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LAUNCHXL-CC13-90: CC13-90 matching at 888MHz

Eleftherios Kampianakis
Prodigy 20 points
Part Number: LAUNCHXL-CC13-90
Other Parts Discussed in Thread: CC1190, CC1310

Hello,

I have an application where I need to transmit a tone at a frequency anywhere in the range of 886-892 MHz and I have identified that the CC1310 + CC1190 has the specs I need so the CC13-90 Launchpad is the natural choice for testing

I have a US-version of the CC13-90 that I removed the A2 inductor and sorted R158 so that I can use the on-board SMA instead of the antenna. I conducted a frequency sweep from 850-930 MHz @ 26 dBm using the SMARTRF Studio and recorded the data using a keysight SA.

As expected,at the frequency range of interest is far from the nominal 26 dBm and it ranges from -16 dBm to 8dBm. I suspected that this is a matching issue so I went into the schematic of the Launchpad and saw that the EU model (tuned at 868 MHz) has a C24 2.2 pF installed whereas in the US model it is DNP. Aside from the differences in the antenna matching (which I'm not using) I didn't see anything else to be different, see here:

So I installed a 1.8 pF cap to try it out but the frequency response barely budged. Am I missing something here?

How can I tune the CC13-90 launchpad to a frequency range of 880-890 MHz?

Thanks!

  • 0
    Prodigy 20 points

    Ok I found the issue. The CC13-90 US launchpad uses the B39921B3588U410 SAW filter after the CC1310 output. The filter has a response that doesn't include the 880-890 MHz band that I'm interested in. Here is the response for reference:

    Which is basically exactly what I measure with the SA.

    Unfortunately the EU launchpad includes a SAW filter that ihas a passband outside of my band of interest. Do you have any SAW filter recommendationsfor that band ? Would I have an issue if I operate my launchpad without it?

    Thanks!

  • 0
    Prodigy 20 points

    Ok after removing the SAW filter and shorting the corresponding pads I get the response that I need see below. I suspect that the 3rd harmonic is gonna be awful but I don't care much for this application.

  • 0 in reply to Eleftherios Kampianakis
    TI__Genius 13660 points

    Hi,

    Glad to hear you've had some success with this. To answer the question in your original post about the addition of C24 (and explain the reason for adding it):


    You're correct that the EU BOM is essentially the same apart from the addition of C24 (to give improved performance at the 2nd harmonic); I would recommend including this component if you are operating in this frequency band.



    This LC filter has a narrowband response, however, so you would need to optimise it for operation at your band of interest to see any benefit (aiming for a resonance at 885 MHz) as it is currently optimised for 868 MHz.

    Regards,

    Zack

  • 0 in reply to ZC
    Mastermind 6160 points

    or "L25/C210 and C24/L27 form two notches to filter the second harmonic" as described in www.ti.com/.../swra542.pdf