Enter The Matrix!

By Michael Browne Published Date
01 - Mar - 2007
| Last Updated
01 - Mar - 2007
Enter The Matrix!

Everyone and their uncles hape hopped on to the LCD bandwagon, but how many of us know about the different kind of LCDs out there?

No two LCDs are created alike

That may sound dubious at first, but as you'll see, it's very true. The differences between LCD technologies are fundamental, based on the actual panel matrix that the LCD (Liquid Crystal Display) uses.

Each type of panel is designed to suit a particular usage pattern-gaming, movies, image editing, etc. This is actually intentional. As far as history is concerned, compared to CRTs, which have been around since 1897, LCDs are rather new products, and constant innovations are being made.

If you're going out to buy an LCD, just reading manufacturer specifications isn't going to clear the fog. If you want to know whether a particular LCD is suited for your needs, you're going to have to understand more about the manufacturing technologies. Almost all LCDs made today are the jack-of-all-trades kind, and the only way to discern a panel's suitability to a task is to check the type of matrix used.

There are broadly four types of LCD matrices being manufactured today:
1. TN (Twisted Nematic) also called TN Film
2. IPS (In Plane Switching)
3. MVA (Multi-domain Vertical Alignment)
4. PVA (Patterned Vertical Alignment)

TN / TN Film
TN panels are the adults of the LCD world. They've been on the scene since the time of Passive Matrices. The term "Twisted Nematic" actually refers to the way the liquid crystals are organised.

How A TN Panel Works
When voltage is applied (see Figure 1) you'll notice the outer set of crystals hardly change position (mostly parallel to the panels surface). All the while, the inner crystals orient themselves in such a way that their axis is perpendicular to the panel's surface-they twist. The problem in reality is the outer crystals aren't really parallel to the surface but nearly parallel. If viewed as a whole (the entire matrix), there are noticeable irregularities. These irregularities cause TN panels to have a characteristically poor Contrast Ratio, which is immediately noticeable while viewing multimedia content. Also, the viewing angles are adversely affected because of such irregularities.

Another disadvantage that TN panel-based LCDs face is the fact that they're natively capable of displaying only 262,144 colours-18-bit colour as opposed to 24-bit colour. TNs are basically 6-bit panels-the 18 bits comprise of 6 bits per colour component, red, green, and blue. However, manufacturers get to the magical figure of 16.7 million colours (24-bit) by a technique called dithering. Dithering is simply a technique for altering the values of adjacent dots (or pixels for that matter) on a matrix so as to create the illusion of a larger gamut of colours than what actually exists.

The advantages that TN panels have is that they're by far the fastest of all the technologies in terms of response times. This, coupled with the fact that TN panel LCDs are the cheapest to manufacture, is the reason that when you go out to buy an LCD, the majority of manufacturers will supply you with a model containing a panel based on this technology.

The second-type of LCDs we're looking at are the much costlier IPS (In-Plane Switching) panels. Developed by Hitachi in 1996, IPS panels were intended to remedy all the problems associated with TN panels mentioned above. Incidentally, IPS panels are natively 8-bit, which means that they can display the entire range of 16.7 million colours without the need for any dithering whatsoever. This makes them a good choice for professionals working with image and graphics applications. A newer version of IPS is S-IPS (Super IPS), which addresses the inherently poor response times that plagued first-generation IPS panels. 

Due to the significantly higher costs involved, S-IPS
technology is seen in larger LCD panels, 20-inch
and above
How IPS Works
As the name suggests, the crystals in the panel do not change orientation during off and on operations, remaining parallel to the panel's plane. Notice the elongation of the liquid crystals as they switch to their active state. Also notice the position of the electrodes-they're on the same wafer. This design is more space-consuming as well, which leads to one of the major shortcomings of IPS panels-a poor contrast ratio which causes relatively lower brightness levels. The benefits of IPS technology are the generously wide viewing angles and the brilliant colour reproduction.

Due to their original design, IPS panels suffered from very slow pixel response times, which made them unsuitable for gaming and multimedia applications because of all the ghosting.

A shot in the arm for IPS came in 1998 when Hitachi Corporation developed S-IPS or Super IPS. S-IPS significantly lowered pixel response times from 50 ms (for IPS) to about 25 ms. Later, in a joint venture,  LG and Philips worked out several chinks in the S-IPS armour, further reducing response times to about 16 ms. None of this affected the brilliant image quality, wide viewing angle and colour reproduction, thus making S-IPS panels the only choice for the discerning.

Due to the significantly higher costs involved in their manufacture, S-IPS technology is reserved for larger panels, above 20-inches.

MVA (Multi-Domain Vertical Alignment) panels came into existence sometime in 1998, thanks to Fujitsu, as a compromise between TN and IPS technologies. TN panels offered superb response times, but suffered from poor colour reproduction. S-IPS panels had amazing colour reproduction and acceptable response times, but suffered from poor contrast ratios. MVA panels walked the middle path to try and address all flaws in previous technologies, and offer actual contrast ratios of 600:1, which translates to blacks actually looking black, and a full spectrum of grey. So do we finally have visual perfection?

Unfortunately, no! MVA panels have been proven to have the worst pixel response times. Also, if a close comparison is done, MVA panels do not offer the same brilliant colour reproduction that S-IPS panels do, although to be pretty honest, MVA panels leave TN based ones chewing the dust on this parameter.

MVA panels are usually natively 8-bit. However, the drive for economy has seen cheaper 6-bit MVA panels that use dithering, similar to TN panels.

Once again, MVA panels are expensive, much more so than TNs, but cheaper than IPS panels, so they're mostly restricted to around the 19-inch-and-above category.

MVA panels attempt to address the shortcomings
inherent in TN and IPS panels

How MVA Works
As the name implies, MVA (Multi-Domain Vertical Alignment) panels see each pixel assigned a domain, or an area all to itself. Now these domains work in synchrony with each other. As you can see in Figure 3, the crystals form a sort of a shutter system whereby if one domain allows light to pass through (in the On position), the neighbouring domain will have its crystals aligned at a certain angle to shut out the light, or deflect it. If the monitor is to display white, you see all the crystals aligned somewhat parallel to the plane surface.

PVA (Patterned Vertical Alignment) was developed by Samsung as an offshoot of the technology used in MVA panels. Some people even criticise the technology stating there's enough in common to conclude that Samsung developed PVA to avoid paying licensing fees to Fujitsu for bulk-producing these panels.

However, a closer look at PVA as a panel technology will suggest differences that lead us to accept PVA as an independent (if not innovative) product that owes its origins to MVA.

In PVA panels, the alignment of crystals is identical to MVA panels. The domain principle is also used. This allows PVA panels to enjoy amazing viewing angles similar to MVA panels. The disadvantage of a slow pixel response times is also present in PVA matrices. A significant advantage is the improved contrast ratios. PVA panels can actually achieve a contrast ratio of up to 1000:1 in real figures, not what manufacturers claim. This is why PVA panels are finding their way into almost all LCD TVs available in the international market today. The fact that Samsung is the only player manufacturing PVA matrices also means that quality of such panels will be more or less identical.

PVA matrices can be found in the 19-inch-and-above categories. A lot of the massive LCD TVs in the range of 65 inches (and even the smaller 26 inches and above) are based on PVA matrices.

The Future
LCDs aren't the future. They are very much the present. As of today, CRT is a dead technology, and manufacturers and consumers alike are focusing on the flat panel market. The binaries of breakthrough technological advances and sharply declining costs is the culprit for the ever increasing popularity of LCD monitors across the globe.

The best news for you, our readers, is the conscious move towards larger LCD panels by the bigger manufacturers. Two of the leading flat panel manufacturers, LG-Philips and Samsung, each with an OEM market share of 22 per cent, are pushing out larger panels to fuel the sudden demand for more desktop space and larger screens for home entertainment. This drives the cost of mainstream panels down, and the trend of falling prices should continue in this product segment through this year and beyond.  

Michael BrowneMichael Browne