LCD Monitor Technology Guide
LCD monitors are obviously very different from CRT monitors. If you’re looking to buy an LCD monitor it might pay to a basic understanding of how the technology works. In a nutshell LCD displays work by having a liquid crystal panel filter light from a fluorescent lamp. but there is more to it than that…
The way the LCD controls the passage of light involves the polarisation of light. Once light has been polarized by a certain angle of polarization with a filter you can control the intensity of the light by adjusting the angle of polarization of another filter.
The first stage of an LCD display involves passing the light through a polarizing filter. It then gets into a layer filled with liquid crystals that are controlled by the transistors. The light then passes through color filters (like CRT monitors, each LCD display pixel consists of three components – red, green and blue). Transistor applies voltage to liquid crystals, that sets their spatial alignment. Light changes its polarization angle when it passes through the ordered liquid crystal molecular structure, and depending on its new polarization angle it will be absorbed completely or partially. This allows the creation of any halftone from black to pure white.
The Three Major Types Of LCD Display
The most widespread type of digital panel is based on technology known as TN TFT or TN+Film TFT (Twisted Nematic + Film). The “Film” term stands for additional external film covering, allowing increasing viewing angle from usual 90 degrees (45 from each of the sides) to about 140 degrees.
TN TFT – was the first LCD technology introduced, and it is still popular today in mid to low end panels on laptops and desktops. This is due to the low manufacturing costs of these panels. LCD panels based on TN TFT matrix due have some drawbacks. The biggest problem is that black color looks more like dark gray on the old panels that results in poor contrast. Over the years this technology has been improved and modern TN panels can show much more depth in displaying dark shades of grey to black. The second problem occurs when a transistor dies leaving a bright “dead” pixel appears on the screen, which is much more noticeable than the black “dead” one.
The next major technology called IPS (In-Plane Switching) was designed to improve some of the TN TFT drawbacks. This technology also called Super-TFT was developed by Hitachi. IPS allowed increasing viewing angle to approximately 170 degrees using more precise method of controlling liquid crystals alignment, which was its main achievement. However contrast ratios have remained at the level of TN TFTs, and the response time even grown more.
Positive side of this method is that dying pixels will be fading into black, unlike the bright white of TN TFT panels. However this design has a major drawback in that the manipulation of an electric field in such system demands considerable amount of energy and occupies more time. This generally leads to a response time increase. IPS represents compromise and while dead pixels are much less noticeable these displays are not really suited to mobile applications.
The third technology, developed by Fujitsu, promises to eradicate (at least in theory) the major drawbacks of LCD panels. It is called MVA (Multi-Domain Vertical Alignment) and is successor to previous VA technology. Basically it’s advantages center on being able to improve viewing angle and color reproduction. It does this by having all of the color elements of the panel split into cells or zones. These are formed by ridges on an internal surface of filters. The purpose of this design is to enable liquid crystals to move in opposite direction to their neighbors. It allows the observer to see the same shade of color irrespective of a viewing angle.
The potential of MVA technology is great. One of its main benefits is the reduced response time. However, this complicated panel layout not only adds to LCD manufacturing cost, but also doesn’t allow manufacturer to fully use all of MVA benefits due to technical problems and manufacturing process complexity. For now the market share of MVA LCD is small, but does steadily grow. At the moment MVA is the most technically advanced solution on mass LCD market.