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Calulation of dimenssion ratio for MOS in subthreshold

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kapil kumar rajput

kapil kumar rajput

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Hi all,
Can sombody tell me how to calculate the Id0 and slope factor "n" so that I can obtain the W/L ratio for MOS working in subthreshold operation. The equation is as followes:

Id=Id0*(W/L)*exp(Vbe/nVT);
Id0 is characteristics current and "n" is slope factor. Is it the way to obtain the dimenssion ratios for the MOSFET in subthreshold operation. As we do for Saturation MOS. If any other please share with me.

Thanks with Regards
 

Hi,

I think that the following book will give you what you need :

Tradeoffs and Optimization in Analog CMOS Design by David Binkley

Check it out and if i remember well it has the equations you are asking for.
I would suggest that you work in parallel with simulations if you are practising on a real design and not be based only on the mathematical expressions to derive the W/L ratios or any other unknown design variable.

ps.If you are using cadence the slope factor "n" is under the menu Print-->Model Parameters of ADE L if i remember it right.Cross-check it with the model that your pdk uses in order to find the respective symbol of the slope factor variable.

Regards,
Jimito13
 

simulate ids-vgs curve, plot ids on log scale, measure the change in vgs for current to increase by one decade, this is called subthreshold slope S. the relation between S and n is \[\dfrac{1}{S}=\ln 10 \times n \times U_t\]. typical value for S is maybe between 80 mV and 90 mV in 130 nm process.
 
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Thnx but I would try the same u told. But can you tell how I will calculate the ID0 i mean characterstics current. You know very less has benn given for Subthreshold design in Books.
Regards
Kapil

Added after 47 seconds:

Thanx Jimito and Overlems!

Added after 5 minutes:

Jimito, I don't have the book u named. Can you fwd me the link on which this is avilable free or you have pdf or scanned page on which this is avilable.
Thanks and regards
Kapil
 

Yes i have the book in pdf format.I will send it to you tomorrow from my office.

Jimito13



Do not post here any ebook or copyrighted materials, MOD: Aya2002
 

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