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118 2. Tutorial
2.7.3 Flow of Transient Circuit Analysis
A Summary of the Transient Analysis Procedure
In this subsection, we summarize the steps which are necessary to perform a transient analysis of a
dynamic circuit with Analog Insydes.
1) Write a netlist of the circuit to be simulated, specifying numerical values for all circuit elements or
use ReadNetlist (Section 3.10.1) for automatically importing netlists from external simulator files.
circuit =
Circuit[
Netlist[ ],
Model[ ],
]
2) Set up a system of time-domain circuit equations using CircuitEquations with the option
setting AnalysisMode −> Transient. For numerical circuit simulation you should use modified
nodal analysis, which is the default formulation. Modified nodal equations are smaller in size and
therefore require less simulation time.
mnaequations =
CircuitEquations[circuit, AnalysisMode −> Transient]
3) Apply the command NDAESolve to the circuit equations to calculate the transient solution in the
time interval t ∈ t t , where t is usually zero.
transient = NDAESolve[mnaequations, {t, t , t }]
4) Use TransientPlot for transient waveform display. Select the variables to be plotted by means
of the list vars and specify the display time interval t a t b . The latter need not be the same as
the simulation time interval t t . You can use any other values for t a and t b to zoom in onto a
particular section of a trace as long as the condition t ≤ t a t b ≤ t holds.
TransientPlot[transient, vars, {t, t a , t b }]
NDAESolve Program Flow
Now, let’s take a closer look at the strategy NDAESolve employs to integrate a system of differential
and algebraic equations. The main idea behind the algorithm is to transform the problem of solving
a nonlinear system of differential and algebraic equations into a sequence of linear and purely algebraic
problems which can be solved rather easily. The transformation is carried out in two stages. In
the first step, the differential equations are discretized by replacing all time derivatives with a finite
difference approximation. The differential equations are thus evaluated and solved at discrete time
steps only. The finite difference approximation scheme used by NDAESolve is an implicit integration
method known as the trapezoidal rule. In a second step the resulting nonlinear algebraic system of