Re: [IBIS-Users] Confused about clamp data in pull-up/down

Kriistiaan
    Different model creators construct models differently, and different 
CAD tools may implement IBIS features differently. A good model creator 
will construct a model so that it will behave properly (and correlate to 
reality) in all simulators. But at a  minimum a model creator should 
construct, validate and document the methods and correlation achieved. 
The IBIS quality committee recommeds the following  regarding IV curves 
(subset);

(4.3.4,4.3.5) The sweep for [Pulldown], (Pullup) should be made between 
-vcc to 2*vcc. The Pulldown,(pullup) table combined with the power and 
ground clamp should be monotonic. Non-monotonic combined I-V tables must 
be documented.
(4.3.6)[GND Clamp] should turn on approximately one Diode drop below 0.0 
(i.e. 0.7 volts). The sweep for [GND Clamp] should be made at least 
between -vccmax and +vccmax (it is permitted to extend the range). 
Non-monotonic I-V tables must be documented.
(4.3.14) Any IBIS models with on-die termination should be labeled as 
such using comment lines. On die termination should be modeled in [Power 
Clamp] and/or [GND Clamp] tables. Document the method used to embed the 
termination into the clamps.


Regards,
Bob Haller
Chair IBIS Quality Committee

De Paepe, Kristiaan wrote:

> Dear experts,
>
> I'm a little confused. While going through some papers, I got confused 
> about data I found in a particular LVTTL IBIS model of a normally 
> trusted source.
>
> At least one source of knowledge tells me that nor the pullup nor the 
> pulldown curves should contain clamping information (3-stated input 
> static clamping).
>
> Although, when viewing the curves, I can clearly observe a typical 
> diode behaviour (for pulldown, gnd relative this appears above vcc, 
> for the pullup, this appears below 0V)
>
> This made me lose my marbles, with only a few to spare...
>
> I tried finding any supporting information, but all sources I found, 
> state the same conditions.
>
> Can somebody pls explain why these curves are (in)correct?
>
> Many thanks,
>
> Kind regards,
>
> Kristiaan
>
>  
>
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