[SI-LIST] Re: Extract an accurate model from TDR IConnect
- From: "Wang, Mingchang" <mingchang.wang@xxxxxxxxx>
- To: <DavidLai@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 5 Feb 2007 16:52:03 +0800
Hi David,
I think you have several questions here.
One is how to extract a model which has a 90 ohm differential impedance using
IConnect, right?
My suggestion is just using Symmetric Coupled Line model or Symmetric Coupled
Lossy Line model in IConnect. Input the waveforms of your DUT under Odd Mode
and Even Mode as Reflection, also input the waveform of Open as your Reference.
And no need to make any fixture to transfer SE 50ohm to Diff 90ohm.
Another question is will there be any discontinuity introduced if adding
improper SMA cable, right?
My suggestion is adding a good/matched SMA cable on the TDR side will NOT
introduce any discontinuity, maybe just time delay there. However how you
connect this SMA cable to your DUT side need to be paid lots of attention.
Normally we see lots of discontinuity here if not proper connected. This will
impact the DUT waveform because of the multi-reflection. I know IConnect does
have some method to get rid of these multi-reflections. So you can just go
ahead and have a try using IConnect... :)
Thanks.
Best regards,
Mingchang
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of DavidLai@xxxxxxxxxx
Sent: 2007年2月5日 13:56
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Extract an accurate model from TDR IConnect
I have a question about extracting an accurate model from TDR IConnect.
The question is that when I want to extract a DUT which the Impedance is
not 50 ohm,
(for example, an USB connector which the differential impedance is 90
ohm).
Should I need to make a fixture to transfer impedance from single end 50
ohm to differential 90 ohm,
And then connect between TDR and DUT.
The purpose is to eliminate the discontinuity that maybe affect the
model accuracy we extract.
Or can I directly use the 50 ohm SMA cable connect the DUT to extract
the model?
The accuracy will be the same or not?
I am worried because the USB connector is very short.
If I directly use 50 ohm SMA cable, I am afraid that the discontinuity
will cover all the model effect.
Please give me some suggestions.
Thanks for help,
I am truly appreciated.
David
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