Question

How can I use the EFR32 sub-GHz RF ports in single-ended way?

Answer

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.

 

RX:

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.

 

TX:

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. 

  • The single-ended RX and TX matches use the series elements of the original differential match without any change: i.e. the series capacitor in the RX match and the series inductor in the TX match will remain the same.
  • The shunt element impedances are halved in the single-ended match and connected to GND: i.e. half shunt inductor value in the RX match and double shunt capacitor values in the TX match are used. As the TX internal capacitor will be small as well an additional external shunt capacitor will be used right at the TX pin as well.
  • Remove the balun and connect the single ended match output directly to the single ended LPF.  

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