Data Sheet

BMD-345 - Data sheet
UBX-19039908 - R07 RF front end – PA / LNA Page 18 of 36
5 RF front end – PA / LNA
The BMD-345 uses an RF front end that incorporates a power amplifier (PA) and low noise amplifier
(LNA) to achieve superior RF performance. The Skyworks RFX2411 PA / LNA IC used to increase TX
power and RX sensitivity, providing a significantly increased link budget for long range connections.
This section covers how to configure the RFX2411 via GPIO for radio operation.
☞ The RFX2411 must be configured by the application firmware to allow for radio operation
By default, if all nRF52840 GPIOs are left in their default state the RFX2411 will be in a shutdown
mode. There are two options for configuring the IC:
 Static method
 Dynamic method
The static method only requires setting GPIO once but results in reduced performance. The dynamic
method results in the best RF performance but requires more in-depth firmware implementation.
This guide will cover implementing both methods. See section 7.3 for allowed antennas.
5.1 Hardware
5.1.1 PA / LNA modes
The table below shows the available modes of the Skyworks RFX2411 PA / LNA IC.
Mode
Description
Shutdown
No RF signal can be received or transmitted
Bypass
All RF signals lose ~10 dB of signal strength compared to receive mode (LNA gain + insertion loss)
and ~29dB compared to transmit mode (with same nRF52840 output power). Compensating for the
nRF52840 transmit power, bypass vs transmit mode power difference is ~10dB.
Transmit
Transmit signal from nRF52840 is amplified by ~24dB. Max allowed transmit power setting for the
nRF52840 is -12dBm (power settings depend on region, modulation mode, and channel).
Receive
Received signals from the antenna are amplified by an effective 5dB for most conditions (+10dB over
bypass mode).
Table 13: Skyworks RFX2411 PA / LNA modes
5.1.2 PA / LNA control
The table below shows the control signal names, pin names and the state they need to be in for each
mode. Switching time between states is < 1 μS.
Signal
nRF82840 signal
Shutdown mode
Bypass mode
Transmit mode
Receive mode
TX_EN
P1.05
Low
Low
High
Low
RX_EN
P1.06
Low
Low
Low
High
MODE
P1.04
Low
High
Low
Low
A-SEL
P1.02
Low
Low
Low
Low
Table 14: PA / LNA control logic
5.1.3 Power Limitations
To comply with regulatory power output and band-edge requirements, the following table shows the
maximum allowable power setting values that can be used in the NRF_RADIO -> TXPOWER register
of the nRF52840.