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ADV7611 Distortion and Losing Lock - PCB Layout Issue?

Question asked by j-r on Dec 24, 2015
Latest reply on Jan 19, 2016 by PaulS

Hi All,

 

I recently made a revised PCB that has an ADV7611 connected as a pass through to an ADV7511.

Low resolution video (1024x768) is received and outputted without problem.

High resolution at 1920x1080 starts showing lots of distortion and the ADV7611 eventually looses lock on the input causing the screen to go black. Distortions include color streaks and noise on the screen, as well as echos of the mouse cursor for example. Movement on the screen causes it to go black as well.

 

 

The PCB is 4 layer with a dedicated ground plane made by OSH Park. The trace length between the HDMI connector and the ADV7611 is 170mil, with 8mil trace width, 6mil gap between TMDS like pairs, and 45mil gap between other TMDS pairs. According to an online differential impedance calculator (shown in bottom picture), the differential impedance of these traces should be 100 Ohm for my existing layout.

 

The PCB stackup according to the Osh Park website:

stackup2.gif

*With dielectric constant of 3.66 at 1GHz.

calculator.gif

 

Any help on this issue would be appreciated!

(Please no suggestions for buying an evaluation board from Analog. This will not solve my problem.)

 

Cheers

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