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Energy Harvesting and Power Management Unit

LDO Design Automation

The design and verification process for analog circuits can be long and tedious, wherein designers rely heavily on manual effort to create circuits and draw layouts, thereby limiting turn-around-time and design scale and increasing costs. Various previous works have tried to solve this issue by leveraging digital automated place-and-route (APR) tools, but they involve replacing analog elements with digital counterparts, thereby dampening performance. In this work, we propose a digital flow-based approach to design all-analog circuits that dramatically speeds up the design and layout process while retaining the benefits of true analog topologies and demonstrate the performance for three low-dropout regulators (LDOs). Fabricated in 65-nm CMOS, measurement results show that the generated LDOs achieve up to 99.95% peak current efficiency, a figure-of-merit (FOM) of 4.6 ps, and up to 63.93% reduction in input offset variability with respect to their manually designed counterparts.


Triple-input Hybrid-Inductor-Capacitor Multi-output EHPMU

Advancements in power and size reduction for integrated circuits (IC) enable integration of self-powered systems into mm-scale fiber strand. Moving towards intricate fiber networks where multiple subsystems interact within textiles or garments, energy harvesting and power management units (EHPMU) require full autonomy, ultra-low quiescent power, high efficiency, and a mm-scale footprint. Additionally, they must coordinate energy across distributed subsystems for enhanced system viability and scalability. A switched-capacitor (SC) based ultra-low-power (ULP) EHPMU [1] realizes distributed energy sharing but its cascade structure restricts the efficiency and dynamic range (<5µW). Also, its single-rail-sharing architecture for distributed systems forces all subsystems to interact with a shared rail, necessitating extra dedicated converters, thereby increasing cost.  Existing multi-input single-inductor multi-output (MISIMO) EHPMUs [2-7] achieve high efficiency with a single power-delivery stage, but they either consume >100nW quiescent power [3-7], have <1000× dynamic range [3][5], lack full autonomy [3][4][6][7], or require large inductor (22µH) with low efficiency due to conventional buck-boost (CBB) conversion [2]. Furthermore, none of them support distributed systems. As shown in the top of Fig. 1, we address these limitations with a fully autonomous triple-input hybrid-inductor-capacitor multi-output (TIHICMO) EHPMU that can harvest energy from dual input sources, regulate three custom output rails, adaptively switch among multi-conversion methods, cold startup (CS) from all the inputs/outputs, and enable energy recycling and sharing among multiple rails. This EHPMU achieves a 5.8nA quiescent current, a wide dynamic range of 8.8x104, a peak efficiency of 90.1%, and a >90% reduction in inductor size compared to [2][7] using a 3×3×1.3mm 200mΩ DCR inductor.

Multi-input Single-Inductor Multi-output EHPMU

Energy harvesting and power management units (EHPMUs) are gaining popularity for self-powered Internet-of-Things (IoT) applications due to their ability of extracting ambient energy and powering load circuits through a single block. Among all EHPMU architectures, the multi-input single-inductor multi-output (MISIMO) [1-6] has the benefits of small form factor, high efficiency, extracting energy from multi-modal energy sources, and powering different types of loads. Self-powered IoT applications also require the EHPMUs to have ultra-low quiescent power, wide dynamic range, and autonomous features to support their deployment without any battery. However, previous EHPMUs either consume too much power [1-3] or only provide a small dynamic range [4,5]. They also suffer from two-stage power delivery causing cascaded power loss [1,5] and lack of essential components such as voltage references [6] for a fully deployable solution. To overcome all these challenges, in this work, we propose a fully autonomous MISIMO EHPMU platform that can extract energy from three energy harvesters with both AC and DC modalities and provide four custom voltage rails together with on-chip maximum power-point tracking (MPPT) and multi-modal cold start-up circuits. This EHPMU achieves 32nA quiescent current, 1.2×105 dynamic range, 3.2× energy-extraction gain for piezoelectric energy harvesting, and 80% efficiency when delivering 1μA output current.

Sub-nW inductor-based buck converter

This work presents a buck converter with sub-nW quiescent power, high efficiency, and a wide dynamic range for ultra-low-power (ULP) IoT SoCs. To optimize the SoC power consumption, the buck converter supports fast dynamic voltage and frequency scaling (DVFS) and enables fast load-transient response (FLTR) through asynchronous control. In addition, the buck converter is fully self-contained with all features integrated on chip including a proposed adaptive deadtime controller. Fabricated in 65nm CMOS, measurement results show the buck converter has an 802pW quiescent power at 1.5V input voltage and a 93% peak efficiency. The measured dynamic range is from 0.5nW to 2.75mW, which is over 6 orders of magnitude. The measured voltage droop is 54mV for a 45nA-to-1mA load current step thanks to the asynchronous load-transient detector. The buck converter achieves the highest efficiency and widest dynamic range among all the state-of-the-art sub-nW switching voltage regulators, which makes it well suited for power management in ULP SoCs. 
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