RFO normal level definition register

[atsen.1]

Hi!

Is there anyone could explain how we could set this register to get better range?

Thank you.

Regards,

Albert Tseng​

[Ulysses HERNIOSUS]

Hi Albert,

I think you are referring to ST25R3911B or ST25R3916?

In general the RFO normal level definition is set to achieve high output power while not violating maximum field strength requirements imposed by standards.

Output power is just one contributor to read range.

Please see e.g. the discussion here: https://community.st.com/s/question/0D53W00000etYnbSAE/st25r3916-what-register-settings-can-be-used-to-maximize-read-range.

Best Regards, Ulysses

[atsen.1]

Hi! Ulysses,

I could not realy understand the meaning of table 66 on the data sheet.

It seems we could have different setting for this regeister' value.

Thank you.

Regards,

Albert Tseng

[Ulysses HERNIOSUS]

Hi Albert,

I assume you talk about table 66 in DS of ST25R3911B which has the binary weighted segments:

As an example setting 5Fh means droff 5=0 and droff7=0. Adding these two parallel resistor segments gives 1/2+1/8 = 5/8 => 1.6ohm output resistance. Actual resistance value can be calculated by multiplying with actual RRFO (see table 101).

Best Regards, Ulysses

[atsen.1]

Hi! Ulysses,

Thank you for your kind response.

I also find some interested material as the following picture.

It looks we could get above 3 cm range by certain setting.

Now our project uses ST25R3915 chip. Would you please give me some hints to extend the range?

Regards,

Albert Tseng​

[Ulysses HERNIOSUS]

Hi Albert,

DPO has one main use case: Avoid exceeding Hmax when a PICC/card is in close proximity to be able to pass relevant standards. Another minor side effect is saving some power when a card is in close proximity.

As discussed in above thread there are various components contributing to the experienced read range. From an overall system perspective there are even more which are related to the reader and the tag, their antennas and their coupling.

Typically there are no settings in our chips to increase a read range. You are reporting 3cm: With which reader board with which tag? Is it your own antenna? How did you match it?

Are you aware of AN4974 which describes the process of antenna matching?

With our demo boards you should be able to get much more than 3cm. E.g. ST25R3911B-DISCO + ID1 ST25TA64K I get something like 10cm. With NFC-V I expect even more.

Best Regards, Ulysses

[atsen.1]

Hi! Ulysses,

It's great that the range of demo board could achieved above ​10cm.

But I would like to know whether the ST25R3911B could also do NFC WLC feature by adding some components. The extra deliever power may destory or limite dynamic range of RFI. How do we get the balance between RFO and RFI?

On the appliaction note, it suggest we measure the antenna parameter at 1MHz than transfer to 13.56MHz by calculation for concerning the skin effect. It quite confuse me that why do we not directly get the parameter at 13.56MHz. What will it be if the tag were hold inside the hand?

Thank you.

Regards,

Albert Tseng

[Ulysses HERNIOSUS · Accepted solution]

Hi Albert,

this is moving now more into analog topics where I am not the expert. If you have more questions on this then please close this question by Selecting "Select as Best" and open a new one.

From my understanding skin effect refers to https://en.wikipedia.org/wiki/Skin_effect and not the human skin.

For WLC please see https://community.st.com/s/question/0D53W00001EyEBTSA3/nfc-wireless-charging-reference-designs-available.

Best Regards, Ulysses