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knowing of vt of nmos using virtuoso

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Junior Member level 1
Jul 15, 2010
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i use virtuoso in simulation, i just want to know the threshold of the nmos i used??
i followed the following steps
-i performed dc analysis and save dc operation point
-from menu -->i choose annotate -->dc operating point
-i go to schematic and expect to find the vth of mos but i didnt find it??
so if any anther method to know vt???
thanks in advance

When you run a dc operating point (using Eldo as your simulator), it puts all the dc operating points of your transistors within the design into a "XXyoucircuitname.chi" file. At the end of the .chi file, you can find the dc operation points (including the Vt) of each transistor. If you use other simulators, the idea is the same except with a different file extension. The location of the .chi file is typically the same as the generated .cir file (the virtuoso simulator builds a .cir file that describes your schematic).


hi sw0ws,

instead of using 'annotate' (that might not work in some PDKs) use 'Print' which always works; you will get a list of all the operating point parameters calculated in the model used for your device

Of course annotate is a lot more convenient: if you want to use it, we need to know...
- simulator
- what you see on the devices (try clicking on annotate voltages and OP again after you switch in to the hierarchy in particular)

It's really easy to know the threshold voltage of the MOSFET using Cadence.
Step1: Construct a correct circuit, whatever, maybe a inverter and perform the TRAN analysis.
Step2: Results->Print->Transient Operating Pionts
Step3: Click the MOSFET of which you want to know the threshold voltage in your schematic.
Then a window with all kinds of parameters, one of which is vth, will pop out. I hope it would be helpful.

Another way is as Paul Gray mentioned in his famous book. You can perform the DC anlysis and obtain the sqr(ID) vs VGS to find the threshold voltage. Pay attention to the fact that the threshold voltage HAS something to do with the dimension of your MOSFET.

Threshold voltage is just for reference. It's unnecessary to invetigate the exact value because the process corner will give you something really differnt from your simulation result.

Virtuoso is not simulation tool. Spectre is used for simulation.
Vt is usually defined by max gm rule.

Thankssssssssssssssss for all of u, i will try this


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