MOD002556
10/03/2014
13:00-16:00
Flat panel displays encompass a growing number of electronic visual display technologies. They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes (CRTs), and are usually less than 10 centimetres (3.9 in) thick. (Some CRTs were designed to have a flat front surface, and equipment using them was advertised as "flat-screen", which can cause confusion.)
Flat panel displays can be divided into two general display technology categories: volatile and static.
In many applications, specifically modern portable devices such as laptops, mobile phones, digital cameras, camcorders, point-and-shoot cameras, and pocket video cameras, any display disadvantages are made up for by portability advantages.
Most of the modern flat-panel displays use LCD technologies. Most LCD screens are back-lit to make them easier to read in bright environments. They are thin and light. They provide better linearity and higher resolution.
A multifunctional monitor (MFM) is a flat panel display that has additional video inputs (more than a typical LCD monitor) and is designed to be used with a variety of external video sources. In many instances, an MFM also includes a TV tuner, making it similar to a LCD TV that offers computer connectivity.
Flat panel monitors receive either:
Analog Signal:
An analog or analogue signal is any continuous signal for which the time varying feature (variable) of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. For example, in an analog audio signal, the instantaneous voltage of the signal varies continuously with the pressure of the sound waves. It differs from a digital signal, in which a continuous quantity is represented by a discrete function which can only take on one of a finite number of values. The term analog signal usually refers to electrical signals; however, mechanical, pneumatic, hydraulic, and other systems may also convey analog signals.
A digital signal is a physical signal that is a representation of a sequence of discrete values (a quantified discrete-time signal), for example of an arbitrary bit stream, or of adigitized (sampled and analog-to-digital converted) analog signal. The term digital signal can refer to either of the following:
- any continuous-time waveform signal used in digital communication, representing a bit stream or other sequence of discrete values
- a pulse train signal that switches between a discrete number of voltage levels or levels of light intensity, also known as a line coded signal or baseband transmission, for example a signal found in digital electronics or in serial communications, or a pulse code modulation (PCM) representation of a digitized analog signal.
A signal that is generated by means of a digital modulation method (digital passband transmission), to be transferred between modems, is in the first case considered as a digital signal, and in the second case as converted to an analog signal.
LCD:
A liquid-crystal display (LCD) is a flat panel display, electronic visual display, orvideo 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 andplasma displays, and since they do not use phosphors, they do not suffer image burn-in. LCDs are, however, susceptible to image persistence.[1]
PDP:
A plasma display panel (PDP) is a type of flat panel display common to large TV displays 30 inches (76 cm) or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically chargedionized gases, or what are in essence chambers more commonly known as fluorescent lamps.
ELD:
Electroluminescent Displays (ELDs) are a type of Flat panel display created by sandwiching a layer of electroluminescent material such as GaAs between two layers of conductors. When current flows, the layer of material emits radiation in the form of visible light. Electroluminescence (EL) is an optical and electrical phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field.
LED:
A light-emitting diode (LED) is a two-leadsemiconductor light source that resembles a basic pn-junction diode, except that an LED also emits light.[7] When an LED's anode lead has a voltage that is more positive than its cathode lead by at least the LED's forward voltage drop, current flows. Electrons are able to recombine withholes within the device, releasing energy in the form of photons. This effect is calledelectroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.
Display Basics:
Pixels:
In digital imaging, a pixel, pel,[1] or picture element[2] is a physical point in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen. The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a two-dimensional grid, and are often represented using dots or squares, but CRT pixels correspond to their timing mechanisms and sweep rates.
Triad:
In CRT or computer terminology, a triad is a group of three phosphor dots coloured red, green, and blue on the inside of the CRT display of a computer monitor or television set. By directing differing intensities of electron beams onto the three phosphor dots, the triad will display a colour by combining the red, green and blue elements. Each triad forms one pixel of the displayed image.
On LCDs, colours are similarly composed of these three colours.
RGB:
The RGB color model is an additive color model in which red, green, and blue light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additive primary colors, red, green, and blue.
The main purpose of the RGB color model is for the sensing, representation, and display of images in electronic systems, such as televisions and computers, though it has also been used in conventional photography. Before the electronic age, the RGB color model already had a solid theory behind it, based in human perception of colors.
RGB is a device-dependent color model: different devices detect or reproduce a given RGB value differently, since the color elements (such as phosphors or dyes) and their response to the individual R, G, and B levels vary from manufacturer to manufacturer, or even in the same device over time. Thus an RGB value does not define the same color across devices without some kind of color management.
Typical RGB input devices are color TV and video cameras, image scanners, and digital cameras. Typical RGB output devices are TV sets of various technologies (CRT, LCD, plasma, etc.), computer and mobile phone displays, video projectors, multicolor LED displays, and large screens such as JumboTron. Color printers, on the other hand, are not RGB devices, but subtractive color devices (typically CMYK color model).
This article discusses concepts common to all the different color spaces that use the RGB color model, which are used in one implementation or another in color image-producing technology.
Graphics Display Resolution:
The graphics display resolution describes the width and height dimensions of a display, such as a computer monitor, in pixels. Certain combinations of width and height are standardized and typically given a name and an initialism that is descriptive of its dimensions. A higher display resolution in a display of the same size means that displayed content appears sharper.
Dot Pitch:
Dot pitch (sometimes called line pitch, stripe pitch, phosphor pitch, or pixel pitch) is a specification for a computer display, computer printer, image scanner, or other pixel-based device that describes the distance, for example, between dots (sub-pixels) of the same color on the inside of a display screen. In the case of a color display dot pitch is a measure of the size of a triad plus the distance between the triads.
Dot pitch may be measured in linear units, usually millimeters(mm), or as a rate, for example dots per inch, with a larger number meaning higher resolution. Closer spacing generally produces a sharper image (as there are more pixels in a given area). However, other factors may affect image quality, including:
- measurement method not documented, complicated by general ignorance of the existence of multiple methods
- pixel spacing varying across screen area (e.g., increasing in corners compared to center)
- differing pixel geometries
- differing screen resolutions when attempting to judge picture quality
- tightness of electron beam focus and aim (in CRTs)
- differing aspect ratios
Refresh Rate:
The refresh rate (most commonly the "vertical refresh rate", "vertical scan rate" for CRTs) is the number of times in a second that a display hardware updates its buffer. This is distinct from the measure of frame rate in that the refresh rate includes the repeated drawing of identical frames, while frame rate measures how often a video source can feed an entire frame of new data to a display.
For example, most movie projectors advance from one frame to the next one 24 times each second. But each frame is illuminated two or three times before the next frame is projected using a shutter in front of its lamp. As a result, the movie projector runs at 24 frames per second, but has a 48 or 72 Hz refresh rate.
On CRT displays, increasing the refresh rate decreases flickering, thereby reducing eye strain. However, if a refresh rate is specified that is beyond what is recommended for the display, damage to the display can occur.[1]
For computer programs or telemetry, the term is also applied to how frequently a datum is updated with a new external value from another source (for example; a shared public spreadsheet or hardware feed).
Vector Display:
A vector monitor or vector display is a display device used for computer graphics up through the 1970s. It is a type of CRT, similar to the oscilloscope. In a vector display, the image is composed of drawn lines rather than a grid of glowing pixels as in raster graphics. The electron beam follows an arbitrary path tracing the connected sloped lines, rather than following the same horizontal raster path for all images. The beam skips over dark areas of the image without visiting their points.
Some refresh vector displays use a normal phosphor that fades rapidly and needs constant refreshing 30-40 times per second to show a stable image. These displays such as the Imlac PDS-1 require some local refresh memory to hold the vector endpoint data. Otherstorage tube displays such as the popular Tektronix 4010 use a special phosphor that continues glowing for many minutes. Storage displays do not require any local memory. In the 1970s, both types of vector displays were much more affordable than bitmap raster graphics displays when a megapixel computer memory was still very expensive. Now, raster displays have displaced nearly all uses of vector displays.
Raster Scan:
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems. The word rastercomes from the Latin word rastrum (a rake), which is derived from radere (to scrape); see also rastrum, an instrument for drawing musicalstaff lines. The pattern left by the lines of a rake, when drawn straight, resembles the parallel lines of a raster: this line-by-line scanning is what creates a raster. It is a systematic process of covering the area progressively, one line at a time. Although often a great deal faster, it is similar in the most-general sense to how one's gaze travels when one reads lines of text.
LCD DISPLAYS:
ACTIVE MATRIX:An active-matrix liquid-crystal display (AMLCD) is a type of flat panel display, the only viable technology for high-resolution TVs, computer monitors, notebook computers,tablet computers and smartphones with an LCD screen, due to low weight, very good image quality, wide color gamut and response time.
The concept of active-matrix LCDs was invented by Bernard J. Lechner at the RCA Laboratories in 1968.[1]The first functional AMLCD display with thin-film transistors was made by T Peter Brody and his team at Westinghouse Electric Corporation in 1973.[2] However, it took years of additional research by others to launch successful products.
PASSIVE MATRIX:
Passive matrix addressing is an addressing scheme used in early LCD displays. This is a matrix addressing scheme meaning that only m + n control signals are required to address a m × n display. A pixel in a passive matrix must maintain its state without active driving circuitry until it can be refreshed again.
The signal is divided into a row or select signal and a column or video signal. The select voltage determines the row that is being addressed and all n pixels on a row are addressed simultaneously. When pixels on a row are being addressed, a Vsel potential is applied, and all other rows are unselected with a Vunsel potential. The video signal or column potential is then applied with a potential for each m columns individually. An on-lighted pixel corresponds to a Von, an off-switched corresponds to a Voff potential.
Active Matrix Displays:
A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin films of an active semiconductorlayer as well as the dielectric layer and metallic contacts over a supporting (but non-conducting) substrate. A common substrate is glass, because the primary application of TFTs is in liquid-crystal displays. This differs from the conventionaltransistor, where the semiconductor material typically is the substrate, such as a silicon wafer.
Within the flat panel display industry TFD more often refers to thin film bi-directional diodes, also known as metal-insulator-metal (MIM) TFDs or nonlinear resistors.[1] Bi-directional MIM TFDs have very low current flow at low applied voltages, but then begin to conduct electricity above a threshold voltage, of either positive or negative polarity. Owing to this behavior these two terminal devices may be used as a switch. The exact threshold voltage at which a MIM TFD switches on and begins to conduct electricity depends on its physical dimensions, such as thickness of the insulating layer, as well as the physical properties of the materials from which it is made, such as the work function of each metal layer.[2]
The Plasmatron, or technically plasma addressed liquid crystal (PALC) is a color television display technology developed by Tektronix and Sony in the 1990s. PALC displays combine rows formed from liquid crystals with columns formed from plasma cells, the later replacing the transistorized switching in a conventional LCD.[1] Although PALC was successfully developed, thin-film transistor based LCD devices improved to offset PALC's advantages, and PALC development has been largely abandoned since the early 2000s.
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