TXPOWER options

[rikhard]

Hi

We have nRF52840 + FEM in our design.  Output power level is mainly controlled by the nRF52840 TX power setting which drives the FEM. However, the txpower options is a list of somewhat sparse txpower options ( -40dBm, -20dBm, -16dBm, -12dBm, -8dBm, -4dBm, 0dBm, +2dBm, +3dBm, +4dBm, +5dBm, +6dBm, +7dBm and +8dBm). In our case, we have 1 dB accuracy requirement for TXPOWER between -20 dBm ... +20 dBm. How the 1dB accuracy of output power can be achieved without using any external HW components. 

[Kenneth]

Hello,

The configurable output power are those stated yes, I would also like to mention that the accuracy of each level is up to +-4dB in worst case (over temperature, production variation and channel in the 2.4GHz band). May I ask why you need such fine resolution and accuracy over 40dBm?

Kenneth

[rikhard]

I referred to output power accuracy with FEM where +-1dB _nominal_ accuracy is required / preferred. 

The gain of the FEM is also a function of the input RF power and therefore options for the output power are limited by the set of the TXPOWER options available. I encourage adding a tunable attenuator in between FEM and nRF to have more accurate output power options. E.g. with gain ~20 dB at ~0 dBm input power, any TXPOWER above 0 dBm are not really usable and the TXPOWER options below 0 dBm are scarce --> output power options are scarce.