Single-Ended NFC Antenna Design

[nextsteve]

Hi I am working on an NFC design based on the CLRC663 controller.

I am wondering if there is a concept for making the antenna single-ended (ground-referenced instead of differentially driven) such as by simply not connecting TXN/ RXN or using a balun in front of the coil.

Thanks,

Steve

 

[weidong_sun]

Hello Steve,

    See attachment,please!

Regards,

Weidong

[AP1]

Hi!

Could you tell me what the difference is between the 3 antenna schematics shown (short, full and alternative) in terms of use case? Why use one and not the other?

Could you also suggest specific Balun part number for me to check?
Lastly, where does the AVSS leg connect to, we couldn't quite figure that out. Should it be TVSS?

Thanks!

[Tomas_Parizek · Accepted solution]

Hello AP1, 

Thanks for your question! 

In the "Short Range", the antenna is powered by one Tx pin (50% of the power). 

While the "Full Range" is powered by both Tx pins. (full power). 

Just for your reference, look at this document :

https://www.nxp.com/docs/en/application-note/AN13892.pdf

It is a different product, but the principle is the same. 

We do have very good experience with the following Balun -> DXW21BN2511NL

Which product would you like to use ? MFRC630?

BR

Tomas 

[AP1]

Hi Tomas!

Thank you for the reply!
We're likely to use either the MFRC630 or MFRC631, yes. There is also the possibility we'll go for the CLRC663 but it is less likely.
Could you also elaborate on why we would want to use one Tx pin to power the antenna vs two Tx pins? what is to be gained by limiting ourselves to the short range design?
Lastly, could you say where the AVSS pin should be connected to? We're not able to come to a conclusion on that.
Thanks again!

[Tomas_Parizek]

Hello AP1, 

"Could you also elaborate on why we would want to use one Tx pin to power the antenna vs two Tx pins? what is to be gained by limiting ourselves to the short-range design?" 

Typically it is about "cost" saving. For a "single-ended" solution with only one Tx pin, you need just half of the components and no BALUN. But as mentioned, you lose 50% of the output power -> less reading performance. 

"Lastly, could you say where the AVSS pin should be connected to? We're not able to come to a conclusion on that." 

Not sure which AVSS pin you mean. MFRC630 or MFRC631 does not have any AVSS pin. 

BR

Tomas 

[AP1]

Hi again!
I see, thank you for the answer.
The AVSS pin appears in the scheme for the 'short range' and 'full range' antenna shown in the 'emc filter for 50 ohm' attachment above. I indeed do not see it when looking at AN11019-
'CLRC663, MFRC630, MFRC631, SLRC610 Antenna Design Guide', though I only saw a typical circuit for the CLRC663 in that document. I assume the same analog circuit applies for MFRC630/1 then?

[Tomas_Parizek]

Hello AP1, 

The AVSS is valid for MF RC500 and RC400 products. 

My colleague shared the "EMC Filter for the 50 Ohm Short Range Antenna 2" document to show the principle generally. Now, you need to adjust it for your NFC Reader IC. 

For ICs, you mentioned the standard connection looks like this:

So I would recommend keeping the Rx connection as mentioned above and adding a BALUN as described in AN13892. 

BR

Tomas 

[ND2]

Dear Wigros,

Thank you for the PDF document.

Can you also please suggest if such a balun will work?

https://www.mouser.com/ProductDetail/murata/dxw21bn2511nl/?qs=byeeYqUIh0N5dfXcIlSvRA%3D%3D&countryco... 

and if so how do we use it?

We are using the PN7462AUHN and not the CLRC663 as suggested by Steve.

Thanks