre simulation, however, is not as simple. It requires that you wrap the IBIS model into a special DML format.. In 16.3, you can use the IBIS model directly when running HSpice or Spectre as the simulator.

As usual, I welcome your feedback.

Jerry "GenPart" Grzenia


By TeamAllegro on April 23, 2010
Hi Jerry - nice write up on a big improvement in Allegro PCB SI.  Your readers may want to watch a short demonstration of PCB SI simulating with an IBIS model using multiple simulators all from the Allegro PCB SI desktop ... www.youtube.com/watch

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