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Design Notes


Switch Views and Switch Lists provide an easy way for a designer to toggle between different versions of a model while maintaining a single layout cell for that instance.  This could include linear models, nonlinear models, EM data, measured results, etc.  Another interesting use for Switch Views is allowing designers to create an LVS view of their schematic parts that normally wouldn't make sense to an LVS engine like Touchstone files or EM models.  This allows designers to run LVS from their real, RF schematics and alleviates the need for a DC schematic, which ultimately is a potential source of error for LVS.  In the attached project, the Switch Lists are used to show how a single subcircuit can have both a linear, nonlinear and EM results representation. 


First a definition:  Switch Views are alternative model views or model implementations.  For example, if a designer had both a linear and nonlinear model for a part, the default model could be the linear model, and a Switch View could be created that contained the nonlinear model.  The name Switch View is derived from the concept that designer can switch in and out between these models during circuit analysis.  Also, the Switch Views get a name of the designer’s choosing.  Normally, this name is standardized for all switch views containing a similar type of model.  For example, the Switch View with the nonlinear model as described above might be called "Nonlinear", while a switch view with EM data might be called "EM".

It is very important that Switch Views for a subcircuit contain the same number of ports as the top level circuit, a consistent port numbering scheme, and the same passed parameters.

To create a Switch View for a subcircuit, make a new Schematic named "Subcircuit_Name/Switch_View_Name" where Subcircuit_Name is the name of the Schematic for which the Switch View is being created and Switch_View_Name is the name of the Switch View that is being created.  For example, in this project the Schematic "BJT" has a Switch View called "Nonlinear" that was created by adding a new Schematic named "BJT/Nonlinear".

Switch Lists are the mechanism through which the user picks the different Switch Views.  In the simple example above where there is a Switch View called "Nonlinear" that contains a nonlinear model a Switch List can be configured that essentially tells the simulator "when evaluating this circuit, see if there is a view called ‘Nonlinear’ for any of the parts in the circuit and use it if you find it, otherwise, just use the normal circuit models."  Not surprisingly, the Switch Lists also get user defined names.  This is normally done in a manner consistent with the Switch Views that they are controlling.  The Switch List for the "Nonlinear" Switch View might also be named "Nonlinear."  Note that Switch Lists can be significantly more complicated than just the single Switch View case, for example telling the simulator to first look for a view called "EM" then “Measured” then "Linear" then "Nonlinear."  In this case the simulator will stop going down the list as soon as one of the views in the list is found on a given subcircuit.  If none of the views are found, then the "default" model, or the model in the subcircuit itself will be used.

Switch lists are chosen on each individual Measurement by selecting them in the Configuration drop down menu as shown below.  The real value Switch Views and Switch Lists is that all Measurements point to the same Schematic and Layout, but can utilize different models.

Switch Views In This Project

1. BJT Schematic - contains the Touchstone file for an active device.  In the project tree it can be seen that the "BJT" schematic also has a Switch View called "Nonlinear."  This view contains the SPICE model for the active device. 

2. Tee Schematic / Layout - contains a microstrip tee circuit made from closed form and X models.  In the project tree it can be seen that the "Tee" schematic also has a Switch View called "EM."  This view contains an EM model of the tee circuit.  Note that the "Tee" schematic defines the layout for the subcircuit, the Switch views simply provide a way to access alternate electrical models.


3. Trace Schematic / Layout - contains a "trombone" line made from a closed for MTRACE2 model.  In the project tree it can be seen that the "Trace" schematic also has a Switch View called "EM."  This view contains an EM model of the "trombone" line.


Switch Lists In This Project

The Switch Lists that have been configured for this schematic can be seen by selecting Simulate > Manage Switch Lists  as shown below. 

There are two Switch Lists:  one called "Nonlinear" and one called "EM".  By selecting the name of each Switch List Configuration it can be seen by looking at the "Design View Lists" that the “Nonlinear” Switch List looks for the "Nonlinear" Switch View.  And the "EM" Switch List looks for the "EM" Switch View.  Note that whenever the named Switch View is not found on an instanced in a schematic that the default model is used.