[SI-LIST] Re: Eye diagram

Hi Stephen

This kind of effect can be from the device you are using as a driver. =
For complex transceivers where you have a lot of control you can create =
that situation if you do not program them correctly. You can also have =
simply a device that is not working properly. Do not concentrate only on =
the PCB board.

If you are using test equipment as a source, it is also possible in some =
equipment to change the cross-over point from 50%.



Jose

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On Behalf Of Stephen Greenhalgh
Sent: Dienstag, 17. Januar 2006 10:03
To: Si-List (E-mail)
Subject: [SI-LIST] Eye diagram

Recently I saw an eye diagram in which all the crossovers occurred at =
70-80% amplitude rather than the ideal 50%. Apart from this obvious =
defect, the eye looked pretty good. Ever since, I have been wondering =
what would cause this effect. My first thought was some difference =
between the +ve and -ve traces of the differential signal path, but I =
cannot formulate a theory that explains this satisfactorily. For =
example, if one trace were longer than the other, I would expect both =
positive-going and negative-going edges on the longer trace to be =
delayed relative to the shorter one, which would mean that some =
crossovers were raised, and others lowered, from the 50% level.
Is this a known phenomenon that I have somehow completely missed? I =
would be glad for any explanation or suggestion that anyone can offer.

Stephen Greenhalgh

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