Power Amplifier and Low Noise Amplifier control configuration (PA/LNA)

The SoftDevice can be configured by the application to toggle GPIO pins before and after radio transmission and before and after radio reception to control a Power Amplifier and/or a Low Noise Amplifier (PA/LNA).

The PA/LNA control functionality is provided by the SoftDevice protocol stack implementation and must be enabled by the application before it can be used.
Note: In order to be used along with proprietary radio protocols that make use of the Timeslot API, the PA/LNA control functionality needs to be implemented as part of the proprietary radio protocol stack.

The PA and the LNA are controlled by one GPIO pin each. The PA pin is activated during radio transmission, and the LNA pin is activated during radio reception. The pins can be configured to be active low or active high. The following figure shows an example of PA/LNA timings where the PA pin is configured active high and the LNA pin is configured active low.

Figure 1. PA/LNA and radio activity timing
PA/LNA and radio activity timing

The SoftDevice uses a GPIOTE connected to a timer through a PPI channel to set the pins to active 5±2 µs before the EVENTS_READY signal of the RADIO occurs. The selected time difference allows for a sufficient ramp up time for the amplifiers, while it avoids activating them too early during the radio start up procedure (which results in amplifying carrier noise etc.). The pins are restored to inactive state using a PPI connected to the EVENTS_DISABLED event on the RADIO. See the relevant product specification (S132 SoftDevice core documentation) for more details on the nRF52 RADIO notification signals.