Distance from antenna to front end

[robhelvestine]

Hello,

I'm using the PN512 front end in one of my designs. Our system design would be a lot simpler if I can design an antenna at the end of a 10 inch long cable, instead of trying to cram my front end solution to where the antenna needs to be. Is there a rule of thumb for how long this distance can be? Can I design the antenna following the design videos taking this into account (1-3uH inductance, etc.)? What are the design reasons for not being able to do this (inductance increases too much, series resistance, etc.)?

Thanks

Rob

[robhelvestine]

Hi Kan‌,

Just to follow up on this, I got NFC communication working on the CLRC663 dev board, with 200mm 30AWG wire from the FPC antenna to the matching components. Our application only requires a sensing distance of roughly 8mm, which makes it easier. We are also only using NFC for authentication. No POS or other applications.

Would you expect radiated emissions to be a big problem in this setup? We do plan on shielding the cable. As this is my first experience with NFC, I'm unsure how big of an issue this is.

Thanks! 

[Kan_Li]

Hi Rob,

No, I don't think it would be a big problem, but shielding the cable would be better.

Have a great day,
Kan

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[deniscollis]

It's always better to connect the matching circuit to the antenna through an RF Balun and a coaxial cable, in the usual way.  Is there any reason why this this is not an option?

[robhelvestine]

Hi Denis,

That’s not an option for us. This is to be used in a consumer electronic

product and so we don’t have the space for a coaxial cable. Which is why we

need to bundle it with the other conductors in a slim cable.

This is not the end of the world. We have the option of moving the NFC

front and circuitry to where the antenna is, it’s just not the most

desirable option.

Thank you

Rob

On Fri, Apr 20, 2018 at 12:40 AM deniscollis <admin@community.nxp.com>

[Kan_Li]

Which type of cable will you choose? Would you please provide more details on it? Thanks for your patience!

Have a great day,
Kan

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[robhelvestine]

The cable is just 30AWG wire, twisted. It is routed alongside about 5 other conductors. 

[Kan_Li]

Hi Rob,

Thanks for the information! so you want to add this 10 inch long cable between the antenna and the matching circuit, right? please kindly clarify.

Best Regards,

Kan

[robhelvestine]

Hi Kan,

Yes that is correct. Just want to see if I can just characterize the front

end with this cable in the system.

Rob Helvestine Senior Electrical Engineer

Phone 415 233 0054

Halo Neuroscience haloneuro.com

[Kan_Li]

Hi Rob,

Actually 10 inch 30AWG twisted wire is quite long and it will definitely have an impact on the performace. Whether or not the reader still will work, depends on the frame conditions as well as the requirements. A simple MIFARE reader can accept, an EMVCo POS surely not.

Please also note that moving and bending the cable changes the behaviour, and from my point of view, better put the cable in between EMC filter and tuning circuit. I have never tried to put in between tuning circuit and the antenna coil, so I am afraid that might not work.

Best Regards,

Kan

[robhelvestine]

Thank you Kan. I appreciate your insight and you bring up good points.

Thanks again.