[SI-LIST] Re: IBIS simulation LVPECL
- From: Bob Tarasewicz <Bob.Tarasewicz@xxxxxxxxxx>
- To: Istvan Novak - Board Design Technology <Istvan.Novak@xxxxxxx>, "Cotton, Chris" <Chris.Cotton@xxxxxxxxxxx>
- Date: Fri, 3 Oct 2008 11:01:46 -0500
Istvan & Chris
The step is about 200ps wide. I am measuring at vias right under
the BGA pads. I don't know how accurate the package model is; the
processor vendor provided it. Here is the package model info for the 2
reciever pins AV21 and AU21
AV21 Len=0 L=0.1n R=1.7m / Len=11391.99 L=0.4p C=0.11f R=0.06m /
Len=0 R=3m / Len=0 L=0.4n R=2.54m /
Len=0 R=3m / Len=0 L=0.08n R=0.04m C= 0.03p /
AU21 Len=0 L=0.1n R=1.7m / Len=10354.47 L=0.4p C=0.11f R=0.06m /
Len=0 R=3m / Len=0 L=0.4n R=2.54m /
Len=0 R=3m / Len=0 L=0.08n R=0.04m C= 0.03p /
I have to make some pretty significant changes in the receiver
ibis model 'Define Package Model' in order for simulation to start showing
a "step". If I change the 'Len' by a factor of 2x and the C by a factor
of 5x (ie make Len=20000 and C=0.55f for both AV21 and AU21) , then
simultion will show a "step". However, I'm not sure if making these
kinds of changes to Len and C is still within a reasonable range or not.
Thanks for your responses.
Bob
Istvan Novak - Board Design Technology <Istvan.Novak@xxxxxxx>
Sent by: Istvan.Novak@xxxxxxx
10/03/2008 09:56 AM
To
Bob Tarasewicz <Bob.Tarasewicz@xxxxxxxxxx>
cc
si-list@xxxxxxxxxxxxx
Subject
Re: [SI-LIST] IBIS simulation LVPECL
Bob,
How wide is the step? Could it come from the round-trip delay from the
pin connection where
you measure, to the die, including possible via(s), package traces, bond
wires -if any - ?
Regards,
Istvan
On 10/03/08 10:42, Bob Tarasewicz wrote:
> My simulations of an LVPECL net (apprx 3" long, 'Y' terminated just
beyond
> receiver) do not seem to be correlating at all with in-lab measurements.
> In the past I've had very good luck with simulations agreeing pretty
well
> with actual scope measurements; however, this is my first experience
> simulating LVPECL. Is there a fundamental reason why perhaps IBIS
models
> won't model the behavior of LVPECL accurately? Or is it that the faster
> edge rate of LVPECL is highlighting flaws/limitiations in my simulation
> methodolgy and/or tool?
> Simulations "at the pin" as well as "at the die" show nice
rising/falling
> edges at the receiver. However, scope captures with a good diff probe
> show a 'step' in the rising/falling edge at the receiver. The 'step'
> looks like what one would expect halfway down a series-terminated net;
not
> sure why I'm seeing a 'step' with an end-terminated net.
>
> Any guidance would be apprecitated.
>
> Bob Tarasewicz
>
>
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