nRF21540 antenna diversity for BLE

[akif]

Hi,

We are working with nRF21540DK and developing a BLE application. nRF21540DK with nRF Connect SDK 2.5.0 . I have couple of questions.

1. In nRF21540DB product page says "The two antenna ports on the nRF21540 DK are useful for antenna diversity scenarios in 802.15.4 based protocols (i.e. Thread or Zigbee) to reduce multipath propagation effects.". I couldn't see any explanation on the datasheet regarding two antenna and BLE.
   
   Does BLE protocol use the both antennas?
2. If BLE doesn't use both antennas, which antenna it use, POUTA or POUTB?
3. POUTA set to 20dB and POUTB set to 10dB as default. Is there any reason you have selected these values as default? For example why it is not 21db which is the maximum value.
4. Why you haven't selected 20dB for both antenna? Why the POUTB is exactly the half value of the POUTA ?
5. In datasheet page 25, CONFREG0 TX_GAIN TX gain control (0: minimum, 31: maximum). What is the unit of this value, obviously it is not dB, because maximum is 21dB. 
6. What is the minimum and maximum dB value we can set for POUTA and POUTAB individually?
   

Thanks.

[JONATHAN LL]

Does BLE protocol use the both antennas?

It can use 

If BLE doesn't use both antennas, which antenna it use, POUTA or POUTB?

POUTB and POUTA is not a reference to what physical antenna or RF output is used, so POUTA/POUTB is not the same as ANT1/ANT2. 


ANT1 and ANT2 is the two physical outputs that will connect to an antenna. It is not any relation between POUTx and ANTx.


POUTA and POUTB is only for the TX gain selection, either option A = 20dBm or B = 10dBm. The UICR option is for a a custom value of choice. 

Why you haven't selected 20dB for both antenna? Why the POUTB is exactly the half value of the POUTA ?

Both the ANT1 and ANT2 port can have any dBm output power. So both can have +20dBm if that is what you want. 

In datasheet page 25, CONFREG0 TX_GAIN TX gain control (0: minimum, 31: maximum). What is the unit of this value, obviously it is not dB, because maximum is 21dB. 

https://infocenter.nordicsemi.com/topic/ps_nrf21540/chapters/keyparameters/doc/electrical_specification.html?cp=8_0_0_6_1#unique_1296948405 

It is a decimal value that  is a ladder with 16 steps and one main range selector, with two options, to get 32 control settings. 

What is the minimum and maximum dB value we can set for POUTA and POUTAB individually?

POUTA = 20dBm,
POUTB = 10dBm,
The pre-programed TX gain settings are not changeable. 

ANT1/ANT2 = 21dBm ±1 


Hope this clears things up for you. 


Regards,
Jonathan

[akif]

Thanks for your comments!

JONATHAN LL said:

It can use 

Could you be more specific? How we can use antenna diversity scenario on BLE? Does it a part of configuration of MPSL on SDK 2.5.0? I think the quote from the product page I mentioned above only mentions 802.15.4 based protocols not BLE for a reason. We possibly make a our custom board with nRF52840 and nRF21540 to use with BLE Mesh. I want to understand if we can have any benefit from the 2nd antenna.

 

JONATHAN LL said:

POUTA and POUTB is only for the TX gain selection, either option A = 20dBm or B = 10dBm. The UICR option is for a a custom value of choice. 

Okay either we use POUTA or POUTB. I understood. I thought we can select antenna gain of individual antennas. So when we set POUTA=20dB, does it set both ANT1 and ANT2 TX gains to 20dB? 

Another question:
The quote from Using nRF21540 GPIO+SPI built-in power model

The nRF21540 built-in power model compensates for the following external conditions:

• Temperature

• FEM supply voltage

• Carrier frequency

• FEM input power.

Sorry I don't have expertise on radio signals, I couldn't see if antenna have any effects on power model compensation. If we use a custom antenna on our custom board, do we need to create our custom power model or can we use built-in power model directly?

Thanks, Akif