HSpice- .MEASURE MIN for difference of two branch currents.

[renz.bagaporo]

Good day!

I am trying to know what ratio of W/L will give me the minimum current difference between the two branches of a current mirror. Here is my netlist:

VDD VDD 0 DC 3.3

R1 VDD 1 10
MNA 1 1 0 0 NCH L=LENGTH W=WN
MNB VDD 1 0 0 NCH L=LENGTH W=WN


.DC WN 0.4U 50U '(50U-1U)/10000'
.MEASURE DC WNSIZE MIN I(MNA)-I(MNB)

I hope to store the minimum difference between I(MNA) and I(MNB) in WNSIZE. However, in the .lis file, I keep getting the warning
"the measured variable for wnsize is not defined", and the output says

wnsize= 0.0000E+00 at= 4.0000E-07
from= 4.0000E-07 to= 4.9998E-05

which I am pretty sure is not the WN at which the current difference is minimum (I've checked the next values and I found an WN size at which the difference is even smaller).

What is the problem?

 

[erikl]

I'm not sure if such a measurement will work for a swept .DC analysis.

In any case, as the error message tells you

"the measured variable for wnsize is not defined"

you must define your measurement result as parameter. Try:

.MEASURE DC WNSIZE=PAR('MIN I(MNA)-I(MNB)')