저온 Poly-Si TFT를 이용한 휴대용 LCD 패널의 구동회로 및 T/CON 설계

Abstract

Because thin film transistor-liquid crystal display (TFT-LCD) panel in low temperature poly silicon (LTPS) backplane has lower threshold voltage and higher mobility than hydrogenated-amorphous silicon (a-Si:H) backplane, not only the gate driver but also source driver, timing controller (T/CON), DC-DC converter can be integrated in the panel. However, the electrical characteristics of Poly-Si TFTs have a variation, so it is hard to make precise analog circuits or high-speed digital circuits. In this thesis, gate and source driver, DC-DC converter, timing controller are designed for TFT-LCD in Poly-Si TFT backplane. When analog buffer of source driver is integrated in poly-Si panel, the image has a non-uniformity because of the channel-to-channel variation of the offset of buffers due to electrical characteristics of Poly-Si TFTs. Because of this reason, driving using external chip is used instead of integration of analog buffer in the panel. Also, a new ramp DAC is proposed for area saving because R-string digital-to-analog converter (DAC) with read only memory (ROM) type decoder has a drawback that the area of DAC is almost doubled when 1-bit of the gray scale increases, because the number of switches and resistors increases 2 times. The present timing controller is hard to generate timing signal in TFT-LCD panel with quarter VGA (qVGA) resolution because of low driving capability of current of poly-Si TFTs. To overcome this, a fast operating circuit is proposed to generate control signals. The designed circuits target to 2-inch qVGA TFT-LCD panel with 8-bit gray level. The timing controller is integrated in the panel, so the timing signals for drivers can be generated in the panel. The maximum voltage error of source driver is under the 1 LSB, and the power consumption is 12.6mW and 9.0mW for the maximum and the minimum case, respectively. The proposed counter in timing controller can operate up to 12 MHz frequency.