TN Film, MVA, PVA and IPS - Panel Technologies
Simon Baker, updated 29 August 2008

TN Film (Twisted Nematic + Film) panels are the mostly widely used in the TFT market, with smaller sized screens (15", 17" and 19") being almost exclusively limited to this technology. Some other sectors are dominated almost entirely by this technology as well, including the 22" market, and the technology is slowly creeping into the larger screen sizes of 24, 26 and 28" even. The TN Film panels are made by many different manufacturers, with the big names all having a share in the market (Samsung, LG.Display, AU Optronics) and being backed up by the other companies including BOE HyDis, CMO, CPT etc.

TN Film has always been so widely used because it is comparatively cheap to produce panels based on this technology. As such, manufacturers have been able to keep costs of their displays down by using these panels. This is also the primary reason for the technology to be introduced into the larger screen sizes, where the production costs allow manufacturers to drive down retail costs for their screens and compete for new end-users. The other main reason for using TN Film is that it is fundamentally a responsive technology in terms of pixel latency, something which has always been a key consideration for LCD buyers. It has long been the choice for "gamers" screens and response times have long been, and still are today, the lowest out of all the technologies (at least on paper). Response times typically reach a limit of around 5ms at the ISO quoted value, and as low as 2ms across grey to grey transitions with Response Time Compensation.

The problem with TN Film is that viewing angles are pretty restrictive, especially vertically, and this is evident by a characteristic severe darkening of the image, especially if you look at the screen from below. Contrast and colour tone shifts are evident with even a slight movement off centre, and this is perhaps the main drawback in modern TN Film panels. Movie playback is often hampered by 'noise' and artefacts, especially where RTC is used. Black depth was traditionally quite poor on TN Film matrices due to the crystal alignment, however, in recent years, black depth has improved somewhat and is generally pretty good on modern screens, especially where dynamic contrast technologies are also used. In some cases it can even rival VA matrices in this regard, and certainly surpases IPS technology. TN Film is only a true 6-bit technology, but is able to offer a 16.2 million, and now even a 16.7 million, colour palette thanks to dithering and Frame Rate Control methods.

VA (Vertical Alignment) technology was developed by Fujitsu in 1996. Small viewing angles were its main disadvantage. This problem was solved by dividing each pixel into domains which worked synchronously. This lead the birth of….

MVA (Multidomain Vertical Alignment) technology, developed by Fujitsu in 1998 as a compromise between TN Film and IPS technologies. On the one hand, MVA provided a full response time of 25 milliseconds (that was impossible at the time with IPS, and not easily achievable with TN), and on the other hand, MVA matrices had wide viewing angles of 160 - 170 degrees, and thus can compete with IPS in that parameter. The viewing angles are also very good in the vertical field (an area where TN panels suffer a great deal) as well as the horizontal field. MVA technology also provides high contrast ratios, which IPS and TN Film can't quite meet (without technologies like DFC at least) and a decent black depth.

In MVA panels, the crystals in the domains are oriented differently, so if one domain lets light pass through, the neighbouring domain will have the crystals at an angle and will shutter the light (of course, save for the display of white color, in which case all the crystals are placed almost in parallel to the matrix plane).

The problem with MVA panels was that traditionally; the response time was not as good as TN film panels. Sadly, the response time grows dramatically when there’s a smaller difference between the pixel’s initial and final states (i.e. G2G transitions). Thus, such matrices are practically unsuitable for dynamic games. Of course, “suitability” is a subjective category, and some people may be quite satisfied with the image produced by an MVA matrix, but they are objectively slower than TN as well as IPS matrices anyway. With the introduction of overdrive technologies, the manufacturers launched a new breed of...

Premium MVA panels (P-MVA) from AU Optronics, and Super MVA (S-MVA) from Chi Mei Optoelectronics and Fujitsu. These offer improved response times across grey to grey transitions which is a great improvement in the MVA market. While responsiveness is still not quite as fast as TN film panels, the improvement is obvious and quite drastic.

The color-reproduction properties of the MVA technology proved to be deficient, too. Such panels give you vivid and bright colors, but due to the peculiarities of the domain technology many subtle color tones (dark tones often) are lost when you are looking at the screen strictly perpendicularly. When you deflect your line of sight just a little, the colors are all there again. This is a characteristic VA panel contrast shift and some users pick up on this and might find it distracting. Thus, MVA matrices are somewhere between IPS and TN technologies as concerns color reproduction and viewing angles. On the one hand, they are better than TN matrices in this respect, but on the other hand the above-described shortcoming prevents them from challenging IPS matrices, especially for colour critical work. Traditionally MVA panels offered 8-Bit colour depth (a true 16.7 million colours) but it seems that some modern versions are only offering 6-Bit with FRC (see here for more info). Black depth is a strong point of MVA panels, being able to produce some of the deepest blacks in the market.

MVA panels also offer some comparatively good movie playback with noise and artifacts quite low compared with other technologies. The application of overdrive doesn't help in this area, but MVA panels are pretty much the only ones which haven't suffered greatly in movie playback as a result. Many of the MVA panels are still pretty good in this area, sadly something which overdriven TN Film, IPS and PVA panels can't offer. 
 

Advanced MVA (AMVA) - Next Generation VA Technology

AU Optronics have more recently been working on their next generation of MVA panel technology, termed 'Advanced MVA' (AMVA). This is designed to offer improved performance including reduced colour washout, and the aim to conquer the significant problem of color distortion with traditional wide viewing angle technology. This technology creates more domains than conventional multi-domain vertical alignment (MVA) LCD's and reduces the variation of transmittance in oblique angles. It productively improves color washout and provides better image quality in oblique angles than conventional VA LCD's. Also, it has been widely recognized worldwide that AMVA technology is one of the few ways to provide optimized image quality through multiple domains.

In addition, AMVA provides an extra-high contrast ratio of greater than 1200:1 (reaching 2500:1 at time of writing) by optimized color-resist implementation and a new pixel design. The result is a more comfortable viewing experience for the consumer, even on dimmer images. This high contrast technology can also achieve wide viewing angles of up to 178 degrees. AMVA, which the Company believes to be the most competitive solution in low color washout technology, has been applied to AUO TV panels ranging from 32" up to 42", and has attracted widespread attention among global brand-name TV customers in the United States, Europe and Japan.  

Further reading: Fujitsu - Super High Quality MVA (June 1999)
                        Chi Mei Optoelectronics - S-MVA Online Information
                        AU Optronics AMVA Press Release
                        AU Optronics AMVA Technology and Product Information
 

PVA technology (Patterned Vertical Alignment) was developed by Samsung as an alternative to MVA. The parameters and the development ways of PVA and MVA are so different that PVA can be truly regarded as an independent technology.

The liquid crystals in a PVA matrix have the same structure as in a MVA matrix  – domains with varying orientation of the crystals allow keeping the same color, almost irrespective of the user’s line of sight. In fact, the viewing angles (as traditionally measured by the reduction of the contrast ratio to 10:1) are limited not by the matrix, but rather by the plastic framing around the screen. Colour reproduction is not perfect, too, like with MVA matrices: when you are looking straight at the screen, the matrix “loses” some shades, which return after you deflect your line of sight from the perpendicular a little. This 'off-centre' contrast shift or 'black crush' as it is sometimes referred to as, is the reason why some colour enthusiasts prefer IPS based screens.

Alas, there was the same problem with traditional PVA matrices as with MVA ones – their response time grew considerably when there’s a smaller difference between the initial and final states of the pixel. Again, PVA panels were not nearly as responsive as TN film panels. With the introduction of MagicSpeed (Samsung's overdrive), response times have been greatly improved and are comparable to MVA panels in this regard on similarly spec-ed panels. They still remain a little behind TN Film panels in gaming use, but the overdrive really has helped improve in this area.

The contrast ratio parameter is really good with the PVA technology though. First, PVA matrices are manufactured by Samsung alone, so there can’t be any variation in quality between different manufacturers. Second, Samsung is actively working to improve the contrast ratio and with some results already: monitors with PVA matrices (they mostly come from Samsung, too) typically have a contrast ratio of anywhere between 600:1 and 1500:1 (static, not dynamic). Generally speaking, PVA matrices are the only matrix type today for which the declared contrast values are often true (sometimes the real characteristic is even better than specified). Black depth is good, and again they offer much better measurements in this area than TN Film and IPS. MVA and IPS are improving, but tend to be a little more exaggerated on paper than PVA which are generally quite reliable in this spec.

Overall, PVA matrices could be said to be an improved version of MVA. Without any new defects, save for those already present in the MVA technology, PVA matrices feature slightly improved viewing angles, better contrast ratios and a much more predictable production quality due to their being manufactured on the facilities of one manufacturer only. Movie playback is perhaps one area which is a weak point for PVA, especially on Samsung's overdriven panels. Noise and artefacts are common unfortunately and the panels lose out fo MVA in this regard. While traditionally PVA panels offered 8-bit colour depth, it seems some modern panels might well use FRC/dithering methods along with a 6-bit panel. This is likely to be in an effort to keep manufacturing and production costs down, but is a disappointment to some users.

Samsung have produced a new breed of...

Super Patterned Vertical Alignment (S-PVA) panels. Most of these are based on the introduction of “Magic Speed” (the Samsung equivalent to Overdrive),  which offer improved response times over traditional PVA matrices. Note that some PVA panels still used this technology, but S-PVA panels almost certainly feature it. Like P-MVA panels, these are really just an extension of the existing technology, but with the MagicSpeed technology, they have managed to make them more suitable for gaming than the older panels. One other difference is that the liquid crystal cell structure is a boomerang shape, splitting each sub pixel into two different sections with each aligned in opposite directions. This is said to help improve viewing angles and colour reproduction when viewed from the side.

Further reading: Samsung Whitepaper - PVA and S-PVA

IPS (In Plane Switching) technology was developed by Hitachi in 1996 to solve the two plagues of TN-matrices: small viewing angles and low-quality color reproduction. The name – In-Plane Switching – comes from the crystals in the cells of the IPS panel lying always in the same plane and being always parallel to the panel’s plane (if we don’t take into account the minor interference from the electrodes). When voltage is applied to a cell, the crystals of that cell all make a 90-degrees turn. By the way, an IPS panel lets the backlight pass through in its active state and shutters it in its passive state (when no voltage is applied), so if a thin-film transistor crashes, the corresponding pixel will always remain black, unlike with TN matrices.

IPS matrices differ from TN ones not only in the structure of the crystals, but also in the placement of the electrodes – both electrodes are on one wafer and take more space than electrodes of TN matrices. This leads to a lower contrast and brightness of the matrix.

The original IPS technology became a foundation for several improvements: Super-IPS (S-IPS), Dual Domain IPS (DD-IPS), and Advanced Coplanar Electrode (ACE). The latter two technologies belong to IBM (DD-IPS) and Samsung (ACE) and are in fact unavailable in shops. The manufacture of ACE panels is halted, while DD-IPS panels are coming from IDTech, the joint venture of IBM and Chi Mei Optoelectronics – these expensive models with high resolutions occupy their own niche, which but slightly overlaps with the common consumer market. NEC is also manufacturing IPS panels under such brands as A-SFT, A-AFT, SA-SFT and SA-AFT, but they are in fact nothing more than variations and further developments of the S-IPS technology.

Enhanced S-IPS is the term given to LG.Philips' latest generation of panels using this technology. More information can be found about the improvements in the technology here, with a ODC (overdrive) technology playing a key role. Advanced Super IPS (AS-IPS) is also a term being used as well, but is just a term for the new Enhanced S-IPS panels used in models by NEC.

S-IPS panels have gained the widest recognition, mostly due to the efforts of another joint venture LG.Philips LCD (now known as LG.Display), which is outputting rather inexpensive and high-quality 19”, 20”, 24" and 30" matrices. Besides the high price, the response time was among the serious drawbacks of the IPS technology – first panels were as slow as 60ms on the “official” black-to-white-to-back transitions (and even slower on grey-to-grey ones!). Fortunately, the engineers dragged the full response time down to 25 ms and then 16ms later, and this total is equally divided between pixel rise and pixel fall times. Moreover, the response time doesn’t greatly grow up on black-to-gray transitions compared to the specification, so some older S-IPS matrices could challenge TN Film panels in this parameter (before overdrive anyway). For a while, S-IPS panels remained at ~16ms as their best response time on paper. However, overdrive has caught up with this technology (what LG.Display call ODC - Over Driving Circuitry) after it's success with TN Film, PVA and MVA panels. IPS has re-emerged offering some excellent quoted response times as well as excellent responsiveness in practice. Some modern IPS panels are even as responsive as the fastest TN Film panels in real use!

The IPS technology has always been better than TN Film in terms of color reproduction and viewing angles. In fact, S-IPS matrices leave no chance to other LCD technologies in the color-reproduction quality. They have soft and pleasant colors, which are natural and close to high-quality CRT monitors. That’s why nearly all LCD monitors for professional work with color are based on S-IPS matrices, starting from relatively inexpensive to hi-end models of the Eizo ColorEdge series with integrated tools for custom hardware color-calibration.

The viewing angles are a treat after TN matrices: you can’t notice any distortions of the image, sitting in front of an IPS matrix. There’s only one specific defect – when you’re looking at the screen from a side, black color acquires a characteristic violet hue (by the way, this defect allows telling an IPS matrix from any other), but the manufacturers are improving on this. In most cases, this is an insignificant defect anyway. Viewing angles are wider than PVA and MVA even and are signified by their listed specs commonly of 178/178 instead of 176/176. Only a guide on paper, but in reality, viewing angles are better on S-IPS based screens. They are also free from the off-centre contrast shift of VA panels, again making them a leading choice for colour critical work.

Demonstration of viewing angles on IPS vs VA matrices

The only real problem of the S-IPS technology traditionally was the low contrast ratio (about 200:1, like that of an average TN Film matrix). In means you see a dark gray instead of pure black. That’s not noticeable at daylight, but if you’re working in a dimly lit room, you may be disappointed at the highlighting of the black color (coupled with the characteristic violet hue when you’re viewing the screen from a side). Black depth was often a problem with S-IPS panels. However, contrast ratios have been improved significantly, and black depth is much better as a result. Whether or not black depth is as good as PVA / MVA panels is debatable, but technologies like Digital Fine Contrast DFC are helping to make blacks better as well in multimedia applications. One area which remains problematic for modern IPS panels is movie playback, again with noise being present, and only accentuated by the heavy application of overdrive technologies.

Horizontal-IPS (H-IPS) is the latest generation of IPS panels, typically manufactured by LG.Display (previously LG.Philips). In simple terms, the manufacturer has reportedly reduced the electrode width to reduce light leakage, and this has in turn created a new pixel structure. In practice, it can be quite hard to spot the difference, but close examination can reveal a less 'sparkly' appearance and a slightly improved contrast. Some IPS panels in high end displays are coupled with an Advanced True Wide (A-TW) polarizer which helps improve black viewing angles and reduce some of the pale glow you can see at wide angles on IPS panels. However, this A-TW polarizer is not included in every model featuring H-IPS and this should not be confused.

The following technical report has feedback from the LG.Philips LCD laboratory workers: "We designed a new pixel layout to improve the aperture ratio of IPS mode TFT-LCD(H-IPS).This H-IPS pixel layout design has reduced the width of side common electrode used to minimize the cross talk and light leakage which is induced by interference between data bus line and side common electrode of conventional IPS mode. The side common electrodes of a pixel can be reduced by horizontal layout of interdigital electrode pattern where conventional IPS pixel designs have vertical layout of interdigital electrodes. We realized 15 inch XGA TFT LCD of H-IPS structure which has aperture ratio as much as 1.2 times of corresponding conventional IPS pixel design." ©2004 Society for Information Display

    
Above: H-IPS (NEC LCD2490WUXi): vs AS-IPS (NEC 20WMGX2)

Further reading: LG.Philips Whitepaper - Enhanced Super IPS (Dec 2005)