[SI-LIST] Re: Do you really ship products at BER 10e-xx ?
- From: "Tom Waschura" <tom_waschura@xxxxxxxxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 12 Apr 2005 15:57:29 -0700
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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