Active Matrix OLED 디스플레이의 고정밀도 전원전압을 가지는 단일 인덕터 다출력 직류-직류 변환기

Abstract

As the use of the active matrix organic light-emitting diode (AMOLED) display with smart devices has rapidly increased, various approaches have been researched to improve the display performance of AMOLED panels [1-3]. As demonstrated in prior studies, the high accuracy of positive pixel power supply voltage and the use of less external components are important in designing the power management block because these are closely related to the portability of mobile devices and the luminance characteristics of AMOLED displays [4-7]. This thesis proposes a single input multiple output (SIMO) DC-DC converter to generate a highly accurate positive pixel power supply voltage (ELVDD) of AMOLED displays. The proposed converter controls the priority of power transfer to improve the accuracy of ELVDD. The converter is designed to supply the ELVDD of 4.75 V and the negative pixel power supply voltage (ELVSS) of -4.90 V alternatively and simulated with maximum output current of 270 mA, which corresponds to 1,920ⅹ1,080 AMOLED pixels for mobile devices. When the load current is abruptly changed from 10mA to 270mA abruptly, ELVDD and ELVSS fluctuate as much as 1.22mV and 135mV, respectively. Because this ELVDD fluctuation is less than 1 LSB of data voltage in an AMOLED pixel with 8-bit gray scale, the luminance variation caused by ELVDD fluctuation is not noticeable. The simulated maximum power efficiency of the proposed converter is 85.2% when the load current is 100 mA at the operating frequency of 1MHz. This simulation result shows that the proposed converter is suitable for AMOLED displays of mobile devices.|최근 들어, 스마트 기기에 AMOLED display 장치의 사용이 빠르게 증가함에 따라, AMOLED 디스플레이 성능 향상을 위해 다양한 접근방법이 연구되고 있다[1-3]. 이전의 연구에서 알 수 있듯이 AMOLED 디스플레이의 휘도 특성과 모바일 기기의 휴대성을 위해서는 각각 정확한 positive 픽셀 전원 전압과 외부 구성 부품 축소를 위한 파워 매니지먼트 블록 설계가 중요한 부분이 되었다 [4-7]. 본 논문에서는 AMOLED display의 매우 정확한 positive pixel 전압 (ELVDD)을 생성하는 single-inductor multiple-output (SIMO) DC-DC converter를 제안하였다. 제안된 converter는 ELVDD의 정확도를 향상시키기 위하여 전력 전달의 우선 순위를 제어한다. 제안된 converter를 1,920ｘ1,080의 해상도를 갖는 휴대용 기기의 AMOLED display에 적합하게 개발하기 위하여, ELVDD, ELVSS 및 최대 출력 전류는 각각 4.75V, -4.90V 및 270mA로 설계하였다. 출력 전류가 10mA에서 270mA로 갑작스럽게 변경될 때 ELVDD 및 ELVSS의 변동은 각각 1.22mV 및 135mV로 나타났으며, 이러한 변동은 8-bit gray scale을 갖는 AMOLED 화소에서의 데이터 전압의 1LSB보다 작기 때문에 발광 특성에 영향이 거의 없는 것으로 확인하였다. 또한 100mA의 출력 전류 및 1MHz의 동작 주파수의 조건에서의 simulation을 통하여, 최대 전력 전달 효율은 85.2%를 나타내는 것을 확인하였으며, 다양한 simulation 결과를 통하여 제안한 converter는 휴대용 AMOLED display에 매우 적합한 것을 확인하였다.; As the use of the active matrix organic light-emitting diode (AMOLED) display with smart devices has rapidly increased, various approaches have been researched to improve the display performance of AMOLED panels [1-3]. As demonstrated in prior studies, the high accuracy of positive pixel power supply voltage and the use of less external components are important in designing the power management block because these are closely related to the portability of mobile devices and the luminance characteristics of AMOLED displays [4-7]. This thesis proposes a single input multiple output (SIMO) DC-DC converter to generate a highly accurate positive pixel power supply voltage (ELVDD) of AMOLED displays. The proposed converter controls the priority of power transfer to improve the accuracy of ELVDD. The converter is designed to supply the ELVDD of 4.75 V and the negative pixel power supply voltage (ELVSS) of -4.90 V alternatively and simulated with maximum output current of 270 mA, which corresponds to 1,920ⅹ1,080 AMOLED pixels for mobile devices. When the load current is abruptly changed from 10mA to 270mA abruptly, ELVDD and ELVSS fluctuate as much as 1.22mV and 135mV, respectively. Because this ELVDD fluctuation is less than 1 LSB of data voltage in an AMOLED pixel with 8-bit gray scale, the luminance variation caused by ELVDD fluctuation is not noticeable. The simulated maximum power efficiency of the proposed converter is 85.2% when the load current is 100 mA at the operating frequency of 1MHz. This simulation result shows that the proposed converter is suitable for AMOLED displays of mobile devices.