應用低溫多晶矽製程實現之液晶顯示器驅動電路

Abstract

本篇論文探討在低溫多晶矽製程上，實現液晶顯示器驅動電路之可行性。液晶顯示器的驅動電路可分為閘級驅動電路及源級驅動電路：其中閘級驅動電路包含移位暫存器、電位轉換器和輸出緩衝器；而源級驅動電路是由移位暫存器、閂鎖器、電位轉換器、數位電類比轉換器及輸出電壓緩衝器組成。 本篇論文著重於源級驅動電路的輸出電壓緩衝器之設計。顧及液晶分子對電場所具有的獨特性及顯示畫面品質的良窳，此一輸出電壓緩衝器具有特殊的輸入訊號和操作方式，以及嚴格要求的靜態功率消耗及電路面積。在此，我們設計一個具有高迴轉率及低消耗功率、密集電路面積的AB類電壓輸出緩衝器，並以VIS 0.35μm 2P4M 18V process實現之。然而在低溫多晶矽製程上，由於臨界電壓漂移及元件本身的扭結效應(kink effect)影響，一個較可能接受的設計方法是，在電壓輸出緩衝器中儘可能少用偏壓電流源。在此，我們也提出一個B類輸出緩衝器，並以Toppoly 6μm LTPS 1P2M process實現之。而為了能夠比較兩者的表現，我們以同樣的負載電路模組做測試。 最後，我們利用低溫多晶矽薄膜電晶體的特性，嘗試把其元件的基底接出來，並利用它來控制元件的臨界電壓。利用這項技術，我們設計了四種電位轉換器來驗證，並將其應用在液晶顯示器的閘級驅動電路。結果證明在適當的基底電壓偏壓之下，電位轉換器可工作於更低的輸入電壓訊號。

In this thesis, the possibility to implement the driving circuits for LCD in LTPS technology is discussed. The driving circuits for LCD can be divided into two groups, the gate driver and the data driver. Gate driver includes shift registers, level shifters, and output buffers. Data driver consists of shift registers, latches, level shifters, a digital to analog converter, and output buffers. The design of output buffers in the source driver is focused in this thesis. Considering the characteristic of liquid crystal molecule to electrical field and the quality of display, the output buffer must satisfy a particular input pattern and operating method. Moreover, it should achieve low quiescent power and small circuit layout area. A class-AB output buffer, which can be operated with high slew rate, low power and small layout area, has been designed and realized in VIS 0.35μm 2P4M 18V process. However, in LTPS technology the current source is significantly affected by threshold voltage drift and the kink effect. Therefore, a proposed way to design output voltage buffer is to use bias current source as less as possible. Thus, a class-B output buffer has been proposed and implemented in Toppoly 6μm LTPS 1P2M process. In order to compare both of their performance, these two buffers with the same loading are measured. Finally, according to the characteristic of TFT, its body is connected out to control the threshold voltage of device. Four kinds of level shifters to proof our idea have been designed to apply them in the gate driver of LCD. The measurement results confirm that the level shifters can be operated with lower input signals by applying adapted bias voltage to body.