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I'm connecting an antenna to Atmel's SAMR21 microcontroller and the datasheet provides this guidance:

an impedance matching framework

I've found 2450BL15B100E, an SMD balun, but I'm not sure if it actually contains a transformer, or if it's in fact a lumped LC balun (in which case I'm guessing I wouldn't need the coupling capacitors?).

So, should I put the coupling capacitors between the processor and the aforementioned part?

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2 Answers 2

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The answer will largely depend on the internal makeup of the input port of the microcontroller. A DC path to ground from the balanced RF input port is likely to be undesirable, especially if the manufacturer has suggested capacitive coupling. These lines could go directly to transistor stages and the DC grounding (through the balun winding centre-tap) would alter the biasing.

Is there a good reason not to include the coupling capacitors?

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  • \$\begingroup\$ There is no reason other than I've already had PCBs made and soldered everything on. :) \$\endgroup\$
    – avakar
    Jan 3, 2016 at 18:52
  • \$\begingroup\$ Can you cut the tracks and fit a tiny cap over the cut? \$\endgroup\$
    – Mark Ch
    Jan 3, 2016 at 18:54
  • \$\begingroup\$ I can't, the balun is right next to the MCU. \$\endgroup\$
    – avakar
    Jan 3, 2016 at 18:55
  • \$\begingroup\$ I guess what I'm asking is, can you tell from the datasheet if the part has a DC path between the balanced ports? It wouldn't if it were a lumped balun, would it? \$\endgroup\$
    – avakar
    Jan 3, 2016 at 18:56
  • \$\begingroup\$ I mean between a port and the ground. \$\endgroup\$
    – avakar
    Jan 3, 2016 at 18:57
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Put the coupling caps in .Even if there is no DC upset without them they still have a role to play.What they do is attenuate the really low frequency stuff. There are lots of unwanted signals around in our crowded RF spectrum .The stronger ones tend to be at the lower end but not always.The coupling caps could make your RF link less likely to get crunched by unwanted interference.

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