ADV7280-M Video chip EMI emmissions

Hi,

We're using an ADV7280-M chip to do our SD video to CSi interface and it's being run in progressive mode with the de-interlacing turned on. During some EMC testing it was noticed that there was a huge amount of noise around the centre frequency of the CSI link (214Mhz) , as shown in the image below. Ignoring the two large spikes either side, as they are from known sources. The rough shape of the noise changes if the camera is pointed at different things making me suspect it's possible the back end CSI link that's generating a lot of it.  We're actually monitoring emissions from cabling attached and the signal is coming either from video lines or the power lines.

Has anyone experienced this kind of situation before? Ideally with ideas of how to help mitigate it?

Best regards,

Marc.

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  • Hi Marc,

    • Before you go back to an EMI test house it might be a good idea to run a near-field probe over your system to hunt for the source of this noise.
      • This could show if it is your switch mode power supply or MIPI transmissions are the source of the EMI.
    • When you do go back to the EMI test house could you run the ADV7282-M in a progressive free-run mode. This causes the clock speed to double. You can see if this affects the EMI capture frequency.
      • Please also do the experiment where the MIPI D-PHY of the ADV7282-M is powered down.
    • FCC is an unshielded ribbon cable correct ? A bend etc in this cable could be a source for EMI. I used shielded SMA cables to transmit the MIPI output from the ADV7282-M to a protocol analyzer.
    • I advise placing ferrite beads and decoupling capacitors on each power supply.
    • I am far from an expert in switch mode power supplies but I have designed board using them where I had to minimize output ripple etc. I found the ADIsimPower Votlage Regulator Design Tool and the ADP232x Buck Regulator Design Tool were really useful in achieving this. These tools can be found here:
    • Also the following article may be useful:

         http://www.analog.com/en/education/education-library/raqs/raq_jb_lock_down_that_noise_issue37.html

    If you post a EZ question in the Power Management section I am sure you will get help regarding you switch mode power supply question.

    Regards,

    Robert Hinchy

    Senior Applications Engineer,

    Video Section,

    ACE Department,

    Analog Devices Inc.

Reply
  • Hi Marc,

    • Before you go back to an EMI test house it might be a good idea to run a near-field probe over your system to hunt for the source of this noise.
      • This could show if it is your switch mode power supply or MIPI transmissions are the source of the EMI.
    • When you do go back to the EMI test house could you run the ADV7282-M in a progressive free-run mode. This causes the clock speed to double. You can see if this affects the EMI capture frequency.
      • Please also do the experiment where the MIPI D-PHY of the ADV7282-M is powered down.
    • FCC is an unshielded ribbon cable correct ? A bend etc in this cable could be a source for EMI. I used shielded SMA cables to transmit the MIPI output from the ADV7282-M to a protocol analyzer.
    • I advise placing ferrite beads and decoupling capacitors on each power supply.
    • I am far from an expert in switch mode power supplies but I have designed board using them where I had to minimize output ripple etc. I found the ADIsimPower Votlage Regulator Design Tool and the ADP232x Buck Regulator Design Tool were really useful in achieving this. These tools can be found here:
    • Also the following article may be useful:

         http://www.analog.com/en/education/education-library/raqs/raq_jb_lock_down_that_noise_issue37.html

    If you post a EZ question in the Power Management section I am sure you will get help regarding you switch mode power supply question.

    Regards,

    Robert Hinchy

    Senior Applications Engineer,

    Video Section,

    ACE Department,

    Analog Devices Inc.

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