Technology trends for industrial LCDs

LEDs, wide formats and viewing angles, and high-resolution color are either on deck or the horizon

BY ROBERT DUNHOUSE
NEC Electronics America
Santa Clara, CA
http://www.am.necel.com

The display industry is entering a very exciting period, with new technologies emerging on several fronts. LED backlighting and wide-format technologies have been the subject of much discussion in the consumer world for applications such as notebook PCs and TV screens.

This year, these consumer-based technologies are being industrialized and beginning to be implemented in factory automation, portable medical, marine, and other devices. High color resolution, enhancement technologies, and wide viewing angle technologies represent a few of the areas experiencing growth in the industrial market.

LEDs, LEDs, and more LEDs

The future of high-efficiency white LEDs looks very promising for non-consumer displays. There is strong growth in areas encompassing test and measurement equipment, portable medical devices, and other applications that require extended life in battery-powered devices.

For some time, white LEDs have been used in small displays — 5 in. and below (typically in the cell phone/PDA space) — but now the technology is moving to mid-range panels, from 5.0 to 12.1 inches in size. While CCFL backlighting is the incumbent and mature lighting technology (read “less expensive”), the industrial market is demanding more efficient, more rugged, and smaller-profile white LEDs to enable differentiation of product and improved performance. Also, LEDs do not contain mercury, making them more “green.” In this segment, performance is a premium over price. LEDs have a “bright” future.

On the high end of LED lighting, RGB LEDs are typically used in the larger (>19.0-in.) high-resolution (>1 Mpixel) panels. In applications where color performance (up to 105% of NTSC) demands more than CCFLs can provide, and precise color reproduction must be maintained to an industry standard, LEDs are a must.

Using an optical feedback sensor enables the drive to each primary color to be independently controlled, thereby realizing real-time color temperature adjustment and calibration. This is a special advantage not only for the industrial consumer but also for the LCD manufacturer. To support the high-end medical diagnosis and imaging markets, several CCFL models were needed, each tuned to separate P45 or P104 medical color temperature standards. This is no longer the case, as one model can be set up to operate in either color temperature through software control.

Another requirement was to maintain the color temperature over time. CCFLs will cause color shift as their spectral output changes during continued use. RGB LEDs using optical feedback sensors can adjust and maintain color temperature instantly and can, to a certain degree, maintain intensity.

It’s a wide world after all

Wide-aspect ratio — the de facto standard for the consumer market, particularly for TVs and notebook PCs — is now being adopted in the industrial market as well, as it provides engineers with more avenues for product differentiation and function enhancement.

Wide-aspect ratio provides more than a different look and feel. For example, the wider format affords test and measurement devices an expanded field of view for time-based measurements, resulting in greater functionality (see Fig. 1 .)

Fig. 1. Wide aspect-ratio displays offer more room for information, and more colors ease data/function differentiation.

Engineers can take advantage of the additional horizontal screen space to display more information, providing a more comprehensive field of data. Alternatively, designers can fill the space with software-based functions accessed through touch screen capability and eliminate some of the hard keys found on the device.

The wide-aspect ratio format also allows designers to migrate consumer-standard formats into smaller form factors for markets such as broadcast monitoring, where they still need to use the established HDTV and movie formats.

As a whole, wide-format LCD modules represent high growth potential, particularly for 7 to 15-in. mid-range displays, consistent with the sizes typically used in the test and measurement, factory automation, broadcasting and other industrial markets.

Mobile 24-bit color

High color resolution is another large-growth area. While 24-bit color resolution for mobile devices is still in the early stages, there is already strong demand for this level of resolution in increasingly smaller panel sizes. Moving forward, it is anticipated that there will be a wider proliferation of 24-bit color into sub-5-in. panels.

This high degree of color resolution — more than 16 million colors — could have a significant impact on portable medical diagnostics, aerial mapping, or portable broadcast environments. These devices rely on imaging technologies to deliver critical information that helps determine the position of mission-critical terrain and personnel, on-site video broadcast quality, or the state of a person’s health.

For example, incorporating 24-bit color resolution into a display could allow on-site review of MRI images for diagnosis. For monochrome panels, this translates into a highly precise gray-scale definition for applications such as ultrasound systems.

Products in the larger LCD panel sizes are currently available and modules in the 4 to 5-in. range are beginning to come out this year.

Factory-made for outdoors

Liquid crystal displays used in outdoor environments have always been at a disadvantage. Over many years, a whole industry was created to enhance standard LCDs for outdoor use. A super-transmissive natural light TFT (ST-NLT) technology developed by NEC LCD Technologies helps boost backlighting efficiency and minimize surface reflections of ambient light to deliver high-contrast, vibrant color displays in the most challenging lighting environments.

Compared to standard transmissive products modified by third-party integrators, these “straight-from-the-factory” enhanced displays offer large gains in performance and reliability. Factory warranties apply with repeatable and guaranteed results.

Two technologies are primarily used to make a panel viewable outdoors. One is based on the ST-NLT technology while the other, a super-reflective (SR) NLT technology, employs an internal reflective layer populated on the TFT layer. Both have advantages and disadvantages, but ST-NLT technology is often chosen for its performance and lower cost.

Companies developing non-consumer applications, such as medical, outdoor kiosks, boating/navigation and avionics applications, are recognizing these benefits and are willing to support the price premiums with the understanding that the total cost of ownership to achieve the outdoor performance will remain highly competitive. As this approach becomes more widely adopted across the industry for the 15-in. and below products, expect price points to adjust accordingly. As prices drop, applications such as in-car entertainment will also be a possibility.

Better viewing angles under 5 in.

Typically based on standard twisted neumatic liquid crystal technology, displays in the sub-5-in. range have defined or somewhat limited viewing angles. Most have sufficient performance when viewed horizontally, but typically are limited to / optimized for a particular viewing angle when viewed vertically.

Recent applications, like the Apple iPhone, require that products be capable of operating in both portrait and landscape orientations. For applications that require this flexibility, viewing-angle technologies once reserved for higher-end large panels are now migrating into sub-5-in. displays. One such technology is a UA-SFT (in-plane switching or IPS). UA-SFT offers an equal viewing cone in every direction and extends as far as 170˚ in every axis (see Fig. 2 ).

Fig. 2. Migrating from larger to smaller displays, greater all-round viewability aids use of handheld devices in the field.

UA-SFT has the advantage of maintaining color stability/accuracy at off-angle viewing, while other displays suffer from color shift relative to viewing direction. In the portable medical market, users can little afford to sacrifice color accuracy. They depend on it for diagnostic information in field environments where the operator cannot always be directly in front of the display.

As upper-end viewing angle technologies filter down into the smaller panels, they provide new opportunities for the system designers and creates new markets. The Society for Information Display (SID) International Symposium in Los Angles, CA, this month will provide a forum to showcase these and other next-generation developments. ■

For more on industrial LCDs, visit http://www2.electronicproducts.com/Opteoelectronics.aspx.