User Guide

8
-
4 Tutorial: Fittin
g
Model Data (Bipolar Transistor)
The Parameters
The model parameters to fit are: Is, Ikf, Br, Bf, Ise, and Ne.
These parameters are a subset of the parameters PSpice uses to
determine the BJT’s DC characteristics. (To fit all of the BJT
model parameters, you would need more measured data than is
provided in this tutorial.)
PSpice Optimizer parameters
There are six PSpice
Optimizer parameters, each corresponding to one of the BJT
model parameters listed above. The initial and current values for
each of these parameters are set up using the OPTPARAM
symbol as follows:
Parameterized expression assi
g
nments
The
model definition is set up with parameterized expression
assignments for the model parameters the PSpice Optimizer will
vary. All other model parameters are left unchanged.
Example: Using the Model Editor, the forward beta is specified
as
bf = {bf}.
Property Parameters
Is Ikf Br Bf Ise Ne
Initial Value 1e-13 5 5 50 1e-10 1.5
Current Value 1e-13 5 5 50 1e-10 1.5
Lower Limit 1e-14 1 1 20 1e-11 1.2
Upper Limit 1e-11 10 10 200 1e-8 2
Tolerance 000000
Refer to Q devices in the online
M
icroSim PSpice A/D Reference
M
anual for more information on
the parameters used for bipolar
transistor models.
To display the Optimizer
Parameters dialo
g
box, double-
click the OPTPARAM symbol in
the schematic.
To see the parameterized
expression assi
g
nments for the
model parameters:
1
Click Q1.
2
From the Edit menu, select
Model.
3
Click Edit Instance Model
(Text).
4
When finished, click Cancel.