What is the recommended distance between antennas in an antenna diversity application?
Antennas in a product that implements antenna diversity have their antennas mounted at a distance of at least ¼ wavelength apart. This amount of spatial separation improves the probability that at least one antenna is NOT in a deeply faded signal condition. Another typical recommendation is ½ wavelength antenna distance, however, it can result quite large board sizes at low frequencies (e.g. for 434 MHz frequency ½ wavelength is 34,5 cm).
Can I use the same matching network for EZRadioPRO and an EZR32 wireless MCU that is based on the same radio?
The answer depends on the actual PCB layer stack-up as the distance between the top and the first inner (ground) layer determines the PCB parasitic capacitances, which plays part in the matching network.
If the same PCB layer stack-up is used (or at least the distance between the top and the first inner layer is similar), in that case the same matching network component values should result very similar TX and RX performance for an EZRadioPRO radio and an EZR32 wireless MCU. If the PCB layer stack-up deviates significantly, it is not recommended to use the same matching network as the detuning can cause lower output power, higher harmonics, higher current consumption and sensitivity loss.
How can I use the EFR32 sub-GHz RF ports in single-ended way?
Both TX and RX sub-GHz RF ports of EFR32 wireless geckos are truly differential ones. However, they can be used in more simple single-ended way as well, which will enable to use more simple matching networks, but, on the other hand, it will sacrifice some RF performance.
For single-ended RX operation, sensitivity degradation of 6 dB is expected. The unused input pin can be connected to GND. Note, that it also affects the performance of RFSENSE.
Regarding the TX, 3 dB lower output power is expected. Also, the harmonic performance will be degraded. The unused TX pin can be connected to GND (to save current).
The single-ended matching network should use halved impedance compared to the differential one, with removed ceramic balun.
At which pins should I apply DC feed for the sub-GHz and 2.4GHz PA of EFR32?
For the 2.4GHz PA, the DC feed should be applied on PAVDD pin.
On the sub-GHz side, the PA DC feed is required through the TX output pins: SUBGRF_OP, SUBGRF_ON.
For more details, refer to the EFR32 radio board reference designs.
In which cases should I apply DC-DC to PAVDD when creating an EFR32 design?
Using the 1.8V output of the internal DC-DC converter of EFR32 for DC supply of the PA provides better efficiency (i.e. lower PA current for the same output power) compared to the case when the PA is running from the main 3.3V. The recommendation for applying the DC-DC output to PAVDD:
Above these power levels, using the main 3.3V supply for DC supply of the PA results better efficiency.