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Part One The History and Technology of VIDEO DISPLAYS By Dr David Maddison This two-part series investigates the history and technology of video displays, from the Nipkow disc and the earliest CRT (cathode ray tube) screens to the latest quantum dot displays. We will focus on two-dimensional displays capable of displaying video, not simple alphanumeric displays or 3D imaging technology. T his first article will cover the history of display technology until the introduction of LCDs (liquid-crystal displays) in the 1980s, which today are dominant in the market (although there are other newcomers like OLEDs making inroads). Like in other areas of technology, there has been a great deal of innovation and progress over the last 150 or so years. Next month, the second and final part of the series will cover all the latest technology from LCDs to OLEDs, quantum dot displays, microLED displays, EL displays, DLP, E Ink and more. The Nipkow disc Scottish inventor Alexander Bain 14 Silicon Chip invented the first device that allowed pictures to be transmitted remotely, sending images telegraphically using his “electric printing telegraph” in 1843. However, that device and another “image telegraph” machine by Frederick Bakewell dating to 1848 were not viable due to very poor image quality. The first viable commercial facsimile machine was the Pantelegraph, invented by Italian physicist Giovanni Caselli in 1861. It could transmit still images but not moving pictures. Arguably, the first video display device capable, at least theoretically, of showing moving images was the Nipkow disc (Fig.1) which was invented in 1883 and patented in 1884. Australia's electronics magazine It consisted of a rotating disc with a pattern of spiral holes that could be used both to generate an image for transmission via radio or wire and for reproducing the image via another synchronised disc at the receiving end. Advantages of this device include the fact that both imaging and receiving devices were similar; it used a simple imaging system requiring only a light sensor and the modulation of a light source; and it had a high resolution for each scan line. Disadvantages included the need to keep the discs synchronised and a practical limit to the number of holes the disc could have, limiting the number of lines of resolution, typically in the range of 30-100. However, up to siliconchip.com.au 200 lines were used experimentally. Also, the scan lines of the images were curved due to practical limits of the size of the disc, and the images produced were small. For example, a 30-50cm disc would yield an image the size of a postage stamp. In 1885, Henry Sutton of Ballarat Victoria designed a mechanical television apparatus for watching the Melbourne Cup live in Ballarat. Unfortunately, he never built the device because the telegraph lines he proposed to use did not have the capacity to transmit the signal. Radio, which had the needed capacity, had not yet been made practical. He called the device the Telephane and published the plans in 1890 (see Fig.2). It used the Nipkow disc, a selenium photocell and the Kerr effect (the change in the refractive index of a material in response to an applied electric field). The Nipkow Disc was a vital step toward the invention of the practical mechanical television, one of the first of which was demonstrated by John Logie Baird in October 1925. Interestingly, the Nipkow disc concept is still used today in one variation of a powerful type of optical imaging device called a confocal microscope. Instantaneous transmission of a moving image In 1909, German Ernst Ruhmer invented an early television system (Fig.3). A selenium cell array was used to detect an image and, through a method not fully disclosed, modulated the light intensity of corresponding parts of an array of a display device. The demonstration device had a 5 × 5 array capable only of displaying simple shapes and was incredibly expensive due to the high cost of the selenium cells. Any practical device with, say, 4000 cells would have been unreasonably expensive. This was followed by Frenchmen Georges Rignoux and A. Fournier, who developed a system capable of displaying an 8 × 8 matrix, enough to display letters of the alphabet. It could transmit several full images per second. These were remarkably modern concepts, comparable to today’s imaging devices, albeit at much lower resolutions. The cathode ray tube (CRT) By far the most familiar display siliconchip.com.au Fig.1: how Nipkow discs are used to reproduce images. Fig.2: Australian Henry Sutton’s never-constructed “Telephane” apparatus from 1885; we have only reproduced the transmitter section. From Telegraphic Journal and Electrical Review, November 7th 1890, p550 (https://hdl.handle. net/2027/mdp.39015012327071) Fig.3: Ernst Ruhmer’s early television system from 1909 with a 5 × 5 selenium cell imaging array and 5 × 5 modulated light-receiving array. Source: Literary Digest, September 11th 1909, p385 (https://hdl.handle.net/2027/ mdp.39015031441952) Australia's electronics magazine September 2022  15 Fig.4: making the first commercial colour CRT in 1954. Source: Early Television Museum and Foundation (www.earlytelevision.org) Fig.5: a typical monochrome CRT display with electrostatic deflection plates, as standard in an oscilloscope. Most TVs used magnetic deflection coils on the outside of the neck of the tube instead of interior deflection plates. EHT stands for extremely high tension. There are three electron guns and a shadow mask in a colour display. 16 Silicon Chip Australia's electronics magazine device of the 20th century was the cathode ray tube, widely used to display television images. Cathode rays and some of their properties had been discovered earlier, but German physicist Karl Ferdinand Braun invented the CRT in 1897 (see Fig.7), and he was the first to think that it could be used as a display. Unlike the heated cathode of more modern devices, it used a cold cathode. Here is a brief timeline of the main developments in CRT technology: • 1876: Eugen Goldstein coined the term ‘cathode rays’. • 1897: the Braun tube, the first CRT, was developed as a modified Crookes tube with a phosphor-coated screen. • 1908, 1911: Alan Archibald Campbell-Swinton writes about “distant electric vision” using the Braun CRT. • 1922: John Bertrand Johnson and Harry Weiner Weinhart develop a commercial hot-cathode CRT. • 1926: Kenjiro Takayanagi demonstrates a CRT TV with 40 lines. • 1927: Takayanagi increases the resolution to 100 lines. • 1929: Vladimir K. Zworykin coins the term ‘cathode ray tube’. • 1932: the Radio Corporation of America (RCA) trademarks the term Cathode Ray Tube. • 1930s: Allen B. DuMont made the first CRTs that could last thousands of hours. • 1934: the first CRT TVs are made by Telefunken of Germany. • 1950: RCA releases the term ‘cathode ray tube’ to the public domain. • 1954: the first colour CRTs are made by RCA. • 1957: US Patent 2,795,731 is granted to William Ross Aiken for flatpanel CRTs. • 1958: Aiken is granted another US patent (2,837,691) on a flat-panel CRT. • 1968: the Sony Trinitron flat-faced CRT is introduced. • 1987: CRTs with flat screens are developed for computer monitors. • 1990s: high-definition CRTs are released by Sony. A diagram of a typical CRT is shown in Fig.5. It is a vacuum tube containing an electron gun (cathode or negative electrode) that generates a beam of electrons that can be steered in both the X (horizontal) and Y (vertical) directions. An electron gun contains a filament siliconchip.com.au Fig.6: the geometric arrangement of electron guns and masks to ensure each colour beam strikes the correct phosphor. There were three ways to do this, each an improvement over the last. that heats an electron-emitting cathode. A grid controls the flow of electrons between the cathode and the accelerating anode and thus brightness/intensity. Up to 20kV is applied to the accelerating anode relative to the cathode, causing the electrons to form a narrow beam travelling toward the screen. A second focusing anode maintains the beam focus. After the beam leaves the electron gun assembly (heater, cathode, control grid, accelerating anode and focusing anode), it is deflected or steered to create an image. This is achieved either by coils that create a magnetic field or by electrostatic deflection plates that generate an electric field. Either way, there are two pairs of coils or plates for horizontal and vertical deflection. The electron beam impinges upon the screen coated with a phosphor, emitting light. In the case of a colour screen, there are three electron beams and three different phosphor colours (arranged as dots or stripes), and the electron beam for each colour only strikes its relevant colour of phosphor. To ensure that each beam strikes the correct phosphor, a shadow mask is employed and each colour electron siliconchip.com.au beam is slightly displaced from the others – see Fig.6. Many approaches were tried in colour CRTs to ensure that the electron beam struck the correct colour of phosphor. Still, the shadow mask concept from RCA, introduced in 1950 led them to drop all other lines of colour CRT research as it proved superior. RCA introduced the first colour tube (the 15GP22) commercially in 1954 – see Fig.4. Shadow masks are made by a lithographic process called photochemical machining. The RCA shadow mask concept was the main one used until Sony introduced the aperture grill in 1968, which serves the same purpose as the shadow mask but uses long slots instead of holes or small slots. From the late 1960s, non-Trinitron sets used rectangular phosphors and rectangular holes in the shadow mask, rather than a triad of phosphor dots and round holes in the shadow mask. You might be wondering where all the electrons go after they have struck the phosphors. The inside of the ‘bell’ of the CRT (the part between the neck and the screen) is coated with a graphite-­based electrically conductive layer called Aquadag. This collects the electrons and forms part of the anode. It also helps maintain a uniform electric field inside the tube. The electrical connection to this part of the tube is the large, prominent wire attached to the side of the bell in a cathode ray tube. Electric vs magnetic deflection The arrangement shown in Fig.5 has electrostatic deflection plates as would be used in an oscilloscope. Most TVs (except for a few early types with small tubes) instead use coils that provide a magnetic field. Magnetic deflection coils enable a higher angle of deflection and therefore a shallower tube, as used in TVs Table.1 – the largest commercial CRTs with time Fig.7: the original Braun cold cathode CRT of 1897. From Eugen Nesper, 1921, Handbuch der Drahtlosen Telegraphie und Telephonie, Julius Springer, Berlin, p78 Australia's electronics magazine 1938 51cm/20in diagonal 1955 53cm/21in diagonal 1985 89cm/35in diagonal 1989 110cm/43in diagonal September 2022  17 Fig.8: the magnetic deflection assembly (yoke) from CRT TV. Source: JHCOILS Fig.9: a type of CRT video camera tube called an image orthicon, commonly used in US television broadcasting from 1946 to 1968. and computer monitors – see Fig.8. They also allow a higher beam current for a brighter image. In traditional CRT oscilloscopes (CROs), a shallow tube was not considered necessary because the image was small, so the tube was also small. More importantly, though, the circuitry was simpler because the vertical deflection plates could be driven directly by amplified signal waveforms. Also, the deflection systems could respond faster to high-frequency signals of many megahertz because electrostatic deflection plates only present a small capacitive load, compared to the highly inductive load of magnetic deflection coils. In a TV or computer monitor, an image is built up by scanning line by line, top to bottom, in a so-called raster pattern. This happens so fast that it is not visible. There’s an excellent video that uses high-speed photography to demonstrate how the raster is scanned at https://youtu.be/3BJU2drrtCM By contrast, in an oscilloscope, the beam is instead swept left-to-right repetitively while it is moved up and down according to the applied signal voltage. As well as displaying video and for oscilloscopes, CRT screens were used for radars, heart monitors, and in some cases, a form of computer memory. From their inception to the mid1990s, they were the only practical and common form of video display device in use. LCD screens were commercially available from the early 1990s in laptops, but they performed very poorly compared to CRTs, only catching up in the late 90s/early 2000s. Flat-panel LCD TVs outsold CRT TVs for the first time in 2007, and in the same year, Sony ceased production of its famous Trinitron brand of CRTs. There were many variations of CRTs produced over the years: • Some could retain an image until it was erased, such as in certain oscilloscopes. • There were vector displays that made images using lines drawn pointto-point rather than in a raster pattern. These were used in early computer monitors for computer-aided design (CAD), in some arcade games and in the Vectrex home gaming system. • Projection CRTs formed an image on a distant passive screen. • A data storage tube from the late 1940s known as a Williams tube stored binary data, typically 256-2560 bits. • The much-beloved Magic Eye tuning device was used on certain valve radios from 1935 until the 1960s. Toward the end of the CRT TV era, CRT TVs managed to compete against LCD and plasma TVs for a while. Flatscreen CRTs were made because they were initially so much cheaper to produce. Eventually, the price of the alternative displays dropped, and the bulky and heavy CRTs went out of fashion. Today, Thomas Electronics (www. thomaselectronics.com) still makes and repairs CRTs as replacements for specialised military and aerospace equipment. In these markets, it is often more cost-effective to maintain the old technology than retrofit platforms with new LCDs screens etc. In these cases, the production cost is not a concern as the R&D cost for replacements would be huge. ► Fig.11: a proposed colour flat-panel CRT radar screen by William Aiken in 1957 (https:// patents.google. com/patent/ US2795731A/en). Fig.12: a diagram ► of the Eidophor from the original US Patent (https:// patents.google. com/patent/ US2391451A/en). 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Figs.10(a) & (b): the Pye Mk III image orthicon CRT camera, first sold in 1952 and used for television test transmissions in Australia and to cover the 1956 Melbourne Olympic Games. It was motorised and could be remote-controlled, including focusing, changing lenses, plus tilting and panning with the right attachments. Source: Australian Centre for the Moving Image, siliconchip.au/link/abf9 Some gamers still use CRTs because they can have faster response times than many LCDs, and some people prefer the look of scan lines. Some vintage video games (such as classic arcade games) were designed specifically for viewing on CRTs, and good luck finding a recent LCD television with an S-Video or SCART connector if you want higher resolutions natively. CRTs also correctly display unusual, obsolete resolutions such as 256 × 224 as used by vintage Nintendo systems. The Aiken CRT William Ross Aiken made an early attempt to design a flat-panel CRT with the electron gun to the side rather than at the rear (see Fig.11). He was awarded US Patents for these designs in 1957 and 1958. Unfortunately, there were patent disputes, and development stopped. After the patents expired, the idea was further developed by Sinclair Electronics and RCA. that emits electrons when struck by photons from a light source due to the photoelectric effect. The Eidophor Very few people have heard of the Eidophor video projector. It was invented by Swiss scientist Fritz Fischer in 1939, and a US Patent for it was awarded in 1945 (see Fig.12 and siliconchip.au/link/abf7). Eidophors were used for large-scale public events, movie and video projectors and most famously by NASA in their Mission Operations Control Room during the Apollo missions. NASA used 34 Eidophor projectors from 1965 to 1969 – see Figs.13 & 14. They had a readiness rate of 99.9% despite their complexity. They cost about $85-90 million of today’s money in total. The Eidophor was a large, complex, expensive device to purchase and run but was reliable and gave the best projected video images at the time. They work as follows. A mirrored disc in a vacuum chamber is coated in an oil film about 14µm thick. An electron beam scans the surface of the oil in much the same way as an electron beam in a CRT screen scans the phosphor. The charge imparted into the oil layer causes it to deform due to electrostatic forces. A light beam from a powerful arc lamp shines onto the oilcoated mirror, and the reflected light is projected through an optical system to an image plane via a striped mirror Another type of CRT did not display an image but was used in early television cameras from the 1930s to 1980s. After that, CRT-based video camera tubes were replaced by charge-­ coupled device (CCD) image sensors, introduced to broadcast technology in 1984, followed by CMOS sensors (a development of CCDs). The principle of a CRT video camera tube is that a cathode ray is scanned across an image created by a photocathode. The returning cathode ray is modulated according to the intensity of the image created by the photocathode – see Figs.9 & 10. A photocathode is a light-sensitive compound siliconchip.com.au ► The CRT as a camera Fig.13: an Eidophor model EP 6 without its covers, of the type used by NASA in the Mission Operations Control Room during the Apollo era and beyond. Source: Swiss National Museum Fig.14: an Eidophor image (centre) at Mission Operations Control Room, Houston, during the mission of Apollo 11 on July 22nd 1969. Source: NASA, Image id=S69-39815 Australia's electronics magazine September 2022  19 Fig.15: the optical path of Eidophor. Original source: www.ngzh.ch/media/njb/ Neujahrsblatt_NGZH_1961.pdf (or similar arrangement) – see Fig.15. The deflection of the light beam to create the image is generated by optical diffraction or refraction of light as it passes through the thin oil film of varying thickness. The light projected onto the oilcoated mirror came via a slotted mirror with alternating transparent and mirrored stripes. The result is that light reflecting off the primary mirror in areas not impinged by the electron beam reflects back onto the slots and is blocked, while regions where the oil is perturbed cause the reflected light to miss the slots and pass through onto the projection screen. So the projection screen remains dark in areas where the electron beam is cut off and is brighter the higher the intensity of the electron beam in that area. For parts of the screen that are not fully light or dark, some light is reflected and is blocked, while some light makes it to the projection screen. This enables a gradation of intensity levels to generate the image, as shown in Fig.16. To remove an already-projected image from the oil in preparation for the next one, the mirrored disc is rotated to an electrode that neutralises the charge of the oil molecules, smooths the surface and resets it in preparation for the next image. Early Eidophors were monochrome, while later versions could project colour images using a colour wheel Fig.16: the function of the Eidophor’s striped mirror. (A) The light is reflected back with no image, and no light goes to the image plane. (B) With a strong image, all light goes through the transparent stripes and is projected to the image plane. (C) With a weak image, some light is blocked, but not all. Original source: www.ngzh.ch/media/njb/Neujahrsblatt_NGZH_1961.pdf 20 Silicon Chip Australia's electronics magazine or three projectors with colour filters. There is a fascinating video on Eidophors from 1944 with English subtitles named “Eidophor: Die bildspendende Flüssigkeit (1944)” at https://youtu. be/w_9NhiGeklI NASA Apollo display screens Many people have wondered how NASA set up the giant screen displays at the Mission Operations Control Room (“Mission Control”) at Johnson Space Center in Houston, Texas, during the Apollo moon landings, shown in Figs.17 & 18. Little has been documented about the technology used. These were possibly the first large video displays many people would have seen at the time and one of the first, if not the first, large-scale video displays. So how did they work? NASA used both graphic slide projectors and Eidophor video projectors. We already described how Eidophors worked, so that leaves the very special graphic slide projectors. YouTuber Fran Blanche has heavily researched these projectors. We highly recommend watching her excellent video titled “How Mission Control’s Big Displays Worked” at https:// youtu.be/N2v4kH_PsN8 According to that video, this system was in use until 1989. Graphic slide projectors displayed Earth and Moon maps, pages from manuals and any other material that could be stored siliconchip.com.au ► Fig.17: an Apollo-era image of NASA’s Mission Operations Control Room (“Mission Control”), showing the large screen displays. There were two 10 × 10ft (3 × 3m) screens on the left and right, plus a 20 × 10ft (6 × 3m) screen in the middle. An Eidophor video image can be seen on the far right, with graphic images in the middle and right. We are not sure about the two left-most images. Fig.18: the large display screens at the front of Apollo-era NASA Mission Control in the late 1960s and early 1970s. This view is from the Visitors Viewing Area to the rear of the Mission Operations Control Room. Source: NASA (www. nasa.gov/sites/default/files/atoms/files/apollo_mcc_press_release.pdf) on projector slides. The appropriate slides could be selected, under computer control, from those stored in a carousel – see Fig.19. The projectors needed to project images clearly under the bright lighting of Mission Control. This meant extremely powerful illumination was required; the heat would destroy traditional slides made of polyester. Glass slides with the images in metal coatings were therefore used. The metal was either absent, letting all the light through, or present and opaque with no gradation, much like copper on a PCB. Colours were generated using colour filters, and multiple slides could be superimposed on each other from multiple projectors. The ability to superimpose slides was important. Illustrated display shows geographical location of a spacecraft. World map is used as background reference with actual and predicted orbital paths plotted against latitude and longitude Optical fold mirror Rear projection viewing screen Projectio n plotting contro electronicsl Control el ec inputs an tronics associated d projectors convert them to p with each project or decod rop to respon e digital Plott d (chang ortionate analog e slides, Slide-acc ing data start plott voltages that cau ess com se mands ing) as re quested lay ce isp rfa r d l inte m e t u ro te mp nt sys Co / co sub Consoles operator closes selector switches to request background display and type of information to be plotted on display Plotting information from remote tracking stations PDSDD Requests go to computer display/ control interface subsystem, which changes requests to digital codes and routes them to RTCC RTCC RTCC accepts coded requests and releases data and slide-access commands to plotting display subchannel data distributor(PDSDD) for distribution to projection plotting control electronics Fig.19: how the Apollo era graphic projection system worked at NASA Mission Control. The equipment was located behind the Mission Control room (called The Pit) and in the Summary Display Projection Room or “Bat Cave”. The Eidophor video projectors are not shown in this diagram. siliconchip.com.au Australia's electronics magazine September 2022  21 Fig.20: an image showing a background map of the moon, a trajectory line, icons for orbital (command module) and landing (LEM) vehicles, plus other icons labelled 1 through 5, presumably corresponding to various landing events. It was made from multiple slides on multiple projectors and the colours were generated by colour filters. That was fine for static images, but how were real-time plots or orbital and trajectory data added? The orbital and trajectory data was generated by IBM 360 System 75 mainframe computers (see https://w. wiki/59xB). They received telemetry data and translated it into plots that could be displayed in real-time. Special charting projectors took the data from the computer. They plotted it using a diamond or similar stylus on an X/Y plotter, inscribing it into a ‘blank’ (fully metallised) slide, scratching a line in the metal. Previously plotted data stayed until a new blank slide was inserted – see Fig.20. Icons like spacecraft were also moved under computer control to show the actual position of the spacecraft. NASA has restored the original Apollo Mission Operations Control Room, which was in use until 1992, back to its original condition; see siliconchip.au/link/abf8 Sinclair TV80 / FTV1 Pocket TV Sinclair released the TV80 (also known as the FTV1) Pocket TV in 1983. It employed an electrostatically deflected CRT with a side-mounted electron gun along the lines of the Aiken CRT above – see Figs.21 & 22. It was a commercial failure, partly due to similar products being released by Sony (the “Watchman”) with other manufacturers using CRTs and later LCDs. The Seiko LCD T001 TV Watch was released in 1982, and the Casio LCD Pocket Television TV-10 (Fig.23) in 1983. For more on the TV80, see the videos titled “Doom on 1983 Sinclair FTV1 TV80 Mini Flat CRT & Teardown” at https://youtu.be/fEcs52lAI3E and Australian David L. Jones’ “EEVblog #554 – Sinclair FTV1 TV80 Flat Screen Pocket TV Teardown” at https://youtu. be/qCJPF6Ei3Vw Plasma displays Plasma displays were the first-flat panel displays over 80cm/32in diagonal and were the first to take over from CRT displays, at least for larger sizes. By 2013, they were surpassed by LCD screens. Plasma displays are now considered obsolete and have mostly been replaced in the market by OLED displays. Hungarian engineer Kálmán Tihanyi first proposed a plasma display in 1936. The first prototype plasma display was invented at the University of Illinois in 1964 by Donald Bitzer, Gene Relevant links ● The Cathode Ray Tube site: www.crtsite.com ● Picture tubes used to be rebuilt. This video is a look at the last picture tube rebuilder in the USA, titled “The Craft of Picture Tube Rebuilding” at https://youtu.be/W3G7b-DcOO4 ● The 8-bit Guy talks about modifying a consumer CRT TV to have RGB inputs for vintage games and using vintage computers in a video titled “Modding a consumer TV to use RGB input” at https://youtu.be/DLz6pgvsZ_I ● THE LAST SCAN – Inside the desperate fight to keep old TVs alive: www.theverge.com/2018/2/6/16973914/tvscrt-restoration-led-gaming-vintage ● A fascinating experiment you can do with a monochrome plasma panel: https://youtu.be/Oj4tRnLKN6U ● “vintageTek Demo of a 1930’s 905 CRT” – https://youtu.be/NBeOMsdPuT8 ● “The Cathode Ray Tube how it works 1943 16mm U.S. military training film” – https://youtu.be/GnZSopHjmYQ ● “Mullard Made for Life Vintage Documentary” – https://youtu.be/32yYfTVIzBE ● “Building A Tektronix Ceramic CRT 1967” – https://youtu.be/G0Dci5RPe94 22 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.21: a Sinclair flat-screen TV80 CRT TV. Source: Wikimedia user Binarysequence, CC BY-SA 3.0 Fig.22: the Sinclair TV80 PCB, with the CRT viewing area at left & electron gun assembly to its right. Source: Wikimedia user Binarysequence, CC BY-SA 3.0 Slottow and Robert Willson. Still, it consisted of only one pixel, so it was of no practical use. It was many more years before the first useful plasma display was developed. By 1972, Owens-Illinois Inc was selling a line of monochrome plasma computer monitors or display assemblies with resolutions up to 512 × 512 pixels – see Fig.24. The advantages of these units were that they were flat, flicker and drift-free, were all-digital and had minimal memory requirements as the display didn’t require constant refreshing like CRTs. Low memory utilisation was significant when memory was extremely expensive, and every byte saved counted. These displays were costly, up to US$2500 for the 512 × 512 unit. They lost popularity by the late 1970s as Fig.24: an advertisement for the first commercial plasma displays from 1972. Source: siliconchip.au/link/abfa Fig.23: the Casio TV-10 LCD pocket TV, released the same year as the CRT-based Sinclair TV80. siliconchip.com.au Australia's electronics magazine September 2022  23 memory became cheaper, making CRT monitors more attractive, even if they weren’t flat. In 1983, IBM produced a 19in (48cm) monochrome plasma panel, the model 3290 “information panel” that could simultaneously display four IBM 3270 terminal sessions. IBM planned to shut down their plant in 1987, but it was bought by Larry Weber, Stephen Globus and James Kehoe, who started a new company, Plasmaco. Plasmaco was subsequently acquired by Matsushita (Panasonic) in 1996 and no longer researches or manufactures plasma displays. In 1992, Fujitsu introduced the first 21in (53cm) full-colour plasma display. Fujitsu sold the first commercial Fig.25: one cell of a plasma display. Each pixel has three cells, each with one primary colour of phosphor, filled with noble gases and a small amount of mercury. The plasma discharge causes the UV light emission from the mercury, converted to visible light by the phosphor. The front electrodes are transparent conductors such as indium tin oxide. Dielectric layer Display electrodes (inside the dielectric layer) Magnesium oxide coating Rear plate gkass Dielectric layer Address electrode Pixel Front plate glass Phosphor coating in plasma cells A schematic matrix electrode configuration in an AC PDP Fig.26: a plasma display panel showing a pixel (picture element) comprised of three cells and the vertical and horizontal electrodes to address each cell. Source: Jari Laamanen, Free Art License 1.3 24 Silicon Chip Australia's electronics magazine colour plasma TV in the USA in 1997. It was 42in (107cm) diagonally with a resolution of 852 × 480 pixels and cost US$14,999. By the 2000s, prices of similar displays had dropped to around US$10,000. Panasonic demonstrated the largest plasma display at 150in/3.8m diagonal in 2008; it was 1.8m tall and 3.3m wide. By 2006, LCDs TVs were outselling plasmas. In 2013, Panasonic stopped producing plasma displays, followed by LG and Samsung in 2014. Plasma displays work much like a fluorescent light bulb. There is an electrical discharge into an inert low-­pressure gas containing a small amount of mercury. The mercury releases ultraviolet light, which then strikes a phosphor that emits visible light corresponding to the colour of the phosphor. Each pixel of a plasma display is made of three cells, one for each primary colour. One plasma display cell is shown in Fig.25, while a display assembly is shown in Fig.26. The gas pressure inside each cell is about 0.66bar (2/3 atmospheric pressure) with a minuscule amount of mercury inside. A typical driving voltage is around 300V. The voltage does not vary to change the cell intensity; instead, it is switched on and off many times per second using pulse-width modulation (PWM). ALiS ALiS (alternate lighting of surfaces) was a plasma display technology developed by Fujitsu and Hitachi in 1999 to enable lower-resolution displays to provide a higher apparent resolution. Instead of a progressive scan as per a regular plasma display, in which all pixels are illuminated every frame, it illuminated alternating lines for interlaced scanning. Thus, a 720-line panel could display an apparent resolution of 1080i. The picture of such a screen was also said to be brighter with lower power consumption. Next month Part two next month will pick up where this one left off, with LCDs taking over the display market in the mid-2000s. We will also cover the latest and upcoming display technology, such as OLEDs and high dynamic range (HDR) screens. SC siliconchip.com.au