PTN3460I video distortion?

[djrs]

Hi. We are using the PTN3460I (F1 firmware) to convert DisplayPort to LVDS. We actually have a three display setup, driven from our computer -- 2 DP channels (using PTN3460I) and 1 DVI channel. Every now and then upon boot-up, one of the DP channels gives a very distorted/"jittery" display. See the attached image. If we let it sit long enough the distortion/"jitter" will eventually go away. Can you tell me what is happening here? Is this a timing or sync issue?

It has taken anywhere from 2-15 reboots to get the distorted screen. Please advise.

Thanks

[reyes]

Hi,

Never seen a similar issue before, but my guess is that the distortion you are seen could be caused by crosstalk between the differential signals at the board(s) or in the cable. A possible solution would be these differential signal bypassing by keeping the output signals as close to the input signals as possible.

Also, make sure that you have the proper external AC-coupling capacitors.

Have a great day,
Jose

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[djrs]

Hi Jose. We are still seeing the issue I posted about in the original message. This time we are seeing it with the Versalogic VL-EPH-V6. We currently have firmware F6, with Frequency Averaging Filter turned ON and PLL set to 6.25%.

We suspect that the Frequency Averaging Filter being ON may be causing our boot-up/wake-up DISTORTION. And we suspect that setting PLL to 6.25% is what fixed our FLICKER issue. Does this make sense to you? When we upgraded the PTN3460I from F1 to F2 we left configuration register 0x99 set to '00', which results in a PLL of 1.56%. We'd like to further support this theory. Would you please let us know what the "default" PLL value was in older firmware versions that did not have the adjustable 0x99 configuration register?

Thanks.

[djrs]

Hi Jose. Thanks for the response. Currently there is only 1.25" - 1.5" between the input miniDP connector and output LVDS connector, with the PTN3460I in between. Trace wise, effort was made to match the pair lengths as closely as possible. I can send you an image of our PCB layout in private if that will help.

We built up another unit to test. We have two separate displayPort channels driving two independent PTN3460I chips. Although we have not seen the original "jitter" issue during any reboots yet, we have seen a different video issue. This time, we see a quick flicker of the displays every now and then. It looks like the screen shifts to the left for a split second and then corrects itself. Please see the attached GIFs to see the flicker occurring in slow-motion. Again, real-time speeds this flicker lasts only a split second. We see this flicker on both displays (both channels), and it happens randomly it seems. We may have to wait 10-15 minutes for a flicker effect on a particular display,  but once it happens it may happen once or may happen 3-4 more times within the next minute. Two different videos show the two different ways we saw the flicker occur in slow-motion.

Do you have any ideas about the flickering? Do you think it's related to the boot-up "jitter" issue seen on the other unit? Thank you for your prompt response.

[djrs]

We decided to revert back to F1 firmware on this new build. After 2 hours with the F1 firmware of we have seen no more flicker. With the F2 firmware we would have seen a lot of flicker by now. We will continue testing but it's looking like the F2 firmware is causing the flickering. What is different in the F2 firmware that would potential cause this problem?

[reyes]

Hi,

While doing video mode (single, clone, extend mode) change frequently, the video noise may be observed because of Frequency Averaging Filter is always enabled in the firmware F1. Firmware F2 has implemented a function which Frequency Averaging Filter can be enabled or disabled through setting in the configuration register 0x8E bit 6 to solve this interoperability issue (default is off).

Jose

[djrs]

Also, it's important to note that we upgraded to firmware F2 for the new build (that has this random flickering).

[djrs]

In case there was a problem with my GIF attachments, here are two slowed-down videos showing the flicker. To note, the GIFs are slowed down much more.