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92 2. Tutorial
2.6 Modeling and Analysis of Nonlinear Circuits
2.6.1 Behavioral Models
In Chapter 2.3 we implemented small-signal equivalent circuits for semiconductor devices as
subcircuit objects composed of the available linear circuit primitives. We cannot use this approach
to model the electrical characteristics of nonlinear elements, such as diodes or transistors. However,
particularly for nonlinear circuit analysis, Analog Insydes provides special support for modeling
arbitrary circuit element characteristics by specifying device equations directly.
Models which are based on sets of mathematical equations describing the behavior of a circuit
element or an analog building block are frequently called (analog) behavioral models, or ABMs. A
behavioral model is similar to a subcircuit object in that it constitutes a box which is connected to a
circuit through electrical ports. As indicated above, the difference is that the interior of a behavioral
model box is implemented in terms of symbolic equations rather than a netlist. With Analog Insydes’
behavioral modeling capabilities you can model a large variety of nonlinear element characteristics.
You can then use the function CircuitEquations (Section 3.5.1), with which you are already familiar,
to set up symbolic systems of nonlinear modified nodal or sparse tableau equations.
2.6.2 Defining Behavioral Models
The Argument Sequence of the Model Command for ABM Definitions
Behavioral models are defined using the Model (Section 3.2.1) command, just like subcircuits (see
Section 2.3.2). Analog Insydes recognizes a request to define a behavioral model by the presence of
the named parameter Variables and the absence of a subcircuit Netlist on the right-hand side of
the Definition argument in a Model call. The full syntax for an ABM definition is shown below.
Again, slanted typewriter font denotes optional arguments.
Model[
Name −> subcircuit class name,
Selector −> selector,
Scope −> scope,
Ports −> {port nodes},
Parameters −> {parameters},
Symbolic −> {symbolic parameters},
Defaults −> {defaults},
InitialConditions −> {initial conditions},
InitialGuess −> {initial guess},
Translation −> {parameter translation rules},
Variables −> {variables},
Definition −> Equations[equations]
]