Search

This paper introduces a fully integrated switched-capacitor (SC) DC-DC boost converter suitable for energy harvesting in miniature sensor systems with varying harvesting source and battery voltages. Unlike the conventional SC DC-DC boost converters, where efficiency is optimized only for a few topology-dependent voltage conversion ratios (VCRs), the proposed soft-charging-based SC converter achieved VCR-insensitive evenly high efficiency for a wide range of input and output voltages. A test chip was fabricated in 180nm process, and the measured peak efficiency and average efficiency are 85.3% and 83.6%, respectively, for 1.8V regulated output voltage and a wide range of input voltages (0.95–1.8 V). Also, a peak efficiency of 88.9% and average efficiency of 87.6% are achieved for a wide range of battery output voltages (3.0–4.2 V) and a 1.2V harvesting source input voltage. [ABSTRACT FROM AUTHOR]

This paper presents a thermal/RF hybrid energy harvester. The energy harvesting system can scavenge energy from a thermoelectric generator (TEG) and a radio-frequency (RF) energy source simultaneously, and deliver the combined power to a single load. Two techniques are employed in the system to increase the end-to-end efficiency; the rectifying-combination technique is proposed to eliminate the power loss associated with a dedicated AC-DC converter before the combiner and an improved fractional open-circuit voltage (FOCV) maximum power tracking (MPPT) is considered for a high average efficiency. A dynamic power path control extracts the maximum RF power from a cross-coupled differential rectifier, and also behaves as an AC/DC energy combiner. The thermal/RF harvester system achieves a measured peak end-to-end power conversion efficiency (PCE) of 63.4%. The shorter sampling time of 26ms every 16s for the proposed FOCV MPPT method reduces the long charging tail required to refresh the sampling capacitor, resulting in a an improved average efficiency of 82.2% for the thermal harvester. Fabricated in 0.18 $\mu \text{m}$ CMOS technology, the prototype operates at a thermal input voltage ranging from 40 mV to 400 mV and an RF power from −18 dBm to −3 dBm and delivers an output voltage of 1.8 V. The total area of the fabricated circuit prototype is 1.22 mm2. [ABSTRACT FROM AUTHOR]

Low-power circuits often employ dynamic voltage scaling and energy harvesting. Such circuits need a power management unit that can convert the voltage source to a wide range of target voltages with high efficiency. Targeting such a power management unit, this paper presents a reconfigurable architecture of switched capacitor (SC) voltage converter. It introduces a design optimization methodology that can determine trade-off among design parameters to meet the goal. The proposed converter employs a reconfigurable topology with four capacitors. It provides 11 conversion ratios: 6 step-down and 5 step-up ratios supporting wide input/output voltage range. An analytical model for the output impedance of the proposed reconfigurable SC topology is presented. Using the model, the proposed optimization methodology can minimize the total power dissipation. To validate the proposed architecture and optimization methodology, the converter has been implemented in a 130-nm CMOS process using integrated capacitors of total size 2.2 nF. Simulation results show that the optimized converter circuit achieves an efficiency range from 83.41% to 74.69% for a load current of $100~\mu \text{A}$. [ABSTRACT FROM AUTHOR]

Energy harvesting is an emerging technology for powering wireless sensor nodes, enabling battery-free operation of these devices. In an energy harvesting sensor, a power management circuit is required to regulate the variable harvested voltage to provide a constant supply rail for the sensor circuits. The power management circuit needs to be compact, efficient, and robust to the variations of the input voltage and load current. A closed-form power expression and custom control algorithm for regulation of a switched-capacitor DC-DC converter with optimal conversion efficiency are proposed in this paper. The proposed regulation algorithm automatically adjusts both the voltage gain and switching frequency of a switched-capacitor DC-DC converter based on its input voltage and load current, increasing the power efficiency across a wide input voltage range. The design and simulation of a fully integrated circuit based on the proposed power managing approach is presented. This power management circuit has been simulated in a 0.25 \mum standard CMOS process and simulation results confirm that with an input voltage ranging from 0.5 V to 2.5 V, the converter can generate a regulated 1.2 V output rail and deliver a maximum load current of 100 \muA. The power conversion efficiency is higher than 74% across a wide range of the input voltage with a maximum efficiency of 83%. [ABSTRACT FROM AUTHOR]

A high efficiency, maximum power point tracking (MPPT) power management unit (PMU), with 3.6 \mmb\mu\bf W quiescent power, aimed at a thermoelectric generator (TEG) array is presented. The proposed energy harvesting PMU is made up of a boost converter with a cascaded capacitor-less low drop-out (CL-LDO) voltage regulator. The segmented approach allows the PMU to match the TEG array's changing dynamic series resistance via the boost converter and simultaneously provide voltage regulation with adaptive, high switching noise rejection via the CL-LDO. The boost converter's switching frequency (f{sw}) is tracked via a Sense-and-Control loop which modifies the CL-LDO's power supply rejection (PSR) characteristics to place a notch in the PSR transfer function around the average f{sw}. Experimental results show an overall system efficiency better than 57% @ 1.6 V output voltage, PSR of 40 dB at f{sw}, and a notch-tuning range of 15–65 kHz. The total active area is 0.93 mm^2 in 0.5 \mum CMOS. [ABSTRACT FROM PUBLISHER]