平面顯示器玻璃基板上具有位階轉換功能之類比輸出級電路設計

Abstract

低溫複晶矽(low temperature poly-silicon, LTPS)薄膜電晶體(thin-film transistors, TFT)已被視為一種材料廣泛地應用於可攜帶式系統產品中，例如數位相機、行動電話、個人數位助理(PDA) 、筆記型電腦等等，這是由於低溫複晶矽薄膜電晶體的電子遷移率(electron mobility)約是傳統非晶矽(amorphous silicon)薄膜電晶體的百倍大。此外，低溫複晶矽技術可藉由將驅動電路整合於顯示器面板之週邊區域來達到輕薄、小巧且高解析度的顯示器。這樣的技術也將越來越適合於系統整合型面板(system-on-panel /system-on-glass)之實現。 近年來，低溫複晶矽技術具有將所有控制與驅動電路整合入玻璃基板的趨勢。一般而言，液晶顯示器的驅動電路包含閘極驅動電路、資料驅動電路以及直流對直流轉換電路。其中，資料驅動電路則是由移位暫存器、閂鎖器、電位移轉器、數位類比轉換器以及類比輸出緩衝器所組成。然而，在量產線上仍無法精確控制複晶矽薄膜電晶體之晶粒大小與晶粒邊界的一致性，這會使得複晶矽薄膜電晶體因為元件特性變化而具有較差的一致性。元件特性的變化對於在液晶顯示面板上的類比電路設計是一個嚴重的問題。也由於這個原因，在本論文中將著重於資料驅動電路中的類比電路設計。 在本篇論文中，提出了一個著重於元件特性變化考量之資料驅動電路的類比輸出緩衝器，並以此緩衝器為基礎提出兩個具有位階轉換功能的類比輸出級電路，以上電路皆以3-um LTPS製程技術實現。類比緩衝器可以在100 kHz的方波輸入訊號下具有0.8 V至9 V的輸出範圍。此具有位階轉換功能的類比輸出級電路也與數位類比轉換電路整合在一起。可以藉由電路本身的位階轉換功能，在不需要修改驅動電路的前提下可驅動不同工做電壓之面板，並且符合該面板所需的珈瑪補償曲線。

Low temperature poly-silicon (LTPS) thin-film transistors (TFTs) have been widely investigated as a material for portable systems, such as digital camera, mobile phone, personal digital assistants (PDAs), notebook, and so on, because the electron mobility of LTPS TFTs is about 100 times larger than that of the conventional amorphous silicon TFTs. Furthermore, LTPS technology can achieve slim, compact, and high-resolution display by integrating the driving circuits on peripheral area of display. This technology will also become more suitable for realization of system-on-panel/system-on-glass (SOP/SOG) applications. Recently, LTPS technology has a tendency towards integrating all control circuits and driver circuits on the glass substrate. In general, the liquid-crystal display (LCD) driver contains gate driver, data driver, and DC-DC converter. The gate drive usually utilizes high voltage to enhance the response time of LCD monitor. The data driver is composed of shifter registers, latch, level shifters, digital-to-analog converters (DACs), and analog output buffer. However, the poly-Si TFTs suffered poor uniformity with large variations on the device characteristics due to the narrow laser process window for producing large-grained poly-Si TFTs. The device variation becomes a very serious problem for analog circuit design on LCD panel. For this reason, the analog circuits of the data driver are focused in my works. In this thesis, an on-panel analog output buffer for data driver with consideration of device characteristic variation and output buffers with level shifting function are proposed in a 3-um LTPS technology. The proposed analog output buffer can be operated at 100 kHz rail-to-rail square wave input with a 0.8-to-9 V output swing. The proposed output buffer with level shifter can be integrated with the digital-to-analog converter (DAC). This circuit can drive different panel without changing DAC circuit and to fit its corresponding gamma curve.