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ADV7611 TMDS Lock Issue

Question asked by j-r on Aug 29, 2015
Latest reply on Aug 31, 2015 by j-r

Hi All,

 

We have an ADV7611 connected to a ADV7511 on a custom board as a pass-through.

The board follows the schematic and layout suggestions of one of the Analog dev boards.

I do not own a dev board, please do not suggest buying one, I'm trying to debug the hardware of our custom board.

I'm initializing the ADV chips with the "6-4c - 1920 x 1080p60, Any Color Space In (YCrCb 444 24bit from ADV761x) Through HDMI Out 444 YCrCb 192kHz 8Ch, VIC 16" script via a microcontroller.

 

When I connect the ADV7611 to a computer and output 800x600, I have no problems. When I increase the resolution to 1024x768, I begin to get artifacts and the video cuts out occasionally due to what looks like a TMDS PLL lock failure (looking at the HDMI register 0x04). Anything over 1024x768 will result in random behavior of the control signals (PCLK, Vsync, Hsync, DE) and no video shows. Outputting 1080p is the ultimate goal.

 

Is it possible that this is an issue related to the XTAL not having correct decoupling capacitors and creating clock jitter?

I'm using an 28.636363MHz 18pF 30ppm XTAL with 50Ohm ESR, and have 39pF capacitors on each lead going to ground. I think it's recommended to have 27pF for this XTAL value.

The schematic has a 390K resistor accross the XTAL which I also have in my design. Out of curiosity, what is this resistor used for, and could this also be causing problems?

 

Any suggestions will be appreciated, thanks in advance.

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