i.MX6 DL Custom Board EMI Issue

[sohailakram]

Hi Everyone,

We recently tested our iMX6 DL custom board with DDR3 for EMI and EMC. The board is primarily based on SABRE Platform with PMIC. For layout, we used layer stack-up as defined in SABRE Platform. 

We are experiencing an unwanted spike at 230 MHz that exceeds the FCC Class B specified level. We tested up to 6GHz. Everything is fine in complete range except that 220-230 MHz spike. We are unable to identify this frequency either as fundamental or a harmonic for all clock frequencies used in iMX6 and PMIC.

The EMI Lab suggested ferrite beads on all power sources. I was wondering if any member of community has experienced anything like this during their EMI testing and what possible solution is there to this kind of problem. 

I'd appreciate your suggestions. 

UPDATE: EMI Testing report for our board is attached for reference.

Sohail

[igorpadykov]

Hi Sohail

i.MX6Q Sabre SD board passed EMI test and its lab report can be obtained

creating service request.

How to create service request :
https://community.freescale.com/docs/DOC-329745

For finding cause of spike one can try to disable peripherals one by one, run test

from iRAM, use system pll spread spectrum, slightly change pll frequency.

Best regards
igor
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[sohailakram]

Hi Igor,

Thanks for your reply.

Could you please help identifying which module operates at this frequency of 220-230 MHz; fundamental or harmonic.

We performed the EMI tests at various stress levels, with and without casing, and the frequency of the spike shifted between 220-230 MHz. 

[igorpadykov]

Hi Sohail

I am afraid it is impossible to say without testing, please try to gate

module clock and check when harmonic disappears.

Best regards
igor