A Multiphase Switched-Capacitor Converter for Fully Integrated AMLED Microdisplay System

A fully integrated switched-capacitor (SC) dc-dc converter is designed for powering up an active-matrix light-emitting diode (AMLED) microdisplay system. The stacking-transistor technique with three voltage conversion ratios is utilized to handle the lithium-ion battery range of 2.6-4.2 V and to reduce the switching loss. A 101-phase interleaving scheme is adopted such that, first, output voltage ripple Delta V-O is significantly reduced; second, no external output capacitor is needed; and, third, SC power-cells are physically cascaded to encircle the LED array and drivers to reduce conduction loss. Two test chips were designed in the 0.18-mu m 1P6M CMOS technology. The first chip is a test chip comprising the SC converter only. The output voltage is 4.2 V, and the measured maximum Delta V-O is 52 mV. The measured power density is 74.4 mW/mm(2), peak efficiency is 81%, and maximum output power is 258 mW. The second chip is a system chip integrating the SC converter with the AMLED array and drivers using flip-chip packaging. The converter delivers a maximum power of 216 mW with a 78% peak efficiency in the SC mode and a 91% peak efficiency in the linear regulator mode.