[SI-LIST] Re: Do you really ship products at BER 10e-xx ?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>, <tom_waschura@xxxxxxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 13 Apr 2005 10:28:29 -0700
Ken, for any given notch / peak below clk/2 translates to a run length of
Fclk / ( 2 * Fnotch_peak ). Fractional values can be interpolated with
repeating patterns on either side of the notch / peak.
Regards,
Steve
At 11:06 AM 4/13/2005 -0600, Ken Cantrell wrote:
>Steve,
>So how is the correlation between data pattern and S-parm determined?
>Thanks,
>Ken
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
>Sent: Tuesday, April 12, 2005 7:30 PM
>To: tom_waschura@xxxxxxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: Do you really ship products at BER 10e-xx ?
>
>
>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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