P2P on 7970 with low RF

Hi Paul,

Which P2P modes and bitrates do you intend to use at Low RF?

By this I mean, will your device be a target device, or an 'initiator' device which polls for other P2P devices. Also are you planning to do Active or Passive P2P communication?

We have an app note which details how to use P2P with our TRF7970A: www.ti.com/.../sloa192.pdf

Also the TRF7970AEVM is not the right platform to use to test or evaluate P2P mode. You will want our BoosterPack+MSP430 LaunchPad combo found here: store.ti.com/nfclink-bndl.aspx

That will work with our latest P2P example firmware which you can download at: www.ti.com/.../sloa227

Hi Ralph,

We want tot use Active P2P for the low RF-signal (<-50dB), where the RF-budget is far too low for load-modulation.
Bitrate is not a concern.
In the many documents about the TRF7970, we can not find the minimum RF-signal at the receiver ,
for reliable detecting the presence of external RF as target.

Is this only set bij threshold-voltage in the ¨NFC Target Detection Level-Register¨ in table 6-16 in  TRF7970A.pdf ?
What RF-sensitivety can be realized with the BoosterPack+MSP430 LaunchPad combo ?

Hi Paul,

I see, we haven't had such an application come up before. I don't believe we have tested the minimum RF sensitivity with our BoosterPack and LaunchPad combo yet, but I will check further into that and what we have/haven't done on that aspect.

Regarding register 0x18, that is for RF wake-up specifically, and that is what the bit thresholds are being set for in terms of detection where is the device is sleeping, no wake-up will occur unless the threshold is passed as defined in Register 0x18.

What device are you looking to communicate with? If we can get some details about the other device then we can better assess if the low RF signal can be detected.

Also what kind of range you looking to get? For such a low power RF signal, you probably will not get the range you would with a normal 'full power' transmission.

Please let us know what you can about those topics, the more we know the better we can look into this and provide you details about what is or isn't possible with our TRF7970A device.

Hi Ralph ,
We have an inductive system, in where an input-power of 200mW, can generate a field at the output of only 0.2A/m.
The receiver-power at that place is limited to 500nW, or 5mV RMS in 50 Ohms, due to the limited size of the coil. Attenuation is 56 dB.
Such low signals can be detected for wake-up (Initiation, Anti-Collision), but why not for communication ?
The RF-sensitivity for P2P is our main argument to use the TRF7970, We like to use it at both sides of the link.
A simple FSK- or ASK- radio, 2-way, will have sufficient RF-budget, but we did not find it for 13.56MHz.

Regards,
Paul

Hi Paul,

With that output power and the size of the coil, I have my doubts that Active P2P is the best way to go about this. Active P2P can be pretty touchy in terms of communication even with more power and larger antennas. I don't think downsizing the coil/power would help that at all and could make it far worse.

Have you tried using passive P2P during any testing yet? That would probably be a better option.

You haven't mentioned the range yet, but given the small size of the coil, I'm assuming it will be pretty short range? How big is the coil?

As I mentioned before, we've never tried to do such low power communications, but I wouldn't flat out rule out that its impossible, it just hasn't come up in any application we have worked on. So I can't say whether or not it would work for communication.

Have you done any testing with that power budget and run into communication issues? If so, what firmware are you using? Custom firmware, or our P2P example? We have an app note: www.ti.com/.../sloa192.pdf and the latest software can be downloaded from: www.ti.com/.../sloa227 - are you using this TI example? Also are you using the BoosterPack on both ends for the hardware?

Hi Josh,

I have been working for > 20 years on various inductive systems, where coupling-factors, field-strenghts, tuning-effects and signal-losses etc,
can be calculated or measured exactly. In the past, our RFID-front-ends contained own designs with linear IC's and discrete amplifirers, in where power, sensitivity and dynamic range are exactly specified.
In modern RFID-transceivers like the 7970 is seems difficult to specify the sensitivity, so after all we have to measure it.
I try to order the eval- set of the 7970 with Booster-Pack.

Regards,
Paul Rebers
REBIX