Re: MOSFET transconductance

"Kevin Aylward" <see_website@xxxxxxxxxxxxx> wrote in message
news:z7ssf.32418$PD2.4989@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Walter Harley wrote:
>> "John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
>> message news:3cj3r1tr6dg1hsdfh405eq4u8bn7e425nt@xxxxxxxxxx
>>> [...]
>>> Why not measure it?
>>
>> Indeed I could. Or I could use a simulator.
>>
>> But it seemed I should be able to analyze such a simple circuit by
>> hand, based on information available in the data***. I guess not!
>
> Yes you can. I already pointed out where the basic equations can be found.
> For the simple model, the device is either in linear (ron) region or
> constant current (saturation) region. The formula for the gm in these
> regions are available. Have you tried google?
>
> In saturation the gm varies as sqrt(I). If you know it at one current,
> then it is known at all currents. Do we need to hold you hand as well?

Hi, Kevin. Yes, some handholding would be welcome; that's why I posted to
s.e.b., rather than s.e.d.

The model you cited earlier was:

..MODEL MM PMOS(LEVEL=1 IS=1e-32
+VTO=-3.73073 LAMBDA=0.0109168 KP=7.97276
+CGSO=1.08608e-05 CGDO=1e-11)

With some Googling I find many references to a 1968 paper by Shichman and
Hodges, in IEEE J. Solid State Circuits. But I can't seem to find the
actual formula itself. (I don't happen to have access to a technical
library, so I don't have the journal itself at hand.) Would you be able to
point me to an online reference that shows the formula that Spice is using
for this model?

And, should I believe that this "Level 1" model (which does not include the
subthreshold region) will be a good fit to the relatively low Id and Vds in
my scenario? After all, the whole reason for the question is that the
region I'm interested in is outside of the range shown in the data***.

Thanks,
-walter


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