Re: [IBIS-Users] Capacitance and transition time

I agree with Tom that IBIS will produce very good resluts 
on different capacitive loads. In some cases, usually LVDS 
drivers(due to their high sensitivity to even resistive 
load), we might face a problem but not very likely.
BR,
Hazem



On Mon, 30 Jan 2006 22:50:21 -0500
  "Andrew Ingraham" <a.ingraham@ieee.org> wrote:
>In normal usage, the actual load (i.e., traces and other 
>devices) connected
>to an output device creates a rather complex, frequency 
>dependent load.
>It's highly unlikely that the output device was 
>characterized with that kind
>of load.
>
>While there may not be a guarantee, one should expect 
>that an IBIS model
>would produce reasonably good results with such complex 
>loads as well as
>simple R/C loads (with not unreasonable values), even 
>though they weren't
>use to generate the VT curves.
>
>Anyway, most VT curves are established with resistive 
>loads (zero
>capacitance), which "never" happens in practice.  The VT 
>curves may be used
>only to "calibrate" the simulator's representation of the 
>ouput device, not
>to generate actual waveforms.
>
>Regards,
>Andy
>
>
>> A coworker wants to simulate what affect connecting
>> different capacitors to the output pin of a device
>> would have on its transtion time.  He doesn't have
>> access to spice models and he asked me if he could use
>> IBIS models.  I told him that since the models are
>> characterized under a given load, changing that load
>> in simulation may not give him very accurate results.
>> Was I correct, or will the simulator use the values of
>> the IV curves and test fixture to accurately skew the
>> rise and fall times specified in the VT curves?
>
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Hazem Hegazy$IBIS modeling manager$Quality 

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