[SI-LIST] Re: What are eye patterns
- From: "Russell D. Moser" <r.moser@xxxxxxxxxxxxxxxxx>
- To: <rakesh@xxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 28 Dec 2004 10:29:29 -0500
If one could imagine a simulation world where a simple pulse was the
only stimulating function and the resultant response evaluated the
ability of a system to transfer information, then our tasks SI engineers
would be simple. However such a condition is rarely the case. In
information systems there are methods of evaluating (simulating)
components concatenated in such a way as to mimic an interconnection
channel. As these "channels" likely are of such length that multiple
pulses can co-exist, engineers developed pulse trains that would be used
as test patterns.
These patterns can go from a few pulses to many. The "eye-pattern"
provides a vehicle for the overlay of successive pulses (bits) onto a
common axis so that humans may interpret the results. Such dynamics as
ISI (Inter-Symbolic-Interference) or data-dependent-jitter are two
examples of certain system-level issues that design engineers must be
aware of.
ISI can be thought of as the "wandering" of a pulse-train in voltage
levels due to the voltage level of the preceding pulse. Jitter is the
"wandering" in time. When the eye pattern is created via the overlay of
successive pulses and oriented onto a common set of pulses, such
variation in voltages can be seen as an opening where the time variation
(jitter) is the delta time of the pulses where they cross a common
threshold.
Silicon mfgs have taken this eye-pattern and incorporated it into their
datasheets with an eye template that shows what is an acceptable eye
pattern.
In closing, eye patterns can be simulated (with accuracy based on the
models and their ability to capture the dynamics of physical devices) or
tested in the lab. Hopefully both are done and correlated to improve the
science of both.
HP has (had) some fine papers as I am sure that others exist as well.
AMP/tyco, SAMTEC and others (as I am a former connector/cable person)
also did some fine work and published papers that may be available.
DESIGNCON seems to always treatises on such subjects.
Hope this helps some!
Regards,
___________________
Russell D. Moser
Orion Group
r.moser@xxxxxxxxxxxxxxxxx
www.theoriongroup.net
US Phone: 717.914.0116
US Facsimile: 717.704.0051
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of rakesh
> Sent: Tuesday, December 28, 2004 12:39 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] What are eye patterns
>
> Hi,
>
> I am interested to know what exactly is an "EYE-Pattern" and
> how does one use it while testing a high speed signal /link.
>
> Also if there are any white papers or references, I would
> like to have them.
>
> Thanx for all the help.
>
> regards
>
> Rakesh Mehta
> BitMapper Integration Technologies Pvt. Ltd.
> Pune : 411 038 - India
> Email : rakesh@xxxxxxxxxxxxx url : www.bitmapper.com
> Tel : 020-25386927 / 28 / 29 / 30
>
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