subthreshold current mos

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rosaeidi

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Hi

I used the following equation in order to model the MOS current in subthreshold region:

ids=I0* exp((Vgs-VT)/(n*Vth))*(1-exp(-Vds/Vth)) •

With Vgs=100mV, I ploted the current versus Vds. But the result is diffferent from the equation!!!

**broken link removed**

•"CMOS Analog Integrated Circuits Based on Weak Inversion Operation," IEEE Journal of Solid-State Circuits, vol. 12, no. 3, pp. 224-231, June 1977.
 

Hi Rosaeidi,

It is normal to expect difference between the hand analysis equation and simulation. How far are the estimation and simulation? The error sources in this estimation are many: second-order effects, short channel effects, error in estimation of the slope factor (by the way, how have you estimated “n”?), and so on. Maybe it would be interesting to plot your simulation results. Regards,
 

Subthreshold slope varies hugely by process (Tox, NSS).
I suppose that's your "n". Did you fit it?
 

I found 'n' by simulation result. Simulation result for Vgs sweeping is good.



I have problem with Vds sweeping.
The following formula is from "Sub-threshold Design for Ultra Low-Power Systems"


The I-Vds plot of this book is:



This plot can't be a logarithmic plot! But the formula has a logarithmic relation with Vds. I think something is rong with formula.

The given formula can't be matched with the given plot.
 
rosaeidi said:
This plot can't be a logarithmic plot! But the formula has a logarithmic relation with Vds. I think something is wrong with formula.

The given formula can't be matched with the given plot.
Click to expand...

If you plot log(ID) vs. VDS with VGS as parameter, you'll see the exponential behavior:

 

Hi

I think it is because of DIBL effect. I apply its effect and the result is ok!

Thanks
 

rosaeidi said:
Hi

I think it is because of DIBL effect. I apply its effect and the result is ok!

Thanks
Click to expand...

Hi rosaeidi I am also trying to figure out NMOS channel current model in subthreshold region, Could you show that equation with the effect of DIBL?
Thank you in advance!
 

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