Low-Power Wireless Solutions Feed IoT Edge Needs

Integration Meets Innovation

Escalating demand for IoT solutions is fueling the need for products and technology that perform wireless communication with low-power edge devices. Using technologies including BLE, LoRaWAN and others, embedded system developers are searching for ways to get efficient IoT connectivity while drawing as little power as possible.

Enabling various nodes of an IoT implementation to communicate can involve a number of wired and wireless network technologies. Because most IoT systems can’t be completely hardwired end to end they must rely on a variety of wireless technologies including everything from device-level technologies to Wi-Fi to cellular networking.

Fortunately, today’s IoT system developers have a rich set of wireless solutions from which to choose from. And these can implement communication from the gateway and the device side using a variety of wireless IoT solutions in both module and chip form. This article focuses the low power subset of these technologies such as LoRaWAN and Bluetooth Low Energy (BLE). Over the last 6 months, technology vendors have announced several design wins and innovative products based on those technologies.

LOW POWER BLUETOOTH
Though not specifically created for the IoT edge market, Bluetooth LE (low energy), also called BLE, is a wireless personal area network technology designed and marketed by the Bluetooth SIG. It consumes only a fraction of the power of classic Bluetooth radios. While it was created for applications in healthcare, fitness, security and home entertainment, Bluetooth LE offers connectivity for any low power device especially systems that need to operate these devices for more than a year without recharging. This makes it ideally suited for the IoT.

Same as the classic Bluetooth, the range of the BLE radio can be optimized according to application. While most Bluetooth devices on the market today offer the basic 10 m range, there is no limit imposed by the specification. Manufacturers may choose to optimize the range to 200′ and beyond, particularly for sensor applications where longer range is a necessity.

The latest BLE microcontroller (MCU) offerings from Cypress Semiconductor are its two low-power, dual-mode Bluetooth 5.0 and BLE MCUs that include support for Bluetooth mesh networking for the IoT. Announced as sampling in February, the new CYW20819 and CYW20820 MCUs each provide simultaneous Bluetooth 5.0 audio and BLE connections.

The CYW20819 Bluetooth/BLE MCU has the ability to maintain Serial Port Profile (SPP) protocol connections and Bluetooth mesh connections simultaneously (Figure  1). The CYW20820 offers the same features and integrates a power amplifier (PA) with up to 10 dBm output power for long-range applications up to 400 m and whole-home coverage. This provides classic Bluetooth tablet and smartphone connections while enabling a low-power, standards-compliant mesh network for sensor-based smart home or enterprise applications.

Both MCUs embed the Arm Cortex-M4 core. It enables operation at 60% lower active power for connected 200-ms beacons compared to current solutions—delivering up to 123 days of battery life from a CR2032 coin cell battery. Previously, users needed to be in the immediate vicinity of a Bluetooth device to control it without an added hub. Using Bluetooth mesh networking technology, combined with the high-performance integrated PA in the CYW20820, the devices within a network can communicate with each other.

LOW POWER AND REAL TIME
The latest Bluetooth offering from STMicroelectronics (ST) are its STM32WBx5 dual-core wireless MCUs. Announced in February, the devices come with Bluetooth 5, OpenThread and ZigBee 3.0 connectivity combined with ultra-low-power performance. Fusing features of ST’s STM32L4 Arm Cortex-M4 MCUs and in-house radio managed by a dedicated Cortex-M0+, the STM32WBx5 is power-conscious yet capable of concurrent wireless-protocol and real-time application execution (Figure 2). It is well suited to remote sensors, wearable trackers, building-automation controllers, computer peripherals, drones and other IoT devices.

Security features of the STM32WBx5 MCUs include Customer Key Storage (CKS), Public Key Authorization (PKA), and encryption engines for the radio MAC and upper layers. The MCUs have up to 1 MB of on-chip flash and a Quad-SPI port for efficient connection to external memory, if needed. Additional features include crystal-less Full-Speed USB, 32 MHz RF oscillator with trimming capacitors, a touch-sense controller, LCD controller, analog peripherals and multiple timers and watchdogs. The balun for antenna connection is also integrated.

Leveraging ultra-low-power technologies of the STM32L4 line, STM32WBx5 MCUs feature multiple power-saving modes including 13 nA shutdown mode, adaptive voltage scaling, and the adaptive real-time (ART) accelerator to maximize energy efficiency and ensure long-lasting performance in self-powered applications. The integrated radio transmitter is optimized for high RF performance and low power consumption to maximize battery runtime. The RF output power is programmable up to +6 dBm in 1 dB increments, and the MCU draws only 5.2 mA when transmitting at 0 dB. Receive sensitivity is -96 dBm for BLE communication at 1mbps. Designed for a link budget of 102 dB, the radio ensures robust communication over long connection distances and includes support for an external Power Amplifier (PA).

IOT MODULE EXAMPLE
In a recent BLE design in example, in January Nordic Semiconductor announced that Nanopower selected Nordic Semiconductor’s nRF52832 BLE System-on-Chip (SoC) to provide the wireless connectivity for its nP-BLE52 module, designed for developers of IoT applications with highly restricted power budgets (Figure 3).

The nP-BLE52 module employs a proprietary power management IC—integrated alongside Nordic’s nRF52832 Wafer-Level Chip Scale Package (WL-CSP) SoC in a System-in-Package (SiP). It enables the SoC’s power consumption in sleep mode to be reduced to 10 nA, making it well suited for IoT applications where battery life is critical by potentially increasing cell lifespan 10x.

In active mode, the nRF52832 SoC runs normally. The SoC has been engineered to minimize power consumption with features such as the 2.4 GHz radio’s 5.5 mA peak RX/TX currents and a fully-automatic power management system. Once the Nordic SoC has completed its tasks, it instructs the nP- BLE52 to put it to sleep and wake it up again at the preset time. The nP-BLE52 then stores the Nordics SoC’s state variables and waits until the nRF52832 SoC needs to be powered up again. On wake-up, the device uploads the previous state variables, allowing the Nordic SoC to be restored to the same operational state as before the power was cut. The SoC’s start-up is much more rapid than if it was activated from a non-powered mode.

The nP-BLE52 module also features a low power MCU that can be set to handle external sensors and actuators when the Nordic chip is switched off. In this state, the module still monitors sensors and buffer readings and can trigger wake-ups if these readings are above predetermined thresholds, while consuming less than 1 µA. The nP-BLE52 also integrates an embedded inertial measurement unit (IMU). The module’s power management is controlled through a simple API, whereby the user can predetermine the duration of the Nordic SoC’s sleep mode, set the wake-up time and date parameters and select pins for other on/off triggers.

LORaWAN GAINING MOMENTUM
The LoRaWAN specification is a Low Power, Wide Area (LPWA) networking protocol designed to wirelessly connect battery operated “things” to the Internet in regional, national or global networks. Managed by the LoRa Alliance, LoRaWAN targets key IoT requirements such as bi-directional communication, end-to-end security, mobility and localization services.

The networking architecture of LoRaWAN is deployed in a star-of-stars topology in which gateways relay messages between end-devices and a central network server. Gateways are connected to the network server via standard IP connections and act as a transparent bridge, simply converting RF packets to IP packets and vice versa.

The wireless communication takes advantage of the long-range characteristics of the LoRa physical layer, allowing a single-hop link between the end-device and one or many gateways. All modes are capable of bi-directional communication, and support is included for multicast addressing groups to make efficient use of spectrum during tasks such as Firmware Over-The-Air (FOTA) upgrades or other mass distribution messages.

In November last year, Microchip Technology introduced a highly integrated LoRa SiP family with an ultra-low-power 32-bit MCU, sub-GHz RF LoRa transceiver and software stack (Figure 4). The SAM R34/35 SiPs come with certified reference designs and interoperability with major LoRaWAN gateway and network providers. The devices also provide ultra-low power consumption in sleep modes, enabling extended battery life in remote IoT nodes.

Most LoRa end devices remain in sleep mode for extended periods of time, only waking up occasionally to transmit small data packets. Powered by the ultra-low-power SAM L21 Arm Cortex-M0+ based MCU, the SAM R34 devices provide sleep modes as low as 790 nA to significantly reduce power consumption and extend battery life in end applications. Highly integrated in a compact 6 mm x 6 mm package, the SAM R34/35 family is well suited for a broad array of long-range, low-power IoT applications that require small form factor designs and multiple years of battery life.

The SAM R34/35 family is supported by Microchip’s LoRaWAN stack, as well as a certified and proven chip-down package that enables embedded systems developers to accelerate the design of RF applications with reduced risk. With support for worldwide LoRaWAN operation from 862 MHz to 1,020 MHz, developers can use a single part variant across geographies, simplifying the design process and reducing inventory burden. The SAM R34/35 family supports Class A and Class C end devices as well as proprietary point-to-point connections.

LORaWAN DESIGN WINS
LoRaWAN continues to gain momentum, with several design wins based on the technology announced over the past several months. In an example along those lines, in November last year Semtech announced that EasyReach Solutions, an Indian startup specializing in smart IoT solutions for industrial applications, has incorporated Semtech’s LoRa devices and wireless radio frequency technology (LoRa Technology) into its industrial and smart vehicle monitoring products. EasyReach’s LoRa-enabled sensors have been developed to include electrical current testing, temperature reading and GPS capabilities. All sensors are compatible with the LoRaWAN protocol and have been verified for GPS tracking ability over 8 km line of sight.

According to EasyReach, the LoRa Technology allows the company to remotely monitor its equipment and vehicles in new ways and to more intelligently manage its industrial resources. Meanwhile, the flexible capabilities of the sensors allow the solution to scale to its needs. EasyReach’s LoRa-based applications for smart industry include sensors for steam traps, concrete mixers, forklifts, diesel tankers, back hoes, water meters and trucks.

Semtech revealed another design win for its LoRa in December, announcing that Lemonbeat, an IoT solution provider, has integrated Semtech’s LoRa devices and technology into its smart metering solutions for easier reading and collection of utility usage. Lemonbeat’s LoRa-connected smart meters work by using embedded LoRa-based IoT technology to connect the meter to their own purpose-built receiver units.

Using this connectivity, meters send data through multiple floors in bigger buildings or all way into the street, where network operators conveniently collect the data without having to enter the building. Using the meters’ other radio frequency, Lemonbeat Radio, meters provide customers accurate data on their energy consumption. With a third-party application, individuals can view and analyze this data, and change their habits accordingly.

PROTOCOL MEETS INDUSTRIAL NEEDS
At the device-level, the ISM 802.15.4 is a popular standard for lower power kinds of IoT devices gear. The IEEE standard 802.15.4 is designed for low-cost, low-speed communication between devices. 802.15.4 is also well suited for data sharing of devices in close proximity that have very limited infrastructure. 802.15.4 is the basis for established industrial network schemes like Zigbee and can be used with protocols like 6LoWPAN to add higher layer functions using IP technology.

For its part, in February Microchip Technology announced what it claims is the industry’s smallest IEEE 802.15.4-compliant module that combines an ultra-low-power MCU with a sub-GHz radio, providing long-lasting battery life in wireless-networked sensors. At half the size of the next smallest module on the market, the SAM R30 module meets the needs of space-conscious designs such as home automation sensors and controls (Figure 5).

Based on IEEE 802.15.4, the SAM R30 module supports proprietary networks that can be easily customized and configured. This is ideal for applications where interoperability is not desired due to their inherent vulnerability to remote attacks, such as alarm systems, building automation, smart cities and industrial sensor networks. A key advantage of an IEEE 802.15.4-based network is that member devices can sleep for extended periods of time and remain part of the network. The SAM R30 module features ultra-low-power sleep modes, with wake from General-Purpose Input/Output (GPIO) or its built-in Real-Time Clock (RTC) while consuming approximately 800 nA. Devices can sleep for years, only waking as needed to transmit data.

The SAM R30 module measures just 12.7 mm x 11 mm and includes the necessary features to drive any remote connected sensor, thereby eliminating the need for a separate MCU in the design. The device also offers up to 256 KB of flash and 40 KB of RAM, as well as serial data interfaces, USB, and digital and analog I/O for advanced sensor development.

Operating in the sub-GHz RF spectrum, the SAM R30 module delivers two times the connectivity range and better propagation through walls and floors than similarly powered devices using the 2.4 GHz frequency band. This robustness is critical in applications such as leak detection, where the sensor may be buried deep in a remote cabinet, or for pool and spa controllers, which require reliable sub-gigahertz solutions that can communicate through exterior walls.

BAW RESONATOR INNOVATION
For Texas Instruments, (TI), its latest solution aimed at low power wireless communications has to do with a new way to do clock synchronization. Its relevance to this article is that the first implementations of this takes the form of a wireless MCU solution. In February TI announced new bulk acoustic wave (BAW)-based embedded processing and analog chips. The first two devices developed with TI BAW technology, the SimpleLink CC2652RB MCU and the LMK05318 network synchronizer clock are expected to enable new levels of reliably in wireless communication systems.

Communications and industrial automation systems with discrete clocking and quartz-crystal devices can be costly, time-consuming and complicated to develop and are often susceptible to environmental stress. The new devices with TI BAW resonator technology integrate reference clocking resonators to provide the highest frequency in a small form factor. This higher level of integration improves performance and increases resistance to mechanical stresses, such as vibration and shock. As a result of stable data transmission enabled by TI BAW technology, data synchronization of wired and wireless signals is more precise and allows for continuous transmission, which means data can be processed quickly and seamlessly to maximize efficiency (Figure 6).

Using TI’s new BAW technology, the SimpleLink multi-standard CC2652RB wireless MCU is the industry’s first crystal-less wireless MCU on the market. The device integrates a BAW resonator within the quad flat no-lead (QFN) package, eliminating the need for an external high-speed 48-MHz crystal. TI says the CC2652RB is the lowest power multi-standard device supporting Zigbee, Thread, BLE and proprietary 2.4-GHz connectivity solutions on a single chip. Unlike many crystal-based solutions currently on the market, the CC2652RB works in the full -40°C to 85°C temperature range. 

RESOURCES
Cypress Semiconductor | www.cypress.com
Microchip Technology | www.microchip.com
Nordic Semiconductor | www.nordicsemi.com
Semtech | www.semtech.com
STMicroelectronics | www.st.com
Texas Instruments | www.ti.com

PUBLISHED IN CIRCUIT CELLAR MAGAZINE • APRIL 2019 #345 – Get a PDF of the issue

Sponsor this Article