Electronics > Beginners

Help in deriving Zin small-signal expression

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The Electrician:
If M3 and M4 are identical, and M5 and M6 are identical, that fact will reduce the size of the expression, but you will probably have to plug in some numbers and see what you get.

Wimberleytech:

--- Quote from: promach on June 02, 2018, 01:11:03 am ---Cox = e0*er / Tox

Where is the missing parameter "area" ? I suppose capacitance equation is something like C = e*A/d


--- End quote ---

No, for transistor models, Cox has units of f/m2

In the simulator, area is derived from the transistor instantiation line (e.g., W and L).

Wimberleytech:

--- Quote from: promach on June 02, 2018, 01:11:03 am ---
Besides, someone told me that calculating gm and ro by hand will not be very useful. What do you guys think ?


--- End quote ---

It is reasonable to calculate gm by hand...assuming a long-channel device (as opposed to short channel), but ro is a crap shoot by hand.  You can do rough approximations in the design process but must rely on the simulator to do a better job.  Designs should never depend on an accurate ro anyway.  In fact, you should not depend on an accurate anything other than matching.

promach:

--- Quote ---It is reasonable to calculate gm by hand...assuming a long-channel device (as opposed to short channel), but ro is a crap shoot by hand.
--- End quote ---

What do you think about http://asco.sourceforge.net/doc/ASCO.html#SECTION00220000000000000000 ?

or in general  http://ngspice.sourceforge.net/docs/ngspice-manual.pdf#page=435 ?

promach:
Is it possible to derive the absolute numerical value of lambda(λ) from the mosfet model files ? Could anyone show how to do so ?

Alternatively, could I just use https://github.com/imr/ngspice/blob/master/examples/xspice/table/modelcards/modelcard.nmos#L38 directly ?

Besides, what does  TOXE = 1.8E-009  actually give ?  1.8*10^(-9) ? I asked this because I saw  LC = 5E-9  in the same file


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