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Liquid-crystal display: too impractical

Like every readout that preceded it, the liquid-crystal display had some severe drawbacks. The earliest digital displays were very crude, but when engineers wanted information as a number, as opposed to a needle position on a scale, they had to devise some way to display numeric digits. One of the earliest instrument displays, the columnar display, often called the thermometer readout, had columns of 10 holes punched in a front panel with a panel lamp behind each hole. A lamp selected in each column would illuminate a number. That had two disadvantages. First, your eye often had to shift up and down across columns to read a number. For example, to read 9284 your eye moved toward the top of the first column, then toward the bottom of the second column, then up, then down again. The second disadvantage: A column of 10 holes demanded a rather tall front panel. In early vacuum-tube instruments, crowded with lots of discrete components and a hefty power transformer, the height wasn't always a problem. In one instrument, Hewlett-Packard reduced the height somewhat by offsetting alternate numbers in a column. The 1 would be above and slightly to the right of the 0, the 3 similarly offset above the 2, and so on, to reduce panel height.

In time, a wide assortment of readouts replaced the columnar display. Non-Linear Systems offered the world's first commercial digital voltmeter in 1953. The display used stacks of 10 Lucite plates, almost an inch deep, each bearing an engraved numeral and a tiny edge-mounted panel lamp. When a lamp was selected, its numeral was clearly visible from the front but not from a sharp angle. That edge-lit display offered one advantage over the columnar display:

It was an in-line display all digits were in a single line. But it was not an in-plane display because nine digits were behind the front one.

In-plane pioneer

It was left to Industrial Electronic Engineers to develop the first in-plane display. It was a projection readout, in which one of 10 tiny lamps would be selected to shine through one numeral on a film with 10 numerals, projecting that numeral onto a front screen, often in focus, making for an in-line, in-plane display.

Sylvania and Westinghouse offered electroluminescent displays whose characters, numeric or alphanumeric, were not only in-line and in-plane but integrated in a panel with desired legends. The problem with those early EL displays was that one could maximize brightness and contrast by increasing voltage and frequency, which, unfortunately, decreased display life. So it was not uncommon for engineers in a lab, after perhaps several hundred hours, to place a cardboard light shield around an instrument's EL display to boost contrast. Later, they might dim the lab lights.

A Japanese company, Ise Electronics, sold vacuum-tube fluorescent-segment displays (VFD), mostly used in Japanese desktop calculators.

At one point, RCA, with its fondness for vacuum tubes, introduced an incandescent seven-filament display, the Numitron, in a vacuum-tube housing. The filaments were arranged in a boxy figure 8, so that selecting the right filaments could yield any digit. The 1 was not centered, so there would be an awkward space in front of it and it would hug the following numeral. Nevertheless, this was indeed an in-line, in-plane display. But eventually the filaments sagged, so horizontal bars, which were illuminated in all numerals except 1, seemed to call for an uplift.

So each display had merits and drawbacks and they competed in the marketplace, sometimes on largely subjective grounds. For example, some people objected to the boxlike numerals on seven-bar displays.

Then along came the Burroughs readout. It used gas-discharge tubes called Nixies. These tubes, invented by two Haydu brothers, who sold their company to Burroughs, had a stack of formed-wire numerals, each on an almost invisible supporting structure. A selected numeral would shine with a neon glow.

Though the Nixie required a high-voltage supply of at least 170 Vdc, a numeral could be switched on with as little as 20 V. The tube consumed no more than about a watt and, despite the fact that numerals were stacked and not in-line, the Nixie soon took over most digital-display applications. Until the light-emitting-diode display came along in the mid-1960s, virtually every digital instrument adopted the Nixie. It cost about $10 at first, but the cost per digit soon plummeted.

Nixie drawback

The Nixie had a different drawback. To extend life, it required a drop of mercury and that kept it off submarines and other confined applications where mercury vapors were considered hazardous.

The LED display had a modest beginning with Monsanto's MAN-1A (for Monsanto alphanumeric). This was a seven-segment numeric display comprising 14 discrete gallium arsenide phosphide chips mounted on a substrate, two chips to a segment. The alphanumeric designation was a bit optimistic because it was based on the fact that several numerics looked like alpha characters. For example, the 5 could be used as an S and a zero could be construed as the letter O.

Then Hewlett-Packard introduced a truly alphanumeric LED display: a 5 x 7 matrix made up of 28 dots with an on-board binary-coded-decimal decoder-driver. Both Monsanto and HP were merchant suppliers of LED displays and both produced test equipment with LED displays.

LED displays began invading territory that was almost the private property of the Burroughs Nixie. Then came the explosion: calculators, especially hand-held battery-operated calculators in the early 1970s. LED displays were now a really serious business, driven at first by calculators, then by digital wristwatches. So it wasn't long before many semiconductor manufacturers joined the fray, including Texas Instruments, Motorola, Fairchild, National Semiconductor and a Monsanto spin-off, Litronix (which was later acquired by Siemens).

901B.jpg (35873 Byte)Many semiconductor companies, worshipping the concept of vertical integration, started manufacturing calculators, then wristwatches. Watch manufacturers warned that this was a jewelry business, a business in which the semiconductor companies had a vast supply of ignorance. The semi companies brushed aside those quibbles, then almost drowned in red ink. Nevertheless, LED displays were on their way to dominating the world. And they might have if it hadn't been for some work going on at RCA Laboratories.

The parent lab

That laboratory fathered many of the industry's breakthroughs, including the MOS FET, CMOS, thin-film transistors, silicon on insulator and the liquid-crystal display.

The parent of the liquid-crystal display, Richard Williams, was a physical chemist and, like others at RCA, his dream may have focused on wall-mount television. But one starts small. In fact, liquid crystals were discovered as far back as 1888, but it was Williams who created a display-a thin layer of between two glass plates with transparent conductive coatings on their inner faces. He filed a patent, "Electro-Optical Elements Utilizing an Organic Nematic Compound," in 1962 and his seminal articles on nematic (threadlike) liquid crystals appeared in 1963 in The Journal of Chemical Physics and in Nature.

Developing that seminal display took a lot of work to find organic materials that would refract light under different temperature conditions and with satisfactory response times when a voltage was applied to the conductive coatings. Most work on liquid crystals took place at pharmaceutical companies, mainly Merck and Hoffman LaRoche, not at electronics companies.

Although most people in electronics never heard of liquid crystals, Williams recalls, it took an electronics company to make a decent thin layer of conductive film that you could see through.

Group development

A co-worker at RCA Labs, George Heilmeier, put together a group to develop Williams' work further. By the fall of 1964, Heilmeier's group had developed rudimentary displays that could change color with applied voltage. Most important, power consumption was minuscule, a microwatt per square centimeter. The wall-sized, flat-panel color TV, Heilmeier mused, was just around the corner.

The flat-panel color TV did not appear just yet. But after lots of toil with different liquid crystals, Heilmeier's group found materials with a turbulent property they dubbed dynamic scattering. An applied voltage would change the appearance from transparent to a light-scattering milky white.

From that point, it was no longer a giant step to deposit a layer of conductive film with images or characters and with conductors going to the outside world so that individual characters or segments of a numeric or alphanumeric display could be selected. Here was a new business for RCA (and for spin-offs like Optel and others) and perhaps one small step toward that wall-panel TV.

el-805s.jpg (35671 Byte)The LCD was a dramatic display, unlike any other. It had a powerful advantage: It consumed almost no power, so it was ideal for applications like handheld digital watches and calculators. (In May 1973, Japan's Sharp Corp. released the EL-805, the first handheld calculator with an LCD display. Battery consumption, said Sharp, was cut to 1/100th of that in earlier calculators.)

Of course, the LCD had an ample supply of detractors. Its limitations, they pointed out, were many and perhaps fatal. Unlike any previous display, it generated no light; it merely refracted ambient light so it could not be seen in the dark. (Perhaps overlooked was the fact that most people do not look at displays in the dark.) Further, the display failed and often died if it was subjected to cold. And it was slow. One could observe the slow transition from one number to another when the voltage applied to a DVM was changed.

Further developments improved the LCD so that its drawbacks were eliminated. In digital watches, it replaced power-hungry LEDs. And it replaced almost all other displays in battery-operated appliances.

As to the future, consider this. Whoever heard of a laptop-computer display in the 1970s and 1980s?

Reprinted from EETIMES with written permission of the author George Rostky.

 

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If you have additions to the above article please email: joerg@datamath.org.

Joerg Woerner, October 21, 2002. No reprints without written permission.