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Personal medical monitoring technology is changing at an astonishing pace. Just a decade ago, the normal way for patients to track general health indicators (such as heart rate and blood pressure) or specific indicators (such as blood sugar) was through invasive medical procedures (such as blood tests). Such tests often required travel away from home and to a local clinic or hospital.
Fast forward to today, and patients are much better off. Anyone—not just those who are treated by a doctor—can benefit from monitoring vital signs as well as other long-term health indicators such as activity and sleep. That’s because a new generation of wearable medical and consumer devices has extraordinary sensors and data processing capabilities built into them. The latest types of products, such as continuous glucose monitors (CGMs) and smart rings, can report on the wearer’s condition 24/7, are small and light, barely unaware of them, and are so convenient and easy to use that they are valuable to anyone.
At the heart of this new class of wearable medical devices is advanced wireless connectivity technology: a low-power Bluetooth system-on-chip (SoC) for connecting to a smartphone, tablet, or PC, and NFC (the technology that enables contactless payments) for authentication, pairing, configuration, and charging.
Long battery life, small form factor
The most important constraints in CGM and smart ring design are the same: space and power. Both devices perform 24/7 monitoring, and long battery life is expected to limit the number of times a user must recharge them. This places great emphasis on the need for low power consumption in both active and standby modes for the wireless SoC.
The size of the device is also a critical design parameter. Its form factor must be comfortable to wear all day, but manufacturers will be eager to pack as many features as possible into the device to increase its value to the user. Therefore, such wearable devices require wireless systems for connectivity and charging that are themselves small and use a minimum number of external components to keep the total board footprint to a minimum.
At the same time, these devices perform a range of complex connectivity functions to support local and remote data access. Despite size and power constraints, their low-power Bluetooth SoCs must provide a strong and reliable connection to the user’s smartphone for data processing and analysis either locally or in the cloud. In addition, NFC connectivity enables features such as accessory authentication, usage tracking, and wireless charging. High performance is therefore an essential requirement.
This is a tough challenge for product designers. But manufacturers have a ready solution: Renesas’ connected products that save space and consume very little power.
High performance and low power for CGM designs
A typical example is the DA1453x series of Bluetooth SoCs, which combine very low power consumption with high integration, reducing the number of external components on the board, thus saving space in CGM designs.
For example, the Bluetooth 5.1 DA14531 is available in a tiny 2.0mm x 1.7mm package, which is half the size of other leading manufacturers’ products. Best of all, it requires only six external passive components and uses a single crystal for timing input.
Record low sleep and active power consumption ensure long operation and shelf life for even the smallest disposable batteries: the DA14531 is compatible with alkaline, silver oxide, and coin cells, and includes an internal buck-boost DC/DC converter to extend the life of these battery types.
This combination of small size and very low power consumption makes the DA1453x SoCs ideal for CGMs, small wearable devices that must perform 24/7 monitoring.
Smart Ring Design: Multiple Functions in One Low-Power Chip
Renesas Bluetooth SoCs such as the DA14695 or DA1459x are outstanding examples of the dual benefits of low power and high integration for smart rings. The DA14695 SoC is based on a 96MHz ArmCortex-M33FCPU core that runs application functions such as processing signals from the smart ring, and a 96MHz Cortex-M0+ core that serves as a sensor node controller and configurable media access controller for the onboard Bluetooth Low Energy v5.2 radio.
The DA14695 offers an exceptional level of integration: on-chip features include a power management IC (PMIC), USB interface and USB charger, motor drivers for haptic feedback and parallel interface drivers for the display, as well as robust security protection. Yet in deep sleep mode, this high-performance device consumes only 10μA.
In stark contrast, other Bluetooth SoCs on the market may offer a CPU, protocol engine, and sensor node controller, but lack many of the peripheral features found in the DA14695, resulting in a significant increase in component cost and the amount of space required on the PCB.
Designers of smart rings and other wearables can use this type of Renesas Connectivity Solutions offering to meet their most stringent design requirements.
All-in-one charger and data exchange components
A similar approach to power and space savings is also achieved with Renesas’ NFC technology. NFC is best known for its use in contactless payment terminals, enabling smartphones or smartwatches to securely exchange data packets to authorize financial transactions.
In a smart ring, this data exchange functionality can also be used for contactless payments. But the same PTX30W NFC tag used for data exchange also supports NFC wireless charging.
Here again, Renesas has pulled off a space-saving integration miracle: the PTX30W packs an NFC tag, rectifier, limiter, battery charger circuitry, and a dedicated core for handling the NFC wireless charging protocol in a tiny 1.78mm x 1.78mm WLCSP package.
The PTX30W is paired with the Renesas PTX130W, a dedicated NFC charging transmitter called a poller that is embedded in the smart ring’s charging case. The PTX130W uses Direct Antenna Connection technology (DiRAC) to deliver maximum power transfer and fast charging. The technology also makes the PTX130W easier to implement in charging case designs than competing products, as it eliminates the need for EMC filters and simplifies antenna matching. The PTX130W’s superior RF performance enables the use of small antennas and allows for flexible placement of the poller and poller antennas.
By eliminating the need for additional components and allowing for the use of small antennas, the PTX30W offers a charging solution that can fit on a tiny PCB in a smart ring, such as the Ring One from Muse Wearables.
Renesas Ecosystem for Fast and Efficient Product Development
High performance and seamless integration are the watchwords for the Renesas Connectivity Solutions portfolio, which fits perfectly with Renesas’ microcontroller and application processor families. The portfolio also gives users access to an unparalleled suite of development tools and resources from Renesas, including the e² studio integrated development environment, Flexible Software Package (FSP) packages for firmware, development kits, and Winning Combinations (pre-vetted sets of compatible components for specific product designs).
Designers of wearable medical devices can now explore the full range of smart connected medical, fitness, and care products in the latest white paper from Renesas Connectivity Solutions: the ultimate guide to designing low-power and space-constrained, yet smart and feature-rich personal or wearable devices.
