Gaussian Distribution with Relative Spread

To define a Monte Carlo netlist parameter with Gaussian distribution and relative spread, use the following syntax:

.PARAM name=GAUSS(mean,rel_spread, num_sigma[,multiplier])

Monte Carlo values will be generated from a Gaussian distribution with standard deviation:

s = (mean ´ rel_spread)/num_sigma

If a multiplier is specified, that many values will be generated, the value that has the highest absolute deviation from the mean will be used in the simulation, and the other values will be discarded. The default is to do one selection.

For example, to define a Gaussian distribution with a mean of 10 and a standard deviation of 50% of the mean, using a relative spread:

.PARAM D1=GAUSS(10, 0.5, 1)

A relative distribution cannot have a mean of zero. To create an actual distribution with relative range and zero mean, you could use a secondary variable:

.PARAM D1=GAUSS(10, 0.5, 1)
.PARAM ACTUAL_D1='D1 - 10'

Alternatively, you could use the expression to set the instance or model parameter:

R21 Vin 0 R='1000 + (D1 - 10)'