A Hybrid Single-Inductor Bipolar-Output Converter With a Concise PWM Control for AMOLED Displays

Abstract

This article presents a compact single-inductor bipolar-output (SIBO) converter for active-matrix organic light-emitting diode (AMOLED) displays. Addressing the demand for a large load capacity within a limited form factor, we propose a hybrid SIBO converter featuring two flying capacitors ( $C_{\mathrm {F}}$ s) which are introduced to further reduce the inductor current ( ${I} _{\mathrm {L}}$ ) and voltage stress of power switches. The proposed converter mainly consists of two operation states that determine the energy charging and distribution, respectively, when the two outputs have the same load currents. To address potential loading imbalance, two auxiliary phases are incorporated into the main operation states. A concise PWM control strategy, consisting of a common-mode (CM) loop and differential-mode (DM) loop, is also proposed for bipolar output regulation with fast transient responses. The converter is fabricated in a 0.18- $\mu $ m BCD process and the measured peak efficiency reaches 94.5% using a $2.5\times 2.0\times 1.2$ mm3 inductor. Furthermore, the converter achieves 3.99 W/mm2 on-die power density with the total off-chip components occupying 15.32-mm3 volume, demonstrating that this design provides a compact solution for AMOLED displays.