User Guide

What are models?
87
What are models?
A model defines the electrical behavior of a part. On a
schematic page, this correspondence is defined by a part’s
Implementation property, which is assigned the model
name.
Depending on the device type that it describes, a model is
defined as on of the following:
• a model parameter set
• a subcircuit netlist
Both ways of defining a model are text-based, with
specific rules of syntax.
Models defined as model parameter sets
PSpice has built-in algorithms or models that describe the
behavior of many device types. The behavior of these
built-in models is described by a set of model parameters.
You can define the behavior for a device that is based on a
built-in model by setting all or any of the corresponding
model parameters to new values using the PSpice
.MODEL syntax. For example:
.MODEL MLOAD NMOS
+ (LEVEL=1 VTO=0.7 CJ=0.02pF)
Models defined as subcircuit netlists
For some devices, there are no PSpice built-in models that
can describe their behavior fully. These types of devices
are defined using the PSpice .SUBCKT/.ENDS or
subcircuit syntax instead.
Subcircuit syntax includes:
•
Netlists to describe the structure and function of the
part.
•
Variable input parameters to fine-tune the model.
For example:
T
h
e .MODEL syntax app
l
ies to t
h
e ana
l
og
models built in to PSpice.
To
f
in
d
out more a
b
out PSpice comman
d
and netlist syntax, refer to the online
OrCAD PSpice A/D Reference
M
anual.
Pspug.book Page 87 Wednesday, November 11, 1998 1:14 PM