A 1-V-Input Switched-Capacitor Voltage Converter With Voltage-Reference-Free Pulse-Density Modulation

A 1-V-input 0.45-V-output switched-capacitor (SC) voltage converter with voltage-reference-free pulse-density modulation (VRF-PDM) is proposed. The all-digital VRF-PDM scheme improves the efficiency from 17% to 73% at 50- μA output current by reducing the pulse density and eliminating the voltage reference circuit. An output voltage trimming by the hot-carrier injection to a comparator and a periodic activation scheme of the SC voltage converter are also proposed to solve the problems attributed to VRF-PDM. The proposed voltage converter is fabricated in 65-nm CMOS and achieves an efficiency value of 73%-86% at 50 μA-10 mA output current range.