[SI-LIST] AW: ??: Re: ??: Re: How to measure the actual impedance of a stripline with DSA8200(TDR)
- From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- To: "John Lee" <venussoso@xxxxxxxx>, "steve weir" <weirsi@xxxxxxxxxx>
- Date: Thu, 13 Jan 2011 11:18:26 +0100
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.
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-----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
> > L6~L10 symmetry
Best Regards!
John Lee
--- 11年1月13日，周四, steve weir <weirsi@xxxxxxxxxx> 写道：
发件人: steve weir <weirsi@xxxxxxxxxx>
主题: [SI-LIST] Re: 回复： Re: How to measure the actual impedance of a stripline
with DSA8200(TDR)
收件人: "John Lee" <venussoso@xxxxxxxx>
抄送: "SI LIST" <si-list@xxxxxxxxxxxxx>
日期: 2011年1月13日,周四,下午5:09
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
>
> --- *11年1月13日，周四, steve weir /<weirsi@xxxxxxxxxx>/* 写道：
>
>
> 发件人: steve weir <weirsi@xxxxxxxxxx>
> 主题: [SI-LIST] Re: How to measure the actual impedance of a
> stripline with DSA8200(TDR)
> 收件人: "John Lee" <venussoso@xxxxxxxx>
> 抄送: "SI LIST" <si-list@xxxxxxxxxxxxx>
> 日期: 2011年1月13日,周四,下午3:59
>
> How are you measuring? Are you using a TDR? If so, did you by
>any
> chance stick a 50 Ohm terminator in series with the transmit cable
> did you?
>
>
>
> Steve
> John Lee wrote:
> > Hi, SI experts,
> > I have a question about impedance measurement for DDR3 register
> memory.
> > I have a register memory that uses 10layers stack-up as follows:
> > L1 signal ----
> > L2 Vdd -----------
> > L3 signal ---- target layer
> > L4 signal ----
> > L5 Vss ------------
> > L6~L10 symmetry
> >
> > Now I want to measure the impedance of L3's signal, so i got a
> PCB (without any resisters, or DRAMs) to do the test, but no
> matter Vdd or Vss I choose for the reference plane, the result is
> only about a half of theoretical value (for instance, the
> theoretical value is 60ohm, but the measurement result is more or
> less 28ohm).
> >
> > Is there anything i missed during the measurement? And how to
> get the actual impedance in this situation?
> >
> > Any reply will be appreciated, thanks in advance.
> > Best Regards!
> > John Lee
> >
> >
> >
> >
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> --
> Steve Weir
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Steve Weir
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(707) 780-1951 Fax
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