[SI-LIST] Re: TDR & Impedance rise in lossy interconnects

  • From: "C.C. Hwang" <cchwang2013@xxxxxxxxx>
  • To: istvan.novak@xxxxxxxxxxx
  • Date: Tue, 26 May 2015 19:44:17 -0700

Hi Boris,
A related question was posted a few weeks earlier.

An 85 ohm DUT can look 87 ohm before a 100 ohm PCB trace is de-embedded. A
test case was placed in http://ataitec.com/test/impedance_test_case.zip

Ching-Chao Huang



On Sat, May 23, 2015 at 4:54 PM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
wrote:

Hello Boris,

As others pointed out, it is not an artifact; it happens on all lossy
interconnects.
For an explanation, you may find our paper from a recent DesignCon useful:

http://www.electrical-integrity.com/Paper_download_files/DC13_Determining_PCB_Trace_Impedance.pdf

Regards,

Istvan Novak
Oracle



On 5/23/2015 4:43 PM, Boris Bakshan wrote:
Hello,
When running a TDR measurement on a lossy channel such as long backplane
I
always see a positive drift of the impedance along the interconnect.
Is it just an artifact or should it account for physical property of the
material?
What's the physical explanation behind this?

Thanks,
Boris.



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