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DVI to CVBS conversion

 

I need to convert a DVI video feed to composite video (CVBS). I am currently looking at using a AD9887 or similar to receive the DVI signal and a ADV7170 to convert the digital video into composite. The questions I have regard the compatibility of the two chips. Alternatively is there a one-chip solution available?

  • You might look at a ADV7611 and ADV739x combination in BT601 or BT656 mode.  There are other combinations that will work as well.  I don't know of any single chip that goes directly from DVI to CVBS. 

  • Thanks for the input, I think that answers that question.

    I have a couple more questions,

    1) The video source need to convert does not use/have EDID or hot plug detect pins, Is the 7611 capable of being set up to receive signals from a source without these pins?  If so how do I do it?

         -I have read other discussions related to this subject but was hoping to get the answer in one place

    2) If I read correctly, it looked like I can manually assert the hot plug detect via I2C control, is there a way to set the input format as well? (The device i am receiving signals from constantly outputs 1024x768 @ 60Hz (XGA) that is compliant with VESA v1.0)

    3) I do not need a lot of features, is there a less flexible dvi receiver than the ADV7611? 

    4) I'm confused about which chip would do the down conversion, am i correct in thinking that the ADV7611 will receive XGA and output BT601 or BT656 and the ADV739x will receive that output and convert it to composite?

      Thanks again for the help

  • 1) EDID is only required by the source.  If the source doesn't care about the EDID and pumps out XGA60 regardless then all's good.  You can override the HPD in the ADV7611 and set it up for XGA just fine.

    2) For the ADV7611, the output resolution will be the same as the input resolution.  The device will not do format conversion.  It can change the color space and package the output into BT656 or what ever, but the timing remains the same.  If XGA60 goes in, that's what will come out.  Also note that XGA60 is an RGB format so the output will either be RGB 444 or YCbCr 444 on a 24 bit bus.  It doesn't make sense to output RGB on an 8-bit bus in BT656 format since you really can't interleave RGB correctly.

    3)  The ADV7611 is the newest part and has the best performance.  It'd stick with it.

    4) Originally I thought the DVI input was going to carry a CVBS format (720x480) so I wasn't worried about it.  However now that the input is XGA60 (1024x768@60) and the output needs to be CVBS, these are two different formats.  You'll need some kind for format converter.  XGA60 has a pixel clock of 65MHz while CVBS pixel rate is 13.5MHz.  You can't just feed the 7611 into the 739x and expect it to work.  Either you run the RGB through an FPGA and down convert yourself or get a chip like the ADV8003 which can do the down conversion.

  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin