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TRF37D73: TRF37D73 inductor selection and schematics

Giovanni Peroni
Intellectual 705 points
Part Number: TRF37D73


I believe, but I'm not certain, that this schematics is wrong for the TRF37D73:

image.png

 

  • The operating frequency is 1.5 GHz, while the 33nH inductor SRF is 1.7 GHz (LQP03HQ33NH02D). The LQP03HQ33NH02D is rated for 150 mA while the TRF requires 50 mA. Is that ok?
  • Is it acceptable to have a ferrite in the line (the thinking was to reduce noise further), but it's probably dumb as it might lead to issues?
  • I assume the feedthrough capacitor is ok. 

Thanks!

 

 

  • +1
    TI__Intellectual 1320 points

    Hi there,

    For RF blocking purposes, you can use an inductor above its SRF, as long as it still has impedance high enough to block the RF from leaking into the power rails. Above its SRF it just is slightly capacitive rather than inductive, which doesn't really matter as long as its impedance is still high enough.

    What using this 33nH 0402 instead of the suggested coilcraft 100nH 0603 (such that is on the EVM) will affect is the frequency response. You will see the lower frequencies have less gain as the RF is being let through sooner into the power rails than with the 100 nH. 

    Similar thing for DC block capacitor. For most purposes, up to like 15 or 20 GHz, most 100nF 0201 ceramic capacitors will perform the same. The biggest impact is actually the package size (0201, 0402, 0603 etc), as this will determine the series inductance at above SRF. The smaller the better. Who cares if it goes inductive, if its only 100pH inductive!

    As for the current concerns, it should be ok. A ferrite in the line is a good idea for filtering out your power supply before it goes to your bias. 

    Thanks,
    Gideon

  • 0 in reply to Gideon Townsend
    Intellectual 705 points

    Hey Gideon, thank you for an extremely informative answer that went in depth and allowed me to understand what the issues at play here are.