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Coarse Variation Analysis

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Full Member level 3
Oct 17, 2009
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Hey all

If I just want to test the circuit behavior at different corners- just a coarse analysis- and not Monte Carlo, what and how should i change parameters?

I understand that SS means NMOS and PMOS both slow and FF means both fast... but is there any correlation in between the amount of change of Vth of one with Vth of the other?

I mean, If I increase Vthn, then by what amount should I increase Vthp for SS? how about SF, FS and FF Vice Versa?

Also, when I try to change 2 or more parameters at a time, how do I know where my device falls in the curve? (Example- changing Vth for both NMOS and PMOS, and then changing Vdd and Temperature- how do I determine the corner of operation- for example is it faster than FS or slower then SF or faster then SF and like wise!?)

Or let me rephrase the question.

Out of Temperature and Vdd and Vth, which one dominates? - this would help me decide the device space and then based on dominance, I can do coarse analysis in each case.

Have one more question:

I did 3 analysis in which 1st case- all the conditions were typical- typical Vdd, Temp, Vth and Leff.

In other one, I kept Temp 125c, Vdd decreased by 10%, Vth increased by 10% and Leff unchanged.

and in 3rd one, I kept Temp 125c, Vdd decreased by 10%, Vth increased by 10% and Leff increased by 10%.

Technically, if I increase Leff, then the circuit performance slows down even more. But surprisingly, I found 2nd case slower than 3rd one. Cant understand why!?

Can anyone tell me?

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