User`s guide

What Are Models? 4
-3
What Are Models?
A model defines the electrical behavior of a part. On your
schematic, this correspondence is defined by a symbol’s
MODEL attribute, which is assigned the model name.
A model is defined as either a:
• model parameter set, or
• subcircuit netlist,
depending on the device type that it describes. Both ways of
defining a model are text-based with specific rules of syntax.
Models defined as model parameter sets
PSpice A/D 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.
The behavior for a part that is based on a built-in model is
defined by setting all or any of the corresponding model
parameters to new values using the PSpice .MODEL syntax.
Example:
.MODEL MLOAD NMOS
+ (LEVEL=1 VTO=0.7 CJ=0.02pF)
Models defined as subcircuit netlists
For some parts, there are no PSpice A/D built-in models that can
describe their behavior fully. These kinds of parts 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 a description of the MODEL
attribute, see
MODEL on
page 5-19.
In addition to the analo
g
models
built in to PSpice A/D, the
.MODEL syntax applies to the
timin
g
and I/O characteristics of
di
g
ital parts.
To find out more about PSpice A/D
command and netlist syntax, refer
to the online
MicroSim PSpice A/D
R
eference Manual.