Thursday 29 November 2012

IPS (In-Plane Switching technology)

IPS (In-Plane Switching technology) panel is a technology used for liquid crystal displays (LCDs). It was invented to solve the main limitations of TN-matrices at the time: relatively slow response times, small viewing angles and low-quality color reproduction. In-Plane Switching involves arranging and switching the molecules of the liquid crystal (LC) layer between the glass substrates essentially in a plane parallel to these glass plates.

History

The first twisted nematic (TN) LCD was invented in Switzerland in 1970 and became the basis for LCD monitors. The TN method was applied in active matrix TFT LCDs in the late 1980s and early 1990s. The early panels showed gray inversion from up and down, and had slow response speed. In the mid 1990s, some technologies—typically IPS and VA (Vertical Alignment)—that could resolve these weaknesses were applied to large monitor panels.

One approach was to use interdigital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates (Abstract). To take full advantage of the properties of this In Plane Switching (IPS) technology further work was needed. After thorough analysis, details of advantageous embodiments were filed in Germany by Guenter Baur et al. and patented in various countries (Abstract). The Fraunhofer Society in Freiburg, where the inventors worked, assigned these patents to Merck KGaA, Darmstadt, Germany.

Shortly thereafter, Hitachi of Japan filed patents to further improve this IPS technology.

Technology

The diagram shows a simplified model of a particular implementation of the IPS technology. In this case, both linear polarizing filters P and A have the same orientation of their axes of transmission. To obtain the 90-degrees twisted nematic structure of the LC layer between the two glass plates shown on the left without an applied electric field, the inner surfaces of the glass plates are treated to align the bordering LC molecules at an angle of approx. 90 degrees. This molecular structure is practically the same as in TN LCDs. However, the arrangement of the electrodes e1 and e2 is different, as they are in the same plane on one glass plate only to generate an electric field essentially parallel to the glass plate. The LC molecules have a positive dielectric anisotropy, i.e. they align themselves with their long axis parallel to an applied electric field. In the OFF state on the left of the diagram entering light L1 becomes linearly polarized by polarizer P. The twisted nematic LC layer rotates the polarization axis of the passing light by 90 degrees, so that ideally no light passes through the analyzer A. When a sufficient voltage is applied between electrodes e1 and e2, the corresponding electric field E will realign the LC molecules as shown on the right of the diagram so that light L2 can pass the display device in the ON state.

The diagram can be misleading as the dimensions are not realistic: the LC layer is only a few micrometers thick and small compared with the distance between the electrodes e1 and e2. In practice, other schemes of implementation exist which have a different structure of the LC molecules, for example without twist in the OFF state.

To achieve a wider viewing angle and faster response speed required using a compensatory film and complicated multi-domain technology to divide pixels into parts. As both electrodes are on the same substrate, they take more space than electrodes of TN matrices. This reduces contrast and brightness.
Super-IPS was later introduced with even better response times and color reproduction.

Super PLS

 Samsung Electronics introduced technology named Super PLS (Plane-to-Line Switching) with the intent of superseding conventional IPS. It seems that Samsung adopted PLS panels instead of AMOLED panels because AMOLED panels still have difficulties in realizing full HD resolution on mobile devices. PLS technology is Samsung’s new wide-viewing angle LCD technology, and it is known as a similar technology to LG’s IPS technology.

Samsung claims the following benefits of Super PLS (commonly referred to as just "PLS") over IPS:

    Further improvement in viewing angle
    10 percent increase in brightness
    Up to 15 percent decrease in production costs
    Increased image quality

Penampil kristal cair (LCD)

Penampil kristal cair (Inggris: liquid crystal display; LCD) adalah suatu jenis media tampilan yang menggunakan kristal cair sebagai penampil utama. LCD sudah digunakan di berbagai bidang misalnya dalam alat-alat elektronik seperti televisi, kalkulator ataupun layar komputer. Kini LCD mendominasi jenis tampilan untuk komputer meja maupun notebook karena membutuhkan daya listrik yang rendah, bentuknya tipis, mengeluarkan sedikit panas, dan memiliki resolusi tinggi.

Pada LCD berwarna semacam monitor, terdapat banyak sekali titik cahaya (piksel) yang terdiri dari satu buah kristal cair sebagai sebuah titik cahaya. Walau disebut sebagai titik cahaya, kristal cair ini tidak memancarkan cahaya sendiri. Sumber cahaya di dalam sebuah perangkat LCD adalah lampu neon berwarna putih di bagian belakang susunan kristal cair.

Titik cahaya yang jumlahnya puluhan ribu bahkan jutaan inilah yang membentuk tampilan citra. Kutub kristal cair yang dilewati arus listrik akan berubah karena pengaruh polarisasi medan magnetik yang timbul dan oleh karenanya akan hanya membiarkan beberapa warna diteruskan sedangkan warna lainnya tersaring.

Gambaran umum

Setiap piksel dari sebuah LCD biasanya terdiri dari sebuah lapisan molekul yang berjajar di antara dua elektrode transparan, dan dua filter terpolarisasi, sumbu transmisi yang (kebanyakan) saling tegak lurus.

From wikipedia.org

Tuesday 27 November 2012

Liquid crystal display (LCD)

A liquid crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals. Liquid crystals do not emit light directly.

LCDs are available to display arbitrary images (as in a general-purpose computer display) or fixed images which can be displayed or hidden, such as preset words, digits, and 7-segment displays as in a digital clock. They use the same basic technology, except that arbitrary images are made up of a large number of small pixels, while other displays have larger elements.

LCDs are used in a wide range of applications including computer monitors, televisions, instrument panels, aircraft cockpit displays, and signage. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones, and have replaced cathode ray tube (CRT) displays in most applications. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they do not suffer image burn-in. LCDs are, however, susceptible to image persistence.

The LCD screen is more energy efficient and can be disposed of more safely than a CRT. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically modulated optical device made up of any number of segments filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in color or monochrome. Liquid crystals were first discovered in 1888. By 2008, worldwide sales of televisions with LCD screens exceeded annual sales of CRT units; the CRT became obsolete for most purposes.

Overview

Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other. With actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer.

The surface of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Electrodes are made of the transparent conductor Indium Tin Oxide (ITO). The Liquid Crystal Display is intrinsically a “passive” device, it is a simple light valve. The managing and control of the data to be displayed is performed by one or more circuits commonly denoted as LCD drivers.

Before an electric field is applied, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This induces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray.
LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel.

The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case the bright and dark states are reversed. The voltage-off dark state in this configuration appears blotchy, however, because of small variations of thickness across the device.

Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field).

Displays for a small number of individual digits and/or fixed symbols (as in digital watches and pocket calculators) can be implemented with independent electrodes for each segment. In contrast full alphanumeric and/or variable graphics displays are usually implemented with pixels arranged as a matrix consisting of electrically connected rows on one side of the LC layer and columns on the other side, which makes it possible to address each pixel at the intersections. The general method of matrix addressing consists of sequentially addressing one side of the matrix, for example by selecting the rows one-by-one and applying the picture information on the other side at the columns row-by-row. For details on the various matrix addressing schemes see Passive-matrix and active-matrix addressed LCDs.

History

    In 1888, Friedrich Reinitzer (1858–1927) discovered the liquid crystalline nature of cholesterol extracted from carrots (that is, two melting points and generation of colors) and published his findings at a meeting of the Vienna Chemical Society on May 3, 1888 (F. Reinitzer: Beiträge zur Kenntniss des Cholesterins, Monatshefte für Chemie (Wien) 9, 421–441 (1888)).

    In 1904, Otto Lehmann published his work "Flüssige Kristalle" (Liquid Crystals).

    In 1911, Charles Mauguin first experimented with liquids crystals confined between plates in thin layers.

    In 1922, Georges Friedel described the structure and properties of liquid crystals and classified them in 3 types (nematics, smectics and cholesterics).

    In 1927, Vsevolod Frederiks devised the electrically switched light valve, called the Fréedericksz transition, the essential effect of all LCD technology.

    In 1936, the Marconi Wireless Telegraph company patented the first practical application of the technology, "The Liquid Crystal Light Valve".

    In 1962, the first major English language publication on the subject "Molecular Structure and Properties of Liquid Crystals", by Dr. George W. Gray.

    In 1962, Richard Williams of RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what are now called "Williams domains" inside the liquid crystal.

    In 1964, George H. Heilmeier, then working at the RCA laboratories on the effect discovered by Williams achieved the switching of colors by field-induced realignment of dichroic dyes in a homeotropically oriented liquid crystal. Practical problems with this new electro-optical effect made Heilmeier continue to work on scattering effects in liquid crystals and finally the achievement of the first operational liquid crystal display based on what he called the dynamic scattering mode (DSM). Application of a voltage to a DSM display switches the initially clear transparent liquid crystal layer into a milky turbid state. DSM displays could be operated in transmissive and in reflective mode but they required a considerable current to flow for their operation. George H. Heilmeier was inducted in the National Inventors Hall of Fame and credited with the invention of LCD. Heilmeier's work is an IEEE Milestone.

    In the late 1960s, pioneering work on liquid crystals was undertaken by the UK's Royal Radar Establishment at Malvern, England. The team at RRE supported ongoing work by George Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals, which had correct stability and temperature properties for application in LCDs.

    On December 4, 1970, the twisted nematic field effect in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261) with Wolfgang Helfrich and Martin Schadt (then working for the Central Research Laboratories) listed as inventors. Hoffmann-La Roche then licensed the invention to the Swiss manufacturer Brown, Boveri & Cie who produced displays for wristwatches during the 1970s and also to Japanese electronics industry, which soon produced the first digital quartz wrist watches with TN-LCDs and numerous other products. James Fergason, while working with Sardari Arora and Alfred Saupe at Kent State University Liquid Crystal Institute, filed an identical patent in the United States on April 22, 1971. In 1971 the company of Fergason ILIXCO (now LXD Incorporated) produced the first LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption.

    In 1972, the first active-matrix liquid crystal display panel was produced in the United States by Westinghouse, in Pittsburgh, Pennsylvania.

    In 1983, researchers at Brown, Boveri & Cie (BBC), Switzerland, invented the super-twisted nematic (STN) structure for passive matrix addressed LCDs. H. Amstutz et al. were listed as inventors in the corresponding patent applications filed in Switzerland on July 7, 1983, and October 28, 1983. Patents were granted in Switzerland CH 665491, Europe EP 0131216, U.S. Patent 4,634,229 and many more countries.

    In 1990, under different titles inventors conceived electrooptical effects as alternatives to twisted nematic field effect LCDs (TN- and STN- LCDs). One approach was to use interdigital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates (Abstract). To take full advantage of the properties of this In Plane Switching (IPS) technology further work was needed. After thorough analysis, details of advantageous embodiments are filed in Germany by Guenter Baur et al. and patented in various countries (Abstract). The Fraunhofer Institute in Freiburg, where the inventors worked, assigns these patents to Merck KGaA, Darmstadt, the world's leading supplier of LC substances.

    In 1992, shortly thereafter, engineers at Hitachi work out various practical details of the IPS technology to interconnect the thin-film transistor array as a matrix and to avoid undesirable stray fields in between pixels (Abstract). Hitachi also improves the viewing angle dependence further by optimizing the shape of the electrodes (Super IPS).

    NEC and Hitachi become early manufacturers of active-matrix addressed LCDs based on the IPS technology. This is a milestone for implementing large-screen LCDs having acceptable visual performance for flat-panel computer monitors and television screens.

    In 1996, Samsung developed the optical patterning technique that enables multi-domain LCD. Multi-domain and In Plane Switching subsequently remain the dominant LCD designs through 2010.

    In the fourth quarter of 2007, LCD televisions surpassed CRTs in worldwide sales for the first time.

    LCD TVs was projected to account 50% of the 200 million TVs to be shipped globally in 2008, according to Display Bank.

    In October 2011, Toshiba announced 2560 × 1600 pixels on an 6.1-inch LCD panel, suitable for use in a tablet computer, especially for Chinese character display.

The origins and the complex history of liquid crystal displays from the perspective of an insider during the early days were described by Joseph A. Castellano in Liquid Gold: The Story of Liquid Crystal Displays and the Creation of an Industry. Another report on the origins and history of LCD from a different perspective until 1991 has been published by Hiroshi Kawamoto, available at the IEEE History Center. A description of Swiss contributions to LCD developments, written by Peter J. Wild, can be looked up as IEEE First-Hand History.

Illumination

LCD panels produce no light of their own; they require external light to produce a visible image. While passive-matrix displays are usually not backlit (e.g. calculators, wristwatches); active-matrix displays almost always are (with a few exceptions, such as the display in the original Game Boy Advance).

Currently, there are several common implementations of LCD backlight technology:

    CCFL: The LCD panel is lit (usually) by two cold cathode fluorescent lamps placed at opposite edges of the display. A diffuser and two polarizers then spread the light out evenly across the whole display. For many years, this technology has been used almost exclusively. Unlike white LEDs, most CCFLs have an even-white spectral output resulting in better color gamut for the display. However, CCFLs are less energy efficient then LEDs and require a somewhat costly inverter to convert whatever voltage the device uses (usually 5 or 12v) to the high voltage needed to light a CCFL. The thickness of the inverter transformer also limits how thin the display can be made.
    EL-WLED: The LCD panel is lit by a row of white LEDs placed at one or more edges of the screen. A light diffuser is then used to spread the light evenly across the whole display. As of 2012, this design is the most popular one in desktop computer monitors. Some LCD monitors using this technology have a feature called "Dynamic Contrast" where the backlight is dimmed to the brightest color that appears on the screen, allowing the 1000:1 contrast ratio of the LCD panel to be scaled to different light intensities, resulting in the "30000:1" contrast ratios seen in the advertising on some of these monitors. Since computer screen images usually have full white somewhere in the picture, the backlight will usually be at full intensity, making this "feature" mostly a marketing gimmick.
    WLED array: The LCD panel is lit by a full array of white LEDs placed behind a diffuser behind the panel. LCD displays that use this implementation will usually have the ability to dim the LEDs in the dark areas of the image being displayed, effectively increasing the contrast ratio of the display. As of 2012, this design gets most of its use from LCD televisions.
    RGB-LED: Similar to the WLED array, except the panel is lit by a full array of RGB LEDs. While displays lit with white LEDs usually have a poorer color gamut than CCFL lit displays, panels lit with RGB LEDs have very wide color gamuts. This implementation is most popular on professional graphics editing LCD displays. As of 2012, LCD displays in this category usually cost more than $1000.

Today, most LCD screens are being designed with an LED backlight instead of the traditional CCFL backlight.


Connection to other circuits

LCD panels typically use thinly-coated metallic conductive pathways on a glass substrate to form the cell circuitry to operate the panel. It is usually not possible to use soldering techniques to directly connect the panel to a separate copper-etched circuit board.

Instead, interfacing is accomplished using either adhesive plastic ribbon with conductive traces glued to the edges of the LCD panel, or with an elastomeric connector, which is a strip of rubber or silicone with alternating layers of conductive and insulating pathways, pressed between contact pads on the LCD and mating contact pads on a circuit board. 


Passive and active-matrix

Monochrome passive-matrix LCDs were standard in most early laptops (although a few used plasma displays) and the original Nintendo Game Boy until the mid-1990s, when color active-matrix became standard on all laptops. The commercially unsuccessful Macintosh Portable (released in 1989) was one of the first to use an active-matrix display (though still monochrome).

Passive-matrix LCDs are still used today for applications less demanding than laptops and TVs. In particular, these are used on portable devices where less information content needs to be displayed, lowest power consumption (no backlight) and low cost are desired, and/or readability in direct sunlight is needed.

Displays having a passive-matrix structure are employing super-twisted nematic STN (invented by Brown Boveri Switzerland; scientific details were published) or double-layer STN (DSTN) technology (the latter of which addresses a color-shifting problem with the former), and color-STN (CSTN) in which color is added by using an internal filter.

STN LCDs have been optimized for passive-matrix addressing. They exhibit a sharper threshold of the contrast-vs-voltage characteristic than the original TN LCDs. This is important, because pixels are subjected to partial voltages even while not selected. Crosstalk between activated and non-activated pixels has to be handled properly by keeping the RMS voltage of non-activated pixels below the threshold voltage, while activated pixels are subjected to voltages above threshold. STN LCDs have to be continuously refreshed by alternating pulsed voltages of one polarity during one frame and pulses of opposite polarity during the next frame. Individual pixels are addressed by the corresponding row and column circuits. This type of display is called passive-matrix addressed, because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Slow response times and poor contrast are typical of passive-matrix addressed LCDs with too many pixels.
How an LCD works using an active-matrix structure

New zero-power (bistable) LCDs do not require continuous refreshing. Rewriting is only required for picture information changes. Potentially, passive-matrix addressing can be used with these new devices, if their write/erase characteristics are suitable.

High-resolution color displays, such as modern LCD computer monitors and televisions, use an active-matrix structure. A matrix of thin-film transistors (TFTs) is added to the electrodes in contact with the LC layer. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is selected, all of the column lines are connected to a row of pixels and voltages corresponding to the picture information are driven onto all of the column lines. The row line is then deactivated and the next row line is selected. All of the row lines are selected in sequence during a refresh operation. Active-matrix addressed displays look brighter and sharper than passive-matrix addressed displays of the same size, and generally have quicker response times, producing much better images.

Active matrix technologies

Twisted nematic (TN)

Twisted nematic displays contain liquid crystals that twist and untwist at varying degrees to allow light to pass through. When no voltage is applied to a TN liquid crystal cell, polarized light passes through the 90-degrees twisted LC layer. In proportion to the voltage applied, the liquid crystals untwist changing the polarization and blocking the light's path. By properly adjusting the level of the voltage almost any gray level or transmission can be achieved.

In-plane switching (IPS)

In-plane switching is an LCD technology that aligns the liquid crystals in a plane parallel to the glass substrates. In this method, the electrical field is applied through opposite electrodes on the same glass substrate, so that the liquid crystals can be reoriented (switched) in the same plane. This requires two transistors for each pixel instead of the single transistor needed for a standard thin-film transistor (TFT) display. Before LG Enhanced IPS was introduced in 2009, the additional transistors resulted in blocking more transmission area, thus requiring a brighter backlight and consuming more power, making this type of display less desirable for notebook computers. Currently Panasonic is using an enhanced version eIPS for their large size LCD-TV products as well as Hewlett-Packard in its WebOS based TouchPad tablet.

IPS LCD vs AMOLED

LG claimed the smartphone LG Optimus Black with an IPS LCD (LCD NOVA) has the brightness up to 700 nits, while the competitor has only IPS LCD with 518 nits and double an Active-matrix OLED (AMOLED) display with 305 nits. LG also claimed the NOVA display to be 50 percent more efficient than regular LCDs and to consume only 50 percent of the power of AMOLED displays when producing white on screen. When it comes to contrast ratio, AMOLED display still performs best due to its underlying technology, where the black levels are displayed as pitch black and not as dark gray. On August 24, 2011, Nokia announced the Nokia 701 and also made the claim of the world's brightest display at 1000 nits. The screen also had Nokia's Clearblack layer, improving the contrast ratio and bringing it closer to that of the AMOLED screens.

Advanced fringe field switching (AFFS)

Known as fringe field switching (FFS) until 2003, advanced fringe field switching is similar to IPS or S-IPS offering superior performance and color gamut with high luminosity. AFFS was developed by Hydis Technologies Co., Ltd, Korea (formally Hyundai Electronics, LCD Task Force).

AFFS-applied notebook applications minimize color distortion while maintaining a wider viewing angle for a professional display. Color shift and deviation caused by light leakage is corrected by optimizing the white gamut which also enhances white/gray reproduction.

In 2004, Hydis Technologies Co., Ltd licensed AFFS to Japan's Hitachi Displays. Hitachi is using AFFS to manufacture high-end panels. In 2006, HYDIS licensed AFFS to Sanyo Epson Imaging Devices Corporation.

Shortly thereafter, Hydis introduced a high-transmittance evolution of the AFFS display, called HFFS (FFS+).

Hydis introduced AFFS+ with improved outdoor readability in 2007. AFFS panels are mostly utilized in the cockpits of latest commercial aircraft displays.

Vertical alignment (VA)

Vertical alignment displays are a form of LCDs in which the liquid crystals naturally align vertically to the glass substrates. When no voltage is applied, the liquid crystals remain perpendicular to the substrate creating a black display between crossed polarizers. When voltage is applied, the liquid crystals shift to a tilted position allowing light to pass through and create a gray-scale display depending on the amount of tilt generated by the electric field.

Blue phase mode

Blue phase mode LCDs have been shown as engineering samples early in 2008, but they are not in mass-production yet. The physics of blue phase mode LCDs suggest that very short switching times (~1 ms) can be achieved, so time sequential color control can possibly be realized and expensive color filters would be obsolete.

Quality control

Some LCD panels have defective transistors, causing permanently lit or unlit pixels which are commonly referred to as stuck pixels or dead pixels respectively. Unlike integrated circuits (ICs), LCD panels with a few defective transistors are usually still usable. Manufacturers' policies for the acceptable number of defective pixels vary greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea. As of 2005, though, Samsung adheres to the less restrictive ISO 13406-2 standard. Other companies have been known to tolerate as many as 11 dead pixels in their policies. Dead pixel policies are often hotly debated between manufacturers and customers. To regulate the acceptability of defects and to protect the end user, ISO released the ISO 13406-2 standard. However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways.

LCD panels are more likely to have defects than most ICs due to their larger size. For example, a 300 mm SVGA LCD has 8 defects and a 150 mm wafer has only 3 defects. However, 134 of the 137 dies on the wafer will be acceptable, whereas rejection of the whole LCD panel would be a 0% yield. In recent years, quality control has been improved. An SVGA LCD panel with 4 defective pixels is usually considered defective and customers can request an exchange for a new one. Some manufacturers, notably in South Korea where some of the largest LCD panel manufacturers, such as LG, are located, now have "zero defective pixel guarantee", which is an extra screening process which can then determine "A" and "B" grade panels. Many manufacturers would replace a product even with one defective pixel. Even where such guarantees do not exist, the location of defective pixels is important. A display with only a few defective pixels may be unacceptable if the defective pixels are near each other.

LCD panels also have defects known as clouding (or less commonly mura), which describes the uneven patches of changes in luminance. It is most visible in dark or black areas of displayed scenes.

Zero-power (bistable) displays

The zenithal bistable device (ZBD), developed by QinetiQ (formerly DERA), can retain an image without power. The crystals may exist in one of two stable orientations ("Black" and "White") and power is only required to change the image. ZBD Displays is a spin-off company from QinetiQ who manufacture both grayscale and color ZBD devices.

Kent Displays has also developed a "no power" display that uses polymer stabilized cholesteric liquid crystal (ChLCD). In 2009 Kent demonstrated the use of a ChLCD to cover the entire surface of a mobile phone, allowing it to change colors, and keep that color even when power is cut off.

In 2004 researchers at the University of Oxford demonstrated two new types of zero-power bistable LCDs based on Zenithal bistable techniques.

Several bistable technologies, like the 360° BTN and the bistable cholesteric, depend mainly on the bulk properties of the liquid crystal (LC) and use standard strong anchoring, with alignment films and LC mixtures similar to the traditional monostable materials. Other bistable technologies, e.g., BiNem® technology, are based mainly on the surface properties and need specific weak anchoring materials.

Specifications

Important factors to consider when evaluating an LCD:

    Resolution versus range: Fundamentally resolution is the granularity (or number of levels) with which a performance feature of the display is divided. Resolution is often confused with range or the total end-to-end output of the display. Each of the major features of a display has both a resolution and a range that are tied to each other but very different. Frequently the range is an inherent limitation of the display while the resolution is a function of the electronics that make the display work.

    Spatial performance: LCDs come in only one size for a variety of applications and a variety of resolutions within each of those applications. LCD spatial performance is also sometimes described in terms of a "dot pitch". The size (or spatial range) of an LCD is always described in terms of the diagonal distance from one corner to its opposite. This is an historical remnant from the early days of CRT television when CRT screens were manufactured on the bottoms of glass bottles, a direct extension of cathode ray tubes used in oscilloscopes. The diameter of the bottle determined the size of the screen. Later, when televisions went to a more square format, the square screens were measured diagonally to compare with the older round screens.

The spatial resolution of an LCD is expressed by the number of columns and rows of pixels (e.g., 1024×768). Each pixel is usually composed 3 sub-pixels, a red, a green, and a blue one. This had been one of the few features of LCD performance that was easily understood and not subject to interpretation. However there are newer schemes that share sub-pixels among pixels and to add additional colors of sub-pixels. So going forward, spatial resolution may now be more subject to interpretation.

One external factor to consider in evaluating display resolution is the resolution of the viewer's eyes. Assuming 20/20 vision, the resolution of the eyes is about one minute of arc. In practical terms that means for an older standard definition TV set the ideal viewing distance was about 8 times the height (not diagonal) of the screen away. At that distance the individual rows of pixels merge into a solid. If the viewer were closer to the screen than that, they would be able to see the individual rows of pixels. When observed from farther away, the image of the rows of pixels still merge, but the total image becomes smaller as the distance increases. For an HDTV set with slightly more than twice the number of rows of pixels, the ideal viewing distance is about half what it is for a standard definition set. The higher the resolution, the closer the viewer can sit or the larger the set can usefully be sitting at the same distance as an older standard definition display.

For a computer monitor or some other LCD that is being viewed from a very close distance, resolution is often expressed in terms of dot pitch or pixels per inch. This is consistent with the printing industry (another form of a display). Magazines, and other premium printed media are often at 300 dots per inch. As with the distance discussion above, this provides a very solid looking and detailed image. LCDs, particularly on mobile devices, are frequently much less than this as the higher the dot pitch, the more optically inefficient the display and the more power it burns. Running the LCD is frequently half, or more, of the power consumed by a mobile device.

An additional consideration in spatial performance are viewing cone and aspect ratio. The Aspect ratio is the ratio of the width to the height (for example, 4:3, 5:4, 16:9 or 16:10). Older, standard definition TVs were 4:3. Newer High Definition televisions (HDTV) are 16:9, as are most new notebook computers. Movies are often filmed in much different (wider) aspect ratios, which is why there will frequently still be black bars at the top and bottom of an HDTV screen.

The Viewing Angle of an LCD may be important depending on its use or location. The viewing angle is usually measured as the angle where the contrast of the LCD falls below 10:1. At this point, the colors usually start to change and can even invert, red becoming green and so forth. Viewing angles for LCDs used to be very restrictive however, improved optical films have been developed that give almost 180 degree viewing angles from left to right. Top to bottom viewing angles may still be restrictive, by design, as looking at an LCD from an extreme up or down angle is not a common usage model and these photons are wasted. Manufacturers commonly focus the light in a left to right plane to obtain a brighter image here.

    Temporal/timing performance: Contrary to spatial performance, temporal performance is a feature where smaller is better. Specifically, the range is the pixel response time of an LCD, or how quickly a sub-pixel's brightness changes from one level to another. For LCD monitors, this is measured in btb (black to black) or gtg (gray to gray). These different types of measurements make comparison difficult. Further, this number is almost never published in sales advertising.

Refresh rate or the temporal resolution of an LCD is the number of times per second in which the display draws the data it is being given. Since activated LCD pixels do not flash on/off between frames, LCD monitors exhibit no refresh-induced flicker, no matter how low the refresh rate. High-end LCD televisions now feature up to 240 Hz refresh rate, which requires advanced digital processing to insert additional interpolated frames between the real images to smooth the image motion. However, such high refresh rates may not be actually supported by pixel response times and the result can be visual artifacts that distort the image in unpleasant ways.

Temporal performance can be further taxed if it is a 3D display. 3D displays work by showing a different series of images to each eye, alternating from eye to eye. Thus a 3D display must display twice as many images in the same period of time as a conventional display, and consequently the response time of the LCD is more important. 3D LCDs with marginal response times will exhibit image smearing.

These artifacts are most noticeable in a person's black and white vision (rod cells) than in color vision (cone cells). Thus they will be more likely to see flicker or any sort of temporal distortion in a display image by not looking directly at the display, because their eyes' rod cells are mostly grouped at the periphery of their vision.

    Color performance: There are many terms to describe color performance of an LCD. They include color gamut which is the range of colors that can be displayed and color depth which is the color resolution or the resolution or fineness with which the color range is divided. Although color gamut can be expressed as three pairs of numbers, the XY coordinates within color space of the reddest red, greenest green, and bluest blue, it is usually expressed as a ratio of the total area within color space that a display can show relative to some standard such as saying that a display was "120% of NTSC". NTSC is the National Television Standards Committee, the old standard definition TV specification. Color gamut is a relatively straight forward feature. However with clever optical techniques that are based on the way humans see color, termed color stretch, colors can be shown that are outside of the nominal range of the display. In any case, color range is rarely discussed as a feature of the display as LCDs are designed to match the color ranges of the content that they are intended to show. Having a color range that exceeds the content is a useless feature.

    Color depth or color support is sometimes expressed in bits, either as the number of bits per sub-pixel or the number of bits per pixel. This can be ambiguous as an 8-bit color LCD can be 8 total bits spread between red, green, and blue or 8 bits each for each color in a different display. Further, LCDs sometimes use a technique called dithering which is time averaging colors to get intermediate colors such as alternating between two different colors to get a color in between. This doubles the number of colors that can be displayed; however this is done at the expense of the temporal performance of the display. Dithering is commonly used on computer displays where the images are mostly static and the temporal performance is unimportant.

When color depth is reported as color support, it is usually stated in terms of number of colors the LCD can show. The number of colors is the translation from the base 2-bit numbers into common base-10. For example, 8-bit color is 2 to the 8th power, which is 256 colors. 24-bit color is 2 to the 24th power, or 256 x 256 x 256, a total of 16,777,216 colors. The color resolution of the human eye depends on both the range of colors being sliced and the number of slices; but for most common displays the limit is about 28-bit color. LCD TVs commonly display more than that as the digital processing can introduce color distortions and the additional levels of color are needed to ensure true colors.

There are additional aspects to LCD color and color management, such as white point and gamma correction, which describe what color white is and how the other colors are displayed relative to white. LCD televisions also frequently have facial recognition software, which recognizes that an image on the screen is a face and both adjust the color and the focus differently from the rest of the image. These adjustments can have important effects on the consumer, but are not easily quantifiable; people like what they like and everyone does not like the same thing. There is no substitute for looking at the LCD one is going to buy before buying it. Portrait film, another form of display, has similar adjustments built in to it. Many years ago, Kodak had to overcome initial rejection of its portrait film in Japan because of these adjustments. In the U.S., people generally prefer a more colorful facial image than in reality (higher color saturation). In Japan, consumers generally prefer a less saturated image. The film that Kodak initially sent to Japan was biased in the wrong direction for Japanese consumers. Television monitors have their built-in biases as well.

    Brightness and contrast ratio: Contrast ratio is the ratio of the brightness of a full-on pixel to a full-off pixel and, as such, would be directly tied to brightness if not for the invention of the blinking backlight (or burst dimming). The LCD itself is only a light valve, it does not generate light; the light comes from a backlight that is either a florescent tube or a set of LEDs. The blinking backlight was developed to improve the motion performance of LCDs by turning the backlight off while the liquid crystals were in transition from one image to another. However, a side benefit of the blinking backlight was infinite contrast. The contrast reported on most LCDs is what the LCD is qualified at, not its actual performance. In any case, there are two large caveats to contrast ratio as a measure of LCD performance.

The first caveat is that contrast ratios are measured in a completely dark room. In actual use, the room is never completely dark, as one will always have the light from the LCD itself. Beyond that, there may be sunlight coming in through a window or other room lights that reflect off of the surface of the LCD and degrades the contrast. As a practical matter, the contrast of an LCD, or any display, is governed by the amount of surface reflections, not by the performance of the display.

The second caveat is that the human eye can only image a contrast ratio of a maximum of about 200:1. Black print on a white paper is about 15–20:1. That is why viewing angles are specified to the point where they fall below 10:1. A 10:1 image is not great, but is discernible.

Brightness is usually stated as the maximum output of the LCD. In the CRT era, Trinitron CRTs had a brightness advantage over the competition, so brightness was commonly discussed in TV advertising. With current LCD technology, brightness, though important, is usually similar from maker to maker and consequently is not discussed much, except for laptop LCDs and other displays that will be viewed in bright sunlight. In general, brighter is better, but there is always a trade-off between brightness and battery life in a mobile device.


Military use of LCD monitors


LCD monitors have been adopted by the United States military, instead of CRT displays, because they are smaller, lighter and more efficient, although monochrome plasma displays are also used, notably for the M1 Abrams tank. For use with night vision imaging systems a U.S. military LCD monitor must be compliant with MIL-STD-3009 (formerly MIL-L-85762A). These LCD monitors go through extensive certification so that they pass the standards for the military. These include MIL-S-901D – High Shock (Sea Vessels), MIL-STD-167B – Vibration (Sea Vessels), MIL-STD-810F – Field Environmental Conditions (Ground Vehicles and Systems), MIL-STD 461E/F – EMI/RFI (Electromagnetic Interference/Radio Frequency Interference), MIL-STD-740B – Airborne/Structureborne Noise, and TEMPEST – Telecommunications Electronics Material Protected from Emanating Spurious Transmissions.

Advantages

    Very compact and light.
    Low power consumption. On average, 50-70% less energy is consumed than CRT monitors.
    No geometric distortion.
    The possible ability to have little or no flicker depending on backlight technology.
    Usually no refresh-rate flicker, as the LCD panel itself is usually refreshed at 200 Hz or more, regardless of the source refresh rate.
    Is very thin compared to a CRT monitor, which allows the monitor to be placed farther back from the user, reducing close-focusing related eye-strain.
    Razor sharp image with no bleeding/smearing when used at native resolution.
    Emits less electromagnetic radiation than a CRT monitor.
    Not affected by screen burn-in, though an identical but less severe phenomenon known as image persistence is possible.
    Can be made in almost any size or shape.
    No theoretical resolution limit.
    Can be made to large sizes (more than 24 inches) lightly and relatively inexpensively.
    Masking effect: the LCD grid can mask the effects of spatial and grayscale quantization, creating the illusion of higher image quality.
    As an inherently digital device, the LCD can natively display digital data from a DVI or HDMI connection without requiring conversion to analog, like a CRT would need.
    Many LCD monitors run on an external 12v power supply, which means that (with a proper cable) they can also be run directly on one of the computer's 12v power supply outputs, removing the overhead and quiescent power consumption of the monitor's own power supply. If the computer has a PFC power supply, this will increase the power efficiency as well, as the cheap switching power supplies included with LCD monitors rarely implement PFC. This is also convenient because the monitor will power on when the computer is switched on, and will power off when the computer sleeps or is shutdown.

Disadvantages


    Limited viewing angle, causing color, saturation, contrast and brightness to vary, even within the intended viewing angle, by variations in posture.
    Uneven backlighting in some (mostly older) monitors, causing brightness distortion, especially toward the edges.
    Black levels may appear unacceptably bright due to the fact that individual liquid crystals cannot completely block all light from passing through.
    Display motion blur on moving objects caused by slow response times (>8 ms) and eye-tracking on a sample-and-hold display.
    As of 2012, most implementations of LCD backlighting use PWM to dim the display,  which makes the screen flicker more acutely (this does not mean visibly) than a CRT monitor at 85 Hz refresh rate would (this is because the entire screen is strobing on and off rather than a CRT's phosphor sustained dot which continually scans across the display, leaving some part of the display always lit), causing severe eye-strain for some people. Unfortunately, many of these people don't know that their eye-strain is being caused by the invisible strobe effect of PWM.[53] This problem is worse on many of the new LED backlit monitors, because the LEDs have a faster turn-on/turn-off time than a CCFL bulb.
    Only one native resolution. Displaying any other resolution either requires a video scaler, causing blurriness and jagged edges; or running the display at native resolution using 1:1 pixel mapping, causing the image either not to fill the screen (letterboxed display), or to run off the lower right edge of the screen.
    Fixed bit depth, many cheaper LCDs are only able to display 262,000 colors. 8-bit S-IPS panels can display 16 million colors and have significantly better black level, but are expensive and have slower response time.
    Input lag, because the LCD's A/D converter waits for each frame to be completely outputted before drawing it to the LCD panel.
    Dead or stuck pixels may occur during manufacturing or through use.
    In a constant-on situation, thermalization may occur, in which part of the screen has overheated and looks discolored compared to the rest of the screen.
    Unacceptably slow response times in low temperature environments.
    Loss of contrast in high temperature environments.
    Not usually designed to allow easy replacement of the backlight.
    Poor display in direct sunlight. Transflective LCDs provide a large improvement by reflecting natural light, but have not yet been widely adopted.
    Cannot be used with light guns/pens.
    Does not support interlaced video.

from: http://en.wikipedia.org/wiki/Liquid_crystal_display


AMOLED




AMOLED (active-matrix organic light-emitting diode) is a display technology for use in mobile devices and televisions. OLED describes a specific type of thin-film display technology in which organic compounds form the electroluminescent material, and active matrix refers to the technology behind the addressing of pixels.

As of 2012, AMOLED technolog and continues to make progress toward low-power, low-cost and large-size (for example, 40-inch) applications.

Design

An AMOLED display consists of an active matrix of OLED pixels that generate light (luminescence) upon electrical activation that have been deposited or integrated onto a thin film transistor (TFT) array, which functions as a series of switches to control the current flowing to each individual pixel.

Typically, this continuous current flow is controlled by at least two TFTs at each pixel (to trigger the luminescence), with one TFT to start and stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel, thereby eliminating the need for the very high currents required for passive matrix OLED operation.

TFT backplane technology is crucial in the fabrication of AMOLED displays. Two primary TFT backplane technologies, namely polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), are used today in AMOLEDs. These technologies offer the potential for fabricating the active matrix backplanes at low temperatures (below 150°C) directly onto flexible plastic substrates for producing flexible AMOLED displays.

Future development

Manufacturers have developed in-cell touch panels, integrating the production of capacitive sensor arrays in the AMOLED module fabrication process. In-cell sensor AMOLED fabricators include AU Optronics and Samsung. Samsung has marketed their version of this technology as Super AMOLED. Researchers at DuPont used computational fluid dynamics (CFD) software to optimize coating processes for a new solution-coated AMOLED display technology that is cost and performance competitive with existing chemical vapor deposition (CVD) technology. Using custom modeling and analytical approaches, they developed short- and long-range film-thickness control and uniformity that is commercially viable at large glass sizes.

Comparison to other technologies

AMOLED displays provide higher refresh rates than their passive-matrix OLED counterparts, improving response time often to under a millisecond, and they consume significantly less power. This advantage makes active-matrix OLEDs well suited for portable electronics, where power consumption is critical to battery life.

The amount of power the display consumes varies significantly depending on the colour and brightness shown. As an example, one commercial QVGA OLED display consumes 0.3 watts while showing white text on a black background, but more than 0.7 watts showing black text on a white background, while an LCD may consume only a constant 0.35 watts regardless of what is being shown on screen. Because the black pixels actually turn off, AMOLED also has contrast ratios that are significantly better than LCD.

AMOLED displays may be difficult to view in direct sunlight compared with LCDs because of their reduced maximum brightness. Samsung's Super AMOLED technology addresses this issue by reducing the size of gaps between layers of the screen. Additionally, PenTile technology is often used to allow for a higher resolution display while requiring fewer subpixels than would otherwise be needed, often resulting in a display less sharp and more grainy compared with a non-pentile display with the same resolution.

The organic materials used in AMOLED displays are prone to degradation over a period of time, resulting in color shifts as one color fades faster than another, image persistence or burn-in. However, technology has been developed to compensate for material degradation.

Current demand for AMOLED screens is high, and, due to supply shortages of the Samsung-produced displays, certain models of HTC smartphones have been changed to use next-generation LCD displays from the Samsung and Sony joint-venture SLCD in the future. Construction of new production facilities in 2011 will increase the production of AMOLED screens to cope with demand.

Marketing terms

 Super AMOLED

Super AMOLED is Samsung's term for an AMOLED display with an integrated digitizer, meaning, the layer that detects touch is integrated into the screen, rather than being overlaid on top of it. According to Samsung, Super AMOLED reflects 5 times less sunlight compared to the first generation AMOLED. The display technology itself is not changed. Super AMOLED is part of the Pentile Matrix Family.

Super AMOLED Advanced

Super AMOLED Advanced is a term marketed by Motorola to describe a brighter display than Super AMOLED screens, but also a higher resolution – qHD or 960 × 540 for Super AMOLED Advanced compared to WVGA or 800 × 480 for Super AMOLED. This display equips the Motorola Droid RAZR.

Super AMOLED Plus

The Samsung Galaxy S II, with a Super AMOLED Plus screen
Super AMOLED Plus, first introduced with the Samsung Galaxy S II and Samsung Droid Charge smartphones, is a branding from Samsung where the PenTile RGBG pixel matrix (2 subpixels) used in Super AMOLED displays has been replaced with a traditional RGB RGB (3 subpixels) arrangement typically used in LCD displays. This variant of AMOLED is brighter and therefore more energy efficient than Super AMOLED displays and produces a sharper, less grainy image because of the increased number of subpixels. In comparison to AMOLED and Super AMOLED displays, the Super AMOLED Plus displays are even more energy efficient and brighter.

HD Super AMOLED

Galaxy Note II subpixels representation, based on 400X image of the Note II display
The Galaxy Nexus, with an HD Super AMOLED screen
HD Super AMOLED is a branding from Samsung for an HD-resolution (>1280×720) Super AMOLED display. The first device to use it was the Samsung Galaxy Note. The Galaxy Nexus and the Galaxy S III both implement the HD Super AMOLED with a PenTile RGBG-matrix (2 subpixels/pixel), while the Galaxy Note II uses an RBG matrix (3 subpixels/pixel) but not in the standard 3 stripe arrangement.
Future

Future displays exhibited in 2012 have shown even higher resolutions with phone displays (4 to 5 inches) having Full HD (1920 × 1200 or 1920 × 1080) resolution capabilities.




From: http://en.wikipedia.org/wiki/AMOLED 

LCD vs AMOLED

Apa keuntungan memiliki smartphone jika layar terlihat silau di bawah sinar matahari—atau jika tidak bisa melihat gambar saat ponsel dimiringkan? Jenis layar di ponsel mempengaruhi pengalaman Anda. Layar AMOLED Super adalah cara baru untuk merasakan pengalaman melihat konten di layar yang bebas pantulan dan dengan gambar yang brilian.


Jangan Takut Dengan Cahaya

Awalnya, muncul layar LCD sentuh. Kemudian muncul layar AMOLED. Sekarang, muncul layar Super AMOLED yang menyediakan fitur layar sentuh. Jika Anda sudah tidak ingin lagi mengerlingkan mata atau menudungkan tangan untuk melihat layar, bacalah untuk mengetahui bagaimana layar Super AMOLED mempermudah interaksi dalam menggunakan ponsel.

Layar sentuh biasanya memiliki dua lapisan, layar tampilan tersendiri dan lapisan sentuh, sehingga akan menghasilkan efek memantul yang silau. Layar Super AMOLED memiliki satu lapisan, yang tidak hanya mengeliminasi adanya celah udara yang menyebabkan silau namun juga dapat mendeteksi sentuhan, serta terintegrasi di layar, bukan diletakkan di lapisan atas. Ini adalah teknologi baru yang memungkinkan Anda dapat melihat dengan jelas berada di bawah sinar matahari dengan layar sentuh bebas pantulan.

Jangan Takut Dengan Cahaya

Awalnya, muncul layar LCD sentuh. Kemudian muncul layar AMOLED. Sekarang, muncul layar Super AMOLED yang menyediakan fitur layar sentuh. Jika Anda sudah tidak ingin lagi mengerlingkan mata atau menudungkan tangan untuk melihat layar, bacalah untuk mengetahui bagaimana layar Super AMOLED mempermudah interaksi dalam menggunakan ponsel.

Layar sentuh biasanya memiliki dua lapisan, layar tampilan tersendiri dan lapisan sentuh, sehingga akan menghasilkan efek memantul yang silau. Layar Super AMOLED memiliki satu lapisan, yang tidak hanya mengeliminasi adanya celah udara yang menyebabkan silau namun juga dapat mendeteksi sentuhan, serta terintegrasi di layar, bukan diletakkan di lapisan atas. Ini adalah teknologi baru yang memungkinkan Anda dapat melihat dengan jelas berada di bawah sinar matahari dengan layar sentuh bebas pantulan.

Siapkan Indera Penglihatan Anda untuk Melihat Gambar yang Luar Biasa

Saat menggunakan smartphone untuk bermain game, menonton film dan menjelajah foto, Anda tahu betapa pentingnya kualitas gambar serta sudut tampilan yang tepat. Layar Super AMOLED tidak hanya memiliki sudut tampilan 180 derajat, namun juga sangat jernih—20% lebih terang dan lebih bening daripada layar AMOLED biasa. Dengan layar ini, warna menjadi sangat hidup berkat adanya reproduksi warna yang 30% lebih baik daripada layar LCD. Layar WVGA (800 x 480) resolusi tinggi di Samsung Galaxy S, menayangkan gambar yang lebih tajam dan lebih jernih di layar 4" yang ekstra lebar.

Jika Anda biasa menonton layar bersama-sama dengan teman, maka sudut tayangan 180 derajat yang lebar paling ideal. Anda dapat memegang layar smartphone sejajar mata dan melihat gambar di layar tanpa kabur atau distorsi. Layar seperti tidak terpengaruh meskipun Anda melihatnya dari samping, atas, bawah, atau dari depan jadi akan memudahkan Anda berbagi video dan foto bersama orang lain di dekat Anda.

Durasi Pemakaian Baterai Lebih Lama

Daya ponsel yang cepat habis dapat membuat Anda repot. Layar yang lebih terang memang menggunakan lebih banyak daya di beberapa ponsel dengan layar LCD, danum layar Super AMOLED seperti yang ada di Samsung Galaxy S series, menghemat daya baterai. Setiap piksel memiliki sumber cahaya sendiri, jadi piksel hitam tidak menyala, dan tidak menggunakan energi. Anda akan mendapatkan kontras yang lebih baik, konsumsi daya lebih hemat dan durasi pemakaian baterai akan 20% lebih lama daripada layar konvensional. Nikmati menonton film dan memutar musik lebih lama, dan merekam video terus-menerus tanpa harus berhenti dan mengisi daya.

Monday 26 November 2012

AMOLED

AMOLED merupakan kependekan dari Active Matrix Organic Light Emitting Diode. AMOLED ini merupakan teknologi layar OLED (Organic Light Emitting Diode). OLED ialah perangkat padat yang terdiri dari film-film tipis. Film-film tersebut mengandung molekul organik yang dapat menghasilkan cahaya apabila dialiri listrik. OLED ini digunakan sebagai layar dalam suatu perangkat dengan tingkat ketajaman yang lebih tinggi serta konsumsi daya yang relatif rendah. AMOLED ini dikeluarkan oleh Samsung, salah satu perusahaan teknologi yang bermarkas di Korea Selatan (Seoul). Sebagai salah satu perusahaan teknologi yang terbesar di dunia, Samsung kembali meluncurkan inovasi yaitu layar sentuh berbasis teknologi AMOLED yang menjadi layar sentuh AMOLED pertama. AMOLED merupakan bentuk perkembangan dari teknologi layar sebelumnya, yang dikenal dengan nama Thin Film Transistor (TFT). Teknologi ini merupakan hasil perpaduan antara teknologi OLED dan active matrix TFT LCD konvensional. AMOLED merupakan bentuk pengembangan dari layar OLED pasif biasa, yang dapat mengubah setiap piksel dengan efisien dan secara langsung. Teknologi AMOLED tersebut memiliki fungsi sentuh (touchscreen) secara langsung, bukan melalui lapisan kedua di atas layarnya. Metode baru tersebut dilakukan melalui penambahan sensor pada sel organik dari LED. Sentuh antar muka ini mampu menambah ketebalan layar mencapai seperseribu millimeter, sehingga tidak akan mengurangi ketajaman atau meredupkan gambar, sebagaimana apabila dipasang dalam dua panel.

Kelebihan
Layar AMOLED ini memiliki tingkat kecerahan (brightness) tinggi dalam tampilannya. Teknologi AMOLED mengemas fitur penyetelan RGB, yang dapat membuat warna foto ataupun video lebih stabil, sehingga tampilannya lebih cerah dan tajam. Teknologi ini memiliki tingkat konsumsi energi yang rendah atau hemat daya, sehingga konsumsi listriknya minimal serta baterai dapat bertahan dalam waktu yang lama. Teknologi ini mampu menghemat daya 40 persen lebih dibanding yang lainnya. Tingkat ketipisan dari layar ini mencapai 0,001 mm. Selain itu layar ini bahkan diklaim mampu menghasilkan tingkat kehitaman yang lebih dibandingkan yang lain, walaupun dilihat dari bawah terik matahari secara langsung, tampilan layar masih tampak terang dan jelas, serta warnanya pun tetap cerah. Layar AMOLED ini juga tidak membutuhkan cahaya latar yang memiliki kemampuan untuk mengatur seberapa besar piksel, dengan konsumsi daya yang lebih rendah, walaupun dalam ukuran yang besar. Selain itu, layar ini juga memiliki rasio kontras lebih dalam daripada kebanyakan LCD lainnya. Keunikan lain dari layar bentuk AMOLED adalah layar ini mampu menyesuaikan tingkat kecerahan pada layar secara otomatis. AMOLED ini membuat waktu respons lebih cepat ketika ponsel berubah posisi on dan off. Ketipisan dan kefleksibelan dari bahan yang digunakan dalam layar ini membuat pabrik-pabrik teknologi dapat membuat layar dalam ukuran yang bervariasi, dari ukuran raksasa sampai yang kecil sekalipun. Misalnya, layar TV Plasma yang ukurannya mencapai 150 inchi sampai ukuran yang paling kecil pada handphone. Selain itu satu kelebihan lain dari teknologi ini jika dibandingkan dengan teknologi LCD adalah kalau pada teknologi AMOLED ini, untuk dapat dilihat oleh mata manusia tidak memerlukan sinar backlight tambahan lagi.

Kelemahan

Namun ada beberapa kelemahan dari layar ini, yaitu pembuatan layar ini masih tergolong cukup rumit. Selain itu karena teknologi ini masih baru, maka harga perangkat yang menggunakan teknologi ini juga relatif mahal. Meskipun layar AMOLED ini menawarkan berbagai kecanggihan yang menggiurkan, namun bukanlah hal yang mudah bagi para vendor untuk mengadopsi AMOLED ini, karena AMOLED tersebut mempunyai komponen harga lebih mahal daripada komponen pada layar sebelumnya. Hal tersebut, tentunya membuat para vendor untuk berpikir ulang. Itulah alasannya mengapa beberapa teknologi, seperti smartphone yang berbentuk tablet relatif jarang dibekali layar AMOLED dan masih bertahan dengan layar TFT, tujuannya adalah untuk menekan harga jual untuk konsumen. Namun, beberapa vendor yang mampu memproduksi teknologi layar AMOLED sendiri lebih mudah mengaplikasikan layar ini, seperti Samsung dan LG.

Bagian-Bagian

Dalam AMOLED ini terdiri dari empat lapisan yang terdiri dari anode layer (lapisan kutub positif), middle organic layer (lapisan organik tengah), cathode layer (lapisan kutub negatif) serta lapisan bawah yang berisi untaian (circuitry). Berikut penjelasan dari beberapa lapisan tersebut 

    • "Lapisan anode : lapisan ini berfungsi menciptakan lubang elektron untuk membuang elektron pada saat dialiri listrik.  

    • "Lapisan organik tengah :lapisan ini terbuat dari polymer atau molekul organik. Pada OLED yang didesain dua lapisan ini memiliki dua bagian, yaitu lapisan penyalur dan lapisan pemancar. Lapisan penyalur ini terbuat dari polyaniline, molekul plastik organik yang berfungsi mengirimkan lubang elektron yang berasal dari lapisan anode. Sedangkan lapisan pemancar berfungsi mengirimkan elektron dari lapisan katode. Pada lapisan inilah cahaya pada layar OLED dihasilkan atau bersumber. Lapisan pemancar terbuat dari polyfluorence yang merupakan molekul plastik organik jenis lain." 

    • "Lapisan katode : lapisan ini dapat bersifat tidak transparan atau bersifat transparan tergantung dari jenis OLED. Lapisan ini berfungsi untuk menyuntikkan elektron apabila dialiri listrik." 

    •  "Lapisan bawah : lapisan bawah ini juga disebut lapisan substrate. Lapisan ini berfungsi sebagai alas bagi layar OLED. Bahan dari lapisan ini ialah plastik, kertas foil, gelas."

  • Cara Kerja

    Layar AMOLED ini terdiri dari piksel OLED (organic light emitting diode) yang disatukan ke transistor film yang kecil (Thin Film Transistor) agar dapat membentuk matriks piksel yang dapat menyinari saat aktivasi elektrik, sehingga dapat mengontrol aliran piksel yang ditampilkan ataupun memberikan sinyal pada setiap piksel guna menentukan seberapa cerah harus memendar. Pada umumnya, aliran piksel ini dikendalikan oleh paling sedikit dua TFT pada setiap pikselnya. Satu TFT untuk memulai pengisian pada kapasitor serta menghentikan pengisiannya. Sedangkan yang satunya lagi berfungsi mensuplai sumber tegangan pada tingkat yang dibutuhkan agar dapat menghasilkan aliran yang tetap atau konstan. Adapun teknisnya adalah, susunan TFT membentuk matriks yang berasal dari elemen lapisan anode, kemudian terjadi aliran arus listrik antara kedua film molekul organik. Lalu, masing-masing piksel diaktifkan secara langsung. Susunan TFT membentuk piksel mana yang dapat menghasilkan gambar. Produksi gambar dilakukan dengan sangat cepat dan terlihat lebih alami. AMOLED ini cukup ideal untuk menampilkan video.

    Bentuk Aplikasi

    Layar AMOLED dapat diaplikasikan pada beberapa perangkat, diantaranya adalah display monitor pada PC, layar TV, maupun display pada perangkat yang bersifat portable seperti ; ponsel, smartphone, PDA, dan lainnya. Perusahaan Samsung mengklaim bahwa impression yang dikeluarkan pada tahun 2009 adalah ponsel pertama yang menggunakan layar AMOLED. Sebelumnya, plastic electronics sebuah perusahaan yang bergerak di bidang pengembangan teknologi mengatakan bahwa perangkat pertama yang sudah menggunakan teknologi AMOLED ini ialah Samsung IceTouch, MP3 player. Perangkat ini bersifat portable all in one, yang dapat memainkan DVD, music, maupun stasiun radio. Harga dari MP3 ini dipekirakan 328 dolar Amerika. Kemudian disusul dengan keluarnya ponsel Samsung lain yang juga menggunakan layar AMOLED ini. Ponsel tersebut adalah Samsung Jet dan Samsung Ultra Touch. Kedua ponsel tersebut diperkenalkan pada pertengahan tahun 2009. Disusul kemudian Samsung W880 yang dikeluarkan pada bulan September 2010. Teknologi AMOLED yang diterapkan pada ponsel Samsung juga dilakukan secara bersamaan dengan penggunaan AMOLED pada display layar LCD dari Samsung. Teknologi AMOLED ini akan dikembangkan melalui beberapa tahap. Setelah sukses dalam meluncurkan layar AMOLED pada beberapa produk ponsel canggihnya, kini SMD (Samsung Mobile Display) kemudian membuat terobosan baru dengan mengembangkan teknologi layar AMOLED yang anti pecah. Lalu untuk merealisasikan ide tersebut, Samsung melapisi panel AMOLED menggunakan plastik serta film transistor yang berukuran tipis atau dikenal dengan metode enkapsulasi plastik. Kemudian pelindung vinyil diganti dengan film polymide. Layar AMOLED jenis baru tersebut memiliki tingkat ketahanan yang tinggi terhadap benturan bahkan dipukul dengan palu sekalipun atau jika ditekuk dan digulung. Hal tersebut tidak mengubah atau mengurangi kualitas gambar (distorsi gambar). Selain itu, Samsung juga mengembangkan modifikasi lain dari teknologi layar AMOLED ini. Modifikasi tersebut misalnya adalah layar AMOLED transparan dan layar AMOLED fleksibel. Layar AMOLED fleksibel tersebut berukuran sangat tipis, namun kelebihannya adalah kemampuannya dalam menghadirkan tampilan gambar yang kaya warna dan cerah.

    Referensi

    John, FRS. 2005. Introduction to Communication Technology, Washington : A CRC Company, ISBN 100-676-243-6
    Heath, Steve. (1995).Multimedia & Communicatons Technology New York: The Free Press, ISBN 537-289-634-2
    Rogers, Everett M. (1986). Communication Technology: The New Media in Society, New York: The Free Press, ISBN 624-361-006-7

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