User`s guide

Monte Carlo Analysis 13
-7
Monte Carlo Anal
y
sis
The Monte Carlo analysis computes the circuit response to
changes in component values by randomly varying all of the
device model parameters for which a tolerance is specified. This
provides statistical data on the impact of a device parameter’s
variance.
With Monte Carlo analysis model parameters are given
tolerances, and multiple analyses (DC, AC, or transient) are run
using these tolerances. A typical application of Monte Carlo
analysis is predicting yields on production runs of a circuit.
For
example.sch in Figure 13-1 on page 13-6, effects due to
variances in resistors RC1 and RC2 values can be analyzed by
assigning a model description to these resistors that includes a
5% device tolerance on the multiplier parameter R. Then, you
can run a Monte Carlo analysis that runs a DC analysis first with
the nominal R multiplier value for RC1 and RC2, then the
specified number of additional runs with the R multiplier varied
independently for RC1 and RC2 within 5% tolerance.
To modif
y
example.sch and set up simulation
1
Replace RC1 and RC2 with RBREAK symbols, setting
attribute values to match the resistors that are being replaced
(VALUE=10k) and reference designators to match previous
names.
2
Select Model from the Edit menu, then select Edit Instance
Model. Create the model CRES as follows:
.MODEL CRES RES( R=1 DEV=5% TC1=0.02 TC2=0.0045 )
By default, MicroSim Schematics saves the definition to the
model file
example.lib and automatically configures the
file for local use with the current schematic.
3
Click on the resistor instance. Select Model from the Edit
menu, then select Change Model Reference to change the
model reference to CRES.
4
Set up a new Monte Carlo analysis as shown in Figure 13-2.
The analysis specification instructs PSpice A/D to do one
nominal run and four Monte Carlo runs, saving the DC
analysis output from those five runs.
not
included
in:
TC1 is the linear temperature
coefficient. TC2 is the quadratic
temperature coefficient.
Fi
g
ure 13-2
Monte Carlo
Analysis Setup for example.sch