[SI-LIST] FW: The standard eye mask test
- From: "chen, jinhua" <chen_jinhua@xxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 22 May 2003 11:06:36 -0400
Hi,
Since I posted my last message. There is no any public responses.
And there is not much private responses as well.
Here I forward one of the response. I don't think there is an easy
Answer to my original question. But we should an industrial standard
to follow. I don't see a clear description about this issue in FC spec.
Anybody like to shed more light on this issue?
Thanks!
Jinhua
-----Original Message-----
From: herbert_lage@xxxxxxxxxxx [mailto:herbert_lage@xxxxxxxxxxx]
Sent: Thursday, May 22, 2003 9:48 AM
To: chen_jinhua@xxxxxxx
Subject: RE: [SI-LIST] The standard eye mask test
Hi Jinhua,
Since no one seems to have re-plied, I have inquired with our application
experts for fiber-optics. Please find below our interpretation on how to
carry out Fibre-Channel jitter measurements. This may not provide a complete
answer but will hopefully get you started. Please note that some of it may
strictly speaking only apply to optical eye pattern measurements. Here is
the response:
Fibre channel FC-PI (rev 13 = final) calls out OFSTP-4 (EIA/TIA 526-4A
Optical Eye Pattern Measurement Procedure, 1997) in clauses 6.2.1 and 6.3.1
(optical interface specifications). Most of the mask testing will be defined
in this reference ... except for code pattern.
a.) Number of samples be taken for each test (hundreds/thousands/forever?).
FC-PI (rev 13, now officially an ANSI document) Appendix A,
Clause A.1.2.1 states "over at least 1000 bit times".
1000 samples seems to be the most common number in use (at
various sites) for DCA based eye mask measurements.
b.) What kind of trigger signal used for the test. Use recovered clock
from CDR, or use golden PLL clock?
FC-PI A.1.2.1 makes a suggestion of a recovered clock (ie. "derived
from the data stream") but only mandates the use of a bit-rate trigger.
For the derived clock the document refers to NCITS-TR-25:1999 ("MJS",
Methodologies for Jitter Specification) for specifics. See clauses
D2.2 and D2.3 which form the basis of eye mask jitter testing ... an
issue related to eye mask testing.
For lab testing most companies seem to use the trigger output of a
BERT tester which is presumed equivalent to a low frequency tracking
golden PLL.
c.) What kind of data patterns should be used (CJPAT/PRBS or others)?
Fibre Channel FC-PI rev 13 hints at patterns in appendix A.1.2.1
(by referring to the MJS document). Unfortunately, it appears that
the MJS document does not specifically advise which of its patterns
are recommended for eye mask testing.
Our recommended patterns are K28.5 or PRBS 2^7-1 ... as they both
run from min to max run length (ie. 1-5 bits for 8B/10B). As the run
length for PRBS is slightly longer it is incrementally more challenging,
but usually not noticeably so. Using valid 8B/10B traffic is most
relevant to the application.
d.) Not any eye mask violation can be accepted? Or a few violations can
be accepted for TX output eye mask?
No violations is pass. One violation is fail. The sample size is
already quite small to guarantee error free performance.
Best Regards,
Herbert.
-----Original Message-----
From: chen, jinhua [mailto:chen_jinhua@xxxxxxx]
Sent: 15 May 2003 22:00
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] The standard eye mask test
Hi,
I know there must be someone in the list can give me help in this topic.
The eye mask test is used in a lots standard specs for signal quality test.
For example, FC standard specified the TX output eye mask and receiver input
eye mask.
When the eye patterns are measured in the lab, there are so many variations.
The uncertainty of anyone of those variations can make the test fail or
pass. Here I list a few variations:
a.) Number of samples be taken for each test
(hundreds/thousands/forever?).
b.) What kind of trigger signal used for the test. Use recovered clock
from
CDR, or use golden PLL clock?
c.) What kind of data patterns should be used(CJPAT/PRBS or others)?
d.) No any eye mask violation can be accepted? Or a few violations cab
be
accepted for TX output eye mask?
In general, is there any STANDARD PROCEDURES to make eye mask measurement
with those standard specs?
Thanks!
Jinhua Chen
Signal Integrity
EMC Corp.
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