RE: [SI-LIST] : connector model for differential signal

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From: 林朝煌 (John@quantatw.com)
Date: Wed Oct 25 2000 - 18:42:56 PDT


Dear Dima,
 
Thank you for your response. After downloading the application note for the
web site, I find
it is exactly what I am looking for.
 
However, I got a little confusion about common mode impedance in the paper
"Characterization of Differential Interconnects from TDR Measurement"
,DIFF-1199.pdf.
 
On the page two, equation 3, the common mode impedance is Z_common=Zeven /
2.
 
Checking the article "Differential impedance ... finally made simple"
(CAPGLTIF.pdf) by Eric Bogatin, from www.BogatinEnterprises.com,
<http://www.BogatinEnterprises.com> Slide 26, I find the
Z_common=Zeven=Z11+Z12.
 
Checking the HP54754A TDR user's manual, I find a description with
measurment waveform shown
"The common mode impedance of two 50 ohm uncoupled lines is 25 ohms". It
match what you described Zcommon.
 
Shall the Z_common be Zeven/2 or Zeven?
 
To meet Zdiff is always mentioned when doing PCB impedance control. Usually,
I totally forget Zcommon
when try to meet Zdiff. What circumstance shall I maintain Zcomm , instead
of Zdiff , or both?
 
 
Thank you for your inputs.
 
Best Regards,

John Lin
SI Engineer, ARD4
Quanta Computer Inc.,Taiwan, R.O.C.
Email: John@quantatw.com <mailto:John@quantatw.com>
Tel: 886+3+3979000 ext. 5183

 

-----Original Message-----
From: Dima Smolyansky [mailto:dima@tdasystems.com]
Sent: Wednesday, October 25, 2000 9:10 AM
To: si-list@silab.eng.sun.com <mailto:si-list@silab.eng.sun.com>
Subject: Re: [SI-LIST] : connector model for differential signal

John:
 
Even and odd mode TDR analysis will give you a pretty good model for your
connector.
 
You may want to check our application note on SCSI connector and cable
characterization and the more generic appnote on differential line
characterization, which can be found on www.tdasystems.com/support.htm
<http://www.tdasystems.com/support.htm> . The appnotes discuss in detail
characterization of differential lines in SCSI connector/cable assembly.
 
Thanks,
 
-Dima
 

----- Original Message -----
From: John Lin <mailto:John@quantatw.com> (林朝煌)
To: si-list@silab.eng.sun.com <mailto:si-list@silab.eng.sun.com>
Sent: Tuesday, October 24, 2000 12:03 AM
Subject: [SI-LIST] : connector model for differential signal

Dear SI gurus,

How to do connector modeling for differential signals, such as SCSI on a
backplane?

Usually, I am used to use IPA510 modeling software with TDR to build a
connector pin model.
The IPA510 will generate a Z-profile for the connector pin, create a RLC
model, and then run spice simulation to verify model's accuracy. All
mentioned above are for single connector pin. But, how about differential
signals on the connector pins? What does the model look like?

Thanks for your comments in advance.

John Lin
SI Engineer, ARD4
Quanta Computer Inc.,Taiwan, R.O.C.
Email: John@quantatw.com
Tel: 886+3+3979000 ext. 5183

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