ST25DV and ST25R3916B operating distance

[OpusOne]

Hello,

I'm currently evaluating the ST25DV chip to implement bidirectional NFC communication with a custom device. So the idea would be to take advantage of the enhanced operating range of ISO 15693 and use the mailbox for direct data exchange.

For the first evaluation step, I have a few ANT7-T-ST25DV64KC boards and a X-NUCLEO-NFC08A1 board that I use on a Nucleo 64 w/ STM32G0B1RE.  To start with, I've built the NFC08A1_PollingTagDetectNDEF example project.

It does work fine and all NFC tags (with various types) I have tested it with do work. The ANT7-T-ST25DV64KC are detected with no problem at a distance up to about 50 mm. Which isn't bad. Now my goal is to reach about 100 mm if that's possible, knowing that in the final device, the tag antenna may be even smaller. So I guess that if that goal is at all possible, that would require either tweaking the parameters on the reader side (ST25R3916B) and/or using a much larger antenna for it.

First things first, are there any possible register settings on the ST25R3916B, compared to the default options in the NFC08A1_PollingTagDetectNDEF example, that would improve range in ISO 15693 mode? I have enabled DPO (which isn't enabled by default) with the following define:

#define RFAL_FEATURE_DPO true

but it didn't seem to make any difference in reading distance. Maybe it's just better to enable it to avoid frying tags when they are very close to the reader? But for maximizing distance, that does apparently not much at all.

Other than changing settings, I see only changing the reader antenna (as I'll need very small antennas for the tag side)? Does achieving 100 mm with antennas as small as on the ANT7-T-ST25DV64KC on the tag, or even smaller, sound at all possible? What would be the minimum reader antenna diameter that would have a chance of working?

Thanks for any help!

(Note: for the record, the reading distance of the ANT7-T-ST25DV64KC doesn't seem to be much different than with other tags - mostly type A - I've tested, while I was expecting to see at least a bit more with ISO 15693.)

[Ulysses HERNIOSUS]

Hi OpusOne,

just setting the feature enable flag for the DPO will not do much: For one it is not called and secondly you would need to configure it properly for the given antenna, matching and the environment. It can be used for limiting the field strength in close distance.

Typically the operating range is limited by the power received by the tag. 

By settings of the chip registers I don't expect that you are able to achieve any range extensions. The settings as done are good. Maybe by boosting the output power (higher supply), lower resistance matching you could achieve something but I am pretty sure that you will not be able to double the range.

BR, Ulysses

[OpusOne]

Hi Ulysses,

ok, so the DPO feature defintely requires more work than just enabling a flag. I'll have a look at this, but as I suspected and you confirmed, it will probably not do much for improving range.

What about the reader antenna? I think a common rule of thumb is that the max usable range for NFC (or inductive communication in general) is roughly the diameter of the reader antenna. On the NFC08A1, the antenna is ~ 47x35mm, so a usable range of ~ 50mm seems to be consistent. I'm guessing that using a larger antenna (say 100x100mm or so) may get us a consistent 100mm range, am I right in thinking so?

The antenna looks detachable on the NFC08A1, but I can tell there is a non-trivial adaptation network that may need to be modified. Do you think that would be time well invested?

 

[Ulysses HERNIOSUS]

Hi,

yes I expect this rule of thumb to hold. You could also experiment with the antenna of STEVAL-25R3916B which is 66x66mm to see how much range you get with that. If you want to do your own antenna you will it would be best to follow the AN on antenna tuning for ST25R3916B.

BR, Ulysses