TRF7970a, RX Special Setting Register

double thread ==> see http://e2e.ti.com/support/wireless_connectivity/f/667/p/370192/1302006.aspx#1302006 

Hi Josh,
I'm sorry, but it's a different topic. I'm asking here about the RX bandfilter cain.

Well, NFC Active and Passive Peer-to-Peer Communication Using the TRF7970A recomends in chapter 3.1 to use setting 0x30. This means 18dB Attenuation and Bandfilter 450kHz to 1.5MHz is selected. But this does not fit to a 106 kbps communication.

I tried to draw a picture from what I read in the data sheet:

Please check and correct if I'm wrong.
Regards

Guenther

i see - well the HF RFID/NFC ISO14443 based passive devices communicate back to the PCD/Initiator using sidebands of ~848kHz, centered on the fundamental, which is used for powering the PICC and downlink communication. ISO15693 devices use either 424kHz or 484kHz, depending on how they have been instructed to respond. This is what register 0x0A is for. 

Hi Josh,
That was my asumption too. But why does the app. note recomend this setting (0x30) for a 106 kHz bandwidth? Recomendation and datasheet do not fit together in my mind. Am I wrong?

Guenther

the section calls out 106kbps (which is a data rate), with the BW setting expected for communications at that data rate, since in P2P, when discussing the use of 106kbps data rate implies using Type A air interface, which uses uplink subcarrier of 848kHz at a data rate of 106kbps...remember or know that in Type A uplink, sequences D, E and F, which result in bit codings for logic 0, logic 1, SOF and EOF are modulations of the carrier by the subcarrier for defined bit durations. 

@106kbps (Type A)

sequence D = 848kHz subcarrier mod of carrier for first half of bit duration = logic 1 and SOF

sequence E = 848kHz subcarrier mod of carrier for second half of bit duration = logic 0

sequence F = no modulation of the carrier for a bit duration = EOF

Hi Josh,
Now it makes sens. Our P2P is 106 kps without subcarrier and active communication. So all transmitters (initator and target) use OOK and communication is just between TRF7970As. As we run in a noisy environment we like to use the smallest possible bandwidth to reach a high signal/noise ratio. A lot of filtering is already done in HW on adaptation. Now it's to setup the TRF in the correct way.

So is seems best filter is C212 or even no filter at all. So what value for RX Special Setting Register (0x0A) to use then?

Guenther

Hello Josh,

We did further testing and found the best setting was B7 (C212) only for a 106kbps active P2P communication in duplex mode without sub-carrier. Below an updated drawing based on our finding.

Adding additional filters or changing to other filters reduced the capability to decode the incomming signal.

Thank you for all your support and help

Guenther