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AD9889 video noise on the display

I got the AD9889 HDMI transmitter working, but I see noise on the display. I generate a color bar as a source image, I see a couple of verticle noise striped on some of the colors. If I wiggle the HDMI cable the noise changes.

I started playing with the register settings and first I noticed that the set provided on the web doesn't work. It also does not match the programming guide documentation. One example is register 0x98. The documentation says must write a 7 to this register. The example code says write 178. But I only got a display working by writing a 170. Registet 0xAF also affects the noise on the display. A value of 6 works best, while a value of 4 makes the video break up once in a while. And last but not lease, I had to increase the drive strength registers 0xA2 and 0xA3 to 255 to minimize the noise on the display.

My resolution is 1280x1024, 108MHz clock, 60Hz frame.

Can someone provide me a register settings that work for this resolution that is different than the one available from the web?

I'm attaching the register setting programming that gives me the best results. This is a read back from all registers.

Thanks,
Ed.

best_settings.txt.zip
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  • I'll look into the register value suggestions you sent me. I'm going to the lab right now to try them out and see what happens. In the meantime, I'm attaching a screen capture of the layout and our schematics page. Notice how the traces are very short and matched in length. The high speed serial pairs are highlighted. Note that they have to go through two vias each to be able to route it to the micro-HDMI. We also performed Hyperlinx simulation of our whole board, so the signals were checked for impedance matching and crosstalk noise. I'll try to get a picture of the color bar noise patterns I see on the screen.

    On the schematics there is a correction. R490 is removed and R141 is populated.

    Let me know if you have any comments on the layout or schematics. Specifically the way we did the analog supplies. It comes from a switcher, not an LDO. But we used a pi filter to reduce the digital noise.

    Thanks,
    Ed.

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  • I'll look into the register value suggestions you sent me. I'm going to the lab right now to try them out and see what happens. In the meantime, I'm attaching a screen capture of the layout and our schematics page. Notice how the traces are very short and matched in length. The high speed serial pairs are highlighted. Note that they have to go through two vias each to be able to route it to the micro-HDMI. We also performed Hyperlinx simulation of our whole board, so the signals were checked for impedance matching and crosstalk noise. I'll try to get a picture of the color bar noise patterns I see on the screen.

    On the schematics there is a correction. R490 is removed and R141 is populated.

    Let me know if you have any comments on the layout or schematics. Specifically the way we did the analog supplies. It comes from a switcher, not an LDO. But we used a pi filter to reduce the digital noise.

    Thanks,
    Ed.

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