A Fully Integrated, Switched-Capacitor DC-DC Buck Converter Featuring an Inverter-Based Comparator

A fully integrated ultra-low-power step-down DC-DC converter in 65nm is presented. The purpose of this converter is to convert battery voltage levels, in the range of 2.5-3V, to digital and mixed-signal voltage levels for low-power always-on domains. A down-conversion with a ratio of 5:1 is employed to provide a digital voltage level near the threshold voltage (Vth), which ranges from 0.55-0.6V. Higher voltage levels, such as 1.2V and 1.8V, are also made available for analog circuits. To achieve high-speed regulation at low power, an inverter-based comparator is utilized. Silicon results indicate an Efficiency-Enhancement-Factor (EEF) of 66% and a power density of 2.56 mW/mm2 at an output power of 100mu W. These parameters represent the state-of-the-art for this level of power. The DC-DC converter exhibits a fast transient response, leading to minimal droops and overshoots, even for a 50pF output capacitor.