Battery-less Smart Autonomous IoT Applications
Ultra-low power chipsets pave the way.
The IoT revolution is now gaining speed with the recent emergence of a variety of innovative home automation, wearables, and industrial applications. The key challenges are to miniaturize sensing and communication electronics for ease of portability and unobtrusive deployment.
Most of today’s solutions are battery operated, with coin-sized CR2032 cells as a popular low-cost choice for energy capacity in a small form factor. Although several years of system operation are feasible with tiny coin cells, the cost to operators of replacing batteries on large numbers of sensor nodes and devices, many of which could be installed in inaccessible locations, is a major hurdle for high-volume IoT device deployment.
As a viable alternative to primary batteries as the energy source for the required sensing/processing/transmitting/receiving operations of an IoT device, energy harvesting elements with dedicated electronic components are now available. Different types of harvesting elements (solar, thermal, electro-mechanical) have existed for a number of years. However, these elements have only recently reached a level of industrial maturity with regard to efficiency, power density, and volume production that opens the door to IoT systems’ use.
Focus on Prevalent Energy Harvesting Front Ends
At the system level a harvesting element is combined with purpose built power-optimized integrated circuits, for which an ultra-low-power design approach must be applied to its complete architecture. A power management chip must offer maximum efficiency when converting the small absolute amount of energy a harvesting element generates, whereas a companion radio chip must feature lowest transmit and receive currents and efficient transients to function properly within the same energy budget.
EM Microelectronic-Marin addresses these system constraints with a family of best-in-class integrated semiconductor solutions supporting IoT product providers with embedded low-power intelligence for their connected objects.
EM’s power management products focus on two of the most prevalent energy harvesting front ends, solar cells and thermo-electric generators.
Solar cell equipped systems have traditionally been operated in high-illumination environments in which even electronic components with moderate efficiency operate satisfactorily. A typical outdoor system functions with incident light at 10000 lux or more. For a solar system to be a true alternative in emerging IoT applications, operating in low-light environments while maintaining key system functions (sensors, MCU, wireless link) is the true differentiating capability. Running a sensor-equipped battery-less solar beacon in an indoor setting offering no more than a few hundred lux illustrates the concept.
The EM8500 power management silicon solution was specifically created to excel in these very use scenarios in which illumination is limited.
It incorporates the flexibility/configurability needed to handle a variety of solar cells (single element, multi-element cells), operate short- and long-term energy storage elements that might be present (caps, primary or secondary batteries), and power a collection of “users” (MCUs, wireless links, sensor banks, timers, displays etc). As a one-chip solar power manager the EM8500 device drastically simplifies integration into IoT devices, while presenting the best performance in power-efficiency figures of merit. A measured EM8500 solar energy harvesting benchmark is shown in Figure 1.
Thermoelectric generator (TEG)- based harvesting solutions have been attracting attention for devices that need to exploit temperature differentials around heat-producing appliances. Thermal harvesters have featured in specialty applications in environments in which substantial thermal energy (in the form of temperature deltas) was available and in which efficiency and cost considerations might have been somewhat secondary priorities. As with the solar system case, the ability to power a consumer or industrial system with a small and inexpensive TEG element, operate on temperature differences as low as 5 ºC, and run the above mentioned IoT functions are key to a usable thermal harvesting system. In the wearables segment running a watch or other wrist-worn device has now become feasible through the use of consumer-grade TEG elements combined with high-efficiency front end DCDC converters.
The EM8900/EM8502 pair of silicon components is EM’s silicon solution for TEG power management front ends. These EM devices target the handling of very small output voltages generated by physically small TEG elements. The use of EM Microelectronic’s own wafer fabrication, combined with modified transistor elements, yields the required converter efficiency in the TEG power management segment. Figure 2 shows the measured EM8900 efficiency at ultra-low input voltage.
Realizing IoT Everywhere
Ubiquitous IoT will be enabled only with tiny and ultra-low-power connectivity solutions. This is the primary underlying focus of EM Microelectronic’s recently introduced EM9304 Bluetooth low energy (BLE) chip.
It combines a 32-bit microprocessor with a state-of-the-art BLE radio on a single die. To enable a variety of application categories, it is designed with a flexible architecture for use as a companion IC to easily add BLE functionality to any ASIC or MCU-based IoT product. Alternatively, the device operates as a complete System-on-Chip (SoC) for standalone applications.
To handle supply from coin-cell batteries or from energy harvesters, the EM9304 includes a sophisticated on-chip power management unit with automatic configuration for 3V or 1.5V batteries, allowing the chip to be supplied with input voltages as low as 1.05V.
The BLE radio section achieves excellent RF sensitivity of -94dBm and offers an output power range from -34dBm to +6dBm. The current consumption has been optimized with as low as 3mA peak receiver current, 5.2mA peak transmit current (for 0dBm output power), less than 1uA in connected sleep mode, and below 5nA in disable mode.
The chip’s architecture is designed for rapid startup and power-efficient sequencing to reduce the energy overhead, namely the energy wasted when the chip is not communicating BLE signals. This allows best-in-class low-energy figures. A mere 25µJ is required for a non-connectable beaconing mode. The device is ideally suited to implement Bluetooth beacons, operating in combination with energy harvesting circuits like EM850x.
The EM9304 achieves the level of performance described above while offering a tiny foot print, tailored to IoT applications’ demand for a high degree of miniaturization. The chip, shown in Figure 3, measures 2.3mm x 2.2mm and is the smallest BLE 5.0 chip on the market today.
IoT devices and systems are routinely equipped with a series of sensing elements. Many platforms include a set of internal sensors, namely accelerometers, gyroscopes, and magnetic sensors, combined with various environmental sensors (pressure, humidity, temperature, gas).
Performing energy-efficient sensor signal processing on the IoT platform itself has become a system design priority. For example, the latest generation motion-sensing tags rely on internal sensors (9-DOF) combined with sophisticated sensor fusion algorithm processing to generate a reliable orientation vector for an object in 3D space.
The EM7180 silicon solution is an elegant answer to these requirements, providing leading heading accuracy (2 degrees RMS), lowest power consumption for sensor fusion calculations, and smallest footprint at 1.6 x 1.6 mm. It is a simple add-on function, bridging sensors and host MCU, and off-loading the latter from power-hungry fusion math (Figure 4.)
These key bricks are mandatory to enable smart IoT devices and have been developed with the system integration mindset of enabling miniaturized modules without jeopardizing operation at the lowest energy levels.
Bluetooth Beacons typify a major IoT deployment driver and are estimated to exceed 400 million units by 2020, according to ABI Research. Bluetooth beacons may be easily added to objects, assets, buildings, or infrastructure to enable message sending and location awareness functionalities for any user’s smartphone.
EM Microelectronic-Marin leverages the Swatch Group’s watch related expertise to produce standard products including its line of smart beacons, the EMBC01 proximity beacon, the EMBC02 3D-accelerometer beacon, or the long-life rugged EMBE01 multi-format beacon, or even flat beacon embodiments just the size of a credit card (see Figure 5).
The availability of energy-efficient silicon components such as EM9304, EM850x or EM7180 is key to the development of next-generation no-battery IoT solutions and BLE beacons.
Vincent Peiris is heading the Wireless and Sensing Business Unit of EM Microelectronic in Switzerland. His principal activities are low-power and low-voltage wireless ICs and modules for Bluetooth low energy and proprietary protocols. He holds MSc and PhD from EPFL, was postdoc at MIT, and has 25+ years of experience in analog and RF microelectronics at LeCroy, CSEM and EM.
Daniel Luthi is a Business Unit manager at EM Microelectronic-Marin SA where he oversees several sensor and energy harvesting product lines. He holds electrical engineering degrees from ETH Zurich and Stanford University with 20+ years of experience in the semiconductor industry.
Yves Théoduloz is a System Architect in the Intelligent Power Solutions Business Unit of EM Microelectronic in Switzerland. He is developing power management IC’s particularly in the Energy Harvesting area. He got an engineer diploma at the “School of Engineering and Management Vaud” – HEIG-VD – in Switzerland.