Using a PAIR of coils with a NFC transceiver

JPehl.1 · ‎2020-12-03

Today I have a project/board which uses the ST25R3911B NFC transceiver from ST, and it uses a dual layer coil (made of PCB copper traces) on the RF part. This coil is dual layer, that is, is a SINGLE coil made on the 2 sides of the board.

But I have a new situation/project where I want to have 2 (TWO/DUAL) coils connected to the NFC transceiver, and these coils would be separated with around 6 centimeters apart (one coil reads each side of the thing). They would be placed connected in parallel with their pair of wires... Is that possible? Is there a NFC transceiver from ST which can drive/read 2 independent coils? What can be done engineers? Or do I need to use a pair of transceivers?

Regards,

Jeferson.

Travis Palmer · ‎2020-12-03

Hello JPehl,

The ST25R3911B can either drive one antenna in differential mode or two antennas single ended. The "single" and "rfo" bit of the "IO configuration register 1" can be used to switch between the two antennas.

In single ended mode for each antenna you will need one EMI Inductor, EMI capacitor, one series capacitance, one parallel capacitance and a damping resistor.

The latest ST25R Antenna matching tool helps you calculating the required components. The same process as for differential antenna can be used.

Important is, that the RFO1 is connected with the RFI1 and RFO2 with RFI2.

please let me know, if you have additional questions.

BR Travis

View solution in original post

Ulysses HERNIOSUS · ‎2020-12-03

Hi Jeferson,

yes we will sell you a pair of transceivers for every board of yours!

However the ST25R39 devices (i.e. ST25R3911B and ST25R3916 + derivates each) support the option to drive two single-ended antenna instead of one differential antenna. Both devices have a single and rfo2 bit which can be used by application software to switch between two different antennas.

Single ended topologies are also supported by STSW-ST25R004

Maybe that is an option for you?

Regards, Ulysses

JPehl.1 · ‎2020-12-03

Hi Ulysses, thanks.

So I understood that we can use OR a pair of ST25R3911B (one for each coil, differential mode) OR a single ST25R3911B driving 2 single ended coils? About the second option, could you provide a simple diagram of it? How I will do in schematic about second option? Would it be the FIRST COIL connected to RFO1/RFI1pins and the the SECOND COIL connected to RFO2/RFI2pins, both in single ended mode?

I need to be even clear.