Youngmin Cho

New overdrive technology for liquid-crystal displays with a simple architecture

We propose a new technique to extract overdrive (OD) values that are indispensable to improve response characteristics of liquid-crystal displays. We show the relation among an OD value (DOD), a previous frame data (DPF), and a current frame data (DCF) can be expressed very well by a third-order polynomial. To make the implementation of the OD technology to be simple, we propose to create a base line that is expressed by the third-order equation and to linearly shift it according to DPF. Our proposed method does not need the large size lookup tables (LUTs), whereas the conventional OD technology requests huge LUTs. Thus, our method can be easily implemented by very small circuits, which enables a low-cost solution. Only six measurements in our method are sufficient to obtain OD values of all the transition, whereas the conventional one wants 256 measurements. We investigate the best position of the base line and show how small the deviation from optimum values is. We prove that the proposed OD technology enables a low-cost implementation, high productivity, and high performance.

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 Behavioral Circuit Model of Active-Matrix Liquid Crystal Displays for Optical Response Simulation

We propose a behavioral circuit model to precisely predict optical responses of an active-matrix liquid crystal (LC) display (LCD) using a patterned vertical alignment (PVA) mode. To get more accurate simulation results, we propose two LC groups with different time constants for a pixel after observing the LCD pixels by using a high-speed camera. In addition, we include a time-delay concept into our behavioral model for brightening or rising transitions. We describe the behavior of the PVA-LCD by using the analog hardware description language Verilog-A. We simulate the PVA-LCD panel by importing the behavioral circuit model in the circuit simulator SmartSPICE. The simulation results of the transient optical responses show excellent matches with the measurement ones.

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.

Universal overdrive technology for all types of liquid-crystal displays

We propose a new overdrive technology using third-order approximations. We can estimate overdrive (OD) values for all the transitions by linearly shifting a third-order base line. We investigate whether the proposed method is applicable to any liquid-crystal display (LCD) panels regardless of their characteristics. We examine the feasibility of the method using 11 LCD panels with different sizes, switching speed of liquid-crystal (LC) molecules, LC modes, and applications. After confirming the feasibility, we examine optimum position of the base line to minimize OD deviations from optimum OD values. We have four unknown coefficients of the third-order base line and a shifting parameter. We investigate if we can adjust only one coefficient with the three remaining coefficients fixed to create a base line optimized to each panel among the 11. We decide that we can adjust only one coefficient after analyzing experimental results. In addition, we look into fixing the shifting parameter. Finally, we conclude that we can accurately estimate OD values of all the transitions by adjusting only one value. Because of the extreme simplicity, we can implement our OD technology with an extremely simple circuit. We anticipate that common users can easily optimize the visual performance of their LCD system.

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.

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.

Hardware-efficient auto-correlation for synchronization of MIMO-OFDM WLAN systems

This paper presents a hardware-efficient autocorrelation scheme for the synchronization of MIMO-OFDM based wireless local area network (WLAN) systems, such as IEEE 802.11n. Carrier frequency offset (CFO) estimation for the frequency synchronization requires high complexity autocorrelation operations of many training symbols. In order to reduce the hardware complexity of the MIMO-OFDM synchronization, we propose an efficient correlation scheme based on time-multiplexing technique and the use of reduced samples while preserving the performance. Compared to a conventional architecture, the proposed architecture requires only 27% logic gates and 22% power consumption with acceptable BER performance loss.

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.