[SOLVED] CMOS Difference between Vt and Vth

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2wice

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I know this is a very basic question. But I'd like to know the difference between Vt and Vth. I know they aren't the same and I also know that they are threshold voltages. But I just cant seem to get the grasp on their differences. any help would be appreciated.
 

crutschow said:
Then you should ask your professor the question. :wink:
Click to expand...

Hahaha I guess. I thought it'd be a very stupid and u know one of those questions to which everyone knows the answer. I guess its not.
 

It isn't clear what they are asking as Crutschow pointed out.
All I can think of is that they mean Vt as the middle point and Vth/Vtl as the limits of lowest high and highest low thresholds. If that is the case, it depends upon the supply voltage to the device. It varies across CMOS families so you really need to look in the data sheet to find out.

Brian
 


Brian I think what you said is right. I think the professor meant the higher and the lower limits of threshold. Thanks for clarifying. I get it now. :-o
 


2wice, I would suggest to use such abbreviations - in case you are asking for the meaning - in conjunction with some explaining wordings only.
I can assume that you mean "theshold voltage" - however, vth could also mean "thermal voltage".
Thus, a reliable answer can be given only if you tell us in which connection (in which formula) these terms do really appear.
 

There is one VT or VT0 model parameter.

There are several "VT"s you can measure, or calculate,
from device I-V curves and you may see more than one
in a WAT report. VTlin, VTsat, ... differ by measurement
conditions and possibly regression method (and, in some
cases, a simple VT(1uA) uses no figuring at all, just force
and measure).

30 years in this game, 15 of it mostly-CMOS, and I'd have
to look it up myself - because it's not really important
enough to have remembered. If, in fact, it was even
significant enough to have been taught.

Professors delight in passing on pedantic and not-
especially-useful distinctions; they just have to fill a
semester, with something.
 


Ah! So its not important after all! That's a relief.

and I wasn't referring to Thermal voltage. Both Vt and Vth are threshold voltages just in different contexts
 

Well, bear in mind that a professor is as happy to mark
off for the trivial, as the significant. The relevance of it
has nothing to do with your "A".

But in real life (or what passes for it in engineering) we
call it VT and move on to whatever we cared about, about
it.
 

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