Design of energy-efficient power circuits for low-power applications

Abstract

Since a system-on-chip (SoC) includes various intellectual properties (IPs), a power management unit (PMU) capable of supplying various voltages is required. In addition, because the SoC is designed to further miniaturize a system, the PMU also aims to be fully integrated within the SoC. This dissertation compares various types of power conversion circuits and proposes a switched-capacitor (SC) power converter supporting fine-grained dual-output that satisfies the PMU requirements in a low-power SoC. The proposed converter generates a much higher number of voltage conversion ratios (VCRs) than the existing dual-output SC converters, so it can maintain high conversion efficiency over a wide output voltage range and can supply various voltages to IPs in the SoC.Recent low-power digital circuits that operate with a very limited amount of energy sources such as batteries, wireless power transfer, or harvesting have necessarily adopted dynamic voltage scaling (DVS) for efficient energy use. In particular, in order to perform efficient DVS, fast and fine-grained voltage control is required. Among power conversion circuits for performing DVS, capacitive converters are most suitable. However, capacitive converters essentially involve additional energy losses while the voltage conversion ratio (VCR) changes, thus they lead to a limitation in performing fast voltage control. In this dissertation, the cause of VCR transition loss in switch-capacitor (SC) DC-DC converters is analyzed and modeled. Through simulation and chip measurement of the previously proposed SC converters, the accuracy of the loss model is verified and a new norm for SC power converters in performing DVS is presented. In addition, this dissertation proposes and analyzes several methods to reduce the energy loss during VCR transitions.Finally, this dissertation proposes an SC converter with a two-dimensional cell array structure that can not only support fine-grained dual-output but also minimize the VCR transition loss. Furthermore, the arbitrary phase selection technique to enhance the versatility of a power converter and the independent pulse control scheme to improve cross-regulation performance are presented.