Vcom Differential Compensation Method for Improving Horizontal Crosstalk in Large-Size Liquid Crystal Display Panels with Narrow Bezel

Abstract

In Recent years, to emphasis on design, narrow width bezel of liquid crystal display (LCD) technologies has been developed for Large sized TV application. To realize narrow width bezel, Vcom line width which is located at the vertical edge of a panel becomes narrow continuously. The side of Vcom line width has been decreased more than 50%. However, in the reversed model type, single Vcom compensation as conventional method has reached the limit to reduce horizontal crosstalk on the top of the panel because the narrow width of Vcom. As the distance is increased in the printed circuit board (PCB), resistance and capacitance (RC) delay is increased. Due to narrow width Vcom line and large RC delay, single Vcom compensation is not affected to reduce horizontal crosstalk on the top of the panel. The Vcom differential compensation method which is applied to 3 Vcom input structure is proposed for reducing horizontal crosstalk due to Vcom fluctuation caused by coupling capacitance between data line and Vcom. To reduce Vcom fluctuation at the region on the top of the panel, the proposed method changes ratio of Vcom compensation depending on the position of panel using two inverting operational amplifiers. One inverting operational amplifier is used to compensate Vcom at the region near Vcom source in panel. Another inverted operational amplifier is used to compensate Vcom at the region far from Vcom source in panel. However, to compensate Vcom of the region far from Vcom source in panel, it is necessary to change of circuit and panel design is required. To supply sufficient current at large RC delay region far from Vcom source on the PCB, design of Vcom line width which is located in vertical bezel of a panel has to be changed to be wide. Conventional Vcom feedback lines which is located at vertical bezel of a panel is used as a path of Vcom differential compensation input voltage from Vcom source on PCB to upside region of the panel to compensate Vcom directly do not pass a large RC delay. One Vcom area which is located at vertical bezel of a panel is used to Vcom input and Vcom feedback. The other Vcom area which is located at vertical bezel of a panel is used to 2 Vcom input. Although Horizontal crosstalk of up and down side of panel is improved, uniformity of horizontal crosstalk on the whole panel is not improved. In order to achieve better uniformity of horizontal crosstalk, a new advanced method is proposed. The Vcom differential compensation method applying the structure of 4 Vcom input consists 4 Vcom input separate Vcom feedback. By applying advanced proposed method on whole panel, it is improved horizontal crosstalk. Experimental results show that the advanced proposed method reduces horizontal crosstalk from more than 4-level to under 1 level at the top and the bottom side on the panel. However, at the center of panel region, image uniformity is poor as more than 3-level. Criteria of horizontal crosstalk are applied to 5 steps. Advanced proposed method improves horizontal crosstalk from more than 4-level to 1-level at the whole panel. Therefore, the new advanced proposed method improves image uniformity of horizontal crosstalk compared to previous method.