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2.6 Modeling and Analysis of Nonlinear Circuits 93
Except for the additional arguments and the keyword Definition, all other named arguments of
the Model function have the same meaning as for subcircuit definitions. Following, we discuss the
two arguments Definition and Variables.
Example: A Diode
Let’s illustrate the steps which are necessary to define a behavioral model by implementing a
nonlinear device model for a junction diode.
A
VD
vd/vt
id(vd)=I s(e -1)
ID
C
Figure 6.1: Junction diode
The diode shown in Figure 6.1 has two terminals, the anode and the cathode, denoted by the node
identifiers A and C, respectively. The branch voltage v D and the branch current i D satisfy the device
equation
i D ⩵ I S e v DV t
where I S denotes the reverse-bias saturation current and V t the thermal voltage. Typical values for I S
are A A. V t is given by k Tq where k denotes Boltzmann’s constant (k ⩵ WsK).
T is the absolute temperature (in Kelvin), and q is the charge of an electron (q ⩵ As).
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