ST25R95 conducted emissions issue

[Paolo Anterri]

Hi everyone,

I developed a NFC antenna with ST25R95-VMD5T device. This antenna is connected to my main board with multipole cables and comunicate via SPI with it.

I tested it in laboratory and when I tried conducted emmission, appears this:

(neglect the rest....)

The schematic of my antenna NFC board is this:

and the PCB layout is this:

My question is: are there some tricks to decrease within the threshold this peak?

Thanks for your help.

Paolo A.

[Travis Palmer]

Hello Paolo,

Such standards directly do not cover cases where a product included radio transmitter. General praxis is that exclusion of carrier RF frequencies is applied, meaning that in the allowed transmission band the measurement can be above the limit. Such approach is generally used but is allowed only for carrier frequency. Higher harmonics must be under the limit. As a help you can take EN 301 489-1 standard. 

Typically the allowed transmission band is checked then by other tests. E.g. spectrum mask or occupied bandwidth. Your lab should be able to waive the conducted emission test.

br Travis

[Paolo Anterri]

Hello Travis,

thank you for your quick reply. I forgot to tell that the project is a medical application and I must to certificate it with EN55011 standard. Also I would like to know if the PCB layout, so as done, can be fine.

Many thanks.

[Travis Palmer]

Hello Paolo,

I do not have access to EN55011. But I think it is also derived from CISPR-11.

To my knowledge it is the same for every conducted emissions. The base band of an intentional radiator can be ignored/excluded.

Can you please share your schematic and Layout (several layers at a different sheet) via private message?

BR Travis

[AJiwa.1]

Hi Travis,

We are facing a similar issue and the lab is okay to ignore this while conducting RF testing as per ETSI EN 300 330 (intentional and unintentional spurious emission testing) but for conducted emission this needs to be below the limit line.

• Do you have a recommendation for Ferrite or Common Mode Choke that can be used to suppress this?
• CE is marked on the X-NUCLEO-NFC03A1 evaluation board, could you please share the conducted emission test reports for it?

Thanks in advance for your reply.

[Travis Palmer]

Hello,

We had exactly the same question to our official test lab.

This was the answer we received from the accredited lab:

For CISPR/IEC/EN standards typically there is a different approach. These standards directly do not cover cases where a product included radio transmitter. General praxis is that exclusion of carrier RF frequencies is applied, meaning that in the allowed transmission band the measurement can be above the limit. Such approach is generally used but is allowed only for carrier frequency. Higher harmonics must be under the limit. As a help you can take EN 301 489-1 standard. 

BR Travis