Techniques for Analyzing and Reducing Voltage Conversion Ratio Transition Losses of Capacitive DC–DC Converters for Fast-DVS-Enabled Systems

Abstract

Switched-capacitor (SC) converters have numerous advantages in supplying fast and fine-grained voltages to microprocessors. However, the losses associated with the voltage conversion ratio (VCR) transition, which has not been investigated in detail, may cause a significant efficiency drop. This letter presents a simple and accurate model for estimating energy losses during the VCR transition of many-ratio SC dc–dc converters. The loss model begins with the assumption that the charge redistribution among flying and load capacitors is the leading cause for the VCR transition losses. The analysis of different types of many-ratio SC dc–dc converters shows that the model is consistent with the simulated results. For more verification, a test chip containing a converter with an algorithmic voltage-feed-in topology was fabricated in a 0.18-μm CMOS process, with the measured results also in good agreement with the model outcomes. Furthermore, to mitigate the VCR transition loss, several techniques are discussed and analyzed based on the presented model. In particular, the SC converter with flying capacitor reordering method shows 28.9% conversion efficiency improvement over the conventional SC converter with negligible circuit overhead.