RF modules have become a crucial element in the adoption of the Internet of Things (IoT) for a broad array of applications ranging from battery-operated IP security cameras to point-of-sale (PoS) scanners, and asset trackers to personal medical devices.
At the same time, however, the IoT bandwagon is reinventing the RF design realm all over again. As a result, the incredibly shrinking radio modules have emerged as a viable answer to the time-consuming RF engineering labyrinth in IoT designs.
Figure 1: The ready-made RF modules allow IoT developers to expand to a wide range of use cases. (Image Source: Persistence Market Research)
The RF modules available in system-in-package (SiP) solutions integrate all essential components including the antenna, and they usually come pre-tested and pre-certified. That abstracts away a lot of design complexity and reduces development time, effort, and risk. Not surprisingly, these pre-certified devices with extensive peripheral capabilities allow IoT developers to focus on their end applications.
But while the adoption of RF modules for a broad range of IoT applications is now well documented, what’s actually new in this rapidly-evolving engineering landscape? First and foremost, power consumption, data throughput, and security remain the key design considerations. However, what’s changing is that these specialized SiP solutions continue to shrink in form factor while they incorporate highly-integrated system-on-chips (SoCs) in RF modules.
Second, a new design ecosystem is taking shape in which RF modules are offering a combination of short- and long-range wireless technologies. These ultra-low-power, dual-mode radios combine short-range wireless technologies like Bluetooth low energy (BLE) with long-range radios, such as LoRa and SigFox.
First, let’s have a closer look at a design case study that reveals the anatomy of an ultra-miniature RF module for space- and power-constrained IoT designs.
RF Module Miniaturization
Take the example of Nordic Semiconductor’s foray into radios for cellular IoT designs aimed at asset monitoring and tracking applications for agriculture, industrial, medical, and smart city environments. It’s worth mentioning that Nordic’s claim to fame in the semiconductor industry is silicon devices built around the BLE standard.
And there is an interesting story behind how the Trondheim, Norway-based chipmaker leaped from short-range BLE technology to long-range cellular IoT. Nordic picked up the cellular radio technology pieces from the retiring units of Nokia, Microsoft, Broadcom, and ST-Ericsson from 2011 to 2014.
The work of these RF engineers assembled from different fallen cellular titans led to the creation of a cellular IoT module that looks more like an SoC despite being an SiP solution. Here, to accomplish an ultra-high integration, Nordic joined hands with Qorvo to leverage its RF front-end, advanced packaging, and MicroShield technology, which eliminates the need for bulky and costly external shields in RF modules.
The nRF9160 radio module combines Qorvo’s multi-band RF front-end with Nordic’s multimode LTE-M/NB-IoT modem and SAW-less transceiver. Moreover, the SiP solution integrates GPS support to ensure that either GPS or cellular data can provide an accurate positioning when used in isolation.
Figure 2: The block diagram of a cellular IoT design built around Nordic Semiconductor’s nRF9160 radio module.
The RF module also features the Arm Cortex M-33 CPU core, supported by 1 MB of flash and 256 kB of RAM onboard memory for wireless protocol stacks and other application requirements. Next, nRF9160 incorporates the Arm TrustZone and Arm CryptoCell security technologies.
According to Nordic, nRF9160 is the first cellular IoT module to incorporate an application processor, which, in turn, eliminates the need for an external MCU to perform tasks such as security—significantly improving the design footprint and cost efficiency.
Arm TrustZone separates the trusted execution zones from non-trusted zones, while Arm CryptoCell facilitates cryptography and other security-centric platforms for designs with power and area constraints. Security is becoming a fundamental part of the IoT design recipe, and it’s worth finding out what level of security an RF module contributes to the overall IoT design.
Nordic is targeting this SiP solution operating at frequencies ranging from 700 MHz to 2.2 GHz, and measuring 10 x 16 x 1 mm at wearable and medical devices. Besides FCC and CE regulatory certifications, nRF9160 has acquired the GCF certification. The RF module also comes with LTE-M firmware and a development kit offering application examples for cloud connectivity.
Dual-Mode RF Module
As mentioned in the article introduction, the combination of short- and long-range wireless in an RF module offers the best of both worlds for many IoT applications. Their simultaneous availability complements each other and creates a matrix of new possibilities.
Insight SiP, for instance, has launched an ultra-miniature RF module that integrates BLE and LoRa radio functionality into a 9.8 x 17.2 x 1.7 mm footprint. The ISP4520 module features an ARM Cortex M4F processor with 512 kB flash and 64 kB RAM to support applications and process BLE and LoRa protocol stacks.
Figure 3: A graphic view of an RF module showing how BLE and LoRa radios co-exist to offer twin wireless flavor. (Image Source: Insight SiP)
The BLE part comes from Nordic Semiconductor’s nRF52832 SoC that encompasses 32 MHz/32 kHz crystals, RF antenna and matching circuit, and DC-DC converter. The radio chip features support for Bluetooth 5, Bluetooth mesh, ANT, and 2.4 GHz proprietary stacks.
Next, Semtech’s SX126x family of radio transceiver chipsets support LoRa modulation for different use cases based on the global LoRaWAN standard or proprietary protocols. The RF transceivers are designed to comply with the physical (PHY) layer requirements of the LoRaWAN specification released by the LoRa Alliance. The ARM Cortex M4F processor in Nordic’s BLE chip also drives the Semtech’s RF transceiver.
Moreover, to counter the inevitable rise in power consumption as a result of catering to two wireless technologies, the RF module is equipped with a range of deep-sleep modes. The standby current is as low as 0.5 uA while the actual current for BLE is around 5 mA; LoRa chipset’s consumption depends on the chosen output power.
The RF module provides a host of analog and digital peripherals including 30 GPIOs, an analog-to-digital converter, and support for SPI, I2C, and UART buses. The RF module also provides NFC connectivity for easy pairing and comes with a development kit and sample software.
Plethora of Wireless Channels
The IoT bandwagon has mostly been responsible for accelerating the shift from traditional radio solutions to ready-made RF modules that efficiently manage data flow between wireless and physical interfaces. That allows IoT developers to quickly utilize wireless channels for a diverse array of applications ranging from smart buildings and cities to utility metering and asset tracking to agricultural and environmental monitoring.
These modules now feature over-the-air (OTA) firmware updates that boost design flexibility, security, and module lifecycle. Then, there are RF modules like Digi’s XBee3 that offer programmability features to introduce new functionality into IoT designs. And such features are especially handy in meeting regional design requirements.
The IoT designs are evolving at a breathtaking pace and that makes RF modules a crucial area to watch. Especially how RF modules accommodate a plethora of wireless technologies, both old and new.
