we currently develop a videoboard with the 7180 and the 7391.
The 7180 is used to convert a analog video signal into a digital signal.
Then the digital Videostream is manipulated by a FPGA.
The ADV 7391 is used to convert the manipulated digital videosignal back to an analog pal signal.
Our PCB-Designer used the specifications in the datasheets an took care to keep noise away from the
We used table 83. on Page 95 rev.C of the datasheet to configure the ADV7391 via I2C-Bus.
The configuration works but the outputvideo we get still has noise in it. We used the Pixelclock from
the ADV 7180 for the ADV 7391.
Here you can see a screenshot. We used a videograbber to get this picture.
Here is a screenshot we took with the scope. This is the pal outputsignal un DAC-1
Generally it looks all right but there is still too much noise.
The signal gets better if we use an analog video inputsignal at the adv7180. If we do this the videograbber shows a picture as follows.
That is strange because the only signal that the 7391 uses that comes from the 7180 is the pixelclock with 27MHZ and
it should be constant.
So my questions are:
1. Do I have to configure the 7180 in a special way to get a special pixelclock?
2. Hoe can I reduce the noise?
3.What can I do to get a good output test signal?
We hope you can help us,