nRF5340: Do you need to configure with high voltage mode to get +3 dBm power?

[kileyhykawy_nu]

It isn't clear from the nRF5340 documentation and the only related post doesn't answer it but if we want +3 dBm output power, do we need to wire the nRF5340 in high voltage mode or is normal voltage mode sufficient?

Why I ask is we have a device in EMC/EMI preliminary tests at a lab and when they look at the output power, it doesn't seem to get up to +3 dBm at the end of a 1 m SMA cable (see 1.65 dBm) so a 1.35 dBm loss. At lower power modes below 0 dBm, we see less than 0.5 dBm.

[Ressa]

Hi,

Thanks for contacting us. Have you calculated the cables and connectors loss in your measurements? It can go up to around 1.5 dB depending on connectors and cables. The high voltage mode you are referring to is chip level and does not impact radio directly. There is an internal and radio specific high voltage request to get power up to 3 dBm. It is different than chip level high voltage you are referring to. 
RADIO — 2.4 GHz radio
VREQCTRL — Voltage request control

Best regards,
Ressa

[kileyhykawy_nu]

Looking at the radio_test sample, it calls `nrf_vreqctrl_radio_high_voltage_set` but never checks to see if it ready before starting the transmit. Could that be the problem? I'm going to tweak our radio test to wait for the radio to say it is ready before proceeding with transmit and test in the lab next week.

[Ressa]

I don't think so. As I mentioned previously first and easy option would be to measure the cables loss at 2.44 GHz frequency and consider it in your power measuremnets. After that if you are still seeing low output power, then it is worth to look for other reasons. 

[kileyhykawy_nu]

We got into the lab this week with more information:

Loss is 1.5 dBm. It seems to be that we are outputting high but as you can see, the power difference is not consistent but seems to *mostly* be within +/- 2 dB. Anything look odd there or is this within spec? 

[Ressa]

Hi ,

Yes it is looking fine. It seems to me the cable loss is a bit less than 1.5 dB. But apart from that, as you mentioned the output power in the range of +\- 2 dB is fine. Also as you can see the accuracy is better for higher output powers which is expected as the lower output powers are more sensitive to the physical variations.