An Inverter-Based, Ultra-Low Power, Fully Integrated, Switched-Capacitor DC-DC Buck Converter

A fully integrated ultra-low-power step-down DC-DC converter is demonstrated in 65nm. This circuit is useful for converting battery voltage levels (2.5 - 3V) to digital and mixed-signal voltage levels for low-power always-on domains. A down conversion of 5:1 is utilized to provide a near-Vth digital voltage of 0.55-0.6V, while making higher voltages (1.2V, 1.8V) available as well. An inverter-based amplifier is utilized to achieve high speed regulation at low power. Measured results show an Efficiency-Enhancement-Factor (EEF) of 66% and a power density of 2.56 mW/mm² at an output power of 100µW. At this power, these parameters represent the state-of-the-art. The DC-DC converter has a fast transient response which results in operation with minimal droops and overshoots even with output capacitors as low as 50 pF.