The nRF21540 is an RF front-end module (FEM) for Bluetooth® LE, Bluetooth mesh, 2.4 GHz proprietary, Thread, and Zigbee range extension.
When combined with an nRF52 or nRF53 Series System on Chip (SoC), the nRF21540 RF FEM’s +21 dBm TX output power and 13 dB RX gain ensure a superior link budget for up to 16x range extension.
The nRF21540’s TX power is dynamically adjustable and output power can be set up to +21 dBm in small increments. This ensures that designs can run with output power within 1 dBm of the allowable range across all regions and operating conditions. The LNA has a low noise figure of 2.5 dB that ensures improved RX sensitivity.
The nRF21540 FEM connects to the nRF52840 SoCs antenna output. It includes two antenna ports for antenna diversity support. The TX output power, TX gain control, and antenna switching can be controlled through SPI, General-Purpose Input/Output (GPIO) pins, or a combination of both.
The nRF21540 is connected to the nRF52840 SoC MCU using the following GPIOs.
| GPIO | MCU function | FEM function |
|---|---|---|
| P1.13 | SPI MOSI | Serial Data In |
| P1.14 | SPI MISO | Serial Data Out |
| P1.15 | SPI CLK | Serial Clock |
| P0.21 | SPI CS | Chip Select |
| P0.23 | GPIO | Power Down |
| P0.17 | GPIO | Mode Select |
| P0.19 | GPIO | RX Enable |
| P0.20 | GPIO | Antenna Select |
| P0.22 | GPIO | TX Enable |
To measure current to nRF21540, you need to cut the solder strap SB16 and place an ampere meter between TP26 and TP48.