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(ADV7390)Noise output from the device.

Hi !

I have some question about ADV7390.

Some kind of noise is output from ADV7390.

I am using ADV7180-ADV7391 Eval-board and using "CVBS auto detect" script.

=> I attached the script file.

And I zoomed the waveform.

The BT.656 data is output from ADV7180 and at the EAV and SAV point , ADV7390 output some kind of noise.

Also I setup the ADV7180's resister, 0x0C to "Force free run mode" and "Output 100% black".

Why does this noise output from ADV7390?

And also to prevent outputting this noise what should I do?

Is it possible to erase this noise by setting resister?

I want to know this because our customer have this issue.

I will attach customers waveform.

Also at the display, blue line is in the display.

Our customer think this happens because of the ADV7390's noise output.

I will check about this(display image) connecting ADV7180-ADV7390Eval board to other Eval board

and moving the image area to check this will happen or not .

But I am out this week so it will be next week.

If you can tell me why this will happen and how to solve this problem, it will help us and our customer very much.

Best regards.

  • Hi GuenterL

    Thank you for your support every day.

    So you mean there is no possibility that ADV7390 output this kind of noise?

    The first image I attached is from EVAL-ADV7180.

    So you mean the noise output is because of PCB layout or something?

    Best regards.


  • Initially I would not say this is directly related to anything the ADV7390 is doing.  This looks like the source or the sync is inserting a noise spike into the system.  And by system I mean the entire source - ADV7390 - sink as a system.  By the placement of these spike is looks like it's related to the end of the back porch and the start of the front porch.

    The extra vertical line of the left side of the screen might be because the sink is not interpreting the back porch correctly.  Normally sinks determine the left edge by timing from the leading horizontal edge.  Maybe the souce can make the back porch shorter or horizontal pulse shorter.

    To check the ADV7390 is generating the spike I would ground the scope directly on one of the ground pins of the ADV7390 and probe the DAC outputs.  Make sure that this is the only ground point of the scope. 

  • Yes, it would be unlikely that noise is generated the ADV7390.  To me that looks like something generated by something else in the system that is locked to the horizontal sync.  If it was an old CRT monitor, I'd say it was the horizontal retrace circuit causing this spike.  I'd check everything that is locked to the horizontal sync.

  • Hi GunterL.

    Thank you for your support.

    I understood what you said and also our customer are using this device 640*480p@25.175MHz DDR.

    So the point is does this device support 640*480p@25.175MHz DDR or not.

    So I will change the question.

    (ADV7390)Does this device support 640*480p@25.175MHz DDR?

    And close discussion .

    Thank you !!

    Best regards.


  • Hi GunterL!

    Thank you for your support every day.

    I told that ADV7390 cannot support 640*480p-BT.656.

    So I and our customer think the blue line is because of no-support input.

    They understood that ADV7390 cannot support but they want to know why this happen.

    So if is possible , can you tell me the mechanism of this issue?

    Please give me some advice.

    Maybe the clock frequency is 25.175Mhz  so this is the reason.

    It is Ok that the answer is guess or not but if you can give us some advice , it will help us very much.

    Best regards.