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Maxed Out: Next-Generation Displays (Part 1)
October 7, 2009 |Estimated reading time: 5 minutes
For many decades, cathode ray tube (CRT)-based computer monitors were the only game in town. But things don't stay the same forever; new display technologies are emerging all the time, and there are some mega-exciting possibilities for the future...
Liquid Crystal Displays (LCDs)In the early 1990s, a number of different companies started experimenting with substances known as liquid crystals (LCs); eventually, liquid crystal displays (LCDs) became available to the market. As usual, the easiest way of summarizing how these things work is by means of a high-level diagram. See Figure 1.
Figure 1. High-level representation of a single pixel in a liquid crystal display.
The key point about liquid crystals (at least from our perspective) is that - by default - they will arrange themselves into a tight (twisted) helix pattern, in which case they will block the passage of light. However, if we apply current to the liquid crystals, they will "untwist" to the extent that they will pass light. Varying the amount of current will affect the amount of light that is being passed.
The illustration above reflects a cutaway portion of the screen showing the tiny red, green, and blue filters forming a single pixel. Each of these filters has a bunch of liquid crystals associated with it, and each of these bunches has an associated transistor (these transistors are not shown here for reasons of simplicity).
Behind all of the crystals is a backlight formed from some source of white light. When individual transistors are turned on, they will activate their corresponding bunch of liquid crystals, which will transmit the light into their associated filter. It's possible to control the bunches of crystals in 256 increments which we might number from 0 to 255; 0 means the crystals are twisted and won't pass any light; 255 means that the crystals are sufficiently untwisted that they will pass the maximum amount of light they can; and the other values correspond to the crystals passing lesser or greater amounts of light.
The great advantage of LCDs over CRT-based displays is that they are very thin, very light, and very flat. Having said this, CRT-based displays still have an advantage in terms of the brightness, contrast, and "vibrancy" of the images that can be achieved. If only there were some other technologies.
Plasma Display Panels (PDPs)You may have seen flat-panel plasma displays at television stores. These displays offer bright, crisp, high-contrast images. In this case, we can think of each pixel as being formed from three tiny fluorescent lights (like microscopic neon tubes). By one mechanism or another, these three tiny neon tubes can be coerced into generating red, green, and blue light, each of which can be controlled to form the final color coming out of that pixel.
Plasma displays are fantastic when it comes to presenting ever-moving images such as films. However, if they are instructed to present the same image over and over again, they suffer from "burn-in" effects that leave "ghost" images on the screen. This means that plasma-based technologies do not make an ideal display for computer applications (although there are always some folks who will try to do so).
Organic Light-Emitting Diodes (OLEDs)These are devices that are formed from thin films of organic molecules that generate light when stimulated by electricity. OLED-based displays hold the promise of providing bright and crisp images while using significantly less power than liquid crystal displays.
At some stage in the future, it may be possible to use OLEDs to create displays that are only a few millimeters thick and are two meters wide (or more); these displays would consume very little power compared to other technologies, and in some cases the display could be rolled up and stored away when it wasn't in use. (OLEDs can be "printed" onto flexible plastic substrates.)
But despite some very exciting "proof-of-concept" demonstrations, this technology isn't ready for "prime time" usage just yet. OLED-based displays are sometimes used for small-screen applications such as cell phones and digital cameras, but their widespread use for applications like large screen computer displays may not come for another five or 10 years at the time of this writing. In fact, they may not make it at all if the SED technology discussed below fulfills its promise.
Surface Emission Displays (SEDs)This is where things start to get very exciting. In the late 1980s, scientists discovered tiny structures called carbon nanotubes. Such nanotubes can be incredibly small, with a diameter only one thousandth of one millionth of a meter. Furthermore, they are stronger than steel, have excellent thermal stability, and are tremendous conductors of heat and electricity.
In addition to functioning as wires, nanotubes can be persuaded to act as transistors. Of particular interest to us here is that they can also be coerced into emitting streams of electrons out of one end. Hmmm, tiny little electron guns; what wonders could we perform with these little rapscallions?
Figure 2. High-level representation of a single pixel in a surface emission display.
Well, imagine a screen that is thin and flat like an LCD, but is as bright and vibrant as a CRT-based display. Well, that's what you end up with if the screen is formed from a carbon nanotube-based surface emission display (SED). In this case, the inside of the screen is covered with red, green, and blue phosphor dots (one of each to form each pixel), and each if these dots has its own carbon nanotube electron gun.
Toshiba hosted the first public demonstration of a large-scale carbon nanotube-based SED at the consumer electronics show (CES) in January 2006. Originally it was predicted that we would be seeing SEDs on the streets toward the end of 2006 and the beginning of 2007. As of the time of this writing, however, this technology has still not been widely deployed. However, many of the issues holding it back have been resolved, so I for one live in hopes that these displays will one day take center stage.
Next Time...
In this discussion, we assumed pixels were formed from three primary colors (red, green, and blue, or RGB for short). This is certainly the way things are usually done, but there have been some interesting experiments with displays based on six primary colors.
About the author
Clive (Max) Maxfield is the author and co author of a number of books, including Bebop to the Boolean Boogie (An Unconventional Guide to Electronics) and How Computers Do Math featuring the pedagogical and phantasmagorical virtual DIY Calculator. This article was abstracted from an ongoing and evergrowing paper on color vision from the author's Web site at www.DIYCalculator.com.