A Bipolar-Output Converter with an Adaptive Ramp Generator and PWM Control for OLED Displays

Traditional power management for organic electroluminescent (OLED) displays is performed by two different converters, providing both positive and negative power rails and thus raising fabrication costs due to the usage of two inductors, in addition to efficiency being dependent on one of the two converters while also suffering from high-voltage stress. This paper introduces a bipolar converter that only uses a single inductor to generate both power rails for OLED displays, along with two additional flying capacitors to reduce inductor currents and voltage stress placed on the power switches. The proposed design implemented in the 180 nm CMOS process occupies a chip area of 0.98 mm2 and achieves a peak efficiency of 93% at 350 mA load current. Furthermore, the ripple voltage is greatly reduced using both common-mode and differential-mode feedback loops in the PWM control scheme, with a maximum ripple of 20 mV across a 100–500 mA current range.