[SI-LIST] Re: Do you really ship products at BER 10e-xx ?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: tom_waschura@xxxxxxxxxxxxxxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 12 Apr 2005 18:30:25 -0700
Tom, Dr. Demming would be proud to hear what you have said. If we have
little random variation then almost any sample will provide a reliable
prediction of performance. OTOH...
I think that this goes to Andy's problem. The things that tend to upset
serial links for substantial periods are those that knock out the
PLLs: Reference clock stability, power supply hits, or EFT / ESD
hits. It might be that there is a resonance in the channel. However,
rather than trying to use random patterns to find the effects, I would
prefer to use the S parameter data to locate the peaks and notches and then
issue patterns that excite them.
Regards,
Steve
At 03:57 PM 4/12/2005 -0700, Tom Waschura wrote:
>Many failure types I've seen fall into the category of causing terrible
>error rates, true; however, many others fall into a more subtle
>category--and these are typically much more difficult to diagnose. In
>general, more random jitter is worse as these PDFs have infinite tails. Any
>frequency null or notch can cause pattern dependent resonances which might
>convolve with other circumstances to cause bit errors. If it takes a PN31
>pattern to stimulate something, the bit error rate might be 1E-9 just based
>on the pattern length. Passing a go/no-go BER test does not give anyone
>insight into what type of bit error is lurking.
>
>Bit error rate contours may help the notion of "waiting for 10E-12
>measurements". This allows a predicted result based on considerably higher
>measurement data. These predictions only follow the random components of
>jitter and would want to be based on real measurement depth at least past
>the test pattern period.
>
>Anyway. Having solved bit error problems in links, components and systems
>for years; I'd hesitate from saying all I needed was a go/no-go test based
>on some rough "terrible BER". This would keep you moving, but your scrap
>pile would grow. I'd say that even just separating out random,
>data-dependent and periodic bit errors in production failures along with
>someone who can diagnose based on this information is a significantly
>net-positive benefit.
>
>Tom
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>Behalf Of Chris Cheng
>Sent: Tuesday, April 12, 2005 2:47 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Do you really ship products at BER 10e-xx ?
>
>I have heard similar case from a third party and the customer service
>engineer starts to explain, "of course, its cosmic rays" with a straight
>face. I can't say how many people remains sitting on their chairs and not
>flipping over after that.
>But it is not my personal experience so that's why I am curious.
>Thanks for sharing though.
>
>-----Original Message-----
>From: Henson, Bradley S [mailto:Bradley.S.Henson@xxxxxxxxxx]
>Sent: Tuesday, April 12, 2005 2:35 PM
>To: Chris.Cheng@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: RE: [SI-LIST] Do you really ship products at BER 10e-xx ?
>
>
>This could make an interesting topic. I have to say that in general, I
>have noticed the same trend: Links work so well the BER is hard to
>determine (lots of test time or link-stress)-or- the links are totally
>messed up. However, I did get called in to troubleshoot a Fibre channel
>application that was just marginal on some of the links. By that I mean
>they would almost make the spec 1E-12 BER sometimes, but usually fell
>short. Some days they operated considerably poorer than 1E-12, but not
>pure garbage.
>
>-----Original Message-----
>From: Chris Cheng [mailto:Chris.Cheng@xxxxxxxxxxxx]
>Sent: Tuesday, April 12, 2005 1:49 PM
>To: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Do you really ship products at BER 10e-xx ?
>
>
>I've been shipping Gb/s serial products for a while and have my share of
>fail parts. However, I have yet to see a physical channel that is not
>either working like a charm or just fall on its face and barfing errors
>like crazy. Sure, chips or disk can fail and generates errors but no
>flaky channels that spits an error every other hour or days. To me, the
>channel is either have a BER that is near 1 (barfing errors like crazy)
>or near 0 (never fail, or at least approaching the life of the product
>it is attached to).
>Are we just kidding ourselves with these fancy BER analyzers or jitter
>instruments ? Do you really let a machine runs at say BER 10e-12 and say
>"ah ha, it only fails once a day and let's ship it" ? Is BER really
>meant for IEEE spec committees and not for real engineers who actually
>have to ship a product ?
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