[SI-LIST] Re: 回复： Re: How to measure the actual impedance of a stripline with DSA8200(TDR)
- From: steve weir <weirsi@xxxxxxxxxx>
- To: John Lee <venussoso@xxxxxxxx>
- Date: Thu, 13 Jan 2011 01:09:21 -0800
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
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> www.ipblox.com
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
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