In this unit we will explore various settings available for the CHARGE solver.
Under the General tab of the CHARGE solver property editor window, the simulation region
parameter selects which of the simulation regions from the objects tree will be used
by the solver.
Note that only one simulation region can be assigned to a solver at a time.
The norm length parameter is only available in two-dimensional simulations.
This parameter is used to define the length of the simulated structure in the third dimension
when the simulation region is two-dimensional.
This information is needed by the solver to calculate volume dependent parameters such
as current at the contacts.
The solver mode and temperature dependence can also be selected under the same tab.
By default, the solver mode is set to “steady-state” and “isothermal” is chosen as the temperature
For more information about different solver mode and temperature dependence options, please
refer to their corresponding units in the course.
The simulation temperature in an isothermal simulation can also be set in this tab.
The continuation feature enables the user to specify a file that has already been run
as the starting point for the current simulation.
In simulations where the starting bias point isn't at zero volt, or multiple contacts are
at non-zero bias, this can be very useful.
The continuation feature is out of the scope of this course and will not be covered.
Under the Mesh tab, the Global Mesh Constraints define the degree of refinement of the simulation
The min and max edge lengths set the minimum and maximum edge lengths of the triangular
or tetrahedral elements used in the finite element mesh.
Smaller values mean a more refined mesh and possibly more accurate results at the expense
of increased simulation time and memory.
“Max refine steps” in the Auto refinement settings sets the maximum number of iterations
in the mesh refinement process.
A larger number here means that the solver is more likely to refine the mesh up to the
limits defined by the local or global mesh constraints.
Local mesh constraint objects will be covered later in the course.
It is important to note that during the meshing process, if the meshing algorithm reaches
the value set by the “max refine steps” and the target level of refinement specified
by the global and local mesh constraints has not been achieved yet, the mesh refinement
will stop and the resulting mesh may not be adequately refined.
It is recommended to increase the number of max refine steps as you change the mesh constraints
toward a more refined mesh.
“Sensitivity” controls the sensitivity of automatic mesh refinement to changes in
properties such as imported optical generation profile in the simulated structure.
A higher sensitivity can result in a better representation of smaller changes in these
properties by using a more refined mesh in the areas where those changes happen.
The advanced mesh options should be left at their default setting in most cases and are
beyond the scope of this course.
The transient and small signal AC tabs include settings for transient and small signal CHARGE
simulations and are covered in the small signal AC and transient simulations section of this
The Results tab contains a list of all the results that can be recorded during a CHARGE
One can pick to enable or disable one or more of the results to reduce file size after the
simulation is run.
The tab also contains basic information about the available results such as their units
Finally, Advanced settings for CHARGE solver are located under the Advanced tab.
These settings should be kept at their default values in most simulations and are beyond
the scope of this course.