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HDMI / DVI to NTSC using ADV7611->ADV7125->AD725

Question asked by MrYan on Feb 11, 2016
Latest reply on Mar 3, 2016 by MrYan

Hello everyone,


I think we know the answer and are embarrassed, but wanted to post and get some feedback on a custom design we did using an ADV7611, ADV7125 and an AD725.


The goal was to take a 1920x1080 interlaced (60Hz) DVI output from a camera, convert it to VGA and then convert that signal to NTSC.  In order to do this, we combined some evaluation circuits using primarily the CN0282 application note (ADV7611 to ADV7125).  The path we use is:

HDMI/DVI input to ADV7611 --->  24 bit RGB to ADV7125 ---> RGB analog out to AD725 ---> NTSC out


I know there are some off the shelf boards that can do this, but we wanted to eventually intercept the data to do some statistics on it as well.


Anyway, the board came up and eventually we got to the point where we can get this image, which should be a black background with menu screen in white text:



Clock values / shapes look correct, and we can change different parts of the ADV7611 startup script successfully with expected results, but nothing makes the image get better.  At first, we thought it might be an EDID issue, but I have a feeling that we should have possibly put some kind of scaling IC in the chain to get the 1920x1280(i) image to fit into NTSC.


Any thoughts?  Any idea how we might be able to recover an image (even semi usable)?