Electronic display

(electronics) An electronic component used to convert electric signals into visual imagery in real time suitable for direct interpretation by a human operator.

An electronic component used to convert electrical signals into visual imagery in real time suitable for direct interpretation by a human operator. It serves as the visual interface between human and machine. The visual imagery is processed, composed, and optimized for easy interpretation and minimum reading error. The electronic display is dynamic in that it presents information within a fraction of a second from the time received and continuously holds that information, using refresh or memory techniques, until new information is received. The image is created by electronically making a pattern from a visual contrast in luminance between (1) individual electrically alterable picture elements (pixels) in a matrix array of pixels in flat-panel displays (FPDs) or (2) electrically excited and nonexcited areas in a phosphor film in cathode-ray tubes (CRTs). High-information-content (HIC) displays are those displays that have a sufficient number of pixels (75,000 to 2,000,000) to show standard or high-definition television images, or comparable computer images.

The use of electronic displays for presentation of graphs, symbols, alphanumerics, and still and video pictures has doubled every several years, in parallel with the rapid expansion of microelectronics. Electronic displays have largely replaced traditional mechanical devices, counters, galvanometers, and, to a degree, hardcopy (paper) means for presenting information. This change is due to the increased use of computers, microprocessors, inexpensive large-scale integration (LSI) electronics, and digital mass memories. The success of the digital watch, hand-held calculator, and personal computer is directly attributable to the availability of inexpensive LSI electronics and electronic displays. See also Calculators; Computer; Computer graphics; Computer storage technology; Integrated circuits; Microcomputer; Microprocessor; Watch.

The major electronic display application is in home color television. The computer terminal using a CRT or FPD is the most important industrial application of electronic displays. With advances in high-information-content FPD technology, the electronic display industry went through a dramatic change in the early 1990s. This was primarily due to breakthroughs and manufacturing advances in liquid-crystal displays (LCDs). Color active-matrix LCDs (AMLCDs) have better performance than color CRTs for video and computer graphics and are thin and portable. However, the AMLCDs are several times more expensive than CRTs, so their use remains restricted to applications such as personal computers and television receivers where the CRT will not fit. See also Liquid crystals.

The primary applications of the CRT are in home entertainment television, computer monitors, scientific and electrical engineering oscilloscopes, radar display, and alphanumeric and graphic electronic displays. See also Oscilloscope; Radar.

Because of the depth dimension of the CRT, there has been a concentrated effort to develop FPDs. A primary motivating factor has been to achieve a flat high-information-content display which could be hung on a wall or carried in a briefcase. Over the years, the electrical phenomena most extensively developed for FPDs have been gas discharge (plasma), electroluminescence, light-emitting diode, cathodoluminescence, and liquid crystallinity. The cost of FPDs is higher than CRTs on a character-per basis for HIC displays. See also Cathodoluminescence; Electroluminescence; Light-emitting diode.

Before the 1990s, cost and performance limitations restricted the use of FPDs to specialized applications. With the advent of two major breakthroughs in the 1980s, LCDs emerged as the leading FPD. These two breakthroughs were the invention of the supertwisted nematic (STN) LCD, often referred to as passive-matrix LCD (PMLCD), and the evolution of a manufacturable AMLCD. The STN inventions improve LCDs so that they can be made as a HIC FPD because of improvements in the matrix addressing capability. Both of these types are made in monochrome and full color. The AMLCD is fast enough for video and for multimedia displays, comparable to a CRT. The PMLCD is fast enough for computer use but not video; however, PMLCDs are about half the cost of AMLCDs.

Applications of LCDs include portable computing devices and memory aids; electronic games; moving map devices in conjunction with global positioning satellites (GPS) for navigation of boats, aircraft, and motored vehicles; educational devices and video for portable handheld devices; and displays for television, entertainment, education, and information dissemination. LCDs are also used in helmet displays and virtual-reality displays. See also Satellite navigation systems; Video games.

The smaller AMLCDs are used in camcorder viewfinders, helmet displays, and projectors. The medium-size displays are used in all the applications that are viewed directly, such as portable computers or television receivers.

PMLCDs are used with the STN configuration of LCD in devices where some reduction in performance is acceptable, such as portable computer displays that do not require video imagery. PMLCDs in the basic twisted nematic (TN) mode are used in inexpensive toys, automotive panels, meter displays, and watches.

Electronic displays can be categorized into four classifications; as shown in the table. Each classification is defined by natural technical boundaries and cost considerations. The categorization is useful in visualizing the extent to which electronic displays are used.

Color can be created on a CRT equipped with a shadow mask duplicating quite closely all colors that occur in nature. This is done in the CRT by using three different electron guns and three phosphors in a triad of red, green, and blue on the screen at each pixel. The shadow mask is a metal screen with one hole for each triad of phosphor dots (pixel). It is precisely located and aligned with the phosphor screen. Electron beams from each of three guns are constrained by each shadow mask hole to hit each respective phosphor dot.

Penetration phosphors are also used to create color on CRT displays to eliminate the need for the shadow mask and extra guns. However, the color is limited and the brightness is low. Normally, two phosphors are placed on the screen in two layers or in microspheres of two layers. The gun and CRT anode are operated in two energy states to produce either a high-energy or a low-energy electron beam switchable in time.

Monochromatic as well as full color is readily produced by FPD technologies. Full color is produced by using a triad of red, green, and blue for each pixel, or sequential flashing at 180 Hz of red, green, or blue at each pixel area. Full color is very important for entertainment television displays. Most industrial electronic displays do not necessarily need full color, but full color has been used more frequently as color display costs have decreased. In these applications, the color display instrument is usually a CRT using the shadow-mask color technique.

The essence of electronic displays is based upon the ability to turn on and off individual pixels (Fig. 1). A typical HIC display will have a quarter million pixels in an orthogonal array, each under individual control by the electronics. The pixel resolution is normally just at or below the resolving power of the eye at one minute of arc. Thus, a good-quality picture can be created from a pattern of activated pixels. The pixel concept for electronic displays has evolved from the modern FPD technologies and digital electronics.

Pixel array used for creating electronic display images.

With flat-panel and CRT digital display techniques, alphanumeric character fonts are created by turning on the appropriate pixels in an array. One standard size is a 5 × 7 array with two pixels between characters and two pixels between rows (Fig. 1). All the letters and numbers can be created on this common array format. A very efficient and elegant array has evolved for portraying numeric characters and many letters of the alphabet, called the seven-bar font (Fig. 2). Each bar is a pixel by definition. This font was initially considered crude when compared to the Leroy font and other more esthetic printer fonts. It is now universally accepted. A similar 14 bar font is sometimes used for alphanumeric characters.

Seven-bar numeric font.