[SI-LIST] Re: AW: ??: Re: ??: Re: How to measure the actual impedance of a stripline with DSA8200(TDR)
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: "'John Lee'" <venussoso@xxxxxxxx>, "'GertHavermann'" <Gert.Havermann@xxxxxxxxxxx>, "'steve weir'" <weirsi@xxxxxxxxxx>, "'Jory McKinley'" <jory_mckinley@xxxxxxxxx>
- Date: Thu, 13 Jan 2011 08:23:55 -0800
All
How clean is the reflected waveform from the trace you are trying to measure?
Are you using IConnect or are you just using the scope and trying to read out
the impedance from the scope?
When measuring impedance with TDR the calculations are looking at the voltage
level of the reflected waveform. With a rising step the lower the returned
voltage the lower the impedance of the corresponding region. But if there are
a lot of or major discontinuities between the launch and the area of interest
the incident voltage at the area of interest is lower than what was launched
into the board. So the predicted impedance would be lower. Tools like IConnect
use a peeling algorithm to remove from the calculations the intermediate
reflections to reveal the true impedance further and further into the measured
trace.
Regards,
Tom Dagostino
Teraspeed Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
www.teraspeed.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of John Lee
Sent: Thursday, January 13, 2011 7:10 AM
To: GertHavermann; steve weir; Jory McKinley
Cc: SI LIST
Subject: [SI-LIST] Re: AW: ??: Re: ??: Re: How to measure the actual impedance
of a stripline with DSA8200(TDR)
Hi, Jory,
Thanks for your kindly reply.
Yes, the theoretical impedance is about 60ohm, but i can not get it by TDR....
I got the right impedance of microstrip line with the same TDR, so i am
confused that why i can not do it on stripline...
Best Regards!
John Lee
--- 11å¹´1月13日，周四, Jory McKinley <jory_mckinley@xxxxxxxxx> 写é“：
å‘件人: Jory McKinley <jory_mckinley@xxxxxxxxx>
主题: Re: [SI-LIST] AW: ??: Re: ??: Re: How to measure the actual impedance
of a stripline with DSA8200(TDR)
收件人: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>, "John Lee"
<venussoso@xxxxxxxx>, "steve weir" <weirsi@xxxxxxxxxx>
抄é€: "SI LIST" <si-list@xxxxxxxxxxxxx>
日期: 2011å¹´1月13æ—¥,周四,下åˆ9:16
Hello John,
Could it be you are interpreting the TDR response incorrectly? Might be the
impedance of the Via's in the Test Coupon (twice the electrical length) you are
measuring? Based on stack and trace impedance measurements should be in the
58ohm range.
-Jory
From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
To: John Lee <venussoso@xxxxxxxx>; steve weir <weirsi@xxxxxxxxxx>
Cc: SI LIST <si-list@xxxxxxxxxxxxx>
Sent: Thu, January 13, 2011 5:18:26 AM
Subject: [SI-LIST] AW: ??: Re: ??: Re: How to measure the actual impedance of a
stripline with DSA8200(TDR)
Hi John,
How is Vdd and Vss connected on your Test coupon? To match the Polar results,
both have to be connected to give a clean GND return path.
BR
Gert
PS I hope this comes out right, from my previous mail the system cut off the
first 3 lines of text.
--------------------------------------------------------------------------
Absender ist HARTING Electronics GmbH & Co. KG; Sitz der Gesellschaft:
Espelkamp; Registergericht: Bad Oeynhausen; Register-Nr.: HRA 5596; persönlich
haftende Gesellschafterin: HARTING Electronics Management GmbH; Sitz der
Komplementär-GmbH: Espelkamp; Registergericht der Komplementär-GmbH: Bad
Oeynhausen; Register-Nr. der Komplementär-GmbH: HRB 8808; Geschäftsführer:
Edgar-Peter Duening, Torsten Ratzmann, Dr. Alexander Rost
-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von John Lee
Gesendet: Donnerstag, 13. Januar 2011 11:03
An: steve weir
Cc: SI LIST
Betreff: [SI-LIST] ??: Re: ??: Re: How to measure the actual impedance of a
stripline with DSA8200(TDR)
Hi, Steve, thanks again.
The stack-up is showed below, trace width is about 4mil.
Besides, the signal lines in L4 maybe is not sufficient to make it as a
reference plane.
>  > L1 signal    ----
4mil
>  > L2 Vdd    -----------
5mil
>  > L3 signal    ----    target layer
4mil
>  > L4 signal    ----
5mil
>  > L5 Vss   ------------
5mil
>Â Â > L6~L10Â Â symmetry
Best Regards!
John Lee
--- 11å¹´1月13日，周四, steve weir <weirsi@xxxxxxxxxx> 写é“：
å‘件人: steve weir <weirsi@xxxxxxxxxx>
主题: [SI-LIST] Re: 回å¤ï¼š Re: How to measure the actual impedance of a
stripline with DSA8200(TDR)
收件人: "John Lee" <venussoso@xxxxxxxx>
抄é€: "SI LIST" <si-list@xxxxxxxxxxxxx>
日期: 2011å¹´1月13æ—¥,周四,下åˆ5:09
John, no don't add one. Having one might have accounted for the error.
Your test coupon should look like the rest of your PCB. Where you have solid
planes in the PCB they should exist in the coupon.
How dense is the copper on L4 in the vicinity of the signal that is giving you
trouble? What are your dielectric thicknesses, and trace widths?
Steve.
John Lee wrote:
> Hi, steve,
> Thank you very much.
> Yes, i used the TDR.
> I did not add a 50ohm terminator in series manually, from the
> datasheet, i have found that the transmit cable itself already has
> 50ohm impedance, did i need to do so? And when i test the coupon in
> L3, the result is about 60ohm.
> Is there any chance that the result is effected by L5?
>
> Best Regards!
> John Lee
>
> --- *11å¹´1月13日，周四, steve weir /<weirsi@xxxxxxxxxx>/* 写é“：
>
>
>  å‘件人: steve weir <weirsi@xxxxxxxxxx>
>  主题: [SI-LIST] Re: How to measure the actual impedance of a
>Â Â stripline with DSA8200(TDR)
>  收件人: "John Lee" <venussoso@xxxxxxxx>
>  抄é€: "SI LIST" <si-list@xxxxxxxxxxxxx>
>  日期: 2011å¹´1月13æ—¥,周四,下åˆ3:59
>
>  How are you measuring? Are you using a TDR? If so, did you by
>any
>Â Â chance stick a 50 Ohm terminator in series with the transmit cable
>Â Â did you?
>
>
>
>Â Â Steve
>Â Â John Lee wrote:
>Â Â > Hi, SI experts,
>Â Â > I have a question about impedance measurement for DDR3 register
>Â Â memory.
>Â Â > I have a register memory that uses 10layers stack-up as follows:
>  > L1 signal    ----
>  > L2 Vdd    -----------
>  > L3 signal    ----    target layer
>  > L4 signal    ----
>  > L5 Vss   ------------
>Â Â > L6~L10Â Â symmetry
>Â Â >
>Â Â > Now I want to measure the impedance of L3's signal, so i got a
>Â Â PCB (without any resisters, or DRAMs) to do the test, but no
>Â Â matter Vdd or Vss I choose for the reference plane, the result is
>Â Â only about a half of theoretical value (for instance, the
>Â Â theoretical value is 60ohm, but the measurement result is more or
>Â Â less 28ohm).
>Â Â >
>Â Â > Is there anything i missed during the measurement? And how to
>Â Â get the actual impedance in this situation?
>Â Â >
>Â Â > Any reply will be appreciated, thanks in advance.
>Â Â > Best Regards!
>Â Â > John Lee
>Â Â >
>Â Â >
>Â Â >
>Â Â >
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>Â Â Steve Weir
>Â Â IPBLOX, LLC
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