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

Yardala, in common circumstances the termination you propose is unusual 
and would cause more problems than it would solve.  My advice is to keep 
things simple and stick with termination at the receiver.  Eric's book 
does an excellent job of discussing the options.  Your alternative is 
to: dig in, do the homework, and figure out what you really have to get 
done and the viable choices for doing so.  I would be very surprised if 
after doing the homework you will find your proposed scheme viable.

Steve.

King Da wrote:
> Steve,
> I know how to use pi termination at far end, but I just consider to 
> reduce power consumption and layout limitation. I measured odd and 
> even mode impedance (48 and 108 Ohm) by Tek TDR, but I don't know 
> which value is the target when I use series termination for each line ?
>  
> Does it work that use a parallel difference termination and two series 
> termination in your opinion?
>  
> Kingda
> On Fri, Dec 5, 2008 at 2:53 PM, steve weir <weirsi@xxxxxxxxxx 
> <mailto:weirsi@xxxxxxxxxx>> wrote:
>
>     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> <mailto: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,
>     RI 02882
>     California office
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>     (707) 780-1951 Fax
>
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-- 
Steve Weir
Teraspeed Consulting Group LLC 
121 North River Drive 
Narragansett, RI 02882 

California office
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(707) 780-1951 Fax

Main office
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http://www.teraspeed.com
This e-mail contains proprietary and confidential intellectual property of 
Teraspeed Consulting Group LLC
------------------------------------------------------------------------------------------------------
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