User`s guide

Monte Carlo Analysis 13
-19
Monte Carlo Histo
g
rams
A typical application of Monte Carlo analysis is predicting
yields on production runs of a circuit. Probe can be used to
display data derived from Monte Carlo waveform families as
histograms, part of Probe’s performance analysis feature.
To illustrate this feature, we will simulate a fourth order
Chebyshev active filter, running a series of 100 AC analyses
while randomly varying resistor and capacitor values for each
run. Then, having defined performance analysis goal functions
for bandwidth and center frequency, we will observe the
statistical distribution of these quantities for the 100 runs.
Cheb
y
shev filter example
The Chebyshev filter is designed to have a 10 kHz center
frequency and a 1.5 kHz bandwidth. The schematic for the filter
is shown in Figure 13-8. The stimulus specifications for V1, V2,
and V3 are:
V1: DC=-15
V2: DC=+15
V3: AC=1
The components were rounded to the nearest available 1%
resistor and 5% capacitor value. In our analysis, we are
concerned with how the bandwidth and the center frequency
vary when 1% resistors and 5% capacitors are used in the circuit.
Creatin
g
models for Monte Carlo anal
y
sis
Since we are interested in varying the resistors and capacitors in
the filter circuit, we will need to create models for these
components on which we can set some device tolerances for
Monte Carlo analysis. The
breakout.slb Symbol Library file
contains generic devices for this purpose. The resistors and
capacitors in this schematic are the Rbreak and Cbreak symbols
from
breakout.slb. Using the model editor, we must modify
the models for these components as follows:
.model RMOD RES(R=1 DEV=1%)
.model CMOD CAP(C=1 DEV=5%)
For information about
performance analysis, see
Example: RLC Filter on
page 12-3.