微發光二極體顯示器之0.18 μm CMOS雙極性高壓驅動微晶片

Abstract

本論文提出一個微發光二極體面板驅動晶片系統，其具備十個通道的電流抽載能力，並在其中的六個通道中提供微發光二極體狀態偵測與自我修復功能。一個完整的微發光二極體面板驅動電路至少須包含以下幾個子電路：負責產生各項電源偏壓的電源產生 ( Power Generation ) 電路、產生同步控制訊號的時序控制( Timing Control )電路、控制面板上薄膜電晶體( Thin Film Transistor, TFT )開關的閘極驅動器( Gate Driver )、提供像素驅動能力的源極驅動器( Source Driver )以及珈瑪校正( Gamma Correction )電路。本論文就其中的閘級驅動器、源極驅動器與時序控制功能進行改良，提供雙極性之閘極電壓控制以及發光二極體狀態偵測、修復和驅動功能，以期達到較佳的顯示效果與顯示壽命。 發光二極體顯示面板的源極驅動方式大致可分為三種，分別為恆定電流驅動( Constant Current Driving )、恆定電壓控制( Constant Voltage Driving )以及脈波調變控制( Pulse Width Modulation Driving )，本論文採用恆定電流方式進行驅動。本論文設計的恆定電流控制電路由電流抽載器( Current Sink )以及位準移位器( Level Shifter )兩者組成，藉由調整電流抽載器的抽載電流大小以控制發光二極體的亮度，並同時配合時序控制電路以及位準移位器正確驅動薄膜電晶體的閘級開關，以達到控制灰階和驅動薄膜電晶體開關的功能。 其中為延長面板顯示壽命，本篇提出在一個像素內( Pixel )內多植入一倍的發光二極體，在一般情況下同色的兩顆發光二極體會同時被驅動發光，而在有其中一顆損毀的情況時則會偵測並停止驅動損毀的該顆發光二極體，僅驅動完好的另一顆發光二極體，以此方式達到延長面板顯示壽命的目的。 本晶片使用台積電0.18微米互補式金屬氧化物半導體( Complementary Metal Oxide Semiconductor, CMOS )製程實現，晶片面積為1.75×2.5 mm2，共可同時抽載十個通道，並在其中的六個通道提供發光二極體狀態偵測與修復功能。數位時序控制時脈為25 MHz，準位為0至1.8V，外部直流偏壓共使用5種，分別為12 V、3 V、2.5 V、1.8 V和-3 V。本設計之閘級驅動輸出準位均為-3至12V，依據驅動薄膜電晶體之不同共分為三種負載規格，此處分別稱為RGB-TFT、RE-TFT、G-TFT，其中負責控制三色開關的RGB-TFT模擬之上升和下降時間分別為20.45 ns和22.66 ns，負責控制開啟或關閉損壞的發光二極體的RE-TFT模擬之上升和下降時間分別為23.87 ns和19.89 ns，負責逐列驅動的G-TFT模擬之上升和下降時間分別為23.01 ns和25.4 ns。電流抽載器切換頻率為1.04 MHz，最大抽載電流為483.5 μA，解析度為8位元，即本晶片可提供0到255的灰階控制。

This thesis present a driving chip for Micro-LED displays, with the ability to drive 10 channels simultaneously. Among the 10 channels, 6 of them have the additional self-repairing and LED condition sensing functions. Most of the Micro-LED display driving systems include the following building blocks: a power generation circuit to provide biases, a timing control circuit to provide synchronous control signals, a gate driver to control the gate of the TFTs on the panel, a source driver to drive the pixel and a gamma correction circuit. The research aims to improve the gate driver, source driver and timing control design to provide a better gate driving ability with bipolar voltage output and a more long-life driving system with the proposed repair function. The driving schemes of micro-LEDs can be roughly divided into three types, which are constant current driving, constant voltage driving and pulse width modulation driving. The thesis adopts the constant current scheme. The constant current driving scheme in the thesis consists of current sink circuits and level shifter circuits. The current sink circuits are in charge of the driving current control, which directly related to the luminance of the micro-LED, and the level shifter circuits are required to effectively turn on and off the TFT switches according to the applied digital control signal. Besides, to lengthen the lifetime of the display, the thesis proposed a novel pixel structure with an additional set of micro-LEDs planted inside. When both micro-LEDs are in good conditions, the chip will drive the two micro-LEDs simultaneously, but when one of the micro-LED burns out, the chip will detect the situation, stop driving the broken one, and increase the driving current of the good one. The chip in the thesis is implemented with TSMC 0.18 m CMOS technology, and occupies an area of 1.75×2.5 mm2. The chip has the ability to sink 10 channels at the same time and provides the micro-LED detecting and repairing functions for the 6 out of the 10 channels. The chip is fed with 25 MHz, 1.8 V serial digital signals and 5 DC biases, which are 12 V, 3 V, 2.5 V, 1.8 V and -3 V, respectively. Three different level shifters are designed to drive three different loadings, however the output levels of the level shifter circuits are all from -3 V to 12 V. The simulated rise time and fall time of the level shifter with RGB-TFT loading are 20.45 ns and 22.66 ns, with RE-TFT loading are 23.87 ns and 19.89 ns, and with G-TFT loading are 23.01 ns and 25.4 ns. The switching speed of the current sink is 1.04 MHz, and it can sink a maximum current of 483.5 A with 8-bit resolution control, which means gray level control of 0 to 255 is achievable with the chip.