TFP403/DS90C397A DVI LVDS bridge, flickering pictures

juergen.duerrwang

Other Parts Discussed in Thread: DS90C387A, LMH6733

Hi,

I am writing in case of some problems with my DVI to LVDS bridge. I have already posted some schematics at the beginning of that project and fortunately some of your engineers (exspecially RossE) helpd me some issues. Now I soldered my first pcb and connected to my panel. But I have some problems to get the system working correctly. The main failure is a flickering picture on the screen and a rough pixel resolution (graphic gard sends in native mode: 1080p). So I try to find may mistakes on my pcb to optimize my design. Perhaps some of your specialist can help me with the task. I attached a pdf 2450.DVItoLVDS module.pdf, where I explained what I have done right now to find the mistake.

I would be very grateful if somebody could take a look on my work. If eagle filse will help to find my mistake, then I can sends these via mail.

Best regards,

Juergen

over 12 years ago

0 Mark Sauerwald88474 over 12 years ago

TI__Genius 13475 points

Juergen

Can you help me to understand what the signals are that you are showing in the attachment? Are these the outputs of the LMH6733? Is it possible to probe the DS90C387A outputs directly?

Also, can you confirm that your graphics card is sending the same resolution as the panel that you are using?

Mark

0 juergen.duerrwang over 12 years ago in reply to Mark Sauerwald88474

Intellectual 420 points

I am sorry. The signals which you can see are measured before input of LMH6733. They are measured between DS90C387A and LMH6733. On the output side of LMH6733 I can not measure any signal.

Perhaps transmitting of Hsync, Vsync and DE from DS90C387A to LMH6733 cause the problems on my panel. What do you thing?

If it is easier for understanding, I can send you my schematic files.

Best reagrds,

Juergen

0 juergen.duerrwang over 12 years ago in reply to Mark Sauerwald88474

Intellectual 420 points

And yes I think, the graphic card is sending the right data. Because I read out the values from my cloned EDID EEPROM and they are equal to the values from original panel EEPROM.

(I bought an ASUS LM229H, where I copied the EDID data on my EEPROM)

0 juergen.duerrwang over 12 years ago in reply to juergen.duerrwang

Intellectual 420 points

I looked over my pcb and I found some issues which can perhaps cause my problems. First I have seen, that the width of high speed line changes. On my main pcb it has a width of 6 mils and on my adapter pcb a line width of 9 mils.

Another point is my voltage supply and the cuople capicators. In the following pictures I draw two configurations of cuople capicator.

The first configuration is how it is on my pcb. It shows that all couple capicators connect to ground via a ground line and not directly to the massvie ground lane. Is that bad and should I switch to configuration two, where each capicator is directly conneted to the massive ground lane?

Best regards,

Jürgen

0 juergen.duerrwang over 12 years ago in reply to juergen.duerrwang

Intellectual 420 points

Is there nobody how can give me a short answer for the power connection above?

0 RE over 12 years ago in reply to juergen.duerrwang

TI__Mastermind 20985 points

Jürgen, your second picture is better, since there's less loop inductance. You want to minimize the PWR/GND loop distance, through the capacitor, through the device, and back. It is also good practice to place a 0.1uF near each device VDD pin.

Best regards,
RE

0 juergen.duerrwang over 12 years ago in reply to RE

Intellectual 420 points

Thanks for your help!

Best regards,

Jürgen

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TFP403/DS90C397A DVI LVDS bridge, flickering pictures