[SI-LIST] Re: [Help] How to do termination in differential signal with series termination ?
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: "'King Da'" <yardala@xxxxxxxxx>, "'steve weir'" <weirsi@xxxxxxxxxx>
- Date: Fri, 05 Dec 2008 10:45:02 -0800
It sounds like it is time to dust off that simulator tool and see what you
can get away with in your circuit based on the real layout you are working
with. If you put in a source termination you are going to lose half of your
signal amplitude, can you live with that? Does your channel have additional
losses that will further reduce the signal amplitude? How sensitive is your
receiver? Source and load terminations may be appropriate for an analog
signal if you require to preserve signal fidelity but may not be required
for a digital signal. Do you have other reflections in your channel that
are going to swamp out any gains with elaborate termination schemes?
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of King Da
Sent: Friday, December 05, 2008 6:41 AM
To: steve weir
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: [Help] How to do termination in differential signal
with series termination ?
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> 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>>
>> 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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>> Teraspeed Consulting Group LLC 121 North River Drive Narragansett,
>> RI 02882
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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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