During the past decade, thin-film-transistor LCDs have rapidly displaced emissive displays, such as CRTs and LEDs, by offering superior resolution, lower power, lighter weight, and thinner profile. But LCDs had their issues, notably their smaller viewing angle. While they looked good when viewed head on, the image quickly faded when the viewer moved off dead center.

The problem

With the wide-angle display placed in privacy mode, people even slightly off center cannot see personal information on the screen. Left shows user view. Right shows view from off center. Photo courtesy: Sharp.

While a CRT can be seen from a 180 Deg viewing angle, the viewing cone for an LCD was limited. Although that did not stop LCDs from becoming the display of choice for applications where the viewer was typically right in front of the display, the limited viewing cone became a major obstacle in the television market segment where there were multiple users viewing the LCD from different angles. LCDs, unlike CRTs or plasma displays, function as a light valve and do not emit any light on their own. LCD technology essentially manipulates ambient light (or light from the backlight) to depict images. Therefore, traditional LCD construction impeded the light coming out of the display from going in all different directions.

Most of the TFT LCDs used twisted nematic technology, which by its nature has a limited viewing cone. These limitations in LCDs manifested themselves in the form of poor off-axis contrast, shifts in color, and in some cases complete reversal of image color. Initially, attempts were made to manage the viewing angle by using films that manipulated light, by orienting the display in portrait or landscape mode, and offering different liquid-crystal material that had slightly different properties that caused a shift in the viewing cone. While these options offered a decent solution for specific applications, they were not universally adaptable. The applications were too diverse for one method to work across the board. Also, while the viewing angle from up/down or right/left was enhanced, viewing the image diagonally was not satisfactory.

The answer came in the form of new devices that were no longer based on twisted nematic technology. Fig. 1 shows the basic TN structure with liquid crystal molecules that twist 90 Deg within the LCD cell. The newer technologies, such as Sharp’s Advanced Super View, have a very different structure, where the molecules are arranged like a continuous pin wheel. This structure renders a wider viewing cone display. Other technologies, like Multi-Domain Vertical Alignment from Fujitsu and In Plane Switching from others, also offer wider viewing angle displays.

The technologies to create wide viewing angle displays migrated from large TV panels to smaller sizes, such as 10.4 in., 12.1 in. and 15 in. These smaller displays are popular in the industrial and appliance markets. Today, Sharp’s Advanced Super View-technology-based 12.1-in. display boasts a 170 Deg uniform viewing cone. This improved viewing angle is not just in the vertical and horizontal perspective; the display can also be viewed diagonally equally well.

The right choice

Fig. 1. The Twisted Nematic physical structure is shown on the left. Sharp’s Advanced Super View, on the right, produces a significantly enhanced viewing cone.

Now that wide viewing cone LCD solutions are available, how does the appliance design engineer pick the right display for the application? Even though most of these new technologies offer a wide viewing cone, not all of them offer the same contrast at different viewing angles. With some technologies, achieving a wider viewing angle comes at the expense of greater power consumption. In others, the wide angle design reduces the speed of response of the display.

Contrast. Contrast is important at wide viewing angles (insufficient contrast would mean insufficient detail reproduction in the image), and as a reference, Sharp specifies that the contrast for its 12.1-in. Advanced Super View display be greater than 10:1 at the extreme end of the viewing cone and at 800:1 when viewed head on. Color shift. Color shift is a phenomenon causing color changes or shifts as the viewer moves off center. This potentially reduces the value of the image being represented on the LCD.

Response time. In applications involving fast moving images and video, LCD response speed is critical. Moving image artifacts can blur the image, potentially causing the viewer to miss subtle changes as the image transitions. As a reference, Sharp offers a response time of 25 ms in its 15-in. Advanced Super View-technology-based LCD.

Other considerations with the new LCD technologies include power consumption, and temperature range.

Too much view?

With viewing angles in newer LCDs no longer a concern, one might ask: Can a display ever have too large of a viewing cone? In applications where privacy is an issue, the answer may be yes.

With emissive displays and now LCDs, the wide viewing cone can become a problem in certain types of applications where a reduced viewing angle may actually be preferred. The classic example is someone using a laptop on an airplane while trying to prevent the adjacent passenger from seeing sensitive information on the screen.

There are ways to reduce the viewing cone. One is to install a privacy filter of some sort, or simply revert to a display with a narrower viewing cone. Designers now have another option, one that allows the user to increase or reduce the viewing cone of the display at will. This option can be found in Sharp’s Switchable View LCD that allows the user to widen or narrow the viewing cone of the display at the touch of a button.

The feature was achieved by use of a proprietary LCD technology that consists of switching liquid crystal material overlaid on an ordinary TFT LCD so that light is prevented from going to the sides, thus turning a wide viewing angle display into a narrow viewing angle display. This technology allows users to view personal information on a variety of devices including cell phones, PDAs, and notebook PCs without having to worry about their privacy being invaded in a public setting.

Conclusion

The improvement in viewing angle is not limited to large size LCDs, even though that is where this work originated. The new technologies that improve the viewing angles are fast migrating to smaller format displays. This will enable better viewing of video on a mobile phones or other hand-held devices. With the issue of LCD viewing angle conquered, researchers have started addressing other optical parameters that will make this already popular display technology even more ubiquitous. Next generation LCD technologies will enable designers to achieve even greater design flexibility and implement new applications that were previously not possible.