What is the optimum load impedance for EFR32 Series 1 wireless gecko at 2.4GHz?
The optimum termination impedance is determined by load-pull measurements at the 2.4GHz frequency band. The optimum load impedance yields the best TX power efficiency, while the RX performance is also close to its optimum.
The EFR32 has a single-ended 2.4GHz RF pin for TX and RX (2G4RF_IOP). The other pin, 2G4RF_ION, has to be tied to the GND and cannot be interchangeable with 2G4RF_IOP.
The 2G4RF_IOP pin does not need to be pulled up to the VDD, since the 2.4GHz PA is supplied from a separate PAVDD pin, moreover the RF pin is DC-grounded.
The optimum termination impedance at the single-ended 2G4RF_IOP pin is 23+j11.5 ohms in the whole 2.4GHz ISM band for higher than +10dBm power output. For lower output power levels this optimum impedance is 20+j10.6 ohms.
Details are in AN930.1 application note.