DS90UB926Q-Q1: SSCG mode issue

David,

I'm not sure what you are asking here - both 926 and 934 are deserializers so what do you mean about connecting 934 to 926? Can you share a block diagram of your system?

Can your panel which is connected to the 926 actually tolerate a SSC signal input? If not that could explain why you see image artifacts when SSCG is enabled

Best Regards,

Casey 

Hi Casey,

It is DS90UB943, not 934.

RnD uses DS90UB925 as TX and DS90UB926 as RX. DS90UB926 has SSCG enabled. Video is normal.

DS90UB925 --> RnD testing tool

DS90UB943 --> End Customer system

DS90UB926: Enable SSCG

DS90UB925 to DS90UB926 : Image is OK

DS90UB943 to DS90UB926 : Image artifacts 

RnD did a comparison of the difference between 925 and 943, and they found that the PCLK spectrum signal was different.

Blue: DS90UB925 , Black:DS90UB943 

DS90UB943 

RnD wants to know what are the possible reasons for white spots appearing in images?

Thanks & best regards,

David,

Can you please send your initialization script for 943A for review? One thing to keep in mind as a difference between 943A and 925 as sources is that 943A will dynamically adjust the horizontal blanking line by line to compensate for PPM offset between the SoC DP video and the video PCLK generated internally. That may be leading to some display artifacting if the display can't handle that adjustment and may be compounding with the SSCG as well. 

Best Regards,

Casey 

Hi Casey,

Casey McCrea said:

Can you please send your initialization script for 943A for review?

983Conf.zip

There are image artifacts in the video. Can you help me to check if there is a problem with the settings?

Casey McCrea said:

One thing to keep in mind as a difference between 943A and 925 as sources is that 943A will dynamically adjust the horizontal blanking line by line to compensate for PPM offset between the SoC DP video and the video PCLK generated internally

Can you kindly tell us how to set this up?

Thanks & best regards,

David,

There doesn't appear to be any immediate problem with the FPD settings, but as I mentioned before, I think this is most likely related to the automatic timing adjustments that 943A does to horizontal blanking to compensate the dynamic PPM offset between the DP source and the FPD VP. This is automatic and there is no way to turn it off - it is the basic working principle of FPD IV. From your description it seems like this combined with SSCG is causing the video signal to get mis-sampled by the panel. 

If you simple disable 926 SSCG, can this issue be eliminated? If so I propose we go with that solution. If not, then we may need to bring the panel TCON vendor into the mix to explain what the blanking tolerance is line to line 

Best Regards,

Casey 

Hi Casey,

Casey McCrea said:

I think this is most likely related to the automatic timing adjustments that 943A does to horizontal blanking to compensate the dynamic PPM offset between the DP source and the FPD VP.

Is this described in the datasheet of 943A? Can you take a screenshot and show it to us?

Because we did not find the datasheet of DS90UB943A on the website.

If we want to obtain the complete datasheet of DS90UB943A, how do we apply?

The RnD of E-Lead requires it, because the car manufacturer in this case uses DS90UB943A.

Casey McCrea said:

If not, then we may need to bring the panel TCON vendor into the mix to explain what the blanking tolerance is line to line 

If we get the information that blanking tolerance is line to line from the panel TCON vendor, what should we do next?

Thanks & best regards,

Hi Casey,

Casey McCrea said:

Can you refer back to my previous question? If you disable SSCG on the 926, can this problem be eliminated?

Disable SSCG on the 926 can resolve Image artifacts, but due to functional requirements, 926 SSGC cannot be diable.

E-Lead RnD found a TX using DS90UB981 in the factory. DS90UB981 to DS90UB926 : Image is OK

RnD looked at the DS90UB981 datasheet and found "horizontal blanking to compensate the dynamic PPM offset".

Is it possible to adjust the register value of DS90UB943A to be the same as the setting of DS90UB981?

Because the purpose of E-Lead RnD is to solve the problem of Image artifacts, do you need us to provide other relevant information to help you find the root cause of Image artifacts?

Thanks & best regards,

David,

981 and 943A use the same averaging function to adjust HBLANK dynamically to compensate PPM offset between the video source and the internally generated PCLK frequency. If you see a difference between 943A and 981, it is because the input video source (DSI or DP) has a different magnitude or polarity of PPM offset, so the HBLANK is getting adjusted in a different way. 

For example, in your 981 case, maybe the DSI PCLK is > the 981 PCLK, so HBLANK pixels are getting removed from the blanking, while in your 943A case, the DP PCLK is < the 943A PCLK, so HBLANK pixels are getting added to the blanking. Or it could be the other way around, or it could just be that the magnitude of the offset is much greater in one case vs. the other. 

One thing you could try would be to adjust the PCLK rate of the 943A initialization script programming up or down in small increments to see if the situation improves. 

Best Regards,

Casey