[SI-LIST] AW: [SI_LIST] Rj pattern Dependency
- From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- To: "ah.vinod@xxxxxxxxx" <ah.vinod@xxxxxxxxx>, SI-LIST <si-list@xxxxxxxxxxxxx>
- Date: Fri, 5 Jul 2013 09:09:46 +0000
Hi Vinod,
there is the so called Data Dependent Jitter which somewhat relates to the
worst case pattern used in BERT. It is caused by low amplitude bits when the
risetime at the receiver is too low to reach the amplitude settling point (very
often the worst pattern is 0000001000000) This closes the eye vertically and
horizontally which means added Jitter in some ways.
This kind of Jitter is affected by losses, GND return, Mode conversion, stub
effect and other disturbance of the passive channel.
I don't know if the Measurement and simulation tools can decompose this Jitter.
I hope this helps.
BR
Gert
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im
Auftrag von vinod ah
Gesendet: Freitag, 5. Juli 2013 09:12
An: SI-LIST
Betreff: [SI-LIST] [SI_LIST] Rj pattern Dependency
Hi All,
I am seeing one more weird issue on Jitter. Below is the same.
I am trying to do PCIE3 Add-in card eye calibration to meet eye height of 46mV
& eye width of 41ps. So i had to set Rj to 30% UI & Sj to 17% UI @ 8Gbps on
BERT to meet the eye width spec for testing PCIe3 Rx circuitry.
What i see is when i change the pattern in BERT from
PCIE_A_ComplianceP7_B_Keep.ram to PCIE_modified_Compliance_Lane0.ram,
i see Rj value shooting up from 2.4ps rms to 9ps rms !!!!. The setup is
untouched during the change of pattern. In fact i get 2.4ps rms Rj in
oscilloscope/SIGTEST with clock pattern with same setup.
Also measured the BERT output directly, there I still see ~2.4ps rms Rj
(irrespective of pattern used), but when i pass the signal through test setup
(BERT--> Riser card --> CBB3 --> CLB3 --> Scope), i see increase in Rj with
pattern change. Riser card + CBB3 + CLB3 is passive 20dB loss FR4 channel and
no power src is connected to these.
As channels cannot introduce Rj, where is the extra Rj coming from? Is there
any pattern dependency along with channel effects is causing this increase in
Rj or is it Jitter post processing tool getting confused with Rj & Dj in this
scenario after signal going through the 20dB channel?
I am using SIGTEST as well as Jitter decomposition software in scope and both
the results match.
Regards
Vinod A H
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