Hi,
A customer of mine is suffering this moment from a bad operating LVDS link. They hope they can use your knowledge and maybe of other TI engineers to help us in determining the root cause of our issue.
They get intermittent errors that are traced back to errors on our LVDS link.
The LVDS communication links are from a module (Module 1) to two other modules (Module 2) as indicated below.
Module 1 selects via a X-point (DS90CP22M-8/NOPB) to which Module 2 it communicates.
They have measured some strange signal behavior in the LVDS link from Module 2 (transmitter part) to Module 1 (receiver part)
They measured with a Lecroy Scope (BW 4GHz / 20Gs/s) on the receiver part of Module 1.
In normal situation we see following Carrier signal:
Green signal is Rx_P single ended.
Red signal is Rx_N single ended.
Yellow signal is differential signal (with math option scoop: Rx_P - Rx_N )
Sometimes however the signal looks very bad:
This is however intermittent, which makes finding the root cause difficult.
They know the signal line is not ideal. They were not able to have a decent 100 Ohm line for the whole interface.
If you want, they can provide the length of the different interface parts.
The red part (cable part connect to Module 2) is a twisted pair cable, with unknown impedance. Unfortunately we were not able to use a neat cable here, due to lack of space.
However the eye pattern measured during qualification of this solution looked fine.
If you want they can share a picture of serial-nr print of two serializer that have the issue.
At the receiver the signal looks sometimes ok, and sometimes really bad as shown above. In the struggle to get the root cause for this they have some questions:
1. Do you know of any issues with the serializer (or a batch of serializer) DS92LV1021A that can cause this issue?
2. Can reflections cause the serializer (DS92LV1021A) on Module 2 to malfunction?
3. Do you have any idea on what the cause of our issue can be (maybe also looking at the picture of the bad signals displayed above)?
Thank you for your help.
