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Bluetooth 5 Technology for the Internet of Things

| Editor: Margit Kuther

The Ultra-Low-Power Multiprotocol SoC nRF52

Bluetooth 5 is now being implemented in devices. For example, the nRF52 family of SoC devices from Nordic Semiconductor is a family of ultra-low-power multiprotocol SoCs built around a 32-bit ARM Cortex-M4F core with 1 MB flash and 256 kB RAM on chip. The latest embedded 2.4 GHz transceiver supports all the Bluetooth 5 low energy data rates in hardware, from the new 2 Mbps and existing 1 Mbps rates to the Bluetooth 5 long range rates at 500 kbps and 125 kbps. The radio supports high resolution RSSI measurement and automated functions to reduce CPU load, including EasyDMA for direct memory access for packet data and assembly. Nordic also provides the protocol stacks for Bluetooth 5 low energy directly – these stacks are known as SoftDevices, and the nRF52840 is supported by the S140 SoftDevice that is a Bluetooth 5 pre-qualified Bluetooth low energy protocol stack.

Many of the existing Bluetooth 4.2 devices have been designed with the next generation in mind, and the Bluetooth element in a SoC for the Internet of Things can be a relatively small part of the chip design. For example, in the CYBL11573 from Cypress Semiconductor, the majority of the chip is devoted to the peripheral handling.

The BLE subsystem for the SoC consists of the link layer engine and physical layer. The link layer engine supports both master and slave roles and implements time-critical functions such as encryption in the hardware to reduce the power consumption, and provides minimal processor intervention and a high performance. The key protocol elements, such as host control interface (HCI) and link control, are implemented in firmware. These are the elements that change in the Bluetooth 5 implementation.

The physical layer also changes to handle the higher 2 Mbps data rate. This already uses the GFSK modulation, converting the digital baseband signal of these BLE packets into radio frequency before transmitting them to air through an antenna. In the receive direction, this block converts an RF signal from the antenna to a digital bit stream after performing GFSK demodulation. The RF transceiver contains an integrated balun, which provides a single-ended RF port pin to drive a 50 Ω antenna terminal through a pi-matching network. The output power is programmable from -18 dBm to +3 dBm to optimize the current consumption for different applications.

Similarly, the EFR32MG family of Bluetooth controllers from Silicon Labs can be upgraded to Bluetooth 5. The current family uses a 40 MHz ARM Cortex-M4 core with scalable memory and radio configuration options that all use footprint compatible QFN packages. Like other IoT implementations, the 12-channel Peripheral Reflex System enables autonomous management of the peripherals, while the integrated 2.4 GHz balun and power amplifier provide up to 19.5 dBm of transmit power.

Conclusion: With the launch of Bluetooth 5 at the start of 2017, chip developers are taking several approaches to providing the functionality in system-on-chip devices that are aimed at the Internet of Things. Using physical and software IP from suppliers such as RivieraWaves or MindTree can allow a developer to focus on the additional peripherals and the power management of the chip with reduced risk.

Others are looking to tightly integrate the Bluetooth 5 functionality within the SoC design to add additional functions or reduce the die size. Both approaches are giving IoT node designers new capabilities. Its lower power consumption, longer range, and higher data rates allow Bluetooth 5 embedded developers to easily add more sophisticated wireless connectivity to their Internet of Things devices.

* The article was first published in Elektronikpraxis

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