6.4 Wide Viewing Angle Technologies

An often-quoted drawback of conventional TN LCDs has been their poor viewing angle behavior. When observed straight on, contrast ratio and color gamut can be excellent. When the viewer turns his or her head and looks at a notebook display under an oblique angle, the contrast ratio drops fast, colors become less saturated and, under some angles, image inversion can even occur. This viewing angle behavior is usually acceptable for devices smaller than 15 in. with a single user, such as notebooks, PDAs, and cell phones.

The origin of the problem was explained in Chapter 5, Sec. 5.3. and illustrated in Fig. 5.9. It can be traced back to the variation of the viewing angle relative to the LC director.

For larger, conventional TN LCDs, such as 17-in. and larger desktop monitors or LCD televisions, a single viewer at a distance of 10 or 20 in. will look at different corners of the screen under different viewing angles and the variation of contrast with viewing angle becomes objectionable. When there are multiple viewers looking at the display from different angles, similar image quality deterioration occurs.

A number of dramatic improvements in viewing angle have been developed over the past 10 years. The most important ones are:

• The addition of retardation compensation films,

• The in-plane-switching (IPS) LC mode, and

• The multidomain-vertical-alignment (MVA) LC mode.