Author Topic: NFC Antenna design  (Read 2991 times)

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Offline iakTopic starter

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NFC Antenna design
« on: July 06, 2018, 10:08:43 pm »
Hello people,

Just a general question. I was looking at some  PCB NFC antenna design from NXP and I have noticed that they go in an interesting fashion.

Lets say I have a 3 loop NFC PCB antenna. It looks like NXP route half of the first loop before jumping into the second with a via and half of the second before jumping to the third by via, the third loop is finished before returning to the second half of the second loop and then it return to the second half of the first loop [Something like this photo http://www.entras.cz/images/foto/microcontroller/IMG_1440_up.jpg ]. Why is it routed like this, I was expecting something like it finish the first loop and jump to the second without any via and then finish the second loop and jump to the third without any via and then finish the third and return to the beginning with two vias something like this https://b2bsol.panasonic.biz/semi-spt/apl/en/tool/nfcdesignnavigator/image/Caution_Gerber.JPG

Apparently both approaches are widely used but I see the former more, what is the reason of doing that. What advantages does it have, any reference when designing the shape of an NFC antenna.

Also I have seen some commercial NFC antenna where the middle of the tracks is connected to GND, why is that so like when it goes through half of the antenna, the track is connected to GND using a VIA before returning to the start, why is that.

I would really appreciate if anybody helped with these two question. A referenced answer where I can read more from the sources would be great, as I am having trouble finding a good source for general practises used when designing NFC antenna.

Thanks !.
« Last Edit: July 06, 2018, 10:14:10 pm by iak »
 

Offline T3sl4co1l

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Re: NFC Antenna design
« Reply #1 on: July 07, 2018, 06:16:23 am »
Just how the PCB designer decided to do it.

The interleaved turns will have more self capacitance, which is generally undesirable for an inductor, actually.  But this is well below the self resonant frequency, regardless, so it makes little difference.

Tim
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Electronic design, from concept to prototype.
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Offline iakTopic starter

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Re: NFC Antenna design
« Reply #2 on: July 07, 2018, 10:02:49 am »
Yeah, I guess. But there should be a reason why somebody would make it more complicated by  going half of each turn, while he can simply do it the other way.

Most NXP antenna with devkits are designed this way, yet I cannot seem to find any document that explains why.

Any comment about connecting the the middle of the antenna to GND. Why from my point of view you would be expecting the voltage level halfway through the antenna to be 0 ?.

Thank you for your comment.
 

Offline T3sl4co1l

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Re: NFC Antenna design
« Reply #3 on: July 07, 2018, 06:22:24 pm »
Centertapped is better: the voltage is balanced around zero, so the net electric field at a distance is zero.  This gives lower RFI and better selectivity to near field objects.  This may be a reason behind the interleaving.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline iakTopic starter

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Re: NFC Antenna design
« Reply #4 on: July 08, 2018, 11:24:19 am »
Thanks Tim. That kinda make sense now 
 


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