User`s guide

13
-
2 Monte Carlo and Sensitivity/Worst-Case Analyses
Statistical Anal
y
ses
Monte Carlo and sensitivity/worst-case are statistical analyses.
This section describes information common to both types of
analyses.
See Monte Carlo Analysis
on page 13-7 for information specific
to Monte Carlo analyses, and see Worst-Case Analysis
on
page 13-25 for information specific to sensitivity/worst-case
analyses.
Overview of Statistical Anal
y
ses
The Monte Carlo and worst-case analyses vary the lot or device
tolerances of devices between multiple runs of an analysis (DC,
AC, or transient). Before running the analysis, you must set up
the model and/or lot tolerances of the model parameter to be
investigated.
A Monte Carlo analysis causes a Monte Carlo (statistical)
analysis of the circuit to be performed.
A worst-case analysis causes a sensitivity and worst-case
analysis of the circuit to be performed.
Sensitivity/worst-case analyses are different from Monte Carlo
analysis in that they compute the parameters using the
sensitivity data rather than random numbers.
You can run either a Monte Carlo or a worst-case analysis, but
you cannot run both at the same time. Multiple runs of the
selected analysis are done while parameters are varied. You can
select only one analysis type (AC, DC, or transient) per run. The
analysis selected is repeated in subsequent passes of the
analysis.
not
included
in:
Generatin
g
statistical results
for Probe
As the number of Monte Carlo or
worst-case runs increase,
simulation takes lon
g
er and the
Probe data file
g
ets lar
g
er. Lar
g
e
Probe data files may be slow to
open and slow to draw traces.
One way to avoid this problem is
to set up an overni
g
ht batch job
to run the simulation and execute
Probe commands. You can even
set up the batch job to produce a
series of plots on paper which
are ready for you in the mornin
g
.