Capacitance-to-Digital Converter for Operation Under Uncertain Harvested Voltage down to 0.3V with No Trimming, Reference and Voltage Regulation

In Paper 5.2, the National University of Singapore and Politecnico di Torino present a capacitance-to-digital converter (CDC) for direct harvester-powered low-cost systems, showing a 7-bit ENOB down to 0.3V at 1.37nW power without any external reference or voltage-regulation requirements

Nanoelectromechanical relay without pull-in instability for high-temperature non-volatile memory

Emerging applications such as the Internet-of-Things and more-electric aircraft require electronics with integrated data storage that can operate in extreme temperatures with high energy efficiency. As transistor leakage current increases with temperature, nanoelectromechanical relays have emerged as a promising alternative. However, a reliable and scalable non-volatile relay that retains its state when powered off has not been demonstrated. Part of the challenge is electromechanical pull-in instability, causing the beam to snap in after traversing a section of the airgap. Here we demonstrate an electrostatically actuated nanoelectromechanical relay that eliminates electromechanical pull-in instability without restricting the dynamic range of motion. It has several advantages over conventional electrostatic relays, including low actuation voltages without extreme reduction in critical dimensions and near constant actuation airgap while the device moves, for improved electrostatic control. With this nanoelectromechanical relay we demonstrate the first high-temperature non-volatile relay operation, with over 40 non-volatile cycles at 200 ∘C

A pW-Power Hz-Range Oscillator Operating With a 0.3-1.8-V Unregulated Supply

In this paper, a pW-power relaxation oscillator for sensor node applications is presented. The proposed oscillator operates over a wide supply voltage range from nominal down to deep sub-threshold and requires only a sub-pF capacitor for Hz-range output frequency. A true pW-power operation is enabled thanks to the adoption of an architecture leveraging transistor operation in super-cutoff, the elimination of voltage regulation, and current reference. Indeed, the oscillator can be powered directly from highly variable voltage sources (e.g., harvesters and batteries over their whole charge/discharge cycle). This is achieved thanks to the wide supply voltage range, the low voltage sensitivity of the output frequency and the current drawn from the supply. A test chip of the proposed oscillator in 180 nm exhibits a nominal frequency of approximately 4 Hz, a supply voltage range from 1.8 V down to 0.3 V with 10%/V supply sensitivity, 8-18-pA current absorption, and 4%/°C thermal drift from -20 °C to 40 °C at an area of 1600 μm². To the best of the authors' knowledge, the proposed oscillator is the only one able to operate from sub-threshold to nominal voltage

Mr.Wolf: An Energy-Precision Scalable Parallel Ultra Low Power SoC for IoT Edge Processing

This paper presents Mr. Wolf, a parallel ultra-low power (PULP) system on chip (SoC) featuring a hierarchical architecture with a small (12 kgates) microcontroller (MCU) class RISC-V core augmented with an autonomous IO subsystem for efficient data transfer from a wide set of peripherals. The small core can offload compute-intensive kernels to an eight-core floating-point capable of processing engine available on demand. The proposed SoC, implemented in a 40-nm LP CMOS technology, features a 108-mu W fully retentive memory (512 kB). The IO subsystem is capable of transferring up to 1.6 Gbit/s from external devices to the memory in less than 2.5 mW. The eight-core compute cluster achieves a peak performance of 850 million of 32-bit integer multiply and accumulate per second (MMAC/s) and 500 million of 32-bit floating-point multiply and accumulate per second (MFMAC/s) -1 GFlop/s-with an energy efficiency up to 15 MMAC/s/mW and 9 MFMAC/s/mW. These building blocks are supported by aggressive on-chip power conversion and management, enabling energy-proportional heterogeneous computing for always-on IoT end nodes improving performance by several orders of magnitude with respect to traditional single-core MCUs within a power envelope of 153 mW. We demonstrated the capabilities of the proposed SoC on a wide set of near-sensor processing kernels showing that Mr. Wolf can deliver performance up to 16.4 GOp/s with energy efficiency up to 274 MOp/s/mW on real-life applications, paving the way for always-on data analytics on high-bandwidth sensors at the edge of the Internet of Things

Capacitance-to-Digital Converter for Harvested Systems Down to 0.3 V With No Trimming, Reference, and Voltage Regulation

In this work, a capacitance-to-digital converter (CDC) suitable for direct energy harvesting is introduced. The nW peak power and the ability to operate at any supply voltage in the 0.3-1.8 V range allow complete suppression of any intermediate DC-DC conversion, and hence direct supply provision from the harvester, as demonstrated with a mm-scale solar cell. The proposed CDC architecture eliminates the need for any additional support circuitry, preserving true nW-power operation, and reducing design and integration effort. In detail, the architecture is based on a pair of double-swappable oscillators, and avoids the need for any voltage/current/frequency reference circuit in the oscillator mismatch compensation. The digital and differential nature of the architecture counteracts the effect of process/voltage/temperature variations. A load-agnostic one-time self-calibration scheme compensates mismatch, and can be run from boot to run stage of the chip lifecycle. The proposed self-calibration scheme suppresses any trimming or testing time for low-cost systems, and avoids any input capacitance disconnection requirement. A 180-nm testchip shows 7-bit ENOB down to 0.3 V and 1.37-nW total power, when powered by a 1-mm2 indoor solar cell down to 10 lux (i.e., late twilight