Wearable devices put extreme demands on the embedded electronics that make them work. Devices spanning across the consumer, fitness and medical markets all need a mix of low-power, low-cost and high-speed processing.
MCUs & Analog ICs Meet Needs
By Jeff Child, Editor-in-Chief
Designers of new wearable, connected devices are struggling to extend battery life for next-generation products, while at the same time increasing functionality and performance in smaller form factors. These devices include a variety of products such as smartwatches, physical activity monitors, heart rate monitors, smart headphones and more. The microcontrollers embedded in these devices must blend extreme low power with high integration. Meanwhile, analog and power solutions for wearables must likewise be highly integrated while serving up low quiescent currents.
Modern wearable electronic devices all share some common requirements. They have an extremely low budget for power consumption,. They tend not to be suited for replaceable batteries and therefore must be rechargeable. They also usually require some kind of wireless connectivity. To meet those needs chip vendors—primarily from the microcontroller and analog markets—keep advancing solutions that consume extremely low levels of power and manage that power. This technology vendors are tasked to keep up with a wearable device market that IDC forecasts will experience a compound annual growth rate (CAGR) of 18.4% in 2020.
MCU and BLE Combo
Following all those trends at once is Cypress Semiconductor’s PSoC 6 BLE. In September the company made its public release of the PSoC 6 BLE Pioneer Kit and PSoC Creator Integrated Design Environment (IDE) software version 4.2 that enable designers to begin developing with the PSoC 6. The PSoC 6 BLE is has built-in Bluetooth Low Energy (BLE) wireless connectivity and integrated hardware-based security.
According to Cypress, the company had more than 2,500 embedded engineer customers registering for the PSoC 6 BLE early adopter program in just a few months. Early adopters are using the flexible dual-core architecture of PSoC 6, using the ARM Cortex-M4 core as a host processor and the Cortex-M0+ core to manage peripheral functions such as capacitive sensing, BLE connectivity and sensor aggregation. Early adopter applications include wearables, personal medical devices, wireless speakers and more. Designers are also using the built-in security features in PSoC 6 to help guard against unwanted access to data.
The PSoC BLE Pioneer Kit features a PSoC 63 MCU with BLE connectivity (Photo 1). The kit enables development of modern touch and gesture-based interfaces that are robust and reliable with a linear slider, touch buttons and proximity sensors based on the latest generation of Cypress’ CapSense capacitive-sensing technology. Designers can also use the board to add USB Power Delivery (PD) with its Cypress EZ-PD CCG3 USB-C controller. The development kit also includes a 2.7-inch E-ink Display Shield add-on board (CY8CKIT-028-EPD) with thermistor, digital mic and 9-axes motion sensor.
Deep Sleep Current Levels
Extreme low power was also the theme behind Microchip Technology’s PIC32MX1/2 XLP family that the company announced in June. The 33-bit PIC32MX1/2 XLP offers current PIC32MX system developers an easy migration path to achieve higher performance at much lower power. It enables both increased functions and longer battery life in portable applications. According to Microchip, the new MCU family increases performance in small pin-count devices with little code rework for existing customers.
Microchip’s XLP technology is designed for wearable technology, wireless sensor networks and other smart connected devices and offers low current operating modes for Run and Sleep, where extreme low-power applications spend 90% to 99% of their time. XLP technology will enable Sleep and Deep Sleep shutdown states on the PIC32MX1/2 XLP devices, enabling Deep Sleep currents down to 673 nA. The devices offer over 40% more performance than the existing PIC32MX1/2 portfolio while reducing average currents by 50%. Figure 1 shows an XLP MCU used in a health/fitness wearable application.
The PIC32MX1/2 XLP family is available in a range of memory configurations with 128/256 kB flash and 32/64 kB of RAM in packages ranging from 28- to 44-pins. They also include a diverse set of peripherals at a low cost including I2S for digital audio, 116 DMIPS performance for executing audio and advanced control applications, a 10-bit, 1 Msps, 13-channel ADC and serial communications peripherals. The PIC32MX2 series also supports USB-device, host and OTG functionality.
In addition to the hardware peripheral features, the series is supported by Microchip’s MPLAB Harmony Software Development Framework, which simplifies development cycles by integrating the license, resale and support of Microchip and third-party middleware, drivers, libraries and RTOSes. Specifically, Microchip’s readily available software packages such as Bluetooth audio development suites, audio equalizer filter libraries, decoders (including AAC, MP3, SBC), sample rate conversion libraries and USB stacks will reduce the development time of wearable device applications.
Transactions with Wearables
Among the new features of some wearable devices is the ability to do contactless transactions. Today’s consumers have become quite comfortable with making secure transactions using their smart devices. As a result, traditional card manufacturers want to extend their offerings into contactless wearable products for uses such as payments, ticketing and access control. These can be difficult to implement within tight size and cost constraints, because conventional separate NFC-radio and security chips demand extra space and complicate design. In addition, wearable form factors tend to need small antennas that can restrict communication performance.
Supporting those capabilities in wearables, ST Microelectronics in October unveiled its technology for easy and secure contactless transactions using electronic wristbands or fashionwear like watches or jewelry. The ST53G System-in-Package solution combines the company’s expertise in Near Field Communication (NFC) and secure-transaction chips. ST’s new ST53G System-in-Package combines a miniaturized and enhanced NFC radio with a secure banking chip in one compact 4 mm x 4 mm module (Figure 2). The company’s proprietary boosted-NFC technology enables wearables with small antennas to deliver a great user experience when interacting with card readers over typical contactless distances.
The simplicity of this all-in-one module helps card enables embedded developers to quickly design functional and attractive wearables that can range from fashion items to one-time devices like event wristbands. ST offers an extensive development ecosystem, including radio-tuning tools and pre-defined antenna configurations. The ST53G meets all relevant card-industry standards, including EMVCo compliance, ISO/IEC-14443 NFC card emulation, and MIFARE ticketing specifications. The ST53G can host ready-to-use STPay smartcard operating systems and optional VISA/ Mastercard/JCB-certified banking applications pre-loaded on the secure microcontroller.
Embedded Security for Wearables
The secure banking chip contained in the ST53G System-in-Package leverages ST’s proven ST31G480 secure microcontroller that is based on the ARM SC000 SecurCore processor. It features a secure architecture with a NESCRYPT coprocessor for public-key cryptography and hardware accelerators for algorithms like AES and triple-DES. Extensive anti-tamper protection including an active shield, environmental monitoring, a unique serial number for each die and protection against numerous other attacks are also built-in. These features complement software-based security running on the SC000 core to ensure the strongest possible protection for users’ credentials.
The contactless IC is the STS3922 RF booster, which uses active-load modulation (ALM) to maximize transaction range and omnidirectional radio performance in card-emulation mode. This enables wearable devices to be easy to use—with equal or better device-to-reader positioning tolerance than conventional contactless smartcards—even though a smaller antenna is used. Using ST53G contributes to final device cost optimization because small antennas can be etched onto the PCB at almost zero additional cost. In some cases, a challenging metallic case can itself be used as part of the RF antenna.
Automatic power and gain control, configurable sensitivity, and configurable signal/reader-field phase difference ensure consistent communication over all ranges. These enhance smooth interoperability with different types of readers and terminals including various transportation ticketing systems. The STS3922 has a dedicated secure-MCU wake-up output. That feature enables the ST53G System-in-Package to maximize battery life by powering down when not in use.
Power Regulation for Wearables
Designing today’s wearable devices requires not just low power on the MCU side. They also require sophisticated analog IC solutions that help regulate power and extend battery life as much as possible. Along those lines, Maxim Integrated in March announced its the MAX17222 nanoPower boost regulator with what the company claims is the industry’s highest efficiency and lowest quiescent current (IQ) of only 300 nA (Figure 3). The 0.4V to 5.5V input, 1.8V to 5V output boost regulator with 500 mA input current limit reduces solution size by up to 50% compared to similar products and offers 95% peak efficiency to minimize heat dissipation.
Aside from very low quiescent current, the MAX17222 also minimizes heat dissipation and shutdown current. In True Shutdown mode, the minuscule current draw of 0.5 nA virtually stops battery drain to provide the longest battery life and eliminate the need for external disconnect switches. The MAX17222 is internally compensated and requires only a single configuration resistor and small output filter for a full power solution. For ease of use, the boost regulator comes in tiny, density-optimized 0.88 mm x 1.4 mm 6-bump WLP and 2 mm x 2 mm 6-pin standard µDFN packages. It operates over a -40°C to +85°C temperature range.
Health monitoring wearable devices have their own particular analog design challenges. Targeting such needs, Analog Devices offers a low power, next-generation biopotential analog front end (AFE) which enables smaller, lighter and less obtrusive cardiac monitoring devices with longer battery life. The AD8233 AFE is a fully integrated, single-lead electrocardiogram (ECG) front end designed in one compact, easy-to-use component. Typically, developers need to design ECG front ends from individual components, which can add incremental cost and design time.
Health Monitoring Solution
The highly integrated, out-of-the-box AD8233 AFE eliminates these unnecessary costs and extra time, helping developers get products to market more quickly. Additionally, the device’s 2.0 mm × 1.7 mm size enables the design of wearable health devices that are smaller, lighter and easier to wear. Bulky, heavy and obtrusive monitors can be unpleasant for patients to wear and may even interfere with their everyday lives. Longer battery life is another crucial attribute for cardiac monitors and is vital to ensure continuous monitoring that provides accurate data without the interruption of a recharge or battery replacement. The AD8233 AFE’s low microamp-range power consumption results in greatly extended battery life.
Along with its small size, the single-supply (1.7 V to 3.5 V) AD8233 features extremely low quiescent current of 50 μA (typical); lead on/off detection even while in shutdown mode (less than 1 μA); and 80-dB common-mode rejection ratio (DC to 60 Hz). Electrical noise, a critical specification for cardiac-monitoring devices, is below 10 μV from 0.5 to 40 Hz. The AD8233 also allows for highly flexible filter configurations which are essential to consistent, confident operation in an inherently harsh electrical environment under a range of use cases. These configuarations include a two-pole adjustable high-pass filter, a three-pole adjustable low-pass filter with adjustable gain and an RFI filter. For ease-of-use and flexibility, it also includes an integrated right leg drive (RLD) amplifier with shutdown plus an uncommitted op amp. Analog Devices also offers an evaluation board, reference design, web based filter design tool and Spice model to facilitate design-in and speed time to market.
The AD8233CB-EBZ evaluation board contains an AD8233 heart rate monitor (HRM) front end conveniently mounted with the necessary components for initial evaluation in fitness applications (Photo 2). Inputs, outputs, supplies and leads off detection terminals are routed to test pins to simplify connectivity. Switches and jumpers are available for setting the input bias voltage, shutdown (SDN), right leg drive shutdown (RLD SDN), fast restore (FR) and AC/DC leads off detection mode. The AD8233CB-EBZ evaluation board is a 4-layer board with components mounted on the primary side only. Rubber feet are available on the secondary side for mechanical stability. The layout diagrams are provided as a visual aid and reference design.
Seamless wireless connectivity has pretty much become a given for today’s wearable devices. With that in mind, Cypress Semiconductor in September announced a new combo solution that delivers ultra-low power Wi-Fi and Bluetooth connectivity to extend battery life for wearables and portable audio applications. The new Cypress CYW43012 solution prolongs battery life by leveraging 28 nm process technology to cut power consumption up to 70% in receive mode and up to 80% in sleep mode when compared to current solutions. The solution is IEEE 802.11a/b/g/n-compliant and 802.11ac-friendly, meaning it is interoperable with 802.11ac access points using standard modes. This enables it to offer higher throughput and better energy efficiency, along with the enhanced security and coverage of 802.11ac Wi-Fi networks.
The CYW43012 combo chip’s advanced coexistence engine enables optimal combined performance for dual-band 2.4- and 5-GHz Wi-Fi and dual-mode Bluetooth/BLE 5.0 applications simultaneously. The CYW43012 solution is supported in Cypress’ all-inclusive, turnkey, WICED Studio IoT development platform, which streamlines the integration of wireless technologies for developers. According to Cypress, battery life is a key differentiator for connected devices like wearables. Users demand a great connected experience for longer without having to recharge.
The Cypress WICED Studio IoT development platform features an integrated and interoperable wireless software development kit (SDK). The SDK includes broadly deployed and rigorously tested Wi-Fi and Bluetooth protocol stacks, as well as simplified application programming interfaces that free developers from needing to learn complex wireless technologies. In line with the IoT trend toward dual-mode connectivity, the SDK supports Cypress’ Wi-Fi and Bluetooth combination solutions and its Bluetooth and Bluetooth Low Energy devices. The SDK enables cloud connectivity in minutes with its libraries that integrate popular cloud services such as Amazon Web Services, IBM Bluemix, Alibaba Cloud and Microsoft Azure, along with services from private cloud partners. WICED also supports iCloud remote access for Wi-Fi-based accessories that support Apple HomeKit, which enables hub-independent platforms that connect directly to Siri voice control and the Apple Home app remotely.
Cypress’ WICED Studio connectivity suite actually is MCU-agnostic and provides support for a variety of third-party MCUs to address the needs of complex IoT applications. The platform also enables cost-efficient solutions for simple IoT applications by integrating MCU functionality into the connectivity device. Wi-Fi and Bluetooth protocol stacks can run transparently on a host MCU or in embedded mode, allowing for architectures with common firmware.
As consumers push for more capabilities in their wearable products, they won’t tolerate any reduction in battery life. Along the way, wireless connectivity and embedded security will have to be supported. These conflicting trends will continue to challenge MCU and analog IC vendors to come up with more integrated solutions at ever lower power consumption levels.