Accurate determination of pretilt angle in twisted‐nematic liquid‐crystal cells by using a rotating analyzer

Abstract— A new optical method for determining the pretilt angle ψ⁰, particularly on twisted‐nematic (TN) liquid‐crystal (LC) cells, is proposed. ψ⁰ was rapidly determined with good reproducibility on a TN‐LC cell by using a rotating analyzer optical system, a twist angle Φ, the azimuth of the director at a substrate, ϕ⁰, and the retardation Δnd as known values. The thickness d was also determined simultaneously with ψ⁰. ψ⁰ and d were determined within minutes. ψ⁰ was previously determined to be in the range of 0.1° with a standard deviation of 0.01°; this was obtained by repeating the measurement 50 times. The principle behind the determination and the experimental set up are described in detail.     

Achromatic quarter‐wave film using two chromatic wave plates and a twisted‐nematic liquid‐crystal cell

Abstract— An achromatic quarter‐wave film using one twisted‐nematic liquid‐crystal (TNLC) cell, a chromatic half‐wave plate, and a chromatic quarter‐wave plate is presented. The Jones matrix is used to calculate the optical properties of the system. An optimal algorithm is used for optimizing the configuration parameters. Simulation results indicate that the designed configuration is capable of turning a linearly polarized light into perfectly circularly polarized light in the wavelength range 400–700 nm. The manufacturing tolerance of the cell gap and twisted angle of the TNLC are good.     

Transflective twisted‐nematic liquid‐crystal display with double twisted‐nematic cell and twisted liquid‐crystal retarder

Abstract— Two configurations, (i) a double‐cell‐gap twisted nematic (DTN) liquid‐crystal display (LCD) and (ii) a single‐cell‐gap twisted‐nematic (TN) liquid‐crystal display (LCD) using a twisted LC retarder, were optimized for transflective liquid‐crystal displays. For the DTN configuration, both the single‐cell‐gap approach and the double‐cell‐gap approach were considered. The optimized configurations exhibit a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. They are easy to fabricate and also possess a perfect dark state. Both are suitable for high‐quality transflective TFT‐LCDs.     

A silicon‐chip‐based light valve with reflective twisted‐nematic mode for high‐definition projectors

Crystalline‐silicon‐chip‐based reflective light valves are suitable for realizing high definition and bright liquid‐crystal projectors. We have developed an XGA (1025 × 769 pixels) silicon‐chip‐based light valve with a diagonal display area of 2.54 cm (1 in.). The reflective twisted‐nematic mode was examined by using the Jones matrix method as a display mode, and the normally white reflective twisted‐nematic mode was selected. This mode is suitable for a narrow cell gap, and a fast response time can be expected. In addition, the driving voltage of this mode is low and has good chromaticity with small retardation. The cell gap of the light valve is 2 μm. The cell gap support is made using spacer posts formed on the silicon chip with a photodefinable resin. The response time is 12 msec, including both rise and fall times. The contrast ratio is more than 1000 at 5 Vrms.     

Heterodyne method for determining the surface tilt angle of nematic liquid‐crystal displays

Abstract— The high‐sensitivity pretilt‐angle measurement of liquid‐crystal displays, based on the modified crystal‐rotation configuration and the use of a common‐path heterodyne interferometer, is proposed. In this technique, environmental disturbance and surface reflection are eliminated to a large extend, thus providing advantages for both constructing a simple‐optics measurement system and achieving fast measurement with high accuracy and sensitivity.     

Cell‐parameter measurement system for a liquid‐crystal cell by using a telecentric lens

Abstract— A two‐dimensional cell‐parameter measurement for determining the pretilt angle in addition to both the cell thickness and twist angle of liquid‐crystal (LC) cells is proposed. Because the measurement images of an LC cell is perfectly focused by using a telecentric lens, the 2‐D cell‐parameter distribution can be determined by measuring the Stokes parameters of the LC cell at several different wavelengths by changing the oblique angle of the incident light on the LC cell.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

Extended Jones matrix method and its application in the analysis of compensators for liquid crystal displays

We describe an extended Jones matrix method which is a powerful tool to treat the transmission of light through birefringent networks, where the incident angle of light and the optical axis of the birefringent media are arbitrary. The method is generalized to cover all dielectric media including uniaxial and biaxial crystals and gyrotropic materials that exhibit optical rotatory power and Faraday rotation. We then apply this method to investigate various birefringent optical thin films that can be used to improve the viewing angle characteristics and gray scale stability of conventional twisted nematic liquid crystal displays (TN-LCDs). The birefringent phase retardation films include negative uniaxial, positive uniaxial and biaxial films of various orientations. The results are presented and discussed.     

New electrical test method for LCD cell‐manufacturing process

Abstract— A new electrical test method resulting in repeatable and unambiguous test results, which solves the drawback of the current lighting test used for the LCD cell‐manufacturing process, is proposed. This paper shows the basic scheme and the wide test coverage of this test method to detect defects in the cell process and gives an example of the actual measurement result.     

High efficient method for calculating S‐parameters of microwave filter from coupling matrix

In this article, a high‐efficient approach is presented for obtaining S‐parameters from coupling matrix of a microwave filter whether it is lossless or lossy (assuming all the resonators with the same unloaded Q). Computing time is usually large because inversion matrix needs to be carried out once at each frequency in traditional method. By making the application of matrix inversion Lemma and eigenvalue decomposition theory, the matrix inversion operation is replaced by one‐time matrix eigenvalue decomposition in the whole process, no matter how many frequency we need to concern. After reorganizing the equations of the S‐parameters, the time complexity is decreased from O( N ³ ) to O( N ). An example of 14th cavity cross‐coupled filter is reported for illustrating the capabilities of the new proposed approach. Compared with the general method, the time spending on computing was shortened by 70% with our new approach. Therefore, the proposed approach will be very popular and suitable in the industry.     

A robust observer‐based stabilization method for systems with uncertain parameters and Lipschitz nonlinearities

This paper deals with the robust observer‐based control design for a class of Lipschitz nonlinear discrete‐time systems with parameter uncertainties. Based on the use of a reformulated Lipschitz property combined with the slack variable techniques and some mathematical artifacts, it is shown that the solution of the discrete‐time output feedback stabilization problem is conditioned by a set of bilinear matrix inequalities, which become linear matrix inequalities by freezing some scalars. Furthermore, we show that some existing and elegant results reported in the literature can be regarded as particular cases of the stability conditions presented here. Numerical examples are provided to show the validity and superiority of the proposed method. Copyright © 2015 John Wiley & Sons, Ltd.     

A 15‐in. XGA thresholdless antiferroelectric LCD addressed by TFTs and using the quasi‐dc driving method

Abstract— A 15‐in. TFT‐LCD with XGA resolution using thresholdless antiferroelectric liquid crystal (TLAF) has been developed. TLAF materials show V‐shaped switching and enable display of analog gray scale, wide viewing angle, and fast response. However, in the case that high‐resolution TFT‐LCDs using materials with large spontaneous polarization such as TLAF were driven by the conventional method, alternating current (ac) driving, the obtained contrast ratio was limited because of a sharp decline of holding voltage due to the growth of a depolarization field. In order to enhance the contrast ratio, a novel driving method referred to as quasi‐dc driving was proposed. In the quasi‐dc driving, the polarity of the applied voltage to liquid crystals inverts at certain intervals of several seconds. Moreover, the applied voltage and the charging time at the time of polarity inversion are increased more than the intended signals. By this method, the 15‐in. TFT‐LCD using TLAF with high contrast ratio (more than 100:1) and wide viewing angle was realized.     

A study of electro‐optical characteristics depending on LC pre‐tilt angle and cell gap in a full‐HD LCOS panel

Abstract— The goal of this work is to achieve a better understanding of the electro‐optical characteristics of a VA‐mode full‐HD LCOS panel via simulations and experiments. The optical parameters, such as reflectance, fill factor, and contrast that vary due to the pre‐tilt angle and cell gap, were also studied. Based on the simulations, the optical fill factor was the highest at an angle of 81° and 2.1 μm under the given conditions. The contrast ratio was the highest at an angle of 89° and 2.4 μm. Five different LCOS panels were fabricated; three different angles (85°, 87°, and 89°) at a 2.1‐μm cell gap and two different cell gaps (1.8 and 2.1 μm) at an angle of 87°. The measured reflected light intensity was compared to the calculated reflectance. The simulated and measured contrasts were compared with each other. The simulation results well‐matched the experimental results and the differences were less than a few percentage points. Based on the comparative studies on reflectance and contrast, the test panel under the condition of an 87° angle and 2.1‐μm gap showed the best performance results.     

New pixel driving circuit using self‐discharging compensation method for high‐resolution OLED micro displays on a silicon backplane

A new 4T2C pixel circuit formed on a silicon substrate is proposed to realize a high‐resolution 7.8‐μm pixel pitch AMOLED microdisplay. In order to achieve high luminance uniformity, the pixel circuit compensates its Vth variation of the MOSFET for the driving transistor internally by using self‐discharging method. Also presented are 0.5‐in Quad‐VGA and 1.25‐in wide Quad‐XGA microdisplays with the proposed pixel circuit.     

Semi‐analytical calculation for sensitivities of the method of moments impedance and excitation matrices

A novel method is presented in this article for calculating the sensitivities of the impedance and excitation matrices of the method of moments. The proposed method evaluates the required derivatives with respect to a design variable semi‐analytically. It is demonstrated that one matrices' fill is enough to achieve the required sensitivities. Two such fills would be necessary to obtain similar results using the conventional finite‐difference approximation method. A microstrip patch antenna example is used to demonstrate the validity of the proposed method. By comparing its results with those obtained using finite‐difference numerical approximation, a high degree of agreement is observed. The accuracy of the numerical approximation is found to be sensitive to the selected value of perturbation. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Voltage‐programming method with transimpedance‐feedback technique for threshold voltage and mobility compensations in large‐area high‐resolution AMOLED displays

Abstract— A voltage‐programming method with transimpedance‐feedback control technique is proposed for compensating threshold voltage and mobility variations of driving thin‐film transistors (TFTs) in large‐area high‐resolution polycrystalline‐silicon (poly‐Si) active‐matrix organic light‐emitting‐diode (AMOLED) displays. Those electrical characteristic variations of TFTs throughout a large‐area high‐resolution panel result in picture‐quality non‐uniformity of AMOLED displays. The simulation and experimental results of the proposed method show that the maximum emission‐current error for 30‐in. full‐high‐definition television (HDTV) applications is less than 1.9% when the mobility variation and the threshold‐voltage variation are ±12.5% and ±0.3 V, respectively. The proposed method is the best programming method for large‐area high‐resolution AMOLEDs among the published methods.     

An optimal design method for minimization of common voltage distortion in large‐sized and high‐resolution liquid crystal displays

This paper proposes an optimal design method that minimizes the common voltage (V_COM) distortion for large‐sized and high‐resolution liquid crystal displays (LCDs). Three design methods are examined using different architectures of the panel and circuit to compensate for the V_COM distortion. The proposed design method adopts a panel architecture that compensates for the V_COM distortion simultaneously at the top and bottom of the panel using a dual compensation circuit. It is implemented using a 27‐in. quad high‐definition LCD, and its V_COM distortion is further minimized by optimizing the compensation ratio of the dual compensation circuit. In addition, the minimized V_COM distortion is evaluated by measuring the horizontal crosstalk of the implemented panel according to the decrease in the charging time of the subpixel. As the charging time decreases from 11.6 to 7.8 μs, the measured crosstalk level varies from 0.10% to 1.06%, respectively, meeting the goal of less than 2%. Therefore, the proposed design method is suitable for large‐sized and high‐resolution LCDs requiring low V_COM distortion.     

Prospects for the application of liquid‐crystal cells for the registration and visualization of mechanical oscillations in biomedical technologies

Abstract— The background involving the use of liquid‐crystal cells (LCC) in biomedical technologies will be discussed. The possible types of sensors of mechanical vibrations can be constructed on the basis of a highly sensitive liquid‐crystal cell with an initial homeotropic orientation. They are especially effective in the registration of low‐frequency processes such as human breathing. The possible methods of improving the technical characteristics of liquid‐crystal sensors due to the application of an electric field or by using specially designed LCCs will be discussed. Such cells can also be applied to the visualization of breathing.     

Space and time basis function design for the method of moments in time‐domain analysis of wire and planar structures

In this article, an algorithm able to deal at the same time with wire frame and surface patch models for the method of moments in time domain is presented. After a unified theory combining both models, attention is focused on stability dependence issues on the time basis function chosen and on other algorithm parameters. An accurate analysis of time interpolation functions and of their time filtering properties is provided. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Improvement strategies for the tools and techniques of quality improvement: Utilization of a performance evaluation matrix in the taiwanese high‐tech industry

This study integrates importance–performance analysis (IPA) and Slack's IPA matrix to provide a more comprehensive performance‐evaluation matrix for prioritizing improvement actions with regard to the tools and techniques of quality improvement. The study undertakes a review of the literature to identify the tools and techniques most widely used by high‐tech businesses in Taiwan. Following a survey of 394 managers and technicians, these tools and techniques are then placed on the integrated performance‐evaluation matrix to determine appropriate priorities for improvement actions. The study finds that “new seven” total quality management tools are used less often than “old seven” total quality management tools, and that education, training, and the efficient use of corporate resources are required to improve the frequency of utilization and the performance of the tools and techniques of quality improvement. © 2011Wiley Periodicals, Inc.