Hi, I just checked ML40X known issues: http://www.xilinx.com/products/boards/ml40x/ml40x_known_issues.htm
Unexpectedly discovered: *"2) ADV7125 Ground Pins * On ML401, ML402, and ML403 boards, some of the ground pins of the Video DAC (ADV7125 - U13) are connected to digital ground instead of analog ground resulting in increased VGA video noise. Ground pins 1, 2, 14, 15, 39, and 40 of U13 should be connected to the analog ground (Pin 2 of FB6). " Its sch. : http://www.xilinx.com/support/documentation/boards_and_kits/ml401_2_3_schematics.pdf After confirmed that online newest adv 7125 datasheet that Figure. 10 Typical Connection Diagram: a) Analog ground are shown clearly enough instead of our wrong connections to digital grounds. b) must be included all below to analog ground : pins 27, 31, 33 of U18 group; pins 1, 2, 14, 15, 25, 26, 39, 40 of U18 group; ground of R144~R146; R142's ground; pins 6, 7, 8 of J17(VGA connector); They are all related to "analog" power rail for DAC and reference circuitry. On analog device web there's a good doc of AN333: Design and Layout of a Video Graphics System for Reduced EMI, http://www.analog.com/static/imported-files/application_notes/5083035100552AN_333.PDF All contents inside this doc is good to reflash and remind us that we've taken less considerations. It's bad that we all missed this significant info. With regards to if this discovery influence audio performance, this is much worthy to pay more experiments. -adam
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