I am using AD725 for converting VGA signal to composite. What resolution of VGA video is needed for ntsc encoding? I tried 640x480 and 600x400 - it does not work. What vga clock frequency required and what timings should I use?
The part won't convert or scale anything. You have to supply the 4 * the subcarrier frequency to the 4SC pin: 14.318180 MHz for NTSC encoding, and 17.734475 MHz for PAL encoding. You would need to use H and V synchs that are correct for the format PAL or NTSC that you are using and you'd have to supply interlaced fields consistent with the format you are trying to get. That would be about 200 lines per field (600 or 720 pixels per line is probably ok as long as the synch signals are correct)
There is more detail from page 12 in the data sheet.
PCs generally do not support any interlaced formats. Composite NTSC video is normally digitized at 720x~244 interlaced. Most video cards can't output this unless they have a special TV output. Many TVs have VGA in these days... why do you want a composite (low resolution) signal?
I am trying to implement a wireless solution for video transmission in our office premises. The wireless modules that I am using accept only the PAL and NTSC signals which we are ok to go ahead as a initial idea to check the feasibilty. The flow is given below
Laptop/PC --> VGA connector --> VGA to NTSC/PAL converter --> WIFI Transmitter --> WIFI Receiver --> NTSC/PAL output to VGA --> TV or Monitor
So I have to convert the VGA signals to composite for connecting them to the WIFI module. Do let me know if there are any other chips that can accomplish my task.
How many of these units are you wanting to produce?
I am not very sure about that at this point. I will get it once I realize the application.
The quality would be very poor doing what you want to do: downconverting progressive PC resolutions to NTSC. You'd need one of our video decoders and and ADV8002, which is an NDA part at the moment. It's the only one that could take in digital video of whatever resolution and scale it to NTSC.
Where do I get the NDA from? Kindly send me the link.
This is a really old thread-- best to start a new one. The current VSP ADV8005 has no NDA anyway; everything is posted.
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