Electronic Design

Get Sharper Pictures And Lower Prices In 2007

The hottest new displays are everywhere, from desktop computers to supermarket aisles to home theaters to cell phones. And this year, their growth will only continue—particularly high-brightness LED displays and organic LED (OLED) displays—due to increases in performance and decreases in cost.

Flat-panel TV prices using LCDs and plasma-display panels (PDPs) continue to fall thanks to an ongoing capacity expansion by top-tier flat-panel display (FPD) makers like Samsung, LG, Philips, AU Optronics, and Sony. FPD TV prices have been cut in half over the last two years, and they keep dropping.

A 50-in. LCD TV now costs less than $1200. A 50-in. PDP TV also can be had for under $1200. Even high-definition rear-projection TVs, which have larger screen sizes and use microdisplays like digital micromirrors, have come down in price, though the largest sales are in LCD and PDP TVs. A 60-in. rear-projection TV now goes for about $2000, while a 55-in. model costs about $1500.

These prices reflect the lowest-cost models at major retail outlets and can be about $1000 or more higher with advanced features. Still, the demand for large-screen LCD TVs will increase this year, followed by large-screen PDP TVs. The future of rear-projection TVs is uncertain, though many industry analysts expect them to gain further market share.

Microdisplays for digital cameras, camcorders, and personal communications products represent key LCD applications. Displaytech’s LightView ferroelectric liquid crystal on silicon (FLCOS) microdisplays leverage the fast switching speeds and optical qualities of FLCOS technology to deliver full-color images that are free of motion smearing (Fig. 1). VGA (640 by 480 pixels), WVGA (852 by 480 pixels), and SVGA (800 by 600 pixels) formats are available on respective active-area diagonals of 9.2, 11.25, and 11.5 mm.

LCD technology also has invaded touchpanel displays. Samsung Electronics has developed the world’s first mobile display driver IC that combines the display driver and readout functions for touch-sensor-embedded display panels. The IC enables the active-matrix LCD (AMLCD) itself to be touch-sensitive.

This eliminates the need for an extra touchscreen panel layer by using a touch-sensitive sensor in the pixel. It also raises light transmissivity, improves brightness, and provides sharper on-screen images. The IC senses either charge or current signals from the thin-film transistor (TFT) sensor array and converts them into data appropriate for image processing for detection of the touched location.

LEDs Light Up The Market
Improvements in efficiency and thermal management are opening LEDs up to applications where they can replace other light sources on a large scale. These developments have largely mitigated the inverse relationship between higher brightness levels and longer lifetimes with lower efficiency and the need to remove more wasted heat. It won’t be surprising to see more LEDs than neons on the Las Vegas strip in the near future.

In fact, LEDs are lighting many more building facades, stadiums, and other large structures, especially newer buildings. They’re also penetrating automotive applications for front-panel lighting as well as rear-brake and headlight lamps, and they’re in almost every traffic signal as well. And LEDs are about to become part of one of the fastest growing categories of consumer electronics—backlighting for flat-panel and rear-projection TVs and mobile phones.

An important segment is high-brightness (HB) white LEDs and even ultra-high-brightness (UHB) LEDs for general office and home illumination, a market that’s expected to grow to over $9.1 billion through 2011 (Fig. 2). In fact, Cree Inc. has achieved a 160-lumen output for a white LED using an indium-gallium-nitride layer on a silicon-carbide wafer.

In the lab, LED performance continues to improve. Philips Lumileds Lighting Co. has come up with a hybrid manufacturing approach using both thin-film and flip-chip techniques. It enables LEDs that outperform units by using either technique alone, in terms of output power and higher brightness levels. Also, the U.S. National Institute of Standards and Technology (NIST) has developed semiconductor LEDs that are more than seven times brighter by etching nanoscale grooves in a surrounding cavity to guide scattered light in one direction.

Here Come OLEDs
OLEDs are another contender for general illumination. White-light OLEDs are the main focus of R&D efforts at OSRAM Opto Semiconductor, which also is pursuing work on OLEDs in a variety of other colors (Fig. 3). Initial research by OSRAM indicates a luminous efficacy for white OLEDs of up to 25 lm/W with an appropriate current. Even at 18 lm/W, they’re more than competitive with the 12 lm/W of conventional light bulbs. And, they’re now nearly on par in brightness levels with the 20 to 26 lm/W of halogen lamps.

Look for major advances in addressing OLED displays that allow for low-cost and low-power dissipation for large-screen sizes. Passive-matrix addressing, which offers lower costs and low power dissipation, has been the norm but has been limited mainly for small displays. Active-matrix addressing, on the other hand, can be used for larger displays but is more costly and dissipates more power.

Now comes a development from Cambridge Display Technology called total matrix addressing, which blends the best characteristics of both passive and active matrix addressing at little or no penalty. CDT, a holder of a large portfolio of OLED patents, is working on bringing the technology to market.

CDT has always contributed to OLED technology by producing light-emitting blue polymers with lifetimes of 25,000 hours from an initial luminance of 400 cd/m2, which is equivalent to 400,000 hours from 10 cd/m2. This is a milestone that further enhances the company’s polymer OLEDs (P-OLEDs), since the production of video-capable OLED displays requires a full range of red, green, and blue colors with long lifetimes and good efficiency.

Other major OLED manufacturers like Universal Display Corp. and Novaled GmbH have reported OLED advances in terms of light output levels and better efficiencies. These developments indicate OLEDs may become a major competitor for LEDs, for both small and large displays, at least in certain applications. Whether or not OLEDs will steal LED’s thunder remains to be seen, but many analysts believe it may happen.

Brighter, Clearer Images At Less Power
In displays of all types—TVs, cell phones, video games, and a slew of handhelds—there’s a growing demand for brighter and clearer images while reducing power dissipation levels. This may seem contradictory, since you need to drive displays harder with more current to get brighter levels.

Clairvoyante Technology has solved this problem with its PenTile technology, which is rapidly being used in a number of applications (see “New-Generation Mobile Devices Will Need Optimized Displays.”)

PenTile technology works by adding a white subpixel to the traditional RGB stripe layout of red, green, and blue. It then applies proprietary subpixel rendering technology to better align those subpixels with the way that humans see images. This ensures that display power and brightness resources aren’t wasted rendering images that cannot be seen by the human eye.

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