Jongbin Kim

Liquid crystal displays with temperature-independent characteristics

A new technology is presented that enables liquid crystal displays (LCDs) to have temperature-independent characteristics. This work shows how severely the color image quality of LCDs is affected by the ambient temperature change in addition to showing how the ambient temperature considerably affects the motion image quality of overdriven LCDs. Transmittance-voltage curve-shifting technology is proposed to compensate for the color change owing to temperature change. This new technology reduces a half-maximum luminance error from 24% to 6% over the temperature range from 0°C to 50°C. The linear overdrive (OD) technology over the wide temperature is presented to overcome the temperature-dependent characteristics of LCDs. With this technique, the distribution of the OD error is reduced by 65%. The color and motion image quality of LCDs can be kept the same with these techniques, regardless of temperature.

A Novel Method to Accurately Predict Color Information of Liquid Crystal Displays With Light Leakage From Black Pixels

This paper proposes a new method to predict color information of liquid crystal displays (LCDs) very accurately. Leaked light from black sub-pixels causes errors of the color prediction based on the individually measured RGB color information. We present a new method to remove the bad influence of the light leakage. We prove that this work can calculate the pure colorimetric information regardless of the shapes of opto-electronic transfer function (OETF) of LCDs. Without this technology, average errors of luminance (ΔY) and chromaticity coordinate (Δxy) over 30 colors were 0.58 cd/m2 and 0.04, respectively. When we applied the proposed method, however, average errors of ΔY and Δxy were 0.03 cd/m2 and 0.005, respectively. Experimental results show that our method can extract pure primary color information with extremely low errors.

Behavioral Circuit Model of Active-Matrix Liquid Crystal Display With Charge-Shared Pixel Structure

This paper proposes a behavioral circuit model to precisely predict optical responses of an active-matrix liquid crystal (LC) display with charge-shared vertical alignment (CS-VA) mode. CS-VA mode consists of two subpixels in one pixel to mitigate the off-axis gamma distortion. We present a new method using overdrive voltages to obtain accurate capacitance versus voltage (C-V) characteristics in CS-VA mode. In addition, we present a new technique to obtain transmittance versus voltage (T-V) characteristics of the two subpixels by using a high-speed camera with image processing. In addition, we analyze the panel to obtain precise voltage levels after sharing charges. We describe the behavior of the CS-VA LC display (LCD) by using an analog hardware description language, Verilog-A, and we simulate the CS-VA LCD panel by importing the behavioral circuit model in a circuit simulator, Smart-SPICE. The simulation results of the transient optical responses show excellent matches with the measurement ones.

Pixel Architecture for Low-Power Liquid Crystal Display Comprising Oxide and Ferroelectric Memory Thin Film Transistors

A new pixel architecture and driving scheme for a low-power liquid crystal display (LCD) with a low refresh-rate is proposed. The proposed pixel architecture comprises two oxide thin-film transistors (Ox-TFTs), two ferroelectric memory TFTs (Fe-MTFTs), and two capacitors. Both TFTs have the same indium gallium zinc oxide film as an active layer. The Fe-MTFT exhibits a hysteresis property owing to the ferroelectric gate insulator that enables it to operate as a memory. A prototype LCD with 6 × 5 pixels is fabricated in this letter. The fieldeffect mobility of Ox-TFTs is 11 cm2V-1s-1. The memory window of Fe-MTFT is 5 V with a gate-voltage sweep from -20 to 20 V. After programming the Fe-MTFTs, the fabricated LCD successfully operates at a 0.5-Hz refresh-rate.

User-friendly minimization technology of three-dimensional crosstalk in three-dimensional liquid crystal display televisions with active shutter glasses

Abstract. We propose a new three-dimensional (3-D) crosstalk minimization method for the active shutter glasses-type 3-D liquid crystal displays (LCD) television (TV). The crosstalk was reduced from 43% to 10% on average with the proposed technology. Furthermore, we propose a user-friendly method to reduce the 3-D crosstalk without any measurement equipment, which enables consumers to make their TVs crosstalk free. It is found that the results of the proposed crosstalk minimization method and user-friendly method are matched well. Thus, 3-D TV consumers can easily minimize the 3-D crosstalk with their eyes only.

A new precharging method without side effects for liquid crystal displays with insufficient charging time

In this paper, a new precharging method without any side effects is proposed to overcome image degradation caused by insufficient charging times. This work explains why the precharging method can compensate for short charging times. However, side effects of the precharging method in the form of horizontal line artifacts are addressed, wherein line artifact-compensating precharging (LCP) is presented to mitigate the side effects. Behavioral modeling is employed to investigate the side effects by estimating transient responses of a liquid crystal display. The LCP proves that it can dramatically reduce line artifacts caused by precharging because the brightness difference of adjacent pixels does not exceed 1.0.

P-137: An Accurate Electrical Model of a Liquid Crystal Cell in Active-Matrix LCD

We propose an electrical model of a pixel in a matrix-driven LCD panel to accurately anticipate transient optical responses. We present a method to get accurate transmittance/capacitance vs. voltage data. Our model can be applied to find overdrive values to improve response characteristics.

Driving technology for improving motion quality of active-matrix organic light-emitting diode display

Abstract. This paper reports transient response characteristics of active-matrix organic light emitting diode (AMOLED) displays for mobile applications. This work reports that the rising responses look like saw-tooth waveform and are not always faster than those of liquid crystal displays. Thus, a driving technology is proposed to improve the rising transient responses of AMOLED based on the overdrive (OD) technology. We modified the OD technology by combining it with a dithering method because the conventional OD method cannot successfully enhance all the rising responses. Our method can improve all the transitions of AMOLED without modifying the conventional gamma architecture of drivers. A new artifact is found when OD is applied to certain transitions. We propose an optimum OD selection method to mitigate the artifact. The implementation results show the proposed technology can successfully improve motion quality of scrolling texts as well as moving pictures in AMOLED displays.

New elliptical parallax barrier pattern to reduce the cross talk caused by light leakage

Abstract. This paper proposes a parallax barrier with an elliptical pattern that reduces the cross talk caused by light leakage from adjacent subpixels in autostereoscopic three-dimensional (3-D) displays. To find the optimum size of the elliptical barrier pattern, the relationship between the reduction of the light leakage and that of the luminance is analyzed. In addition, we analyze the relationship between the cross talk and the luminance. By using these relationships, we propose an optimum size of the ellipse. An autostereoscopic 3-D display with the elliptical barrier is compared with 3-D displays with the slanted barrier and the rectangular one. The measured cross talk of the slanted-type 3-D display whose pixel size is 98×294  μm was 57%. However, the cross talk of the ellipse-type 3-D display was 32% at the similar luminance condition when the minor and major axes are 92 and 278 μm, respectively. For generalization, we investigate autostereoscopic 3-D displays with different pixel sizes and different viewing distances. We find the optimum area of the ellipse is 70% of the subpixel area to reduce the cross talk.

Precise prediction of optical responses of liquid-crystal display products using a behavioral model of liquid crystal

We propose a precise circuit model to estimate transient optical responses of an active-matrix liquid crystal display (AMLCD). Liquid crystal (LC) molecules in the pixel is behaviorally modeled by using the first-order system that is described by Verilog-A. Capacitance-voltage (C-V) characteristics of a pixel determine the accuracy of the dynamic responses. Measuring C-V characteristics is impossible because pixels are driven by switching transistors in the AMLCD. We propose a method to obtain the C-V data from natural optical responses. Estimated optical responses based on the C-V data extracted by our proposal show more accurate results than those based on C-V data obtained by using transmittance-voltage data. It is demonstrated that our behavioral model enables us to predict very accurate transient responses, which makes it possible to design LCD products with lower costs.