0.18-μm Light-Harvesting Battery-Assisted Charger–Supply CMOS System

Abstract

Wireless microsensors in hospitals, factories, and farms can manage and save lives and critical resources. Although tiny batteries cannot sustain them for long, harvesters can because ambient energy is abundant. Photovoltaic cells are popular in this regard because they output close to 100× more power from solar light than piezoelectric, electrostatic, and thermoelectric generators can from motion and heat. But since millimeter cells can only supply microwatts of the milliwatts that microsystems can draw, and light is not always available, battery assistance is necessary. So to supply functions and sustain operation across extended periods, the system should extract maximum ambient power, draw minimal battery assistance, and deliver as much of what it receives as possible. The 0.18-µm CMOS harvester presented here does this, draws 10-100 µW from a 3 × 3 × 1-mm 3 cell and assistance from a battery to supply a 1-mW load and recharge the battery with excess cell power. The switched-inductor charger-supply regulates 1-V within ±25 mV with 73%-86% power-conversion efficiency and keeps the cell within 1% of its maximum power point. This way, the cell outputs 100 µW/mm 2 from solar light and 1 µW/mm 2 from direct indoor light.Index Terms-Ambient light energy, harvester, CMOS photovoltaic (PV) cells, microsystem, switched-inductor converter, wireless microsensor, charger, and power supply.

Low Voltage Delay Element with Dynamic Biasing Technique for Fully Integrated Cold-Start in Battery-Assistance DC Energy Harvesting Systems

“…Both the battery-less energy harvesting system [2][3][4][5][6][7][8][9][10][11][12] and the battery-assistance energy harvesting system [13,14] have been reported upon in the literature, as shown in Figure 1. For the battery-less energy harvesting system, as indicated in Figure 1a, the issue of battery replacement is fundamentally solved and all the energy consumed by loads is harvested from the surrounding environment.…”

“…A high voltage (VDDH) generated by the battery is employed to assist the oscillation of the cold start-up ring oscillator under an extremely low input voltage (Vin). General categories for energy harvesting systems: (a) battery-less energy harvesting system [2][3][4][5][6][7][8][9][10][11][12]; (b) battery-assistance energy harvesting system [13,14].…”