A Two-Channel High-Performance DC-DC Converter for Mobile AMOLED Display Based on the PWM–SPWM Dual-Mode Switching Method

Abstract

In this paper, we propose a design of a two-channel high-performance DC-DC converter that provides a positive voltage VPOS with a low ripple, and a negative voltage VNEG with high power efficiency, for the purpose of enhancing power efficiency and output ripple under light loads of 100 mA or less for mobile active-matrix organic light-emitting diode (AMOLED) displays. The VPOS was designed as a boost converter using a novel input voltage variation reduction circuit (IVVRC), which rapidly changes the pulse width for input voltage fluctuations, using a feed-forward path. The VNEG was designed as an inverting buck–boost converter based on the pulse width modulation–set time variable pulse width modulation (PWM–SPWM) dual-mode switching method to enhance power efficiency, especially under light loads, and to reduce the overhead of the circuit configuration using a voltage-controlled oscillator. In addition, an adaptive dead-time using voltage detection of switching node (ADTVS) circuit was proposed to enhance power efficiency, which detects the voltage of the switching node at every cycle, and keeps the dead-time constant irrespective of changes in driving conditions. The proposed converter was fabricated with a chip size of 1.67 mm × 2.44 mm, using a 0.35 μm BCD process. Measurement results showed that the power efficiency of our converter was 72.9%~90.4% at 5 mA–100 mA light load output current, which is 2.7%~5.8% higher than the output of the previous converter. Furthermore, the output voltage ripple of VPOS and VNEG at 5 mA light load output current was 3.0 mV and 5.3 mV, respectively, which improved by 19% and 25% as compared to those of the previous converter, respectively.