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TRF7970A: Antenna Recommendation and Testting

Lawrence Wong
Genius 16730 points

Part Number: TRF7970A
Other Parts Discussed in Thread: DLP-7970ABP,

Customer is considering TRF7970A for a future design but they want to try different antenna pattern. They have the DLP-7970ABP EVM but the schematics are incomplete. They are not RF experts, and they are looking at off the shelf antenna pattern that can fit in under 10mm width, length they have some room to go longer than 10mm so they are open for options and any recommendation on matching circuit. Also is there a different EVM that is better suited to try different antenna? The 7970ABP schematic is incomplete, but the TRF79x0ATB looks better suited but no longer available?

  • 0
    TI__Guru*** 135355 points

    Hello Lawrence,

    What do they mean by schematics are incomplete? The schematics should be found on this TI design page: http://www.ti.com/tool/TIDM-NFC-RW

    As far attaching antennas go, they should be able to reference that just fine? Perhaps they are a bit tied up with how the module piece works but it's definitely a complete schematic.

    To attach an external antenna they only need to disconnect R11 and then attach to the CN1 pad on the right side of the module:

    I don't really have enough experience with off the shelf antennas to know if they can find that form factor easily. I suspect it will be difficult to find such a small antenna. Generally we have gotten our own off the shelf antennas from Taoglas: https://www.taoglas.com/product-category/nfc-antennas/

    An off the shelf antenna should already be matched to 50 ohms so no tuning is required.

    The DLP-7970ABP is the only EVM offered and should be fine for antenna testing as long as they understand where the pads to connect the antenna are located.

  • 0 in reply to Ralph Jacobi
    TI__Genius 16730 points

    Ralph,

    Do you mean pin 19 via/pad and not the GND pad that is labeled CN1?   So how does the EXTANT get routed? From the schematic it was not clear if RF_OUT was the same as EXTANT.  For the small size customer is looking at this antenna So you are saying no matching circuit is needed?

  • 0 in reply to Lawrence Wong
    TI__Guru*** 135355 points

    Hello Lawrence,

    Interesting antenna style, I have not worked with such antennas.

    The off the shelf antennas I am familiar with are some form of PCB antenna, typically flex. Not ferrite core.

    It mentions the impedance is 50 ohms already so maybe a match isn't needed? It is not very clear to me...

    If a match is required, then what can be done is either:

    1) Create a match network PCB w/ u.FL or SMA connector to attach to DLP-7970ABP

    2) Re-do match network for DLP-7970ABP, cut trace to PCB antenna (permanent damage), and connect the ferrite core at C29 and GND pads..

    In either of those cases, customer will have to tune the antenna themselves unless the manufacturer gives them information on recommended match circuit. Hopefully not. If they do, we have an antenna tuning app note, SLOA241.

    Lawrence Wong said:
    Do you mean pin 19 via/pad and not the GND pad that is labeled CN1?   So how does the EXTANT get routed? it was not clear if RF_OUT was the same as EXTANT.

    RF_OUT and EXTANT are the same, yes.

    For connectors like SMA / u.FL, there needs to be ground pad as well. The pads are set to be used with typical antenna connections. I was unclear in my prior message, but I mean that they should attach the antenna around the CN1 pad by placing down an antenna connector which goes there and also ties to Pin 19 (which isn't labelled clearly, so I like to reference CN1). I think u.FL will be easiest, but there should be SMA that also fit that pad style.