[SI-LIST] Re: Routing diff pair HDMI signals at 85 Ohms as opposed to 100 Ohms reduces radiation?
- From: "Orin Laney" <olaney@xxxxxxxxx>
- To: <vinu@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 Dec 2012 19:19:00 -0800
An industry standard is only as good as the problems it solves. If the
electrons disagree, how are you going to argue with them? Example: a design
is constrained to run differential signals through a series of 38999 series
aerospace connectors. Adjacent pins TDR @ 85 ohms. Which is better, 100
ohm cables and traces, or 85 ohms end to end? This is an actual design I
handled, not a hypothetical one.
Note that 100 ohms is only a nominal value. +/-15% is a common system
tolerance that says everything should play together for impedances as low
as... 85 ohms! IMHO, to guarantee data integrity the actual cliff edge
ought to be not less than 20%. Not that we aren't asked to push things to
the hairy edge, design with typical parameters rather than guaranteed, etc.
Orin
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Vinu Arumugham
Sent: Tuesday, December 18, 2012 5:56 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Routing diff pair HDMI signals at 85 Ohms as opposed
to 100 Ohms reduces radiation?
Right now Company A optimizes for 85 ohm, Company B for 100 ohm and we have
to make these parts talk to each other.
We end up with the worst of both worlds on our boards. We have industry
standards for a reason!
Thanks
Vinu
On 12/18/2012 05:05 PM, Lee wrote:
> Just one man's opinion! As I often tell my students, I'm from
> Missouri the "show me" state and need a lot of convincing to change my
> ways! I know that the 85 ohm spec is being placed on a number of
> designs based on the paper that was sited. I also know that this makes
many things more difficult.
>
> -----Original Message-----
> From: Michael Vrbanac
> Sent: Tuesday, December 18, 2012 9:35 AM
> To: leeritchey@xxxxxxxxxxxxx
> Cc: michaelv@xxxxxxxxxxxxxxxx ; jeff.loyer@xxxxxxxxx ;
> si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Routing diff pair HDMI signals at 85 Ohms as
> opposed to 100 Ohms reduces radiation?
>
> I'm with you on that one, Lee. There is just too much going on when RF
> measurements are made in environments that are significantly unmatched.
>
> Best Regards,
>
> Michael Vrbanac
>
> On 12/17/2012 3:32 PM, Lee wrote:
>> I'm not sufficiently convinced by the paper that I plan to deviate
>> from 50
>> /100 ohm which matches most connectors and test equipment.
>>
>> -----Original Message-----
>> From: Joseph.Schachner@xxxxxxxxxxxxxxxxxx
>> Sent: Monday, December 17, 2012 1:27 PM
>> To: jeff.loyer@xxxxxxxxx
>> Cc: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: Routing diff pair HDMI signals at 85 Ohms as
>> opposed to 100 Ohms reduces radiation?
>>
>> Re: "Much of the reasoning for 85 ohms is outlined in the paper
>> "Improve Storage IO Performance by Using 85Ohm Package and Motherboard
Routing"..."
>> I bought that paper today and read it, after seeing your reference.
>> The paper seeks to prove that 85 ohms is in fact better, and has a
>> small (one
>> sentence) explanation in the first section that gives a couple of
>> reasons why that should be so. I think I am within the license terms
>> if I quote that one sentence:
>> "Generally speaking, the reasons for 85Ohm design over 100Ohm include
>> less loss, ease in routing (cost saving), and better overall
>> impedance match (and hence better interconnect performance) when via
>> on board and vertical path in package are considered. "
>>
>> The rest of the paper seems focused on demonstrating, by simulation
>> and measurement of a particular structure, that 85 ohm design is in
>> fact better. It does not go further into the reasoning behind why we
>> expect that that is so. Is there something more that you could say
>> about that? It does not give any guidance in the way vias should be
>> constructed to yield better impedance, for example.
>>
>> ---- Joe S.
>>
>> ------------------------------------------------------------------
>> To unsubscribe from si-list:
>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>> or to administer your membership from a web page, go to:
>> //www.freelists.org/webpage/si-list
>>
>> For help:
>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>> List forum is accessible at:
>> http://tech.groups.yahoo.com/group/si-list
>>
>> List archives are viewable at:
>> //www.freelists.org/archives/si-list
>>
>> Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2013.0.2805 / Virus Database: 2637/5966 - Release Date:
>> 12/17/12
>>
>> ------------------------------------------------------------------
>> To unsubscribe from si-list:
>> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>>
>> or to administer your membership from a web page, go to:
>> //www.freelists.org/webpage/si-list
>>
>> For help:
>> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>>
>>
>> List forum is accessible at:
>> http://tech.groups.yahoo.com/group/si-list
>>
>> List archives are viewable at:
>> //www.freelists.org/archives/si-list
>>
>> Old (prior to June 6, 2001) list archives are viewable at:
>> http://www.qsl.net/wb6tpu
>>
>>
>>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List forum is accessible at:
> http://tech.groups.yahoo.com/group/si-list
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2013.0.2805 / Virus Database: 2637/5966 - Release Date:
> 12/17/12
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List forum is accessible at:
> http://tech.groups.yahoo.com/group/si-list
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
> .
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
