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

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)?

Thanks!

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  • 0
    •  Analog Employees 
    on Mar 4, 2016 2:02 AM

    Hello,

    4:2:2 or 4:4:4 is fine either way. Not sure why you would use the secondary VSP instead of the primary, but it doesn't particularly matter. You could output Y/C separately in parallel with CVBS, but you don't have to.

    Not sure I see why you would use an AD725-- it can't do anything the ADV8005 DAC's can't do, and you'd have to use TTL in and TTL out in that case.

    Yep, -8N would be the one you want. I'm pretty sure you need the memory to downscale and interlace. You can always not populate it if you find you don't need it later.

    Unless you are an HDCP adopter, you'll need to get the EVAL-ADV8003-SMZ-P and then replace the AD8003 with a -8N ADV8005. The ADV8005 SMZ evaluation board requires an HDCP adopter since it's got ADV7625 on it. Note that we don't populate the DAC circuits on our eval boards but the footprints are all there. You should be able to order the EVAL-ADV8003-SMZ-P from the website.

    Dave

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  • 0
    •  Analog Employees 
    on Mar 4, 2016 2:02 AM

    Hello,

    4:2:2 or 4:4:4 is fine either way. Not sure why you would use the secondary VSP instead of the primary, but it doesn't particularly matter. You could output Y/C separately in parallel with CVBS, but you don't have to.

    Not sure I see why you would use an AD725-- it can't do anything the ADV8005 DAC's can't do, and you'd have to use TTL in and TTL out in that case.

    Yep, -8N would be the one you want. I'm pretty sure you need the memory to downscale and interlace. You can always not populate it if you find you don't need it later.

    Unless you are an HDCP adopter, you'll need to get the EVAL-ADV8003-SMZ-P and then replace the AD8003 with a -8N ADV8005. The ADV8005 SMZ evaluation board requires an HDCP adopter since it's got ADV7625 on it. Note that we don't populate the DAC circuits on our eval boards but the footprints are all there. You should be able to order the EVAL-ADV8003-SMZ-P from the website.

    Dave

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