Output - Broadband Model File
NOTE: The Broadband Spice feature is an optional feature which must be purchased separately. Please see your system administrator if you are unsure of the availability of this program.
In order to create a Broadband Spice model, you select Output - Broadband Model File from the main menu of the response viewer which opens the Output Broadband Model File dialog box. The functions of the fields and objects in the dialog box are described below. You may also set up an external data file to be generated during the analysis by using the Output Files page of the Circuit Settings dialog box in the project editor tab.
There are two tabs in the dialog box: Basic and Advanced.
NOTE: Be aware that the processing time needed to create your Spice models can be significant. The processing time is proportional to the number of analysis frequencies times the square of the number of ports in your circuit.
Format: The output data may be formatted in the PSpice, Spectre or HSPICE format. The PSpice and HSPICE files use a ".lib" extension and the Spectre files use a ". scs" extension.
De-embedded: This allows you to select de-embedded or non-de-embedded data. Select "Yes" for de-embedded data and "No" for non-de-embedded data. Normally, you should choose De-embedded data when creating a broadband Spice model.
Error Threshold: Enter the desired error threshold here. The error threshold is the difference between the source response data and the predicted S-Parameter data and is calculated as follows:
The calculation of the Broadband Spice model stops when this error threshold is reached or when it proves impossible to improve the error. Processing time increases as you decrease the error threshold. The default value is 0.5 and we recommend that the error threshold not be set lower than 0.1.
Include Comments: Click on this checkbox if you wish to export the comments. The comments are generated by the software and include the file type, software version, project name and modification dates.
Stability Factor: The Broadband Spice stability factor allows you to control the amount by which the model fitting forces the poles of your model away from the unstable region. The factor represents a magnitude ratio for which the real part of a pole cannot be less than the magnitude of the pole. The default value is 0.001. Reasonable values for the stability factor are between 1.0e-5 to 0.5.
Model file name: Enter the name of the output file here. A default filename consisting of basename of the project and the extension based on your File Format is the default. If you wish to change the filename, you may edit the default.
Select Parameter: Click on this button to open the Select Parameter dialog box which allows you to select for which parameter combination you wish to export data. You may only select one combination per output file. This button only appears if your project contains parameters.
Remember settings: Turn this checkbox on if you wish to save your choices for future exports.
Restore Defaults: Clicking on this button changes all the settings in this dialog box to the defaults used upon installation of the software.
Extract: Clicking on this button commences the processing which creates the Spice model file which you have specified in this dialog box. A progress bar is displayed in the Basic tab of the dialog box while the Spice model file is being created. If for some reason you need to stop the process before it completes, you may use the Cancel button under the progress bar to do so. Once the model creation is complete, the Broadband Spice Details dialog box appears on your display.
Details: Click on this button to re-open the Broadband Spice Details dialog box.
Override default additional frequencies: In order to test the stability of the model, extra frequencies outside of the original analysis band are calculated as part of the predicted data. By default, these extra frequencies start at the highest frequency of your original analysis and stop at three times this value, with a step size set to the last step size of your original analysis. Select this checkbox if you wish to specify a different set of extra frequencies to be calculated from the model and used to test stability. Selecting this checkbox enables the Start, Stop and Step text entry boxes below. If you wish to specify only one additional frequency, enter that frequency in the Start text entry box. Otherwise, Start provides the beginning frequency, Stop the ending frequency and Step the spacing. All predicted data is written to a data file if the Write data file checkbox (see below) is checked.
Write data file: Selecting this checkbox creates a file which contains the predicted S-parameter data produced by the rational polynomial used to generate the Broadband Spice model. The filename to which the predicted data is written appears just below and may not be changed. This file is created in the same directory in which the output Spice model file is created. This file allows you to visually inspect how close a fit your broadband model is to your source data. Checking the Accuracy of the Broadband Spice Model in the Sonnet User's Guide.
Lower Limit: By default, the full range of analysis data in the project is used as input to create the Broadband model. If you wish to limit the data used to create the model, enter the lowest frequency you wish to use in this text entry box. Any lower frequencies contained in the analysis data will not be used as input. If no value is entered, then all of the analysis data up to either the Upper Limit, or to highest frequency in the analysis data, is used as input.
Upper Limit: By default, the full range of analysis data in the project is used as input to create the Broadband model. If you wish to limit the data used to create the model, enter the highest frequency you wish to use in this text entry box. Any higher frequencies contained in the analysis data will not be used as input. If no value is entered, then all of the analysis data from either the Lower Limit, or from the lowest frequency in the analysis data, is used as input.
Maximum Order: Enter the desired maximum order of the rational polynomial which produces the Broadband Spice model here. This entry may be used to limit the complexity of the model. The default value is 40.
Additional Options: This field should only be used at the direction of Sonnet support personnel.