[SI-LIST] Re: Question on IBIS: rising/falling waveform - How complete waveform created?

Adeel,

I am not sure what you are referring to as alpha and beta, because
I haven't read that paper.  The way I explain this is that the Vt
curves are basically used to regenerate the family of IV curves
which correspond to all gate voltages between power and ground.
This can also be viewed as a scaling factor of the IV curves with
respect to time.

However, the IV curve's output current is also a function of the
drain-source voltage, which depends on the loading conditions.
This is why IBIS simulators can reproduce correct waveforms even
if the load is different from the Rfixture that was used when the
Vt curves were generated.

I hope this will help you to understand this better.

Arpad
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=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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-----Original Message-----
From: adeel.ahmad@xxxxxx [mailto:adeel.ahmad@xxxxxx]
Sent: Sunday, January 26, 2003 10:54 PM
To: si-list@xxxxxxxxxxxxx
Cc: Muranyi, Arpad
Subject: [SI-LIST] Re: Question on IBIS: rising/falling waveform - How
complete waveform created?



hello Arpad,

having gone through all the replies to my question on SI-list regarding
IBIS V-t curves and having read the 2 IEEE papers referred by Herbert, i
hope i have understood how and what information the V-I and V-t curves
carry with them.The next step is how the simulator interprets it for
simulations.
And i am trying to figure out how the IBIS models allow simulations for
loads other than the R_fixture as you said "waveform will adjust to the
loading conditions"(and it should do that). If i have rightly =
understood,
it is the "Transient V-I curves" and the load line intersections that
allow this. But for getting Transient V-I curves, alpba and beta values
are required.
One of the IEEE papers quoted by Herbert says "each set of alpha and =
beta
provides an instantaneous I/V curve for upper and lower devices of the
buffer." Obtaining one complete Transient V-I curve(say,for time=3Dt1) =
from
a single alpba and beta is, i suppose, by scaling the dc V-I curve
proportionally by factor of alpha and beta.
Now with transient V-I curves available, for different loads, new
waveform is obtained by plotting voltages(against time) at which each
transient curve is intersected by the load line.
i am unsure if thats the way things happen.
so do comment.

regards
ADEEL

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