A Robust Near-Zero Power Wakeup Timer With a Hybrid Reconfigurable FLL Directly Powered by Uncertain Harvested Voltage Down to 0.3V

Energy-harvesting systems require circuits to operate under ultra-low voltage supplies. Though the batteries are removed, a power management circuit is necessary to ensure a consistent voltage supply. In contrast to the state-of-the-art works, this work proposes a wakeup timer that is directly powered by harvested energy, thus obviating the need for additional power management circuits. In addition, we propose a hybrid FLL with an extended range of operation using digital-intensive architecture. Fabricated in 65 nm CMOS process, the chip consumes a total power consumption of 696 nW under 0.3 V supply. In addition, a temperature coefficient of $29 \mathrm{ppm} /{ }^{\circ} \mathrm{C}$, and a line sensitivity of $0.95 \% / \mathrm{V}$ are measured over a temperature/supply range of $0-100^{\circ} \mathrm{C}$ and $0.3-0.6 \mathrm{~V}$, respectively.