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Original question:

TMS3705: Methods to increase the read range of the receiver

TMS3705: Methods to increase the read range of the receiver

Michael Shamis
Prodigy 70 points
Part Number: TMS3705
Other Parts Discussed in Thread: TRF4140-Q1

We are about to design our first base station for HDX animal tags based on the TMS3705.

We plan to make it as a research / development platform for our application, with an aim to get as long reading range as possible with our antenna being limited in size.

One of the optional circuit we are planning to include there is an additional RF amplifier with an active band-pass filter with the centre frequency of (around (134.2 + 123.2) / 2 =) 128.7 kHz to increase receiver sensitivity.

My attempts to prototype it on the breadboard and to hook it up to the RI-ACC-ADR2-10 have not been successful so far, as I am getting a lot of "false positive" readings out of TMS3705. I presume that this is due to the TMS3705 receiver picking background noise from the connecting wires.

To avoid further efforts, may I ask you please for your professional opinion: do you think that TMS3705 receiver is as sensitive as it can get in practice or adding an extra pre-amplifier could improve the overall system sensitivity (and, therefore, the reading range)?

  • 0
    TI__Guru*** 128255 points

    Hello Michael,

    Adding an amplifier stage can improve the output power and reading range.

    Please see our range extender app note for details of a solution that TI has proven works for range increase: http://www.ti.com/lit/an/scba031/scba031.pdf

  • 0 in reply to Ralph Jacobi
    Prodigy 70 points
    Hi Ralph,
    Thanks for your reply. I have read this app. note (that is quite excellent, BTW), as well as any other document I was able to find on the TI site. My question, though, was about receiver, not transmitter. During our investigations of the existing TIRIS products (RI-RFM-007 / RI-RFM-008) we have found (using a sniffing antenna) that transponders keep sending data after the charging period well beyond the reading range of the base station. I am aware that these TIRIS devices use TMS3705 predecessor RI45530ns, but the question remains the same: if receiver's sensitivity could be improved, the reading range may be extended (perhaps, only in some circumstances). It is quite apparent that the developers of base stations ICs at TI were trying hard to make receivers as sensitive as possible - but there are, perhaps, some ways to further improve them with external pre-processing of the receive signal from the antenna...
    Hence, I would like to rephrase my original question, please: would your engineers recommend trying to improve TMS3705 receiver sensitivity by adding an active bandpass filter / amplifier between antenna and SENSE input of the TMS3705 (or by any other means)?
    Kind regards,
    Michael
  • 0 in reply to Michael Shamis
    TI__Guru*** 128255 points
    Hello Michael,

    Understood, I discussed this with an expert on the device and have the following feedback:

    1) For the TMS3705, we have never used any pre-amp or filtering like described and we don't think it would be necessary. From all we have seen with operating the device, the receiver can pick up the transponder signal until the uplink becomes incomplete because of a lack of energy. Therefore, maximizing the TX energy is most important for amplifying read range and we don't believe that increasing the receiver sensitivity will provide any notable impact on read range.

    2) You may want to look into the TRF4140-Q1 as another option for evaluation given your system requirements. While it is a device intended for automotive use and may be overkill for your use case, it has more output power and has a more sensitive RX path, so it may be a possible fit for you. You can request the full datasheet online.
  • 0 in reply to Ralph Jacobi
    Prodigy 70 points

    Hi Ralph,

    Thank you very much for the comprehensive info. We are progressing now with our project and are getting some promising results.

    Please send my regards to your engineering team.

    Best regards,

    Michael