Driving Methods for Low-Power and High-Image-Quality TFT-LCDs

Flat-panel displays using thin film transistor-liquid crystal display (TFT-LCD)s were developed in the early 1990's based on the characteristics of thin thickness, low power consumption, and so on, and were applied to the notebook product family. Since then, due to the development of large size, high resolution, and high color reproduction rate of TFT-LCDs, they replaced cathode ray tube (CRT) and plasma display panel (PDP) as computer monitors and TV screens in the early- and mid-2000s. Particularly in the TV product family, many technologies have been continuously developed to overcome the TFT-LCD disadvantages and improve performance such as viewing angle, color reproduction rate, low power consumption, thickness reduction, contrast ratio, high resolution, and size increase. As the result of these technology development, flat-panel displays using TFT-LCDs currently occupy a $110.7 billion market. Since the mid-2000s, TFT-LCD flat-panel displays have been expanded to include smart phones, automobiles, and commercial displays, along with the development of other related industries. In addition to improving basic image quality, 3D technology and production efficiency have been continuously developed. However, there is a disadvantage in that such performance improvements and new value-imparting technologies entail increases in power consumption. Therefore, the development of power consumption reduction technology should be pursued in tandem with the aforementioned development. In this dissertation, based on the power consumption reduction technology developed in the past, various suitable driving methods of the TFT-LCD product family with new value-added functions are proposed, so that the power consumption of both the driving part and backlight unit part is reduced. In this dissertation, a power reduction technique suitable for four product families is proposed: First, a TV with a 3D function using a film-type patterned retarder(FPR)second, monitor (), which applies negative liquid crystal with high liquid crystal transmission efficiencythird, the notebook PC (NBPC), which doubles the data driving rate to have the source driver IC, which reduce the costfourth, each optimized driving method is proposed to reduce power consumption of the TV product with a narrow bezel using an integrated scan driver of oxide TFT. The proposed method and its effects are summarized as follows. First, in order to reduce the power consumption in the 3D TV, the function of the black matrix, which realizes the 3D picture by distinguishing the data recognized by the right and left eyes by covering a lot of pixels, is replaced with individual pixels being driven as needed. In displaying the 3D picture, the pixel operates as the black matrix, and when the 2D picture is displayed, the pixel operates as a normal pixel, so that the power consumption of the 2D picture is reduced. In this way, the 47-inch full high definition (FHD) can be driven with 67 W of power consumption, which is reduced by 28% when operating in 2D mode. Second, negative liquid crystals can be used to improve the transmittance of the panel. However, the driving voltage of the negative liquid crystal exceeds the driving voltage range of the commercialized source driver IC. To solve this problem, a VCOM modulation method was developed without image degradation. Using this method, a 17-inch FHD TFT-LCD was driven with 22.5W of power consumption, which is 10% lower than when using positive liquid crystals. Third, a new dot inversion data addressing technique is proposed to achieve a high image quality in low-cost TFT-LCDs using a double rate driving method, which reduces the number of source driver ICs by half while reducing the power consumption. The power consumption of the data driver IC when displaying a mosaic pattern is reduced to 3.6 W at a 13 V supply voltage. In addition, a new pixel structure with a high (59.4%) aperture ratio reduces the power consumption of the backlight unit to 9.8 W, which is 16% less than a conventional design. Fourth, a small-area and low-power scan driver using a coplanar amorphous indium-gallium-zinc oxide (a-IGZO) TFT with a dual gate for 55-inch ultra high definition (UHD) TFT-LCDs is proposed. The width and measured power consumption of the fabricated scan driver with the proposed TFT are 2.63 mm and 2.41 W, which are both reduced by 20% compared with those of the scan driver with the conventional TFT.Docto