Appendix 1. PA Optimum Impedance Determination
The matching network should present an optimum impedance for the PA at the 2G4RF_IOP pin if a 50 Ω termination is applied at the
antenna port. The optimum impedance depends on the power level and the package version. Fortunately, as shown below, they are
quite close to each other, so one proper match is a good compromise for all versions and power levels. The optimum impedances are
determined empirically by load-pull methods.
Figure A below shows the 2.4 GHz load-pull curves measured at the TX pin of the 7x7 mm, 48-pin 2.4 GHz single band EFR version
with 20 dBm power setting. The optimum impedance point here is ~23.7+j7.1 Ω and is quite constant with frequency. For example, in
the middle of the 2.4 GHz band (2.45 GHz), it is only very slightly off (~24.1 + j7.2 Ω).
Figure B below shows the measured 20 dBm, 2.4 GHz load pull data for the 7x7 mm, 48-pin dual band EFR version at the TX pin.
Here, the optimum impedance is approximately 23 + j11.5 Ω. At 2.45 GHz, the optimum is slightly lower: ~21 + j10.4 Ω.
Figure C below shows the measured 20 dBm, 2.4 GHz load-pull data for the 5x5 mm, 32-pin single band EFR version at the TX pin.
The optimum impedance here is approximately 20 + j14 Ω.
Figure 1.1. Load-Pull Curves and Optimum TX Load Impedances at the 2G4RF_IOP Pin of the Different EFR32 Package Ver-
sions: a) 7x7 mm Dual Band, b) 7x7 mm Single Band, c) 5x5 mm Single Band, d) Optimum TX Impedances Shown in One
Smith Chart
The 2.4 GHz, 20 dBm level optimum termination impedances for the three EFR versions are shown together in D of the above figure.
As only one common match will be used for all variations, a compromise must be found. Fortunately, the three optimum impedances
are close to each other i.e., within the ~0.3 dB degradation load-pull circles if one chooses the middle point, so if a good compromise is
AN930: EFR32 2.4 GHz Matching Guide
PA Optimum Impedance Determination
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