Liquid Crystal Display System Research Articles

Fabrication of Complementary Electrochromic Device Based on Ag Deposition / Prussian Blue: Its Optical Modulating Properties and Memory Functions

Electrochromism is a phenomenon of reversible color change induced by electrochemical redox reactions of functional materials. Simple structure, large viewing angle, and low power consumption are some of the advantages of electrochromic (EC) devices for optical modulation systems in comparison with the conventional systems such as liquid-crystal display systems with backlight or organic light-emitting diodes. Electronic papers, digital signages, and smart windows are examples of potential applications of the EC system. Recently, we have reported Ag deposition-based EC device based on reversible electrodeposition of Ag nanoparticles. The EC devices basically composed of a pair of transparent electrodes with a gel electrolyte containing Ag+ between them.1-3 The application of a negative voltage causes the Ag metal deposition on the electrode substrate to construct metal nanoparticles or thin film that alters the optical properties of the surface.However, the Ag deposition-based EC device did not have enough color retention property. This is due to the oxidative dissolution of Ag deposits by Cu2+, mainly functioning as counter reaction material, contained in the electrolyte. To achieve color retention properties, we utilized Prussian blue (PB) instead of copper ions. The PB film was fabricated on the counter electrode as a counter reaction material to compensate for the reaction charge on the working electrode. We investigated fabrication condition of PB-modified electrode and EC properties of Ag deposition-based EC device incorporating the PB electrode.PB-modified electrode was prepared by electrolytic deposition on the ITO electrode. The EC device was fabricated by sandwiching DMSO based gel electrolyte solution, containing AgNO3 as EC material and LiCl as supporting electrolyte, between ITO electrode and PB-modified electrode. EC properties of the device were investigated by applying constant voltages. Transmission spectra at both optical states by applying voltage of −1.0 V (colored state, black line) and +1.0 V (bleached state, dashed black line) are shown in Figure. The transmission spectrum of the as-prepared device before applying voltages is also shown in the Figure (dashed blue line). When we applied −1.0 V, the transmittance decreased according to electrochemical deposition of Ag metal, and the device tuned to mirror state (inset photo in the figure). On the other hand, by applying +1.0 V, the transmittance increased, and the device returned to a transparent state as the result of dissolution of Ag metal (inset). In this way, the device demonstrated distinct color changing between transparent and mirror state by applying constant voltage of ±1.0 V.Then the color retention property at the mirror state of this device was evaluated. After applying the coloring voltage of -1.0 V, the change in transmittance at 600 nm was recorded. As a result, the device kept its colored state (transmittance below 20 ％) under the open-circuit condition for 5 h. As for the conventional device, the colored state of the device was completely returned to the initial transparent state in a few minutes due to the dissolution of Ag deposit by Cu2+. The replacement of counter reaction materials from copper ions dissolved in the electrolyte to PB layer fixed on the counter electrode successfully achieved this great improvement of color retention properties. This novel structure of Ag deposition-based EC device is expected to contribute to effective power savings of EC devices such as smart windows, digital signages, information displays, and e-papers. References Araki, K. Nakamura, N. Kobayashi, Adv. Mater., 14, 122 (2012).Tsuboi, K. Nakamura, N. Kobayashi, Adv. Mater., 25, 3197 (2013).Tsuboi, K. Nakamura, N. Kobayashi, Chem. Mater., 26, 6477 (2014). Figure 1

Halo effect in high-dynamic-range mini-LED backlit LCDs.

We develop an optical model including the glare effect in the human vision system to analyze the halo effect of high-dynamic-range (HDR) mini-LED backlit liquid crystal displays (LCDs). In our model, an objective function is first introduced to evaluate the severity of the halo effect with different image contents. This function is further combined with PSNR to establish a new evaluation metric to analyze the image quality affected by the halo effect. A subjective visual experiment is also conducted to verify the above-mentioned evaluation metrics. In addition, we analyze the influence of ambient environment (viewing angle and ambient light illuminance) on the halo effect. After considering the requirements on local dimming zones, dynamic contrast ratio, gamma shift, and color shift for practical applications, we find that fringe-field-switching mode is a strong contender for the mini-LED backlit LCD system.

Nano P(VDF-TrFE) doped polyimide alignment layers for twisted nematic liquid crystal devices

ABSTRACTThe rapid development of consumer electronics and portable devices imposes a great demand for energy efficient information display systems. Among the information display devices, liquid crystal display (LCD) devices stands in the front. The fabrication of energy-efficient LCD systems demands new material and techniques. In this work, the conventional polyimide alignment layer of twisted nematic liquid crystal device (TNLCD) was replaced with ferroelectric polymer nanoparticle doped alignment layer. Morphology of the alignment layer was analysed using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The ferroelectric nature of the polymer alignment layer was studied using dynamic contact electrostatic force microscopy (DC-EFM). TNLCD cells are fabricated with this modified alignment layer and the switching characteristics are compared with the conventional TNLCD devices. The TNLCD with modified alignment layer has shown a reduction of 50% in threshold (Vthr) and 47% reduction in saturation voltage (Vsat).

Algorithm and Architecture Design of Multirate Frame Rate Up-conversion for Ultra-HD LCD Systems

In current liquid crystal display (LCD) systems, the frame size becomes larger than the ultra-HD ( $3840\times 2160$ ) resolution, and the refresh rate becomes higher than 120 Hz or more. However, the available video frame rates are usually at 24, 30, or 60 frames/s only, which are lower than the refresh rate of LCDs. To fill the gap between the video and LCD systems, frame interpolation techniques are usually adopted. Although frame rate up-conversion (FRUC) is regarded as the most efficient method, many design challenges are encountered in the current high-resolution and high-frame-rate LCD systems. In this paper, we developed a hardware-efficient multirate FRUC, which is capable of increasing the video frame rate from 24 or 60 to 120 frames/s. We improved the accuracy of motion vectors (MVs) between the video frames using predictive square search motion estimation (ME), followed by Markov random field (MRF) correction. Subsequently, we applied the block-based forward motion compensation (MC) to interpolate the intermediate frames. Thereafter, we performed subblock refinement to enhance the visual quality. The experiments show that the proposed algorithm performed well in both subjective and objective evaluations. We also designed hardware architecture for our multirate FRUC to support the current ultra-HD LCD systems. We proposed ping-pong two-way scheduling to eliminate the dependence among blocks. We realized 54%, 70%, and 35% cycle reduction and 62%, 82%, and 35% bandwidth reduction in the ME, MRF MV correction, and MC, respectively. The SRAM was shared by all modules, and its total size was reduced by 88%. We also implemented our design to a chip using the TSMC 90-nm cell library.

Recent Advances on Quantum-Dot-Enhanced Liquid-Crystal Displays

We review recent advances in quantum dot (QD)- enhanced liquid crystal displays (LCDs), including material formulation, device configuration, and system integration. For the LCD system, we first compare the color gamut difference between the commonly used Gaussian fitting method and that using real emission spectra. Next, we investigate the Helmholtz-Kohlrausch effect. Our simulation results indicate that QD-enhanced LCD appears 1.26X more efficient than organic light-emitting diode (OLED) display due to its wider color gamut. Finally, two new trends for QD-LCDs are discussed: 1) replacing conventional color filters with a QD array, and 2) emerging quantum rod (QR)-enhanced backlight. Their inherent advantages, technical challenges, and potential solutions are presented. We believe the prime time for QD-enhanced LCDs is around the corner.

How accurate is an LCD screen version of the Pelli-Robson test?

To evaluate the accuracy and repeatability of a computer-generated Pelli-Robson test displayed on liquid crystal display (LCD) systems compared to a standard Pelli-Robson chart. Two different randomized crossover experiments were carried out for two different LCD systems for 32 subjects: 6 females and 10 males (40.5±13.0years) and 9 females and 7 males (27.8±12.2years), respectively, in the first and second experiment. Two repeated measurements were taken with the printed Pelli-Robson test and with the LCDs at 1 and 3m. To test LCD reliability, measurements were repeated after 1week. In Experiment 1, contrast sensitivity (CS) measured with LCD1 resulted significantly higher than Pelli-Robson both at 1 and at 3m of about 0.20 log 1/C in both eyes (p<0.01). Bland-Altman plots showed a proportional bias for LCD1 measures. LCD1 measurements showed reasonable repeatability: ICC was 0.83 and 0.65 at 1 and 3m, respectively. In Experiment 2, CS measured with LCD2 resulted significantly lower than Pelli-Robson both at 1 and at 3m of about 0.10 log 1/C in both eyes (p<0.01). Bland-Altman plots did not show any proportional bias for LCD2 measures. LCD2 measurements showed sufficient repeatability: ICC resulted 0.51 and 0.65 at 1 and 3m, respectively. Computer-generated versions of Pelli-Robson test, displayed on LCD systems, do not provide accurate results compared to classic Pelli-Robson printed version. Clinicians should consider that Pelli-Robson computer-generated versions could be non-interchangeable to the printed version.

Efficacy of global dimming backlight and high‐contrast liquid crystal panel for high‐dynamic‐range displays

AbstractUsing an RGB organic light‐emitting diode display to emulate liquid crystal display systems, we examined the efficacy of different global dimming strategies for cinematic content. A global dimming solution with smoothed transitions was preferred over solutions using a static backlight level or the highly aggressive frame‐by‐frame backlight adjustment scheme. We compared two such smoothing approaches, one making use of causal data, and another using future information (which could be available via latency or dynamic metadata) and did observe some opportunities for an improved experience, but found the causal data to be a competitive approach. We also evaluated the importance of native panel contrast and how global dimming compares to local dimming approaches. For most content tested, a global dimming display with a high‐contrast liquid crystal panel was judged as being equivalent or more preferred to a full‐array local dimming display with a low‐contrast panel. These results build on the existing evidence that native panel contrast remains one of the strongest predictors of high‐dynamic‐range image quality even as backlight technologies continue to improve.

Polarizing grating color filters with large acceptance angle and high transmittance.

We design and simulate a polarizing color filter with a sub-wavelength metal-dielectric grating. It manifests several advantages: a large acceptance angle (up to ±50°), high transmittance (74.3%-92.7%), low absorption loss (∼3.3%), and a high extinction ratio. This polarizing color filter can be integrated into a liquid-crystal display (LCD) backlight system to simultaneously recycle the light according to its color and polarization. In combination with a specially designed directional backlight, this newly proposed LCD system can theoretically improve optical efficiency up to ∼2.5×, and also provides a large ambient contrast ratio and a wide view. Our approach enables an ultra-low-power LCD without using the complicated field-sequential-color technique.

Behavioral Circuit Models of Stereoscopic 3-D Liquid Crystal Displays and Shutter Glasses

In this paper, behavioral circuit models of a stereoscopic 3-D liquid crystal display (LCD) and shutter glasses (SGs) are proposed. Until now, no study has been conducted on a model that can demonstrate the optical behavior of a 3-D LCD panel, because it includes black frame insertion. In addition, a circuit model of SGs should be established to completely illustrate the behavior of a stereoscopic 3-D LCD system. These circuit models can accurately predict the optical responses of dynamic transitions in 3-D LCD systems and those of SGs. We can then develop a complete behavioral model of the stereoscopic 3-D LCD system by combining the behavioral models of both the 3-D LCD panel and SGs. SmartSPICE simulations are performed to verify our model, which is implemented by an analog hardware description language, Verilog-A. On the basis of these simulation and measurement results, we can conclude that the proposed behavioral circuit models can accurately describe the optical responses of combined displays such as stereoscopic 3-D LCDs.

Simplex based method for compensation films optimization in TN-LCD

The narrow viewing angle (VA) and low contrast ratio (CR) are two of the problems associated with liquid crystal display (LCD). A novel optimization method for the LCD system based on simplex algorithm is demonstrated. A LCD model is constructed using two negative O-plate films, LC cell and one negative C-plate film. The compensator thickness and tilt angel can be successfully used as optimization variables to compensate for narrow VA and low CR. Results show that this approach is faster and more accurate than other approaches. In addition, we show that the oblique leakage light of the dark state is reduced and that high CR, wide VA are obtained.

Tailoring the light distribution of liquid crystal display with freeform engineered diffuser.

We propose a versatile design approach of engineered diffuser based on freeform optics that can tailor the light distribution of a liquid crystal display (LCD) to meet different applications. The proposed LCD system consists of a quasi-directional backlight, liquid crystal panel, and an engineered diffuser. It offers high efficiency, wide view, high contrast, as well as low ambient light reflection. For large size LCDs, we design a wide view diffuser to match the light distribution with state-of-the-art organic light emitting diode (OLED) TV. For mobile displays, we design a diffuser to replicate current LCD performance. Our design can also provide flattop light intensity distribution for privacy protection. These exemplary designs prove that our engineered diffuser is versatile for different applications.

Planar apparatus for uniformly emitting light with angular color-separation.

This study proposes a slim planar apparatus that can function as a color-separation backlight for the color-filter-free liquid-crystal display (LCD) system. It has a two-level folded configuration comprising a composite light-guide plate (LGP) and light-emitting diode (LED) couplers. The LED couplers generate the highly collimated beams of the three primaries (R, G, and B) that enter the composite LGP at their separate angles; then the three primaries were uniformly extracted out of the top surface of the LGP at their respective angles differing in the longitudinal direction. In the simulation, a lenticular lens array was used to focus the three primaries onto their respective subpixels; each pixel of the LC panel comprised three subpixels, identical to the traditional layout. The proposed apparatus can be applied in backlight modules with a maximal diagonal dimension of 39 inches and a thickness of 15.5 mm. The simulation results indicated that the spatial uniformities of the three primaries ranged between 84% and 87%, the area of the color gamut of the LCD system was 99.5% of that defined by the National Television System Committee, and the total optical efficiency was 41%, as the double of a traditional LCD system. Thus, the proposed apparatus improved the total optical efficiency markedly and provided the LCD system with a wide color gamut.

An Iterative Fourier Transform Algorithm for digital hologram generation using phase-only information and its implementation in a fixed-point digital signal processor

An Iterative Fourier Transform Algorithm (IFTA) for digital hologram generation from a digital image using phase-only information is described in this paper. The algorithm is implemented in a Texas Instruments TMS320C64x fixed point digital signal processor (DSP). The holograms are reconstructed in real time using a liquid crystal display system and a He–Ne laser. The ideas described in this paper can be extended to digital hologram generation of three-dimensional objects and their reconstruction in real time using liquid crystal spatial light modulators, which could be a way for 3D-display systems.

Design of Digital Advertising Screen Display

Design of LCD(liquid crystal display) screen system based on DSP has been put forward. There are two parts of the hardware interface circuit and the software design about whole system. Chinese characters, characters and graphics can be displayed in the LCD system. The result of simulation shows that the system can effectively solve the drive and display of LCD based on DSP and can save resources for I /O port. This design will offers a certain reference value for a variety of display terminal design of the portable system. The simulation shows that the system can realize the basic expected goal.

A 1.4‐Gbps intra‐panel interface with low‐power and low‐EMI schemes for Tablet PC applications

AbstractAn intra‐panel interface addressing all of the high‐speed, low‐power, and low‐electromagnetic interference (EMI) requirements for tablet personal computer applications is presented. This work proposes an adaptive clock window scheme to achieve 1.4‐Gbps data‐rate. For EMI suppression, data scrambling, horizontal blank period pattern scrambling, and novel clock and data recovery circuit are introduced. Lastly, for power‐saving, the proposed interface dynamically biases source driver's output buffers and employs early charge sharing by controlling the configuration data. For verification, a WQXGA thin‐film transistor liquid crystal display system is implemented with the timing controller and source driver ICs that are fabricated using 65‐nm and 180‐nm complementary metal‐oxide semiconductor (CMOS) processes, respectively. The liquid crystal display system demonstrates maximum operation speed of 1.4 Gbps and suppression of EMI noise in LTE Band‐20 and GSM 850 bands. The proposed power‐saving schemes achieve 4.3% reduction in total power consumption by source driver IC, which reaches about 85% of power consumption by enhanced reduced‐voltage differential signaling interface circuit.

A Survey of Low-power Techniques for Liquid Crystal Display Systems with Light Emitting Diode Backlight Units

As the technology evolves, end-users are stuffed with many kinds of handheld devices along with an enor-mous number of interactive multimedia applications and communication functionalities. These devices con-sume much power, especially for displaying their services or functions. In contrast, the battery, which is the main power supplier for such devices, has a much lower capacity growth compared to the power demands. This gap has inspired many researchers to study low-power display techniques. In the mean time, there came the invention of a light emitting diode (LED) as a new backlight source for a display panel. LEDs have been adopted in the most widely used Liquid Crystal Display (LCD) system. This paper focuses on recent noticeable low-power display techniques based on LCD systems, especially associated with an LED back-light unit as its light source. We categorize these techniques into four groups: 1) low-power techniques with backlight dimming, 2) low-power techniques with dynamic voltage scaling, 3) software-based low-power techniques, and 4) hardware-based low-power techniques, and review the core of each technique briefly. Among many techniques, concurrent brightness and contrast scaling technique in a color sequential LED-backlit display system achieved the largest power saving ratio by up to 90% of the total system power with a small distortion level. As future research, it is one of important methods to combine the pros from each beneficial technique into one synergistically in the aspect of the whole system power.

Transflective digital holographic microscopy and its use for probing plasmonic light beaming

We present a novel digital holographic microscopy technique termed transflective digital holographic microscopy in order to probe plasmonic beaming fields and to view their platform structures. Here, we borrow the term, 'transflective', a portmanteau meaning a blend of transmission and reflection according to the light-collecting condition, which is conventionally used in liquid crystal display systems. Incorporating the transmission type holographic microscopy with the reflection type, achieved by the utilization of polarization property of coherent light waves, we propose an application of the system to probing the beam path and its corresponding structure in plasmonic beaming phenomena.

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.

Pseudo Zero-Dimension Dimming for Power Reduction in Field Sequential Color Liquid Crystal Display Systems

Expensive hardware is required by the conventional two-dimensional (2-D) light-emitting diode (LED) dimming technique to obtain high-contrast and low-power in the field sequential color (FSC) technique. Thus, based on real-time image data, the pseudo zero-dimension (0-D) LED dimming technique is proposed to further reduce power dissipation in the D-FSC technique, which allows the intelligent selection of an adequate color sequence. The multi-liquid crystal and backlight (LC/BL) algorithm utilizes the D-FSC technique in temporal and spatial domains. It not only utilizes the pseudo 0-D technique to effectively reduce the color breakup (CBU) effect without greatly increasing frame rate, but also to reduce power consumption. On the backlight module, CBU suppression can be substantially improved and power dissipation can be reduced by at least 12.5%. Power consumption can also be further reduced through the re-dimming improvement in the proposed pseudo 0-D dimming technique.

29.4: A RGB‐LEDs Backlight Driver with Field Color Sequential (FCS) and Energy‐Recycling (ER) Techniques for Minimum Power Loss on LCD System

AbstractA field‐color‐sequential (FCS) LCD technique with a direct‐lit red, green, and blue (RGB) light‐emitting diode (LED) backlight driver is proposed to achieve the demands of weightless, thickness, perfect image‐quality, and low power‐consumption of liquid crystal display (LCD) television (TV). In this paper, the proposed FCS‐LCD controller uses only one single LED driver to alternatively switch driving voltage between 40V for driving 12‐serie G‐ or B‐LEDs and 26V for 12‐serie R‐LEDs. In addition, In order to, the proposed energy‐recycling (ER) technique can harvest the extra energy when the driving voltage switches from 40V to 26V. Experimental result shows the energy‐saving be higher than 17% of the conventional driving method.