PN7462/PN5180 RSSI Measurements

[j_bechtold]

Hello,

For an NFC application we are developing, we would like to extract some path loss information from the channel between the reader and the tag. In particular, we would like to be able to modify the transmitter power levels during transmission and extract the received signal strength when receiving.

During my search for NFC transceivers, I came across the PN7462 NFC mcu and the PN5180 NFC frontend that both possess the AN11742 Dynamic Power Control (DPC) feature by which the transmitter field strength can be modified. However, what I was not able to find was the possibility of measuring the received signal strength. Is there any way of extracting the RSSI? Might there be another chip more suitable for our requirements?

Given that there is a possibility of extracting the RSSI, we were considering using the OM25180FDK development kit for our first tests, but any other suggestions are very welcome.

Looking forward to hearing from you.

Best Regards,

Jonathan

[j_bechtold]

Dear Jonathan,

Thank you for your insights.

I went ahead and purchased the respective development boards (PN5180) in order to take some measurements and observe the close coupled effects. Do you have any sample project in which the DPC Calibration (similar to that in the NFC Cockpit) is done and where I can switch the DPC gears and measure the respective AGC on demand?

That would be very helpful!

Best Regards,

Jonathan

[Jonathan_Iglesias]

Please check the following datasheet https://www.nxp.com/docs/en/application-note/AN11742.pdf

it explains what is the DPC which registers are involved and how it works, you can use this to check the registers in the library, since there is no specific example for DPC.

BR

Jonathan

[Jonathan_Iglesias]

Dear Jonathan Bechtold,

Hope you are doing great, I think the PN7462 and PN5180 are suitable for your need since they have the same moduel of DPC. but  is is important to mention that  in a normal radio communication we have device 1 = Tx and device 2 = Rx. The carrier is transmitted by the Tx, and the Rx can measure the RSSI. In NFC the Rx (our Reader) transmits the carrier itself, while the Tx (the card or tag) just "loads" the field. The NXP ICs are build to provide the optimum reception, if the design guidelines are taken into account. For PN7462 family or PN5180 this level is even adjusted automatically, as long as the AGC value (can be checked by reading a register) is within a valid (and very wide) range. This AGC value can be seen like the TI's RSSI, but is controlled automatically. First of all, there is no reason to believe that a tag, which is closer to the antenna, causes a stronger response signal. In close coupled systems normally position detection of tags is a very sophisticated topic.  That requires a 1:1 solution, with carefully designed tags and tight tolerances. Then the AGC_VALUE  ( used by the DPC) can indeed be taken as an indication of the reader-tag distance. But as said, that require a very careful design.

I explain this because RSSI is an interesting topic in NFC.

let me know if you have more questions.

Have a great day !

BR

Jonathan