Front end module is Nordic Semiconductor’s first PA/LNA

To boost the range of multi-protocol wireless SoCs, Nordic Semiconductor has developed its first power amplifier/low noise amplifier (PA/LNA), the nRF21540 RF front end module. The range extender is optimised to boost the link budget of Nordic’s nRF52 and nRF53 series multi-protocol wireless SoCs.

The nRF21540 RF front end module (FEM) has a PA which offers a highly adjustable TX power boost up to +21dBm, with the LNA providing +13dB RX gain, for a link budget that is up to 16x range extension, says the company.

The LNA’s low noise figure (NF) of only 2.5dB also ensures increased RX sensitivity for Nordic’s Bluetooth 5/Bluetooth Low Energy (Bluetooth LE), Thread, Zigbee, and 2.4GHz RF low power wireless solutions. When combined with an nRF52840 SoC running Bluetooth LE at 1Mbits per second, for example, the nRF21540 improves the RX sensitivity by 5dBm. Coupled with the increased output power, the connection link budget is raised by 18dBm. For other devices with less than +8dBm TX power on-chip, the improvements are even larger, the company reports. The increase in connection link budget offers significantly longer range and helps lower the number of retransmissions due to corrupt packages.

The nRF21540 can be used where increased range or robust coverage is required, for example asset tracking, audio, smart home, or industrial applications.

The nRF21540 connects to the SoC’s antenna output and has two additional antenna ports for antenna diversity features. The device’s gain control, antenna switching and power modes are controlled via GPIO or SPI or a combination of both. In addition to use with other radios, further enhanced driver support will be rolled out as part of future releases of Nordic’s nRF5 SDK, nRF5 SDK for Thread and Zigbee, and the nRF Connect software development kit (SDK).

The nRF21540’s TX power is dynamically adjustable and output power can be set up to 21dBm in small increments. This ensures designs can run with output power within 1dBm of the allowable range across all regions and operating conditions. During use the power setting can be dynamically controlled by the SoC to take into account the requirements of the current connection. For example, received signal strength indication (RSSI) and other parameters can be monitored to determine power requirements for a particular connection and TX power raised or lowered to manage power consumption. Any variations due to temperature can be counteracted so the output power is stable at the desired level.

Operating across a 1.7 to 3.6V supply range, the nRF21540 offers 115mA at TX tuned to +20dBm, 4.1mA in RX mode and 30nA in power down mode. The device is qualified across a -40 to +105 degrees C range to complement Nordic’s high-temperature-rated nRF52833 and nRF5340 in applications such as professional lighting. The chip is supplied in a 4.0 x 4.0mm QFN16 package. Nordic also offers development boards that enable evaluation of the RF FEM performance using lab equipment, as well as real application performance combined with an nRF52 Series device.

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