A Reconfigurable Voltage Converter With Split-Capacitor Charging and Energy Recycling for Ultra-Low-Power Applications

Abstract

This paper presents a reconfigurable on-chip switched capacitor (SC) voltage converter aimed at ultra-low- power applications. The proposed voltage converter provides an additive advantage of energy saving during both sleep-to-active and active-to-sleep transitions. This is done by incorporating two techniques, so called, split-capacitor charging (step-wise charging), and energy recycling. Split-capacitor charging is proved to reduce the energy loss during the sleep-to-active transition by 66%. An existing symmetric energy recycling technique recovers 75% of the energy from the capacitor bank at the expense of a large-output voltage ripple. In this paper, an improved method called asymmetric energy recycling reconfiguration (s) is introduced. The asymmetric energy recycling reduces the output voltage ripple by 50% compared with the symmetric recycling technique, without sacrificing the recycling efficiency. It can salvage 75.42% of the capacitor energy in active-to-sleep transition that would have been wasted through leakages during a long sleep period. Circuit simulations of the proposed SC voltage converter demonstrate up to 23.13% improvement in energy efficiency compared with conventional SC converters for a short active period.

Keywords

• Switched capacitor
• DC-DC converter
• ultra-low power converter
• step-wise charging
• energy recycling