ST25R3911B with two antenna in single ended mode

[jmartinez1]

Hi,

I am working with the X-NUCLEO-NFC05A1 for testing and prototyping purpose. My goal is to detect and read RFID cards on two different card slots.

I am able to read the RFID cards using the differential antenna mode with only one antenna connected at RFO1 and RFO2.

However, since I want to read cards on two different location, I thought about using 2 antennas in single ended mode.

I configured the IO configuration register by setting the bit Single (bit 7) and multiplexing the two antennas by toggling the bit RFO2 (bit 6) when needed as cited in point 1.2.2 Transmitter

The antennas are respectively connected to RFO1 and RFO2 and both at ground using the Connector J300 on the eval board. With this configuration, I am not able to detect or read any cards. No inductive or capacitive wakeup IRQs occurs with this connection and configuration.

I could not find more information in the Datasheet on how to use the single ended mode.

Am I missing something important?

What more should I modify?

Is my goal doable?

Thank you for your help

Junior Martinez

[Travis Palmer · Accepted solution]

Dear Junior,

You are absolutely right. The "single" bit of "IO Configuration Register 1" puts the the IC into single ended mode. The "RFO2" bit of the same register then lets you decide which RFO/RFI shall be used.

This allows you to switch between two antennas just by changing one bit in the registry.

By default - without changing the hardware/antenna/matching - you should be still able to reader the tag in single ended configuration.

For more information about single ended antenna tuning, please have a look at the following thread:

ST25R3911B SINGLE-ENDED CONFIGURATION EXAMPLES AVAILABLE?

BR Travis.

[VK Verma]

Hi Tarvis !

I saw that everybody is looking support on "ST25R3911B with two antenna in single ended mode" and as no such application note is available on ST web, all are expecting few inputs/ informations from you and I am also one of them,

1. Circuit diagram/ connection diagram of two antenna design with single ended interface for ST25R39118.
2. I have posted one antenna design layout image which ST provides for STM32WB Bluetooth antenna (en.DM00470410.pdf) and that speeds up design because it does not required expertise and expensive network analyzers setup , similarly if such information is provided by you then it will accelerate the whole design activity with high degree of success rate.
3. Any STM32 based software application which can support such antenna arrangement and can be taken up for future application development reference.

I think I tried my best to sum up requirements effectively.

Thanks in advance,

VK Verma

[Travis Palmer]

Hello Verma,

Many Thanks for your inputs! They are really appreciated.

Let me quickly answer your hot topic questions:

1.) The ST25R3911B-DISCO schematic and layout is basically two single ended antennas driven in deferentially.

The upper and lower section of the above picture is exactly symmetric. Also the antenna itself can be separated in two single ended antennas.

This means, by setting the "single" and "rfo2" bit someone could already switch between these two antennas.

2.) The antenna proposal of the STM32WB does not really fit to the frequency range of NFC products. For operating at 13.56MHz a magnetic loop antenna and proper matching network is required.

To your point, there are schematic and layout files (PDF, Altium and Gerber) of our ST25R3911B-DISCO and X-NUCLEO-NFC05A1 available.

If someone does not really want to invest in a VNA, he could just copy the antenna design of those boards on his PCB and reuse the same matching components. Nevertheless, checking the matching network is highly recommended before going into mass production 😉

Surrounding / nearby traces could detune the antenna and therefore require an adaption of the matching network.

3.) Flipping the two above mentioned bits is already possible in the ST25R3911B DISCO GUI. Modifying the two bits in the "CHIP_GENERAL" mode of the Dynamic config tab are all the changes you need to do to operate the reader in single ended mode.

BR Travis