[SI-LIST] Re: Correlation to lab measurement

  • From: Vishwanath Elechithaya <elechi@xxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Thu, 24 Jun 2010 17:47:57 +0530

Hi Steve,
Please correct me if I am wrong as I am new to this. I would like to know
more about this correlation.

I am suspecting this due to either the termination modeling or the waveform
models.

What kind of Termination models do you have on IBIS?.

Do your IO Pad cell have both Common mode as well the differential
terminations?

Could you please share the IBIS model details (Especially the Clamp Curve
data, if the pad cell inside the chip has common mode terminations too).

Do the waveforms capture the step (due to reflection) in the IBIS models?

Regards,
elechi

On Tue, Jun 8, 2010 at 7:52 PM, Santangelo, Steven <SSantangelo@xxxxxxxxxxxx
> wrote:

> Hi All,
>
>
> I'm trying to correlate some lab measurements to my simulations in
> Cadence PCB SI (SpectraQuest).  I have a 400MHz unidirectional LVDS
> interface between two Xilinx devices that is terminated in 100ohms
> inside one of the devices.  My lab measurements show a pretty good
> reflection occurring on the rising and falling edges of the waveform.
> I'm trying to determine if this is being caused by the ball to I/O pad
> trace length in the package (plus my BGA breakout).   My simulation only
> shows a slight bend in the waveform rather than the non monotonic ring
> that I see in the lab.  The bend does correlate well time wise (location
> on the edge) with the lab measurement.  I don't really know much about
> the limitations of IBIS models so I'm wondering if some of the
> discrepancy could be due to that.
>
>
>
> FYI: I'm using the models that Xilinx "ibiswriter" puts out.  The
> rise/fall times of the waveforms are in the neighborhood of 300pS.
>
>
>
> Thanks
>
>
> Steve
>
>
>
>
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