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How are Vtlin and Vtsat extracted from simulation results (Read 93 times)

modelman New Member Offline Posts: 5	How are Vtlin and Vtsat extracted from simulation results Feb 01^st, 2011, 5:26am I often see curves that show VTlin vs Length or VTsat vs Length VTlin vs width, VTsat vs width etc. I know how to create a netlist to sweep Length or Width and look at drain current. Could you please explain how can I back calculate the threshold voltage?
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Geoffrey_Coram

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Re: How are Vtlin and Vtsat extracted from simulation results
Reply #1 - Feb 1^st, 2011, 10:03am

Experimentally, I think people usually sweep VG and define VT by a feature of the ID-VG plot; then they repeat this for the available widths on the test chip.

You could do the same in simulation, or, if you like the definition of VT reported in the op-pt info of your simulator, you can sweep W or L and look at the op-info.

If at first you do succeed, STOP, raise your standards, and stop wasting your time.

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modelman

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Re: How are Vtlin and Vtsat extracted from simulation results
Reply #2 - Feb 1^st, 2011, 12:48pm

Thank you Geoffrey. �

Is there a standard that is followed in calculating Vt from Id?

I recall mention of 300mA but I am not sure what it refers to. �I guess the device gets biased to produce Id=300mA and Vt is calculated based on a simple expression for Id as a function of mu, cox, W, L, Vgs, Vds and Vt

I suspect one would get different Vt values using this approach at different values of Vgs and Vds �(clearly Vt is a function of bias, otherwise there would not be different values for Vtlin and Vtsat)

What am I missing here? � Huh

Thanks.

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Mooraka Junior Member Offline Posts: 20 Lexington, KY	Re: How are Vtlin and Vtsat extracted from simulation results Reply #3 - Feb 1^st, 2011, 3:24pm I think for scaled technologies, Vt is usually calculated using constant current method. For eg. Vtlin is defined as Vgs at Ids=300nA*(W/L) and Vds=50mV. Vtsat is calculated similar way but at Vds=Vcc. You can check your Technology/Foundry documentation for exact definition/Id numbers.
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