Using S-Parameters in Genesys

This section shows how S-Parameter data can be incorporated into Genesys designs and exported to other programs.

S-Parameters are commonly used in RF circuits to represent incident and reflected traveling waves. S-Parameters are created by a linear simulation and are generally available from component manufactures. Several libraries of S-Parameter data ship with Genesys. S-Parameters in Genesys are imported and exported in the Touchstone format.

Creating S-Parameter Data

1. Create the schematic for which the S-Parameter data will be represented
2. Add a linear analysis and point it to the desired schematic
3. Set the frequency range and step size of the linear analysis to the desired resolution of the S-Parameter data
4. Run the linear analysis
5. Export the linear analysis data as a S-Parameter file

Importing S-Parameters

When S-Parameters are imported a dataset is create and placed in the workspace tree. This dataset is saved and loaded with the workspace and will be cached in memory to increase the simulation speed. The dataset can be deleted from the workspace. Memory cache will be used until there is a need to re-read the dataset from the workspace tree or if the dataset is not found the original file will be re-imported and cached once again.

S-Parameter can be imported in one of several ways.

Importing from a library

1. Open up the Parts Selector (Ctrl+Shift+A) or click the part selector button (!part_selector_button.gif! )
2. Change the Current Library to the S-Parameter library of interest
3. Click the library part of interest (the mouse cursor will change to a + sign) # Place the part in the schematic by clicking the schematic

   NOTE: On first use of the selected library it will be unzipped and the S-Parameter file associated with the part will be imported into the workspace tree

Or

Importing from the Main Menu

1. Select File, Import, then S-Data File from the main Genesys menu
2. Browse to the S-Parameter file

Or

Importing from a Part

1. Place a S-Parameter part in the schematic (1-port, 2-port, n-port). This can be done from the Linear Toolbar or the Part Selector
2. Double click the part to bring up the part properties
3. Click the Browse button to browse to the S-Parameter file

Using S-Parameters in a Simulation

The use model for S-Parameters manually imported into the workspace versus file based S-Parameter is slightly different. The model used in the schematic determines how the S-Parameters will be managed.

File Based S-Parameters

File based S-Parameter import the S-Parameters from a file into a dataset providing simulation cache. This dataset is used when reloading the workspace to re-cached the data. If the dataset is deleted the S-Parameters will be re-imported the next time a simulation needs the data.

1. Place a S-Parameter file based part in the schematic (1-port, 2-port, n-port). This can be done from the Linear Toolbar or the Part Selector
2. Double click the part to bring up the part properties
3. Click the Browse button to browse to the S-Parameter file
4. Add an analysis and point it to the desired schematic
5. Run the analysis

Manually Imported S-Parameters

Manually imported S-Parameters don't use a filename name. The data must exist on the workspace tree. If the dataset is deleted then there is insufficient information to correctly build the model. The model has no need of the filename and simply needs to know the name of the dataset.

1. Place a dataset part in the schematic (NPOD). This can be done from the Linear Toolbar or the Part Selector
2. Double click the part to bring up the part properties
3. Set the dataset name to the name of the imported S-Parameters
4. Add an analysis and point it to the desired schematic
5. Run the analysis

Exporting S-Parameters

Noise parameters are not exported with the S-Parameters.

S-Parameters can be exported in one of two ways.

Exporting from the Workspace Tree

1. Right click the linear analysis dataset in the workspace tree and select Export from the menu
2. Set the name and directory of the S-Parameter file (*.snp)

Or

Exporting from the Dataset Window

1. Open the linear analysis dataset (it must be the active window)
2. Select File, Export, and then S-Parameters from the Genesys menu
3. Set the name and directory of the S-Parameter file (*.snp)

Displaying S-Parameter Data

The easiest way to display S-Parameter data is to open up the S-Parameter dataset and the right click on the S variable. Then select Create Table or Graph and the type of graph. The data will automatically be displayed.

See also S-Parameter Basics and Touchstone File Format.

Physical S-Parameters

S Parameters can be taken or formed in such a way that they represent non physical elements like negative resistors. Realistic real world answers only come when S-Parameters are physical. If S-parameters are physical, then the corresponding Y-parameters will meet all of the following requirements:

1. The real part of every diagonal entry must be positive. i.e. Real.Yp[i,i] > 0
2. The real part of every non-diagonal entry must be negative. i.e. Real.Yp[i,j] < 0 where i is not equal to j
3. The absolute value of the row real summation, excluding the diagonal, must be less than real value of the diagonal in that row. i.e. abs ( sum( Real.Yp[i,j] ) ) < Real.Yp[i,i] where i is not equal to j
4. The absolute value of the column real summation, excluding the diagonal, must be less than the real value of the diagonal in that column. i.e. abs ( sum( Real.Yp[i,j] ) ) < Real.Yp[j,j] where i is not equal to j

Note: Is is assumed the Y parameters are in Real + j Imaginary format.

Examples:
Here are some typical Y-parameters (which is converted from S-parameters):

The Y parameter matrix for F = 3000 is:

0.077 - j0.122   -0.078 + j0.123

-0.078 + j0.123   0.078 - j0.121

This matrix meets items 1 and 2 but not 3 and 4, because abs( Real.Y[1,2] ) > Real.Y[1,1] or abs( Real.Y[2,1] ) > Real.Y[1,1], so these S parameters are non physical.