DC–DC switching converter with positive and negative outputs for active-matrix LCD bias

Abstract

A DC–DC switching converter chip is proposed to generate both positive and negative voltages for active-matrix LCD (AMLCD) bias. An inductive boost converter and two inverting charge pumps are integrated in a proposed chip by using a 0.5 µm 5 V, 3.5 µm 30 V CMOS process. A conventional scheme used to bias AMLCD employs a switching-boost converter with several off-chip components to generate the required positive and negative voltages. The circuit proposed in this study achieves high performance with a minimum number of off-chip components. Additionally, the proposed method is capable of generating a wide range of negative voltages by varying the reference voltage to supply optimised power for the AMLCD system. Because the supply voltage of the developed inverting charge pump is supplied by the output voltage of the boost converter through a linear regulator, the operations of switching-boost converter and inverting charge pump are independent and are without cross-regulation problems. The boost converter's input power supply range is 2.8–5.5 V, the output voltage range is 10–20 V and the clock frequency is 780 kHz. The maximum efficiency is 84% with the input power supply at 5.5 V, an output voltage of 10 V and a load current of 100 mA. The integrated inverting charge pumps have two outputs that generate −2× and −4× the reference voltage. The overall core size is 2150 µm×2150 µm.