Driving passive‐matrix LCDs with low hardware complexity and reduced supply voltage

In passive‐matrix liquid‐crystal displays (LCDs), multiplexing is achieved by using the intrinsic non‐linear characteristics of the liquid‐crystal material. If the electro‐optic characteristic is steeper than necessary for the matrix display, the selection ratio need not be maximized. Instead, the selection ratio can be reduced to match the electro‐optic characteristics of the display. This leads to a reduction in the supply voltage of the drive electronics. We have considered the possibility of using addressing techniques with low hardware complexity along with displays having steep electro‐optic characteristics. Supply voltages for these techniques are compared with that of multi‐line addressing (MLA). The supply voltages of the Hybrid Addressing Technique (HAT), Improved Hybrid Addressing Technique‐S3 (IHAT‐S3), and Improved Hybrid Addressing Technique‐S4 (IHAT‐S4) are lower than that of MLA for the lower range of N. These hybrid addressing techniques with lower hardware complexity are a better choice for driving passive‐matrix LCDs, especially in portable equipment.     

Minimum‐voltage driving of small STN‐LCDs by optimized multiple‐row addressing

Abstract— In small STN‐LCDs for portable applications, rows and columns are driven by one IC. The LC supply voltages are generated on‐chip from the battery voltage by voltage multiplying. The total LC supply voltage should be as low as possible to minimize the accompanied power losses. By using multiple‐row addressing, the row and maximum column voltages can be made equal, leading to a minimum LC supply voltage. This occurs when the number of simultaneously addressed rows is equal to the square root of the number of rows in the panel. The LC supply voltage may be minimized further by using a liquid crystal which allows multiplexing of more rows than are actually present in the display panel, while at the same time fewer simultaneously addressed rows are required.     

Floating drive schemes for dual-frequency addressing of complex liquid crystal displays

A circuit configuration for the dual-frequency addressing of complex liquid crystal matrix displays is described. After division of the high and multilevel drive voltages into several digital signal components, they are superposed in digital 15 V CMOS ICs. The signals so produced have an amplitude which exceeds the value of the supply voltage and which involves three or four levels. The technique is suitable for modification of existing display drive systems to reach a higher number of multiplexed lines or to allow better selection.     

Microcup® displays: Electronic paper by roll‐to‐roll manufacturing processes

Abstract— Rolls of flexible displays or electronic paper have recently been prepared by a high‐speed roll‐to‐roll manufacturing process based on SiPix's novel Microcup® and top‐sealing technologies. Both Microcup® electrophoretic displays (EPDs) and LCDs have been demonstrated. The display rolls are format flexible and may be cut into desirable size and shape for a variety of applications. High‐performance flexible passive‐matrix Microcup® EPDs having a wide range of threshold voltages have also been demonstrated.     

Novel concept for full‐color electronic paper

Abstract— Despite a steep increase in commercial devices comprising paper‐like displays, a much desired feature is still missing: bright full‐color electronic paper. A new reflective‐display technology has been developed to solve this issue. For the first time, the principles behind this in‐plane electrophoretic technology will be presented, which enables the realization of full‐color reflective displays with a higher brightness than presently available e‐paper technologies, without compromising paper‐like properties such as viewing angle and ultra‐low power consumption. An additional major advantage (e.g., for future low‐cost manufacturing) is that, besides direct‐drive and active‐matrix configurations, a passive‐matrix option with analog gray levels has been successfully developed.     

2‐D/3‐D displays based on switchable lenticulars

Abstract— An attractive concept for 3‐D displays is the one based on LCDs equipped with lenticular lenses. This enables autostereoscopic multiview 3‐D displays without a loss in brightness. A general issue in multiview 3‐D displays is their relatively low spatial resolution because the pixels are divided among the different views. To overcome this problem, we have developed switchable displays, using liquid‐crystal (LC) filled switchable lenticulars. In this way, it is possible to have a high‐brightness 3‐D display capable of fully exploiting the native 2‐D resolution of the underlying LCD. The feasibility of LC‐filled switchable lenticulars was shown in several applications. For applications in which it is advantageous to be able to display 3‐D and 2‐D content simultaneously, a 42‐in. locally switchable prototype having a matrix electrode structure was developed. These displays were realized using cylindrically shaped lenticular lenses in contact with LC. An alternative for these are lenticulars based on gradient‐index (GRIN) LC lenses. Preliminary results for such switchable GRIN lenses are presented as well.     

In‐band scalable video coding with integrated wavelet‐based display driving

Abstract— The increasing demand for multimedia over networks and the heterogeneous nature of today's networks and playback devices impose the stringent need for scalable video coding. In this context, in‐band wavelet‐based video‐coding architectures offer full scalability in terms of quality, resolution, and frame‐rate and provide compression performance competitive with that of state‐of‐the‐art non‐scalable technology. Despite these advances, video streaming over wireless networks to handheld terminals is lagging in popularity due to the high power consumption of the existing portable devices. As a possible approach to alleviate this problem, the integration of wavelet‐based passive‐matrix‐display driving into the inverse discrete wavelet transform (IDWT) block of the in‐band video decoding architecture was investigated. In a nutshell, the IDWT no longer needs to be performed by the decoder, being synthesized instead by the display itself. This integration reduces the number of calculations required to generate the driving waveforms for passive‐matrix displays and inherently leads to reduced power consumption on portable terminals. Moreover, the wavelet transform and the considered video‐codec architecture are both resolution‐scalable. Hence, the resolution‐scalability feature of the video codec, enabling resolution‐scalable display driving, is another means to control the power consumption of the portable device.     

Vt Compensated voltage‐data a‐Si TFT AMOLED pixel circuits

Abstract— Active‐matrix organic light‐emitting‐diode (AMOLED) displays are now entering the marketplace. The use of a thin‐film‐transistor (TFT) active matrix allows OLED displays to be larger in size, higher in resolutions and lower in power dissipation than is possible using a conventional passive matrix. A number of TFT active‐matrix pixel circuits have been developed for luminance control, while correcting for initial and electrically stressed TFT parameter variations. Previous circuits and driving methods are reviewed. A new driving method is presented in which the threshold‐voltage (V_t) compensation performance, along with various circuit improvements for amorphous‐silicon (a‐Si) TFT pixel circuits using voltage data, are discussed. This new driving method along with various circuit improvements is demonstrated in a state‐of‐the‐art 20‐in. a‐Si TFT AMOLED HDTV.     

Passive‐matrix displays based on light‐emitting polymers

Abstract— The design architecture, product specification, and reliability of the first high‐resolution commercially available passive‐matrix displays based on light‐emitting polymers will be presented. Also, the applications and benefits of this new low‐cost display technology will be discussed.     

Latest developments for “system‐on‐glass” displays using low‐temperature poly‐Si TFTs

Abstract— A 2.3‐in.‐diagonal QVGA‐formatted “System‐On‐Glass” display has been developed by using low‐temperature poly‐Si TFT‐LCD technology. This display fully integrates 6‐bit RGB digital interface drivers as well as all the power supply circuitry to drive the LCD, which requires neither external driver ICs nor power‐supply ICs. This paper discusses the newly developed TFT circuit technologies used in this LCD. The development trend of the “System‐On‐Glass” display is also reviewed.     

A novel TFT‐OLED integration for OLED‐independent pixel programming in amorphous‐Si AMOLED pixels

Abstract— The direct voltage programming of active‐matrix organic light‐emitting‐diode (AMOLED) pixels with n‐channel amorphous‐Si (a‐Si) TFTs requires a contact between the driving TFT and the OLED cathode. Current processing constraints only permit connecting the driving TFT to the OLED anode. Here, a new “inverted” integration technique which makes the direct programming possible by connecting the driver n‐channel a‐Si TFT to the OLED cathode is demonstrated. As a result, the pixel drive current increases by an order of magnitude for the same data voltages and the pixel data voltage for turn‐on drops by several volts. In addition, the pixel drive current becomes independent of the OLED characteristics so that OLED aging does not affect the pixel current. Furthermore, the new integration technique is modified to allow substrate rotation during OLED evaporation to improve the pixel yield and uniformity. The new integration technique is important for realizing active‐matrix OLED displays with a‐Si technology and conventional bottom‐anode OLEDs.     

Driving large‐sized OLED TVs with an amorphous‐silicon backplane

Abstract— A 20‐in. OLED display driven by an amorphous‐silicon backplane has been demonstrated. It has been widely believed that the characteristics of amorphous‐silicon TFTs are not sufficient to drive OLED display. This paper challenges this hypothesis and proves that amorphous silicon can be applied to large active‐matrix‐driven displays and discusses many possible approaches that lead to good front‐of‐screen quality. Superior‐video‐image‐quality amorphous‐silicon‐driven OLEDs opens a bright future for a new generation of wall‐hanging televisions.     

The Zenithal Bistable Display: From concept to consumer

Abstract— The first commercial use of the Zenithal Bistable Display (ZBD?) is for electronic point‐of‐purchase (epop?) signage in the retail sector. As a reflective bistable display, this novel LCD technology only consumes power if new information is required and the image is updated. This allows complex images to be shown constantly for several years from the energy of a single low‐cost battery, when the display is updated up to ten times each day — ideal for signage applications. Excellent performance characteristics are achieved in a TN‐like STN‐LCD in which one of the alignment surfaces is a relief grating. Correct design of the grating shape and surface properties not only imparts the bistability, but allows control of the optical performance, the latching voltages, and the temperature range. Being addressed using a simple passive‐matrix approach, without the need for a thin‐film‐transistor backplane, large amounts of information may be displayed by STN drivers. Alow‐cost fabrication method has been devised that is compatible with conventional TN and STN manufacture, and with negligible equipment outlay. The device operating principles, manufacturing method, and performance of ZBDs are reviewed.     

Optical rewritable liquid‐crystal‐alignment technology

Abstract— A new optical rewritable (ORW) liquid‐crystal‐alignment technology has been developed to create a display and to demonstrate its maturity and potential. ORW displays have no electrodes and use polarizers as substrates. The display requires no photolithography on plastic. Its simple construction secures durability and low cost for mass production. The on‐screen information is optically changed in a writing unit that consists of an LCD mask and an exposure source that is based on LEDs, low power, and low cost in comparison with Hg lamps or lasers. A high contrast image can be easily written, viewed, and rewritten through a polarizer, while the multi‐stable gray‐level image requires zero power to maintain the image. Reconfigurable LC alignment using ORW technology best suits plastic‐card displays as well as for LC photonics and various one‐mask processes of patterned LC‐alignment applications.     

Auto‐calibration of drive condition for cholesteric liquid crystal displays

Dynamic drive scheme (DDS) is known widely as passive matrix addressing that obtains both high‐speed re‐writing and a high contrast ratio in the field of cholesteric liquid crystal displays (LCDs). However, DDS has a serious problem in that the proper drive condition is very narrow and it is largely influenced by individual differences in LCDs that arise during their production. We have developed a new auto‐calibration system that adjusts both the contrast ratio and color balance automatically using capacitances of effective pixels and temperature compensation models that utilize the physical properties of cholesteric LCDs. We have managed to optimize the driving conditions between 5 and 35 °C with this method, and obtained both stable and high‐quality color images where the reflectance is 36%, contrast ratio is 8, and NTSC ratio is 20%. This auto‐calibration system has been able to greatly improve the production yield of cholesteric LCDs and made it possible to make practical use of cholesteric LCDs.     

Flexible OLED display development: Strategy and status

Abstract— In this paper, the current status of flexible OLED (FOLED®) display development will be reviewed, including previous results for passive‐matrix displays on plastic and current progress on active‐matrix displays on steel foil. The displays incorporate high‐efficiency small‐molecule phosphorescence OLED (PHOLE?) technology. The ultimate goal is to develop high‐information‐content high‐performance long‐lived, and large‐area FOLED displays that can be pulled or rolled out from a smaller pen‐like housing. The strategy for achieving this goal will be presented.     

Review Paper: Multi‐primary‐color displays: The latest technologies and their benefits

Abstract— Multi‐primary‐color (MPC) display technology is one of the fastest emerging research areas in recent years. Wide‐color‐gamut display devices have been required for visually sufficient and/or accurate color reproduction. It is well known that MPC displays can reproduce accurate colors with high efficiency. In addition, not only the image‐quality improvement but some other performance of display devices is also required for display devices. This paper reviews achievements in MPC display technologies and focuses on the benefits of MPC displays: power‐savings and high resolution.     

Fabrication and performance characteristics of black‐dielectric electroluminescent 160 × 80‐pixel displays

Abstract— We report on recent technological progress in black‐dielectric electroluminescent (BDEL) displays. Fabrication of the first monochrome BDEL 160 × 80‐pixel 4‐in. displays driven with commercial low‐power (<5 W) drive circuitry is presented. Preliminary results on blue‐dielectric EL full‐color displays are also reported. Improvements in both BDEL display performance and display manufacturability underscore the recent development path.     

Total matrix addressing

Abstract— A new passive‐matrix OLED drive technology, Total matrix addressing (TMA?), has been developed, which substantially extends the application space for passive panels beyond the limited panel size and resolution of existing passive‐matrix drive schemes. A number of demonstration systems have been constructed to test the viability and performance of this drive scheme. The development of both the TMA drive methodology and image factorization algorithm will be described, and preliminary performance figures from the demonstration systems presented.     

Passive‐matrix polymer light‐emitting displays

Abstract— Organic light‐emitting device research focuses on the use of small‐molecule and polymer materials to make organic electroluminescent displays, with both passive‐ and active‐matrix technologies. This paper will focus on the characteristics of red, green, and blue electroluminescent polymers suitable for fabricating monochrome and full‐color passive‐matrix displays. The stability of polymer OLEDs, and the use of ink‐jet printing for direct high‐resolution patterning of the light‐emitting polymers will also be discussed. It will be shown that the performance of light‐emitting polymers is at the brink of being acceptable for practical applications.