eldo_user

Monte Carlo Analysis
Problems in Statistical Modeling
Using the final example in “Macros EM(.) and M(.)” on page 542, modifying the subcircuit
definition to replace the .PARAM statements with .MCMOD commands:
.SUBCKT BIPNPN 1 2 3 4
Q0 1 2 3 4 NPNBIP
.MODEL NPNBIP NPN IS=24.5E-18 BF=121 NF=1 VAF=35 IKF=32E-3 ISE=847E-18
+ NE=1.9 BR=3.81 NR=1 VAR=3.2 IKR=2E-3 ISC=847E-18 NC=1.9
+ IRB=80E-6 RBM=5 XTB=0.5 EG=1.2 XTI=3 CJE=59.6E-15 VJE=0.895
+ MJE=0.41 TF=11E-12 XTF=15 VTF=1.5 ITF=40E-3 PTF=0 CJC=45.8E-15
+ VJC=0.642 MJC=0.33 XCJC=0.3 TR=5E-9 CJS=75.5E-15 VJS=0.65
+ MJS=0.33 FC=0.875
+ TRB1=1.05E-3 TRB2=4.4E-6 TRC1=1E-3 TRC2=3.1E-6 TRE1=0 TRE2=0
+ KF=1.32E-10 AF=1.8
+ RE=3.5 RC=25 RB=100
+ ISS=1E-16
.MCMOD NPNBIP RB LOT=5% DEV=2.5%
.MCMOD NPNBIP RE LOT=5% DEV=2.5%
.MCMOD NPNBIP RC LOT=5% DEV=2.5%
.MCMOD NPNBIP ISS LOT=5% DEV=2.5%
.ENDS
then Eldo will generate several warning messages during the first phase of simulation:
Warning 921: In file “./test71_2.cir” line 22:
+ MC variation on BIPNPN.NPNBIP: new MC LOT (5.000000e-02 ) on
parameter RB specified.
+ Previous specification is ignored.
Warning 921: In file “./test71_2.cir” line 22:
+ MC variation on BIPNPN.NPNBIP: new MC DEV (2.500000e-02 ) on
parameter RB specified.
+ Previous specification is ignored.
...
The reason for these warnings is that the .MCMOD introduces local modifications of the
NPNBIP model while the .MODEL card has global scope in the netlist (it is placed at the top
level). The .MCMOD commands therefore redefine and overwrite the previous definitions. This
situation should be avoided.
Here is another example. The example of the 2-stage operational amplifier given in the previous
section is used.
Eldo® User's Manual, 15.3 545