[SI-LIST] Re: Routing diff pair HDMI signals at 85 Ohms as opposed to 100 Ohms reduces radiation?
- From: Vinu Arumugham <vinu@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 18 Dec 2012 17:55:32 -0800
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.
>>
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