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Forum Post: RE: CC2540 Antenna Matching

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CJ,

#1.  I simulated about 11 dB return loss @ 2.4 GHz -- L252, C253 & L253 form a LPF.  Also, at these freqs you have to include the PCB traces and of course component parasitics.

#2. If you don't use the same vendor for the parts and the same P/N's (they used Murata C's & L's) and if you don't use the recommended layout, you will probably need different component values for best output power & eff.  The device impedance is the complex conj of the 70 + j30 load impedance so it's 70 - j30 which is 82.86 ohms in par with 343 fF @ 2.4 GHz.  The 18 pF caps are coupling caps but could be adjusted. I did a quick sim of the impedance matching parts (L251, C252, L261 & C262) and found 2.2 nH and 0.8 pF worked better.  Of course this was only a simulation.  It is best to keep the L's & C's the same for symmetry which is what I did.  The match return loss was 18 dB at the node that feeds the T-LPF.

BR,

Eric Hooker

RF Consultant 


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