eldo_user

Monte Carlo Analysis
Problems in Statistical Modeling
.SUBCKT N D G S B PARAM: W=1U L=1U
M1 D G S B MODN W=W L=L
.PARAM TOX=19E-09 A_MM_TOX=0.4543U B_MM_TOX=0.1435
+ DEV_MM_TOX =’A_MM_TOX/SQRT(W*L)+B_MM_TOX’
.PARAM VTH0=.3322 A_MM_VTH0=0.40654U B_MM_VTH0=0.11654
+ DEV_MM_VTH0 =’A_MM_VTH0/SQRT(W*L)+B_MM_VTH0’
.PARAM U0=388.3203 A_MM_U0=0.565745U B_MM_U0=0.264563
+ DEV_MM_U0 =’A_MM_U0/SQRT(W*L)+B_MM_U0’
.MODEL MODN NMOS
+LEVEL=53
+TOX = TOX DEV/GAUSS={DEV_MM_TOX}%
+VTH0 = VTH0 DEV/GAUSS={DEV_MM_VTH0}%
+U0 = U0 DEV/GAUSS={DEV_MM_U0}%
+KF=1E-27 AF=2
+TNOM=27.0
...
.ENDS
We will have 51 random variables (17 transistors and 3 three statistical parameters with DEV
variations) in the Monte Carlo sampling: EM(XM1.M1, TOX), EM(XM1.M1,VTH0),
EM(XM1.M1,U0), etc. See the definition above of the macro EM(.).
In this case, it is important to note that Eldo will create one model entry for each instance of the
subcircuit N. This is due to the definition of the model parameters TOX, VTH0, U0 which are
functions of the instance parameter W and L (the geometry). The .MODEL MODN definition
has a local scope. This implicit rule may have some unexpected side effects. Consider this
simple modification of the previous netlist:
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Eldo® User's Manual, 15.3