[SI-LIST] Re: TDR measure / Simulation

Calibration is the key, and it isn't easy unless you have a long trace =
test run of which you know the exact length.=20

I've found TDR's do certain things really well, they measure =
reflections, impedance, and time very accurately.=20

But there are things they do that need calibration : distance and the =
dielectric constant. If you have a length that is really accurate then =
you can derive the Er and thus prop delay of your other traces. But on a =
regular board I could get no closer than 10-20% because of the =
parasitics that lengthened the edges (vias, stubs, probe/launch =
attachments).

If you don't have an accurate Er then prop times won't agree in your =
sims and measurements.

Jim Peterson
Honeywell

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of si09604@xxxxxxxxxxxx
Sent: Tuesday, November 27, 2007 10:23 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] TDR measure / Simulation

Hello,
I try to understand the TDR (Time domain reflection) in=20
the measure and in the simulation, to identify the=20
elements.=20
I have seen that The TDR measure is more long in time that=20
the simulation.=20

Do you know what happens?

Thank you.

B.R

N=FAria
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