[SI-LIST] Re: [Help] How to do termination in differential signal with series termination ?

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: King Da <yardala@xxxxxxxxx>
  • Date: Thu, 04 Dec 2008 22:53:20 -0800

King, the line to line impedance ( odd mode ) is roughly twice the line 
to reference impedance of each line ( even mode ).  Terminating the 
energy from both modes is desirable.   Maybe you have special 
requirements, but I would normally terminate both modes at the 
receiver.  Eric's book discusses both pi and T end terminations to do that.

Steve
King Da wrote:
> Dear Steve,
> Thanks for your answer, but I don't really know what your mean "you've 
> got your impedances backward" ? Could you explain more detail ?
>  
> I use 100 Ohm for differential termination for diffrential signal 
> and also want use series termination for each line for common mode 
> signal termination. How to choose the series resistor value ?
>
>  
> On 12/5/08, *steve weir* <weirsi@xxxxxxxxxx 
> <mailto:weirsi@xxxxxxxxxx>> wrote:
>
>     Parallel terminations absorb energy at the far end and is related
>     only to the channel, not the driver Z.    Also, you've got your
>     impedances backward.
>
>     Steve.
>     King Da wrote:
>
>         Hi,Folks,
>         I have a differential pair which odd mode impedance is 48 Ohm
>         and even mode
>         impedance is 108 Ohm by TDR measurement.
>         I would like use 100 Ohm for differential termination at far
>         end, but how to
>         choose series termination resistor for each trace at near end?
>
>         I refered Bogatin's "Signal Integrity:Simplified" book that
>         said parallel
>         termination R2 equal Zeven, So, I should use 108 Ohm subtract
>         20 Ohm of my
>         driver's Ro is 88 Ohm for my series termination at near end,
>         am I right?
>
>         The Rseries = 108 (Zeven) - 20 (Driver's Ro) = 88 Ohm, right ?
>
>         Does the differential termination resistor is 100 Ohm better
>         than 91Ohm ?
>
>         Thanks,
>
>         Yardala
>
>
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>     -- 
>     Steve Weir
>     Teraspeed Consulting Group LLC 121 North River Drive Narragansett,
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-- 
Steve Weir
Teraspeed Consulting Group LLC 
121 North River Drive 
Narragansett, RI 02882 

California office
(866) 675-4630 Business
(707) 780-1951 Fax

Main office
(401) 284-1827 Business 
(401) 284-1840 Fax 

Oregon office
(503) 430-1065 Business
(503) 430-1285 Fax

http://www.teraspeed.com
This e-mail contains proprietary and confidential intellectual property of 
Teraspeed Consulting Group LLC
------------------------------------------------------------------------------------------------------
Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC

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