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Adding Variation to a Two-Port S-Parameter File for Yield Analysis
This project demonstrates how to add variability to a two-port S-Parameter file in order to perform Yield Analysis. This may be necessary if you do not have enough S-Parameter files to represent statistical variations of an element. However, it should be noted that in this method, there is no correlation between the variations of the S-Parameters (such as S11 and S21), which may not be the case with the actual element. Furthermore, this may lead to the simulation of gain from a passive element.
The S-Parameter File must be formatted as a text file. Using equations in the schematic, the magnitude and phase of each S-Parameter is multiplied with a variable that is enabled for yield analysis. The redefined S-Parameters are then assigned to an S2P_BLK element. This schematic can now be used as a subcircuit.
In order to access the contents of the S-Parameter file, the file must be in text format. If the S-Parameter file has already been imported as a Touchstone file, create a new text Data File, and copy and paste the contents of the Touchstone file into the new text file. Otherwise, import the S-Parameter file as text file type. In this project, the contents of the Data File Afm02n5b (Touchstone Format) was copied into Afm02n5b_text (Text Format).
This schematic shows how to add variability to an S-Parameter file for yield analysis. The functions DataFile() and Col() are used to access the data contained in text file Afm02n5b_text.
First, the frequency list of the S-Parameter file must be determined, because the simulation frequency list must equal that of the data file. Then, the magnitude and phase of each S-Parameter is assigned to a variable, which is then multiplied with another variable that represents the statistical variation of that S-Parameter. In this example, the multipliers have Statistics Mode enabled, with uniform +/- 2% variation. Right Clicking on the equations and selecting Properties will bring up the dialog box to edit these settings.
The redefined magnitude and phase of the S-Parameters are recombined into a complex number with the function Polar(), and assigned to an S2P_BLK element. This schematic can now be used as a subcircuit. Yield analysis can be performed either at the subcircuit level, or top circuit level.
Yield analysis is performed on schematic Top. First simulate to compare the original S-Parameter file with the redefined S-Parameter block. The results are identical in the graphs. To perform yield analysis, select Simulate>Yield Analysis from the top menu. Enter the maximum number of iterations, and click on Start.
For passive, linear S-Parameters, the sum power graph can be enabled to check whether yield analysis results have remained passive.