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In-plane switching (IPS) is a technology used inliquid-crystal displays (LCDs). In IPS,liquid crystal molecules are sandwiched between, and alignedparallel to, two panels (planes) ofglass substrate. The molecules are reoriented by applyingelectric field, while remaining essentially parallel to the surfaces to produce an image.[clarification needed] It was designed to remedy issues of poorviewing angle andcolor reproduction of thetwisted nematic field effect (TN) matrix LCDs prevalent in the late 1980s.[1]
Computer monitors start utilizingactive matrixTFT LCD panels in the 1980s and early 1990s, as an alternative technology to thecathode ray tube. These early LCD displays suffered from invertedgrayscale, loss ofcontrast andcolor reproduction accuracy when viewed from extreme angles,[2] and had significantdisplay motion blur due to poorresponse time. IPS andvertical alignment (VA) are designed to alleviate these issues.
An early experimental IPS-LCD is described in a 1974 patent. It used inter-digitatedelectrodes on only one glasssubstrate, to produceelectric field essentially parallel to the glass substrates.[3][4] However, the inventor was not able to implement IPS-LCDs with superior quality to contemporary TN displays.
After thorough analysis, details of advantageous molecular arrangements were filed inGermany by Guenter Baur et al. and patented in various countries including the US on 9 January 1990.[5][6] TheFraunhofer Society inFreiburg, where the inventors worked, assigned these patents toMerck KGaA, Darmstadt, Germany.
Shortly thereafter,Hitachi of Japan filed patents on improvements to the technology.[7] In 1992, engineers at Hitachi worked out various practical details of the IPS technology to interconnect thethin-film transistor array as a matrix and to avoid undesirable stray fields in between pixels.[8][9] Hitachi also improved the viewing angle dependence further by optimizing the shape of the electrodes (Super IPS).NEC and Hitachi became early manufacturers of active-matrix addressed LCDs based on the IPS technology. This is a milestone for implementing large-screen LCDs having acceptable visual performance for flat-panel computer monitors and television screens. In 1996,Samsung developed the optical patterning technique that enables multi-domain LCD. Multi-domain and in-plane switching subsequently remain the dominant LCD designs through 2006.[10]
Later,LG Display and other South Korean, Japanese, and Taiwanese LCD manufacturers adopted IPS technology.
IPS technology is widely used in panels forTVs,tablet computers, andsmartphones. In particular, mostIBM products marketed asFlexview from 2004 to 2008 have IPS LCDs withCCFL backlighting, and allApple Inc. products marketed with the labelRetina Display[11][12] feature IPS LCDs withLEDbacklighting since 2010.
| Name | Nickname | Year | Advantage | Transmittance or contrast ratio | Remarks |
|---|---|---|---|---|---|
| Super TFT | IPS | 1996 | Wide viewing angle | 100/100 Base level | Most panels also support true8-bit-per-channel colour. These improvements came at the cost of a lower response time, initially about 50 ms. IPS panels were also extremely expensive. |
| Super-IPS | S-IPS | 1998 | Colour shift free | 100/137 | IPS has since been superseded byS-IPS (Super-IPS,Hitachi in 1998), which has all the benefits of IPS technology with the addition of improved pixel refresh timing.[quantify] |
| Advanced Super-IPS | AS-IPS | 2002 | High transmittance | 130/250 | AS-IPS, also developed byHitachi in 2002, improves substantially[quantify] on the contrast ratio of traditional S-IPS panels to the point where they are second only to someS-PVAs.[citation needed] |
| IPS-Provectus | IPS-Pro | 2004 | High contrast ratio | 137/313 | The latest panel from IPS Alpha Technology with a wider colour gamut[quantify] and contrast ratio[quantify] matching PVA and ASV displays without off-angle glowing.[citation needed] |
| IPS Alpha | IPS-Pro | 2008 | High contrast ratio | Next generation of IPS-Pro | |
| IPS Alpha Next-Gen | IPS-Pro | 2010 | High contrast ratio |
| Name | Nickname | Year | Remarks |
|---|---|---|---|
| Horizontal IPS | H-IPS | 2007 | Improves[quantify] contrast ratio by twisting electrode plane layout. Also introduces an optional Advanced True White polarizing film from NEC, to make white look more natural[quantify]. This is used in professional/photography LCDs.[citation needed] |
| Enhanced IPS | E-IPS | 2009 | Wider[quantify] aperture for light transmission, enabling the use of lower-power, cheaper backlights. Improves[quantify] diagonal viewing angle and further reduce response time to 5 ms.[citation needed] |
| Professional IPS | P-IPS | 2010 | Offer 1.07 billion colours (30-bit colour depth).[citation needed] More possible orientations per sub-pixel (1024 as opposed to 256) and produces a better[quantify] true colour depth. |
| Advanced High Performance IPS | AH-IPS | 2011 | Improved colour accuracy, increased resolution and PPI, and greater light transmission for lower power consumption.[15] |
In this case, both linearpolarizing filters P and A have their axes of transmission in the same direction. To obtain the 90 degree twisted nematic structure of the LC layer between the two glass plates without an applied electric field (OFF state), the inner surfaces of the glass plates are treated to align the bordering LC molecules at a right angle. This molecular structure is practically the same as in TN LCDs. However, the arrangement of the electrodes e1 and e2 is different. Electrodes are in the same plane and on a single glass plate, so they generate an electric field essentially parallel to this plate. The diagram is not to scale: the LC layer is only a fewmicrometers thick, very thin compared with the distance between the electrodes.
The LC molecules have a positive dielectricanisotropy and align themselves with their long axis parallel to an applied electrical field. In theOFF state (shown on the left), entering light L1 becomes linearly polarized by polarizer P. The twisted nematic LC layer rotates the polarization axis of the passing light by 90 degrees, so that ideally no light passes through polarizer A. In theON state, a sufficient voltage is applied between electrodes and a corresponding electric field E is generated that realigns the LC molecules as shown on the right of the diagram. Here, light L2 can pass through polarizer A.
In practice, other schemes of implementation exist with a different structure of the LC molecules – for example without any twist in theOFF state. As both electrodes are on the same substrate, they take more space than TN matrix electrodes. This also reduces contrast and brightness.[16]
Compared to TN displays, IPS ones may consume more power, cost more to manufacture, have slower response times, and suffer from uneven backlight brightness ("backlight bleeding") more easily.[22][23]
Samsung Electronics's use themarketing term Super PLS (Plane-to-Line Switching) to refer to IPS panel technologies with similar features and performance characteristics to LG's offering.[24][25]
However, [twisted nematic] suffers from the phenomenon called gray scale inversion. This means that the display has one viewing side in which the image colors suddenly change after exceeding the specified viewing angle.(see imageInversion Effect)
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