HDMI EMI issues, i.MX6 DualLite

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HDMI EMI issues, i.MX6 DualLite

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Contributor I

Hi,

I have encountered EMI issues on HDMI on my custom iMX6 DL board. My HDMI interface is the same as in the Sabre design with the CM2020 as ESD/level shifter.

The peaks i measure is at 65MHz, 130MHz, 325MHz. The 65MHz reach as high as 40dBuV. I have patched in common mode filters (Murata DLP11SN900HL2L) on the diff pairs between the CM2020 and the HDMI connector and ferrite beads (Murata BLM18HE102SN1D) on the rest of the HDMI signals without any improvement.

Simply turning off (or pulling the HDMI cable at the monitor side) the monitor will completely quiet the EMI issues.

I have tried several different HDMI cables. I found 1 cable with slightly better performance. I also tried different monitors/TVs but no improvement.

My board is a 8 layer with the following stackup:

1 signal

2 gnd

3 signal

4 pwr

5 signal

6 signal

7 gnd

8 signal

The HDMI diff pairs are carefully routed (impedance matched) on layer 1 between HDMI connector, CM2020 and to the iMX6 edge. Then on layer 8 a short bit and then up through vias to the iMX6.

Has anyone used the CM2020 with good EMI results?

Any input on this would be appreciated.

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Contributor I

I figured I should round up the thread I started. The EMI issues on HDMI are now solved. I found that there are in fact some ways to improve the EMI. The HDMI signal levels can be adjusted to comply with the Eye Pattern. This will have impact on the EMI. Read about it here: http://cache.freescale.com/files/32bit/doc/app_note/AN4671.pdf. Also by simply changing the resolution and refresh rate on the HDMI output will have impact on the EMI. In my case it was the pixel clock that was the big noise issue.

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NXP TechSupport
NXP TechSupport

Hi Magnus

there are no i.MX specific ways for resolving that, it may be suggested to

look at resources devoted to HDMI shielding, like below

http://www.cepro.com/article/understanding_fixing_hdmi_noise/K35

Best regards

igor

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