the possible maximum reading distance with ST25R3916

[DSai.1]

We are developing a IC card skipass Reader product for ski resort market. 

I checked TRF7961 from TI, but it can provide only 200mW output power.

In the datasheet of ST25R3916, this IC can give up to 1.7W output power.

I wonder these two are same index or not. I would like to know the maximum reading distance with ST25R3916. Could you give me some information or advice?

If possible, we want a distance about 30cm. With TRF7961, about 15cm can be obtained.

Thank you very much for your help in advance.

[Peter BENSCH]

Welcome,@DSai.1​, to the community!

With the ST25R3916 you should be able to reach the reading distance - but be careful: the reading distance depends not only on the output power, but especially on the antenna geometry.

It is also important to observe the maximum power values defined by the NFC forum, because otherwise you will pump too much energy into the tag if its too close. For this reason, reader devices such as the ST25R3916 contain a function called DPO (Dynamic Power Output).

Does it answer your question?

Regards

/Peter

[DSai.1]

Dear Peter,

thank you so much for your quick answer.

It is an exciting information for our project.

Because we don’t need a design with extra

amplifier, it will reduce a lot of time for development. In our application, we will use ISO15693 card tag. Do you have any hardware and software sample for our reference?

best regard

Sai

[Brian TIDAL]

Hi Sai,

on HW side, you can use either:

1. the X-NUCLEO-NFC06A1 NFC card reader expansion board on top of Nucleo-64 MCU board such as NUCLEO-L476RG, or
2. the Discovery kit for the ST25R3916

Solution #1 is intended for a standalone system whereas solution #2 is designed to work with a PC GUI over USB. Both solutions come with an antenna that can be easily cut and replaced by your custom antenna. Of course, when using your own custom antenna, the matching circuit will have to modified accordingly: you can use the Antenna Matching Tool for ST25R NFC/HF reader family or the online eDesign suite to design your matching circuit.

On SW side:

1. the Discovery kit for the ST25R3916 comes with the STSW-ST25R011 package containing all source files to compile the firmware

• the X-NUCLEO-NFC06A1 comes with the ST25 Embedded NFC library including various demos

Both software solutions are based on the same RF Abstraction Layer (RFAL) and support NFC-V - ISO/IEC 15693 communication.

The PC GUI that communicates with the Discovery kit for the ST25R3916 provides an easy way for changing analog settings. Therefore, this might be your preferred solution during the antenna setup and test phase.

Rgds

BT

[DSai.1]

Dear Brian,

Thank you very much for your detailed advice and information.

We will do based on your advice.

best regards

Sai

[Brian TIDAL]

Hi @DSai.1​ 

as far as I know, most of the skipass reading systems are based on NFC-V - ISO/IEC 15693 standard as this technology provides greater reading distances as compared to ISO/IEC 14443 (NFC-A/NFC-B) or NFC-F. Can you confirm that your plan is also to base your system on ISO/IEC 15693?

Regarding the reading distance, there was similar questions on the community in various ST25R readers. The following ones may help:

https://community.st.com/s/question/0D50X0000AvgiHoSQI/st25r3911b-with-antenna-size-30x40cm

https://community.st.com/s/question/0D50X00009XkWCSSA3/design-questions-around-st25r3911b

https://community.st.com/s/question/0D50X0000Bh5zQqSQI/how-to-use-st25r3911b-for-long-reading-distance40cm

Rgds

BT

[DSai.1]

Dear Brian,

Thank you very much for your great help.

We use ISO15693 for a longer reading distance in our application.

I will study the links you mentioned.

By the way, could you recommend me any dealer for obtaining the board or kits in Japan?

Best regards

Sai

[Peter BENSCH]

You will get a quote from your preferred distributor in your region, which you can find here and where you can filter for By Contact Type = Distributors and By country/region = Japan.

Good luck!

Regards

/Peter

[DSai.1]

Dear Peter,

I have a new question for obtaining the maximum output power. For STR25R2916, there are power input pins VDD and VDD_TX.

My question is what voltage is need for obtaining the maximum output power. In our application, the power is from a lithium battery which voltage is

about 3.7 ~ 4.0V.

I wonder the maximum output power may be obtained with the voltage lower than 5V for VDD_TX and VDD?

In the system diagram Fig.2 in page 14 of ST25R3916 datasheet, VDD and VDD_TX are connected together. Is it possible to

connect VDD to a 3.3V power and VDD_TX to batter which is from 3.7 to 4.0V?

In our application, the SoC can provide a 3.3V power source for peripherals connected.

thank you in advance for your help.

best regards

Sai

[Ulysses HERNIOSUS]

Hi Sai,

please see 4.2.11 of the DS:

• "VDD and VDD_TX must be connected to the same power supply."
• You may connect VDD_IO to to the 3.3V from your SoC.
• Output power of course depends on the voltage. You have also options to bypass the VDD_RF regulator if your supply is stable enough (short VDD_RF and VDD_TX). Please refer here also to symbols IVDD_LDO and IVDD_EXT.

BR, Ulysses

[DSai.1]

Dear Ulyssess,

thank you very much for your advice.

Based on your advice, I read the 4.2.11 in datasheet.

It said there are two basic operation modes 3V and 5V.

I wonder if we can use 5V , if we connect VDD and VDD_TX

to a battery that output is 3.7V ~ 4.1V. or if we want to use

5V mode, we must give a power supply that is over 5V?

best regards

Sai

[Peter BENSCH]

First of all, it is questionable whether a significant increase in range can be achieved by increasing the power. The overall system includes not only the TX but also the passive tag, which does not transmit itself but can only modulate the surrounding field. For a range increase, it might be more important to increase the RX sensitivity.

Regarding VDD and VDD_TX:

As can be found in the datasheet, section 4.2.11:

• VDD is the main power supply pin. It supplies the ST25R3916/7 blocks through two regulators (VDD_A, VDD_D)
• VDD_TX is the transmitter supply pin. It supplies the transmitter via two regulators (VDD_RF, VDD_AM). VDD range from 2.4 to 5.5 V is supported. VDD and VDD_TX must be connected to the same power supply.

Does it answer your question?

Regards

/Peter

[DSai.1]

Dear Peter,

thank you very much for your help always.

I think maximum output power should be a sufficient condition for a long reading distance.

If the maximum output power can be obtained, we can have more possible adjust margin

to achieve a long distance.

If possible, would you teach me the possible approach to increase the RX sensitivity?

best regards

Sai

[Peter BENSCH]

The RX sensitivity can be adjusted within limits via register 3 and 4 (see datasheet, section 4.5.16 and 4.5.17).

If you fixate only on the maximum output power, you will inevitably reach the limit at which tags can be destroyed if the distance is too small.

Essentially, several things affect the maximum tag reading distance: Auto Antenna Tuning (AAT), Dynamic Power Output (DPO) and antenna size. The first two points are already covered by the ST25R3916, so that only the antenna size remains as a factor that can be influenced for the reading distance.

However, I do not assume that the reading distance will be much greater than approx. 20...22cm even with huge Class 1 antennas.

Good luck!

If the problem is resolved, please mark this topic as answered by selecting Select as best. This will help other users find that answer faster.

/Peter

[DSai.1]

Dear peter

thank you very much for your detailed explanation.

I will study the datasheet more and try to design our solution. If possible, we would like to use an antenna with about 20cmX40cm size, and try to obtain a 30cm reading distance.

For our reference, could you tell me the size of Class 1 antennas?

best regards

Sai