[SI-LIST] Need help with DisplayPort

[Joel Brown]

Hi,
We are working on a new project where we have a DisplayPort (DP) to HDMI
bridge at the input.
When we look at the DP signals on the scope the higher frequencies are
obviously attenuated, but we are able to pass the signal through to an FPGA
and get a display on the LCD. The DP interface has all four data channels
active.

When we connect the same source and cable to an eval board that has the
same exact DP to HDMI bridge chip, the DP signals look much better, there
is no noticeable high frequency attenuation. The overall signal is somewhat
attenuated at about 200 mV pk-pk.
In this case there are only two DP data channels active compared to four
above.

We cannot come up with a reason for the difference in behavior between the
two circuits.
My best theory is that DP training is causing the source to use different
settings (signal swing, de-emphasis) between the two boards. I am thinking
higher de-emphasis is being used with the eval board setup. But we have no
way to know what is happening during training or what the results are. The
traces from the DP connector to the DP to HDMI bridge chip are pretty short
so I don't think that would explain the difference in behavior.

Thanks for any ideas / advice

Joel


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-***@freelists.org with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-***@freelists.org with 'help' in the Subject field


List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:
http://www.freelists.org/archives/si-list

Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu

[subeg singh sran]

Hi Joel,
Please check board layout of evalkit if lane are too close more cross talk.
In serdes RX has internal eye scan check if eye is margin and check BER.

Check which jitter parameters are exceeding limits.
Check for power supply noise.


Thanks ,
Subeg

Post by Joel Brown
Hi,
We are working on a new project where we have a DisplayPort (DP) to HDMI
bridge at the input.
When we look at the DP signals on the scope the higher frequencies are
obviously attenuated, but we are able to pass the signal through to an FPGA
and get a display on the LCD. The DP interface has all four data channels
active.
When we connect the same source and cable to an eval board that has the
same exact DP to HDMI bridge chip, the DP signals look much better, there
is no noticeable high frequency attenuation. The overall signal is somewhat
attenuated at about 200 mV pk-pk.
In this case there are only two DP data channels active compared to four
above.
We cannot come up with a reason for the difference in behavior between the
two circuits.
My best theory is that DP training is causing the source to use different
settings (signal swing, de-emphasis) between the two boards. I am thinking
higher de-emphasis is being used with the eval board setup. But we have no
way to know what is happening during training or what the results are. The
traces from the DP connector to the DP to HDMI bridge chip are pretty short
so I don't think that would explain the difference in behavior.
Thanks for any ideas / advice
Joel
------------------------------------------------------------------
http://www.freelists.org/webpage/si-list
http://tech.groups.yahoo.com/group/si-list
http://www.freelists.org/archives/si-list
http://www.qsl.net/wb6tpu

------------------------------------------------------------------
To unsubscribe from si-list:
si-list-***@freelists.org with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-***@freelists.org with 'help' in the Subject field


List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:
http://www.freelists.org/archives/si-list

Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu

[Havermann, Gert]

Joel,
if you see high frequency attenuation, then there is too much capacitance in the link. Maybe some stubs or coupling. The missing high frequency content means worse risetime and thus less horizontal eye opening, so the signal looks degraded. The link training is assuming an almost linear Insertion Loss, to work properly. I would check IL, RL and crosstalk. Or TDR into the inputs to check for discontinuities.

Best Regards
Gert


----------------------------------------
HARTING Stiftung & Co. KG | Postfach 11 33, 32325 Espelkamp | www.HARTING.com
Persönlich haftende Gesellschafterin:
HARTING Führungsstiftung | Amtsgericht München | HRA 108479 | München
Vorstand: Dipl.-Kfm. Philip F. W. Harting (Vorsitzender), Dipl.-Kffr. Maresa W. M. Harting-Hertz, Dipl.-Kfm. Dr.-Ing. E. h. Dietmar Harting,
Dipl.-Hdl. Margrit Harting, Dr. rer. nat. Frank Brode, Dipl.-Ing. (FH) Dipl.-Wirtsch.-Ing. (FH) Andreas Conrad, Dr. iur. Michael Pütz
Sitz der Gesellschaft: Espelkamp | Amtsgericht Bad Oeynhausen | HRA 9021 | UST-ld Nr. DE812136745

-----Original Message-----
From: si-list-***@freelists.org <si-list-***@freelists.org> On Behalf Of Joel Brown
Sent: Wednesday, October 31, 2018 1:22 AM
To: SI-List <si-***@freelists.org>
Subject: [SI-LIST] Need help with DisplayPort

Hi,
We are working on a new project where we have a DisplayPort (DP) to HDMI bridge at the input.
When we look at the DP signals on the scope the higher frequencies are obviously attenuated, but we are able to pass the signal through to an FPGA and get a display on the LCD. The DP interface has all four data channels active.

When we connect the same source and cable to an eval board that has the same exact DP to HDMI bridge chip, the DP signals look much better, there is no noticeable high frequency attenuation. The overall signal is somewhat attenuated at about 200 mV pk-pk.
In this case there are only two DP data channels active compared to four above.

We cannot come up with a reason for the difference in behavior between the two circuits.
My best theory is that DP training is causing the source to use different settings (signal swing, de-emphasis) between the two boards. I am thinking higher de-emphasis is being used with the eval board setup. But we have no way to know what is happening during training or what the results are. The traces from the DP connector to the DP to HDMI bridge chip are pretty short so I don't think that would explain the difference in behavior.

Thanks for any ideas / advice

Joel


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-***@freelists.org with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-***@freelists.org with 'help' in the Subject field


List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:
http://www.freelists.org/archives/si-list

Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-***@freelists.org with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-***@freelists.org with 'help' in the Subject field


List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:
http://www.freelists.org/archives/si-list

Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu

[Chris Chalmers]

Joel,

Can you not look at the signal waveforms at the source to see if they are noticeable different
between the two. This might indicate if the link manager has set up more pre-emphasis or signal swing on one
setup rather than the other. Also if you have access, read the MSA parameters to find out what
it has set up.

Another thing is, are you definitely carrying the same resolution and refresh rate on both
setups? Normally the edid holds this information. If the bandwidth required was near a transition
it could use two lanes, higher line rate or 4 lanes and lower line rate. Really the link manager is
black magic ;-)


-----Original Message-----
From: si-list-***@freelists.org [mailto:si-list-***@freelists.org] On Behalf Of Joel Brown
Sent: 31 October 2018 00:22
To: SI-List
Subject: [SI-LIST] Need help with DisplayPort

Hi,
We are working on a new project where we have a DisplayPort (DP) to HDMI
bridge at the input.
When we look at the DP signals on the scope the higher frequencies are
obviously attenuated, but we are able to pass the signal through to an FPGA
and get a display on the LCD. The DP interface has all four data channels
active.

When we connect the same source and cable to an eval board that has the
same exact DP to HDMI bridge chip, the DP signals look much better, there
is no noticeable high frequency attenuation. The overall signal is somewhat
attenuated at about 200 mV pk-pk.
In this case there are only two DP data channels active compared to four
above.

We cannot come up with a reason for the difference in behavior between the
two circuits.
My best theory is that DP training is causing the source to use different
settings (signal swing, de-emphasis) between the two boards. I am thinking
higher de-emphasis is being used with the eval board setup. But we have no
way to know what is happening during training or what the results are. The
traces from the DP connector to the DP to HDMI bridge chip are pretty short
so I don't think that would explain the difference in behavior.

Thanks for any ideas / advice

Joel


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-***@freelists.org with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-***@freelists.org with 'help' in the Subject field


List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:
http://www.freelists.org/archives/si-list

Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-***@freelists.org with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-***@freelists.org with 'help' in the Subject field


List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:
http://www.freelists.org/archives/si-list

Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu