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Terminology in Hspice

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dhaval4987

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I want to know about the terms 'AS', 'AD', 'PS' and 'PD' in spice.

I am running timing analysis in nanotime and it gives warning that value of 'AS' for is too big (or small) for the simulation. And after that- it gives no results. However it runs without error.

So i thought knowing the terminology would help me and modifying it correctly would lead me to correct results.

Thanks.
 

keith1200rs

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AS is the area of the source. PS is the perimeter of the source. Ditto AD for the drain.

Keith
 

dhaval4987

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Thanks Keith. One more question. How does one determine the value of Diffusion areas and perimeter? Because the tool says it is too big for the technology. I am using 45nm technology.
 

keith1200rs

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It is probably part of the PDK. You can look in the design rules to work it out. What are the W, L, AD, AS, PD & PS values you are using?

Keith
 

dhaval4987

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Thanks Keith. But Sorry I did a mistake in reading the error... Due to a misunderstanding, I thought that the error is about AS and AD. But it said Acde=1 may be too small in model. It is one parameter in the model I am using. I am using 45nm PTM model.
 

keith1200rs

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Assuming it is a BSIM4 model ACDE is "Exponential coefficient for charge thickness in CAPMOD=2 for accumulation and depletion regions" with a default value of 1mV/V.

In BSIM3 it is "Exponential coefficient for charge thickness in capMod=3 for accumulation and depletion regions" with the same 1mV/V default value.

Keith.
 

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