Big Challenges for Small Devices
Wearable devices continue to rank among today’s most dynamic segments of electronics design. Devices spanning across fitness, consumer and medical markets all need highly integrated processing and advanced power management technologies to perform as expected.
The design of wearable devices has moved beyond the basic functionalities of first-generation products. Simple communication, health-monitoring and position tracking are now considered routine. As wearable system developers embark on new designs, there are a treasure trove of new functionalities, performance levels and battery-life improvements being enabled by innovations in chip-level products from microcontroller (MCU) vendors, analog IC companies, IoT SoC providers and others.
The next-gen of wearable devices are integrating ultra-wideband (UWB), energy harvesting, air quality monitoring and other new features. At the same time, they must meet the ever-present strict challenges inherent in wearable system designs. These include an extremely low budget for power consumption—and a requirement for rechargeability, because replaceable batteries aren’t practical for wearables. Meanwhile, wearables demand some kind of wireless connectivity that doesn’t eat up the power budget.
Helping designers keep pace, technology providers over the several months have announced a generous mix of solutions to help keep power consumption low, to aid recharging and to enable new capabilities while maintaining narrow power constraints.
BLUETOOTH SOC FOR WEARABLES
Obviously, Bluetooth Low Energy (BLE) is a key technology for wearables devices. As an example of it in action, in July Nordic Semiconductor announced that India-based Titan selected Nordic’s nRF52832 Bluetooth 5.2/BLE general-purpose multiprotocol SoC to provide the core processing power and wireless connectivity for its “Fastrack Reflex 3.0″ smart band (Figure 1).
India-based Titan selected Nordic’s nRF52832 Bluetooth 5.2/BLE general-purpose multiprotocol SoC to provide the core processing power and wireless connectivity for its “Fastrack Reflex 3.0” smart band. Featuring a full-touch color display, a 24/7 continuous heart rate monitor and sleep tracker, the smart band is provided in an IP67-rated silicone housing.
Featuring a full-touch color display, more than 10 different sports modes, a 24/7 continuous heart rate monitor and sleep tracker, the Fastrack Reflex 3.0 smart band is provided in an IP67-rated silicone housing with a range of dual color straps, and has been designed for the youth-oriented fitness market. The smart band records a range of user data—including step count, calories burned, distance run or cycled—and relays this to a partner app on the user’s Bluetooth 4.0 (and later) smartphone using the BLE wireless connectivity provided by the nRF52832 SoC. From the smart band, the user can also remotely control smartphone functionality, for example to operate the camera or playback music, as well as view notification alerts.
Once the smart band has been paired with a user’s smartphone, wearers can analyze their activity and sleep patterns from the iOS and Android “Fastrack Reflex Word” app, with detailed daily fitness and sleep statistics, as well as a full monthly report. Sleep and step goals can be set through the smart band or app, and “Z points” are earned by completing various fitness tasks. These points are then collated, and rank the user local and globally, to provide a sense of community in their fitness journey.
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The “AutoHR” feature also measures the wearer’s heart rate at set intervals, providing the user with a comprehensive overview of their most effective fitness activities each day. The Nordic SoC’s 64MHz, 32-bit Arm Cortex M4 processor with floating point unit (FPU) provides ample computational power to manage the complex algorithms that convert sensor data inputs into meaningful fitness and sleep feedback to the user. Sedentary reminders can also be set to ensure the user remains on-track with their fitness goals.
Nordic’s nRF52832 SoC embeds a 2.4GHz multiprotocol radio (supporting Bluetooth 5, ANT, and proprietary 2.4GHz RF protocol software) featuring -96dB RX sensitivity, with 512KB flash memory and 64KB RAM. The SoC is supplied with Nordic’s S132 SoftDevice, a Bluetooth 5-certifed RF software protocol stack for building advanced BLE applications.
SCREENLESS WEARABLE
In another example of embedded technologies enabling wearable designs, in June Infineon Technologies revealed that its chips were used by Deed, a start-up from Turin, Italy, to create a screenless, feature-rich wearable. Deed’s wearable is called the “Get” bracelet. It is able to interpret human gestures and uses biometric data, to pick up a call or to make payments (Figure 2).
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Figure 2a. The “Get” bracelet is able to interpret human gestures and uses biometric data, to pick up a call or to make payments. -
Figure 2b. Image shows the internal components of the Get bracelet, including a rigid-flex PCB.
At the core of Get is a system consisting of components from Infineon that enable the wearable with connectivity, computing, sensing and security capabilities. Infineon’s SECORA Connect provides the bracelet with payment functionality. The XENSIV MEMS technology enables high-fidelity voice recording during phone calls. And the PSoC 6 MCU offers its high performance dual-core M4/M0 architecture. This is paired with Infineon’s AIROC Wi-Fi and Bluetooth combo device.
Patented techniques enabled the manufacturer to create a seamless, ultralight and water-resistant wearable made up of several layers of high-tech fabrics. Inside of it, there is a rigid-flex PCB. The intuitive human machine interface (HMI) allows for the most natural way to operate the wearable without having to swipe on screens or touch any display. Motion sensors with artificial intelligence (AI) for gesture recognition interpret human gestures, for example, to pick up a call, to check the time or to make payments.
Consumers can use the Get to listen to audio or answer calls by holding their finger to their ear by “wrist bone conduction,” sending the sound through the body to the inner ear. Contactless payments can be released after individual electrocardiogram-based biometric identification. In addition, the bracelet also enables fitness and health monitoring.
AIR QUALITY MONITORING
Outdoor air quality is a new, but popular feature emerging in wearable device designs. Feeding those needs, in June Renesas Electronics expanded its ZMOD4510 outdoor air quality (OAQ) gas sensor platform with an IP67-qualifed waterproof package and a new AI-based algorithm that enables ultra-low power selective ozone measurements (Figure 3). Renesas claims the enhanced ZMOD4510 is the industry’s first fully calibrated, miniature digital OAQ sensor solution with selective ozone measurement capabilities. It offers visibility into the air quality in the users’ immediate environments.
The ZMOD4510 outdoor air quality gas sensor platform has an IP67-qualifed waterproof package and an AI-based algorithm that enables ultra-low power selective ozone measurements.
Ozone gas is a significant cause of poor outdoor air quality that poses health risks, says the company. Based on Renesas’ new ultra-low power firmware, the enhanced ZMOD4510 can detect specific ozone levels—without reporting on other pollutants—while maintaining power consumption under 200µW. This selective measurement capability enables devices such as smart watches, phones and smoke detectors to monitor for harmful ozone gases typically found outdoors but which can drift indoors through open windows and doors. Optimizing the ZMOD4510 for very low power is key to enabling the longer life cycles required for these types of battery-powered devices.
Renesas’ software-configurable ZMOD platform provides design flexibility for smart sensing systems, which allows firmware updates in the field to enable new, application-specific capabilities such as selective ozone detection. The ZMOD4510’s ability to quantify selective ozone levels in concentrations as low as 20 parts per billion (ppb) coupled with its low power, small size and outstanding flexibility makes it an ideal solution for mobile and wearable devices, as well as industrial applications such as wireless security cameras and parking meters.
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The waterproof packaging allows the sensor to operate in harsh and submersible environments. The IP67-rated sensor maintains high accuracy and high performance while eliminating the need for expensive waterproofing systems—all in a tiny 3mm × 3mm × 0.9mm LGA package. The sensor is shipped fully calibrated in the hydrophobic and oleophobic package, and customers can apply a conformal coating on their circuitry rather than adding an external membrane to the module. The ZMOD4510 is calibrated to the US Environmental Protection Agency’s (EPA’s) Air Quality Index for measuring ozone, and is highly resistant to siloxanes, enabling exceptional reliability for use in harsh environments.
SOLAR HARVESTER IC
Energy harvesting is a natural overlap technology for wearables because of the extreme low power budgets of wearable devices. For its part, earlier this year Maxim Integrated announced the MAX20361, a single-/multi-cell solar harvester with maximum power point tracking (MPPT) (Figure 4). The company claims it as the industry’s smallest solar harvesting solution. It’s targeted at space-constrained applications such as wearables and emerging IoT applications.
The MAX20361 is a single-/multi-cell solar harvester with maximum power point tracking (MPPT). It’s targeted at space-constrained applications such as wearables.
According to Maxim, designers are often challenged with the trade-off between small size and long runtime for wearable and IoT applications. By enabling solar charging in these highly space-constrained products, the MAX20361 can extend the runtime of those devices by providing a supplemental power source.
This solar harvester reduces solution size by at least half compared to the closest competitor. In addition, Maxim says the MAX20361 increases harvested energy with up to 5% better boost efficiency than the closest competitor, coupled with an adaptive MPPT approach, which can improve the overall system level efficiency even further. The MAX20361 is available at Maxim Integrated’s website for $2.64 (1,000-up, FOB USA) and also available from authorized distributors. The MAX20361EVKIT# evaluation kit is available for $57.
UWB TOOLS FOR APPLE WATCH
Development tools are a part of the story for wearable systems designs. Along those lines, in June NXP Semiconductors announced that it now offers beta Ultra-Wideband (UWB) development tools from its NXP Trimension portfolio that interoperate with the U1 chip in supported Apple products.
The beta development tools will allow developers to kick-start the design of innovative applications that interact with UWB- enabled Apple products including iPhone and Apple Watch. This enables app developers to create more precise, directionally aware app experiences.
UWB provides spatial awareness, which is a new dimension of information. Knowing where a device is in relation to other devices, with an extreme level of accuracy, provides valuable location context, says NXP. With access to Apple’s Nearby Interaction protocol and API, developers will have the ability to leverage the spatial awareness of UWB to build apps that can communicate with accessories simply by being in close proximity to an U1-equipped iPhone or Apple Watch.
NXP’s development tools are based on NXP Trimension SR150 and SR040, a dedicated portfolio of UWB IoT solutions that run UWB autonomously with all firmware running on chip. All PHY/MAC operation is handled within the UWB IC in accordance with FiRa Consortium specifications, helping developers to get solutions to market fast
By working with regional partners, NXP offers a growing range of tools to access Apple’s Nearby Interaction protocol, says the company. The UWB Development Kit by Murata (Figure 5) enables a wide range of IoT devices to perform localization tasks or create a setup with multiple UWB anchors. With its partner group MobileKnowledge (www.themobileknowledge.com), NXP further provides a UWB Development Kit with Arduino Connector to bring UWB to IoT devices, such as coin-cell battery-powered trackers and tags. More tools are planned to be released this year.
Ultra-Wideband (UWB) development tools from the NXP Trimension portfolio interoperate with the U1 chip in supported Apple products, like the Apple Watch. The UWB Development Kit by Murata (shown) enables a wide range of IoT devices to perform localization tasks or create a setup with multiple UWB anchors.
EKG/ECG MONITORING
Medical wearable devices are an important subset of the wearables market. Playing in that space, in July B-Secur announced launching an electrocardiogram (EKG/ECG) solution based on the Texas Instruments (TI) AFE4950 analog front end (AFE) for photoplethysmography (PPG) and EKG/ECG sensing (Figure 6). The solution is aimed at accelerating the design of next-generation consumer wearables, says B-Secur.
B-Secur’s electrocardiogram (EKG/ECG) solution is based on the TI AFE4950 analog front end (AFE) for photoplethysmography (PPG) and EKG/ECG sensing. The solution is aimed at accelerating the design of next-generation consumer wearables.
The integration provides high-performing sensing capabilities for wearable devices like premium smartwatches and Wi-Fi-connected optical heart-rate monitors, and enables advanced features for identification, wellness and health monitoring in IoT devices. The company claims it as the industry’s first solution with a fully integrated EKG/ECG and PPG signal chain that allows for synchronous sampling of cardiac activity with dry electrodes used in battery-operated products.
The news followed an announcement from B-Secur that it had received US Food and Drug Administration (FDA) clearance for its HeartKey ECG/EKG software. The combination of HeartKey and TI’s AFE4950 enables device manufacturers and partners around the world to eliminate months of R&D with a fully integrated sensor, electrical and signal processing solution. B-Secur’s HeartKey consists of a suite of powerful ECG/EKG algorithms that uniquely combine user identification, health and wellness to generate accurate data encrypted through the user’s unique heartbeat.
TEAM EFFORT
For its part, STMicrolectronics (ST) offers a wide variety of sensor products, several of which provide solutions for wearable system developers. Last Fall, ST teamed up with Qualcomm by developing software solutions using technology from Qualcomm Technologies through the Qualcomm Platform Solutions Ecosystem program.
In this program, ST is contributing pre-validated software to OEMs for its MEMS and other sensing devices to deliver advanced features to the next generation of smartphones, connected PCs, IoT and wearables. Most recently, Qualcomm Technologies pre-selected ST’s latest high-accuracy, low-power, motion-tracking IC with intelligent sensor software, along with ST’s most accurate pressure sensor, for use in its latest advanced 5G mobile reference platforms (Figure 7).
Qualcomm selected ST’s latest high-accuracy, low-power, iNEMO LSM6DST motion-tracking IC with intelligent sensor software for use in its latest advanced 5G mobile reference platforms. The IC is a 6-axis Inertial Measurement Unit (IMU) that integrates a 3-axis digital accelerometer and a 3-axis gyroscope.
The motion-tracking sensor, the new iNEMO LSM6DST, is a 6-axis Inertial Measurement Unit (IMU) that integrates a 3-axis digital accelerometer and a 3-axis gyroscope into a compact and efficient system-in-package (SiP). ST claims it offers the industry’s lowest power consumption—0.55mA in high-performance mode and as little as 4uA in accelerometer-only mode. As a result, the LSM6DST enables always-on high-accuracy motion tracking with minimal impact on power consumption. In concert with ST’s low-noise (0.65Pa), high-accuracy (±0.5hPa), and industry-first I3C-enabled LPS22HH pressure sensor, the pair provides highly accurate location tracking while meeting the most restrictive power budgets.
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For imaging applications, the LSM6DST fully supports EIS and OIS (Electronic and Optical Image Stabilization) applications because the module includes a dedicated configurable signal processing path for OIS and auxiliary SPI, configurable for both the gyroscope and accelerometer. And, in turn, the auxiliary SPI and primary interface (SPI/ I²C and MIPI I3CSM) can configure the OIS.
Benefiting from ST’s mature low-power ThELMA1 process technology, the LSM6DST supports and simplifies integration in low-power circuit designs and offers I²C, MIPI I3C or SPI from the sensing element to the application. It also contains a 9KB FIFO to allow dynamic data batching and 16 finite state machines that recognize programmed data sequences from the sensor and further reduce system-level power consumption.
POSITION SENSING FOR WEARABLES
Position sensing technology is a useful feature in wearables devices, but they must meet the tight power and space budgets of such designs. Doing just that, U-blox’s latest highly integrated GNSS (global navigation satellite system) platform was designed fully in-house for ultra-low power high-performance positioning applications (Figure 8). According to U-blox, the M10 defines a new level of positioning performance in a wide range of applications such as sport watches or asset and livestock trackers, all in an extremely compact format and with very long battery life.
The M10 positioning platform can track up to four GNSS constellations at once to deliver positioning data even in challenging environments such as deep urban canyons. The receiver’s Super-S technology helps distinguish positioning signals from background noise to capture positioning data even when satellite signals are weak.
The new U-blox M10 positioning platform can track up to four GNSS constellations at once to deliver positioning data even in challenging environments such as deep urban canyons. The receiver’s Super-S technology helps distinguish positioning signals from background noise to capture positioning data even when satellite signals are weak. Its high RF sensitivity also enables it to work well with small antennas, making it well suited for compact product designs. In sport watches, for instance, U-blox M10 guarantees highly dynamic positioning accuracy during a run in cities, woods or under an open sky, while preserving battery life.
U-blox M10 is designed to consume 12mW in continuous tracking mode, five times less than the power consumed by previous U-blox meter-level GNSS technology, making it ideal for battery-powered applications. U-blox M10’s enhanced RF sensitivity also cuts the time it takes for the platform to achieve a first position fix when initialized, further reducing systemic power consumption. And switching to the improved Super-E mode can extend battery life even more.
This new GNSS platform will be supported by AssistNow, U-blox’s well-established assisted GNSS service, to accelerate positioning and improve accuracy. Depending on the required level of assistance, the service is available free of charge or for a recurring fee. The first products based on the U-blox M10 positioning platform are the MAX- M10S GNSS module and the UBX-M10050 GNSS chipset, which are both available now. Design-in of the new U-blox M10 platform is enhanced and simplified with the newly designed U-center GNSS evaluation software.
TINY DIGICAM FOR WEARABLES
Tiny cameras—enabled by image sensors—are now possible as part of wearable devices. Offering a solution along those, in July AT&S announced an image sensor that’s smaller than a grain of rice, lighter than a postage stamp but more powerful than any previous development of its kind. With a size of 1mm² and a weight of about 1g, the image sensor is so small that it can be installed in smartphones, VR cameras and other wearables.
According to AT&S, the image sensor not only creates sharp images due to its 100,000-pixel resolution, but it also has low power consumption thanks to the company’s smart connection architecture. AT&S developed the PCB for the sensor, while the sensor itself was built by Ams OSRAM.
AT&S’ ECP technology is made possible by a special manufacturing process. After the respective components have been integrated into a resin layer in special manufacturing steps, they are connected by copper-filled, laser-drilled microvias. This eliminates the need for solder joints for the embedded component, while at the same time enabling finer designs on the outer layer and providing the components with the best possible protection against external influences. With the innovative ECP, more components can be integrated into the PCB while the size of the end device remains the same. On one hand, this increases functionality and, alternatively, the PCB can be shrunk while maintaining the same range of functions, which in turn enables more compact end devices. 
RESOURCES
AT&S | www.ats.net
B-Secur | www.b-secur.com
Infineon Technologies | www.infineon.com
Maxim Integrated | www.maximintegrated.com
Nordic Semiconductor | www.nordicsemi.com
NXP Semiconductors | www.nxp.com
Renesas Electronics | www.renesas.com
STMicroelectronics | www.st.com
Texas Instruments | www.ti.com
U-blox | www.u-blox.com
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • September 2021 #374 – Get a PDF of the issue
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Jeff served as Editor-in-Chief for both LinuxGizmos.com and its sister publication, Circuit Cellar magazine 6/2017—3/2022. In nearly three decades of covering the embedded electronics and computing industry, Jeff has also held senior editorial positions at EE Times, Computer Design, Electronic Design, Embedded Systems Development, and COTS Journal. His knowledge spans a broad range of electronics and computing topics, including CPUs, MCUs, memory, storage, graphics, power supplies, software development, and real-time OSes.
