BT840NE Amplification in ESB packet retransmissions

[Yanis]

Hello,

I am developping an application based on ESB protocole using BT840NE module (nrf52840 + nRF21540) SDK 3.2.0.

on the PTX side, I am measuring the current using the PPK2, we cut the link with PRX to see the current for packet retransmissions also. Current shows a strong peak of 45 mA (main TX transmission) followed by very weak peaks of 5 mA related to packet retransmission.

My question is: why does the current drops for packet retransmissions ? Does it mean that emission power is lower and the range is compromised when packets are retransmitted ?

Here is a screen shot of the current with the BT840NE :

 

When I use the Nordic nRF21540-DK I get another behavior (more reasonable levels) with a first peak of 20 mA and retransmissions peaks of 15 mA as shown in the following screen shot :

Best Regards,

Yanis

[Håkon Alseth]

Hi,

 

Thank you for sharing this information. I have been able to reproduce the scenario, and it looks like the issue is related to how esb handles re-transmissions when FEM is enabled.

Looking at the PDN pin of the nRF21540, it indicates that the subsequent re-transmissions are not enabling the FEM:

 

I have reported this internally to the ESB team.

Calling "mpsl_fem_enable()" in esb.c::on_radio_disabled_tx_wait_for_ack() seems to fix the issue, but I cannot guarantee that this is does not have any unforeseen side-effects at this point.

diff --git a/subsys/esb/esb.c b/subsys/esb/esb.c
index 9a148554a3..004f794936 100644
--- a/subsys/esb/esb.c
+++ b/subsys/esb/esb.c
@@ -1473,6 +1473,7 @@ static void on_radio_disabled_tx_wait_for_ack(void)
                update_radio_tx_power();
 
                /* Transmission is armed on TIMER's CC1. */
+               mpsl_fem_enable();
                esb_fem_for_tx_retry();
                esb_ppi_for_retransmission_set();

 

Kind regards,

Håkon

[Yanis]

Hi,

Thanks for your quick response.

What you suggested worked, here is the new ppk2 current measurement, both the main transmission and retransmissions are at the same current levels :

Regards,

Yanis

[Håkon Alseth]

Hi Yanis,

 

Glad to hear that this shows good results on your end as well.

Please note that this is a quick-fix from my side, and it is not fully verified. As mentioned, I have reported this internally to the ESB team.

 

Kind regards,

Håkon