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ADV7623 EMI issue

Question asked by kermes on Sep 8, 2014
Latest reply on Sep 11, 2014 by kermes

Hi everyone,


I have a ADV7623 design and there is too much conducted EMI on HDMI output cable shield at the video TMDS clock frequency.


The design is made with using ADV7623 demo board and other HW documentation as reference.


There should be a solid ground plane, the output TMDS lanes are very short and have no vias, and the power supply portion is made as recommended. TMDS trace lengths should be inter-pair and intra-pair matched.


Q1: Are there any software tricks that could be tried to reduce EMI, like limiting TMDS output drive strength or slew rate?

Q2: Also are there any ideas what might cause the EMI problem or what to try to reduce it?

Q3: Although not in the example design, would adding common mode chokes to TMDS lanes help with conducted EMI?


I read in the latest ADV7623 documentation about some undocumented TX charge injection control register 0xDF in main map, would this have an effect?


Thanks in advance,

- K