Design of a High Efficiency Inverting Buck-Boost Converter for OLED Displays

This thesis addresses the design of high-efficiency inverting DC–DC converters for AMOLED display applications in mobile devices. AMOLED panels require negative bias voltages whose magnitude varies with operating conditions and luminance, imposing stringent constraints on efficiency, silicon area, and passive component count in power management integrated circuits. The work presents a comprehensive analysis of different converter topologies, including inductive, switched-capacitor, and hybrid solutions. Their operating principles, advantages, and limitations are discussed with particular attention to efficiency, scalability, and integration feasibility. Hybrid architectures combining inductors and flying capacitors are shown to offer an effective trade-off between performance and implementation complexity. A switched-capacitor inverting buck–boost converter is identified as a particularly suitable solution for the target application. Analytical models are developed to describe its steady-state operation, power losses, and design constraints, enabling an in-depth understanding of the key trade-offs among switching frequency, passive component sizing, efficiency, and silicon area. An optimization methodology for power switch sizing under area constraints is proposed, allowing efficient operation across a wide load range in advanced CMOS technologies. In addition, a dedicated control strategy is introduced to address capacitor voltage balancing in multi-level architectures, ensuring stable operation without additional sensing circuitry. Simulation results validate the effectiveness of the proposed design and control approaches. Overall, this thesis provides a systematic design framework for inverting DC–DC converters in low-power integrated applications, offering methodologies and insights that can be extended to a broad class of power management systems beyond AMOLED displays.