NTAG I2C Plus antenna board capacitor

[kaibuechler]

Hello,

I need to desgin a nfc antenna. Therefore I read the AN11276 NTag Antenna Design Guide. I was wondering why there is an additional capacity of 130pF on the antenna board (see Picture below)? I did not found any Information in the design guide.

Anyone knows why it is placed there?

Thanks

[Kan_Li]

Hi Kai,

The capacitor of 130pF is used to tune the antenna frequency oscillation, it is not a MUST option, if you can tune the coil antenna to the target frequency, you need not put this capacitor.

Hope that helps,
Have a great day,
Kan

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[kaibuechler]

Hi Kan,

I guess this tuning you mentioned is more like a smart design choice. Using a 130pF (with low tolerance) results in only +-6% inductance change, if the estimated internal capacities of the antenna, the IC and the connection would vary by +-20%. Without this capacitor the required inductance would vary by ~13%.

Thanks and regards,

Kai