Nordic Semiconductor is sampling its first RF front-end module (FEM) integrating a power amplifier (PA) and low noise amplifier (LNA), which was developed to complement Nordic's nRF52 and nRF53 multi-protocol systems-on-chip (SoC). The nRF21540 FEM is well suited for applications requiring increased range or robust coverage, such as asset tracking, wireless audio, smart home and industrial use cases.
The nRF21540 FEM integrates a PA with adjustable transmit power to +21 dBm and an LNA with 2.5 dB noise figure and 13 dB gain. The low noise figure provides increased receive sensitivity for Nordic's Bluetooth®5/Bluetooth Low Energy (BLE), Thread, Zigbee and 2.4 GHz low power wireless solutions.
For example, combined with an nRF52840 SoC running Bluetooth LE at 1 Mbps, the nRF21540 FEM improves receive sensitivity by 5 dB; including the increased output power of the PA, the link budget increases 18 dB. The increase in link budget ensures longer range and reduces the number of retransmissions caused by corrupt data packages. For devices with less than +8 dBm transmit power, the improvements are greater.
The nRF21540's transmit power is dynamically adjustable and can be set to 21 dBm in small increments, ensuring designs can run with the output power within 1 dB of the allowable range, across all regions and operating conditions. During use, the power setting can be dynamically controlled by the SoC, accounting for the connection. For example, received signal strength indication (RSSI) and other parameters can be monitored to determine the power requirements for a particular connection, with the transmit power raised or lowered to manage power consumption. Variations due to temperature changes can be offset to keep the output power at the desired level.
Biased with a 1.7 to 3.6 V supply, the nRF21540 offers competitive power dissipation, drawing 115 mA with an output of +20 dBm. The FEM draws 4.1 mA in the receive mode and 30 nA when powered down. The device operates from −40°C to 105°C, complementing Nordic's nRF52833 and nRF5340 rated for high temperature, which are used for applications such as professional lighting. The FEM is supplied in a 4 mm x 4 mm QFN16 package. With the release of the nRF21540 IC, Nordic also offers development boards to support evaluation of the RF FEM using lab equipment or the actual performance when combined with an nRF52 SoC.
The nRF21540 is plug and play with Nordic's short-range wireless SoCs. The nRF21540 connects to the SoCs’ antenna output and provides two antenna ports for antenna diversity. The device's gain control, antenna switching and power modes are controlled via GPIO, SPI or a combination of both.
While the device can be used with other radios, the ease of using Nordic’s SoCs is enhanced with the driver support planned for future releases of Nordic's software development kits: the nRF5, nRF5 for Thread and Zigbee and the nRF Connect.
"Many applications benefit from the significant range boost offered by an external RF front-end module. But it's important the FEM doesn't compromise other features of the radio's performance or has significant impact on battery life. Our engineering team has designed a competitive RF FEM that is optimized for, and perfectly complements, the company's advanced multi-protocol SoCs, at a size and price that minimizes impact on the BOM and board real estate,” said Kjetil Holstad, director of product management at Nordic Semiconductor.