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Monte Carlo analysis
289
Monte Carlo analysis
The Monte Carlo analysis calculates the circuit response to
changes in part values by randomly varying all of the
model parameters for which a tolerance is specified. This
provides statistical data on the impact of a device
parameter’s variance.
changes in part values by randomly varying all of the
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.
tolerances, and multiple analyses (DC, AC, or transient)
are run using these tolerances.
For EXAMPLE.DSN in Figure 74 on page 12-288, you can
analyze the effects of variances in the values of resistors
RC1 and RC2 by assigning a model description to these
resistors that includes a 5% device tolerance on the
multiplier parameter R.
analyze the effects of variances in the values of resistors
RC1 and RC2 by assigning a model description to these
resistors that includes a 5% device tolerance on the
multiplier parameter R.
Then you can perform a Monte Carlo analysis. First, the
simulator performs a DC analysis with the nominal R
multiplier value for RC1 and RC2. Then it performs a set
number of additional runs with the R multiplier varied
independently for RC1 and RC2 within a 5% tolerance.
simulator performs a DC analysis with the nominal R
multiplier value for RC1 and RC2. Then it performs a set
number of additional runs with the R multiplier varied
independently for RC1 and RC2 within a 5% tolerance.
To modify example.dsn and set up simulation
1
Replace RC1 and RC2 with RBREAK parts, setting
property values to match the resistors that are being
replaced (VALUE=10k) and reference designators to
match previous names.
property values to match the resistors that are being
replaced (VALUE=10k) and reference designators to
match previous names.
2
Select PSpice Model from the Edit menu. Create the
model CRES as follows:
model CRES as follows:
.MODEL CRES RES( R=1 DEV=5% TC1=0.02
+ TC2=0.0045 )
+ TC2=0.0045 )
From the File menu, choose Save. By default, Capture
saves the definition to the model library
EXAMPLE.LIB and automatically configures the file
for local use with the current schematic.
saves the definition to the model library
EXAMPLE.LIB and automatically configures the file
for local use with the current schematic.
3
In Capture, set up a new Monte Carlo analysis as
shown in Figure 75. The analysis specification tells
PSpice to do one nominal run and four Monte Carlo
shown in Figure 75. The analysis specification tells
PSpice to do one nominal run and four Monte Carlo
Monte Carlo analysis is frequently used to
predict yields on production runs of a
circuit.
predict yields on production runs of a
circuit.
TC1 is the linear temperature coefficient.
TC2 is the quadratic temperature
coefficient.
TC2 is the quadratic temperature
coefficient.
Pspug.book Page 289 Wednesday, November 11, 1998 1:14 PM