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TRF7970A: Read Holes

Joshua Yam
Prodigy 100 points
Part Number: TRF7970A

Hi E2E-ers,

The TRF7970A is designed to have 2 RX inputs to eliminate the possibility of communication holes.

Also, there is an old (but unofficial) TI app note on an external NFC PA amplifier where the external filtering implemented separates RX_1 and RX_2 by a phase shift of 40-60deg for this very same purpose. 

Can anyone explain what read-holes actually are, how they impact/degrade NFC communication and how the phase shifting mitigates this. Tried googling these very same questions but very little coverage is out there. I have a feeling these are not the read holes referred to when a reader antenna has such a big coil that the center of the antenna has a H-field hole in the center of the antenna. 

Appreciate it

Thanks!

Josh 

  • 0
    TI__Guru*** 135355 points
    Hello Joshua,

    It's true that the datasheet discusses this point loosely, but with our years of experience with the device, we have found very limited uses for the dual RX architecture providing better results. On rare occasions in system specific configurations between reader and tag, the secondary channel gets better reception of replies.

    In general the idea behind using both channels would be to check the RSSI receiving a command from each channel and then use the one that is highest. Often there is no difference, and also the checks are usually more to improve the robustness of communication at the edge of read range rather than extend the maximum read range a notable amount.

    As far as the term 'read-hole', I never quite agreed with that usage in the datasheet given the context of the feature. A better way to describe the use case where the dual-RX architecture can be beneficial is that is aids with communicating at the edge of the read range where the RF field is weaker. Because the tag replies with load modulation onto the RF field, there are cases where the phase shift allows the receiver to better decode the load modulation data and correctly receive a packet.

    Please let me know if there are specific points you would like further clarification about.
  • 0 in reply to Ralph Jacobi
    Prodigy 100 points
    Hi Ralph,

    Thank you very much for the very well written explanation.
    This really helps.

    Cheers
    Josh