Display technologies continue to march forward, with LCDs, LED displays, organic LEDs (OLEDs), and electrophoretic displays (EPDs) leading the charge. LEDs and OLEDs may even overtake LCDs for some applications, while EPDs carve out a niche in electronic-ink displays for portable and flexible electronic products. Nonetheless, LCD applications are flourishing and becoming more diverse, requiring equally diverse design challenges to meet different performance requirements.
NEC Electronics America foresees important industrial and medical applications that require innovative approaches to satisfy various demands. Topping the list are the needs for portability, low power consumption, ruggedness, energy efficiency, environmental friendliness, and the ability to operate in variable lighting conditions both indoors and outdoors.
LCDs are still used in all kinds of products, large and small, despite a downward revision of market size as price erosions affect profits. For example, LCD 14-, 15.4-, 7-, 19-, 22-, 32-, and 42-in. panels are reportedly being sold at cost and sometimes at a loss. Despite this, LCD TV shipments are expected to rise 20% this year, up from 18.9% last year.
POWERING DOWN • Two major trends permeating the display industry are lower power consumption and greener LCD panels. For instance, NEC’s use of LED backlighting offers distinct advantages over cold-cathode fluorescent lamps (CCFLs). It addresses the needs for low-voltage and low-power operation, as well as low electromagneticinterference (EMI) levels. Also, it eliminates the need for an inverter; reduces thickness and weight; increases reliability; and lowers the risk of damage due to vibration and shock.
For indoor and outdoor environments, NEC incorporates two proprietary transflective LCD technologies: super-reflective and super-transmissive natural light technology (SR-NLT and ST-NLT, respectively). SR-NLT is based on transflective (semi-transmissive) technology with both transmissive and reflective characteristics, allowing users to change backlight modes on and off in response to changes in the outdoor lighting environment. ST-NLT is transmissive and can produce high-contrast images even in bright outdoor light.
According to NXP Semiconductors, adaptive smart-LED backlight dimming for LCD screens can be used to calculate the brightness level for each LED to satisfy different lighting requirements. This saves power and increases contrast ratio.
LCDs are now finding use in outdoor displays. Targeting these applications, Samsung’s 70-in. diagonal “super bright” LCD digital signage panel boasts a 1500-nit output, which the company calls the brightest such panel to date. The key is the use of local dimming of backlighting LEDs that continually adjust picture brightness in very precise increments.
By doing so, the technology doesn’t have to brighten areas that don’t require it. It increases the panel’s dynamic contrast ratio up to 200,000:1, too. Separately, Samsung says it has also developed the first “blue phase” LCD panel, which achieves 240-Hz driving speed for high-speed video.
Increasing an LCD’s efficiency is another way of cutting power consumption. A new design from Fairchild Semiconductor reduces the traditional four layers of printed-circuit boards (PCBs) used in a thin-film-transistor (TFT) LCD down to two, using highly integrated Fairchild FAN5069 and n-channel MOSFETs. The result is 90% efficiency.
Researchers at Scotland’s University of Strathclyde developed a reflective bi-stable LCD that can maintain static images in full daylight without using an external power supply. The scientists are looking to license this technology for solarpower display advertisements, mobile phones, PDAs, ATMs, electronic paper, smart cards, and disposable displays.
Thinner LCDs are also in the offing. Philips Research Labs developed a prototype lightweight (10-kg), 32-in. LCD TV that’s just 8 mm thick—about 20% the thickness of the slimmest commercially available panels. The key is a 1-mm thick light-guide plate that distributes light from highpower LED backlights.
Two competitive approaches to LCDs, using shutters and LED light sources to boost performance and lower cost, are being tried as well. Both exploit MEMS technology and existing TFT fabrication techniques.
One such approach is Pixtronix’s digital MEMS micro-shutter technology to produce the PerfectLight display, which uses a TFT backplane. The company says it consumes 75% less power than a traditional LCD panel while delivering exceptional image quality that’s 105% the National Television System Committee (NTSC) color gamut with 24-bit depth, a 1000:1 contrast ratio, and a 170° viewing angle.
A time-multiplexed optical shutter (TMOS) technology being developed by Uni-pixel also utilizes MEMS technology and LED light sources. It promises to deliver brighter, thinner, and less expensive LCDs via a light guide with TFTs and a special micro-optical MEMS layer (called the Opcuity active layer) to boost brightness and efficiency levels and reduce the display’s thickness (Fig. 1).
LEDS FINDING NEW APPS • Another hot area for LEDs involves energy savings, with designers using discrete LEDs in red, orange, blue, and green as well as high-power white sources for greater operating efficiencies and lower power consumption. According to ElectroniCast Consultants, LEDs used in residential and commercial/government exterior lighting represented an 86% share of worldwide consumption of solid-state illumination last year. Although that will drop to 67% this year, it will increase in value to $631.68 million in 2012.
Ruediger Mueller, CEO of Osram Opto Semiconductors, estimates that 19% of worldwide electricity goes toward lighting and that LEDs can help reduce light energy consumption by 30%. That figure can rise to 50% by adding more intelligence to the LED.
Continue to page 2
Reprints
