AnsweredAssumed Answered

ADV7604 Low-bit Noise on VGA (1600x1200@60Hz)

Question asked by cottrela on Dec 17, 2014
Latest reply on Jan 7, 2015 by GuenterL

Dear Sirs,

We are using the AD7604 in a video frame rate converter application to capture 1600x1200 @ 60HZ (UK VGA standard blanking).

In the digital output (24-bit RGB), we see what appears to be a noise reflection approximately 40 pixels after the left-hand edge. This reflection then repeats, causing additive noise, every 40 or so pixels.

When we apply a small amount of coolant to the AD7604, this noise/reflection completely vanishes.


As the silicon warms back up the reflection/noise slowly returns.



Has anyone seen a similar effect with the AD7604?


What could be causing this issue within the AD7604?


Does anyone have any advise on how to fix?


Some background to the issue:


We have a very low power design (<5 Watts) and the AD7604 silicon is always cool to the touch.


The design is based on the standard AD7604 reference design.


Our test system uses a high-end Matrox VGA card to drive 1600 x 1200 @ 60 Hz using a very short VGA cable i.e. we have tried very hard to eliminate all VGA cable reflections.

We cannot see an issue with the clocks, power supplies, or input video signal going into the AD7604.

We are using the standard settings for 1600x1200 taken from the ADV7604_RecommendedSettings_Rev2.5.pdf.

In our tests, we only connect the blue channel from the video source (i.e. red and green are grounded), but the noise can be seen appears equally on all three ADC.

The following bitmaps show the screen before cooling (repeating artifacts clearly visible in the black):-

1.png


And here is how it looks after (noise profile is more uniform):-

2.png


Note - in the above bitmaps, the contrast has been adjusted using a paint package so that the fault can be clearly seen without having to adjust your monitor's contrast setting!


Thanks in advance for any help offered.


Regards,
Adam

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