Self-powered systems (SPSs) that harvest energy from the ambient environment, eliminating the battery, are gaining traction due to the increasing need for large-scale data collection in the Industrial Internet of Things (IIoT) space. The ultra-low-power receiver (ULP RX) is one promising solution for this application space that provides benefits from its energy-efficient operation. This paper discusses the requirements of self-powered wireless systems for IIoT applications and the challenges of designing ULP RXs for real-world deployments. Circuit design techniques to address the issues are summarized, and an ULP RX design with a proprietary protocol that is being adopted by commercialized SPSs is presented. Finally, the prospects and future trends for ULP receivers are summarized.

Ultra-low-power (ULP) receivers are gaining traction in consumer and industrial IoT solutions as standards such as WiFi 802.11ba, BLE, and NB-IoT have adopted wakeup messages into their protocols to reduce synchronization energy overhead. ULP wakeup receivers (WRX) enable lower average power, lower latency, and precise time synchronization which leads to more dense network deployments [1–5]. This paper presents a $2.7\ \mu$W WRX that supports a simplified 802.15.4g MAC/PHY baseband, RSSI and clear channel assessment (CCA), forward error correction (FEC), and cryptographic checksum. The novelty of this WRX is the parallel-path rectifier and charge-domain analog front-end (AFE), which provides low power, wide dynamic range, pulsed interference rejection, and reliable operation across harsh environments and industrial wireless conditions in real-world deployments.

This paper presents a system-on-chip (SoC) that enables commercial self-powered systems (SPSs) by flexibly managing application needs, harvesting energy from multiple modalities, coordinating low-latency/high-density network communication, and optimizing power across the system. To scale to a trillion IoT nodes, devices must untether from batteries by achieving energy autonomy. A SPS must balance harvested power $(\mathrm{P}_{\mathrm{H}})$ with load power $(\mathrm{P}_{\mathrm{L}})$ to enable continuous operation, which becomes challenging in real-world harvesting conditions for applications with stringent functional needs. While this SoC can support many IoT applications, we demonstrate the SoC in a machine health monitoring (MHM) product that uses multi-modal sensors to forecast motor failure to minimize downtime.

Batteryless operation and ultra-low-power (ULP) wireless communication will be two key enabling technologies as the IC industry races to keep pace with the IoE projections of 1T-connected sensors by 2025. Bluetooth Low-Energy (BLE) is used in many consumer IoE devices now because it offers the lowest average power for a radio that can communicate directly to a mobile device [1]. The BLE standard requires that the IoE device continuously advertises, which initiates the connection to a mobile device. Sub-1s advertisement intervals are common to minimize latency. However, this continuous advertising results in a typical minimum average power of 10's of μW at low duty-cycles. This leads to the quoted 1-year lifetimes of event-driven IoE devices (e.g. tracking tags, ibeacons) that operate from coin-cell batteries. This minimum power is too high for robust, batteryless operation in a small form-factor.

Batteryless operation and ultra-low-power (ULP) wireless communication will be two key enabling technologies as the IC industry races to keep pace with the IoE projections of 1T-connected sensors by 2025. Bluetooth Low-Energy (BLE) is used in many consumer IoE devices now because it offers the lowest average power for a radio that can communicate directly to a mobile device [1]. The BLE standard requires that the IoE device continuously advertises, which initiates the connection to a mobile device. Sub-1s advertisement intervals are common to minimize latency. However, this continuous advertising results in a typical minimum average power of 10’s of μW at low duty-cycles. This leads to the quoted 1-year lifetimes of event-driven IoE devices (e.g. tracking tags, ibeacons) that operate from coin-cell batteries. This minimum power is too high for robust, batteryless operation in a small form-factor.

A boost converter for thermoelectric energy harvesting in 130 nm CMOS achieves energy harvesting from a 10 mV input, which allows wearable body sensors to continue operation with low thermal gradients. The design uses a peak inductor current control scheme and duty cycled, offset compensated comparators to maintain high efficiency across a broad range of input and output voltages. The measured efficiency ranges from 53% at VI=20 mV to a peak efficiency of 83% at VI=300 mV. A cold-start circuit starts the operation of the boost converter from 220 mV, and an RF kick-start circuits starts it from -14.5 dBm at 915 MHz RF power.

Most systems require a voltage reference independent of variation of power supply, process, or temperature, and a bandgap voltage reference (BGR) often serves this purpose. For ultra-low power (ULP) systems, the BGR may constitute a significant component of standby power, and the system start-up voltage is often determined by the voltage, Vin, at which the BGR becomes operational. Lowering Vin can also allow an ULP system to continue operation longer as its battery or energy harvested input voltage decreases. The minimum Vin for state-of-the-art BGRs is restricted by VEB+VDS [1], where VEB is the emitter-base voltage of a pnp transistor, and VDS is the drain-source saturation voltage of a MOS transistor. Recent work brings the Vin voltage down to 700mV [2]. There is a need to reduce the standby power and Vin of a BGR to increase the lifetime of ULP systems. This paper presents a BGR circuit with measured minimum operating Vin of 500mV, reducing the Vin of [2] by 1.4x. Further, the power consumption of the proposed circuit is 32nW, which is 1.6x lower than the non-duty cycled BGR reported in [2]. A 2x-charge pump based bandgap core, a switched-capacitor network (SCN), and a current controlled oscillator and clock doubler circuit enable a BGR with a temperature variation of 75ppm/°C and power supply rejection (PSR) of up to -52dB at DC.

We present a 187kHz to 500kHz ADPLL-based clock generator that consumes 300nW from a 0.5V VDD, has a jitter <;0.1% and was implemented in a 0.13μm CMOS process. The entire ADPLL was implemented using standard digital design flows and automatic place and route (APR). Moreover, an integrated crystal oscillator (31.25 kHz) is included and serves as the reference for the PLL. Therefore, this is a complete clocking solution for ultra-low power near-threshold SoCs.

This paper presents a low-power, long-range 433MHz transceiver designed for 2-FSK modulation at 1kbps in 8 different physical channels capable of communicating with a Texas Instruments CC1101. Designed in a 130nm CMOS process with an area of 1.1mm2, the transmitter's output power is 0dBm and the receiver has a sensitivity of -102dBm producing a link budget >100dB and a theoretical range >5km assuming 1/d2 path loss. Low transmitter power is achieved using a 0.5V Class-E PA and low receiver power is achieved by implementing a digitally-assisted demodulator with further power reduction achieved through bit-level duty cycling with an off power of 110nW.

A 1 trillion node internet of things (IoT) will require sensing platforms that support numerous applications using power harvesting to avoid the cost and scalability challenge of battery replacement in such large numbers. Previous SoCs achieve good integration and even energy harvesting [1][2][3], but they limit supported applications, need higher end-to-end harvesting efficiency, and require duty-cycling for RF communication. This paper demonstrates a highly integrated, flexible SoC platform that supports multiple sensing modalities, extracts information from data flexibly across applications, harvests and delivers power efficiently, and communicates wirelessly.

This paper presents a batteryless system-on-chip (SoC) that operates off energy harvested from indoor solar cells and/or thermoelectric generators (TEGs) on the body. Fabricated in a commercial 0.13 μW process, this SoC sensing platform consists of an integrated energy harvesting and power management unit (EH-PMU) with maximum power point tracking, multiple sensing modalities, programmable core and a low power microcontroller with several hardware accelerators to enable energy-efficient digital signal processing, ultra-low-power (ULP) asymmetric radios for wireless transmission, and a 100 nW wake-up radio. The EH-PMU achieves a peak end-to-end efficiency of 75% delivering power to a 100 μA load. In an example motion detection application, the SoC reads data from an accelerometer through SPI, processes it, and sends it over the radio. The SPI and digital processing consume only 2.27 μW, while the integrated radio consumes 4.18 μW when transmitting at 187.5 kbps for a total of 6.45 μW.

There is a growing class of event-driven devices that require instant-on wireless connectivity, but only use the radio to communicate intermittently throughout their lifetime. Home automation devices and most wellness monitors fall into this class, only using or needing their radios when prompted by an event. In these applications, the radios dominate the amount of energy consumed from the batteries. More specifically, the energy spent synchronizing the radios, or maintaining a connected state, dominates, as opposed to the energy spent communicating data.

We present Literacy in Technology (LIT), a low power, low cost audio processor for information dissemination among illiterate people groups in developing regions. The 265 K gate, 8 million transistor, 23 mm(2), ARM Cortex M0 processor uses a novel memory hierarchy consisting of an on chip 128 kB true LRU cache and off-chip NAND Flash. LIT reduces initial acquisition cost through a high-level of integration that results in a low board-level component count. In addition, it also reduces recurring cost through design decisions that lower energy consumption. LIT's multiple power operational modes and power management schemes are specifically designed for efficient operation on Carbon Zinc batteries. These are commonly found in developing regions and allow LIT to be priced at a point that is viable for illiterate people groups in developing regions.

This paper presents a 116nW wake-up radio complete with crystal reference, interference compensation, and baseband processing, such that a selectable 31-bit code is required to toggle a wake-up signal. The front-end operates over a broad frequency range, tuned by an off-chip band-select filter and matching network, and is demonstrated in the 402-405MHz MICS band and the 915MHz and 2.4GHz ISM bands with sensitivities of -45.5dBm, -43.4dBm, and -43.2dBm, respectively. Additionally, the baseband processor implements automatic threshold feedback to detect the presence of interferers and dynamically adjust the receiver's sensitivity, mitigating the jamming problem inherent to previous energy-detection wake-up radios. The wake-up radio has a raw OOK chip-rate of 12.5kbps, an active area of 0.35mm(2) and operates using a 1.2V supply for the crystal reference and RF demodulation, and a 0.5V supply for subthreshold baseband processing.