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IPS panel (In-Plane Switching technology) is a screen technology used for liquid crystal displays (LCDs). It was to solve the main limitations of TN-matrices at the time: relatively slow response, small viewing angles and low-quality color reproduction. In-Plane Switching involves arranging and switching the molecules of the liquid crystal (LC) layer between the glass substrates essentially in a plane parallel to these glass plates.
The TN method was applied in active matrix TFT LCDs in the late 1980s and early 1990s. The early panels showed gray inversion from up and down, and had slow response speed. In the mid 1990s, some technologies—typically IPS and VA (Vertical Alignment)—that could resolve these weaknesses were applied to large monitor panels.
One approach was to use interdigital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates. After thorough analysis, details of advantageous applications were filed in Germany by Guenter Baur et al. and patented in various countries. The Fraunhofer Society in Freiburg, where the inventors worked, assigned these patents to Merck KGaA, Darmstadt, Germany.
Shortly thereafter, Hitachi of Japan filed patents to further improve this IPS technology
The diagram shows a simplified model of a particular implementation of the IPS technology. In this case, both linear polarizing filters P and A have the same orientation of their axes of transmission. To obtain the 90-degrees 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 an angle of approx. 90 degrees. This molecular structure is practically the same as in TN LCDs. However, the arrangement of the electrodes e1 and e2 is different. Because they are in the same plane and on only one glass plate, they generate an electric field essentially parallel to the glass plate. Note that the diagram is not to scale: the LC layer is only a few micrometers thick and so is very small compared with the distance between the electrodes e1 and e2.
The LC molecules have a positive dielectric anisotropy and align themselves with their long axis parallel to an applied electric field. In the OFF 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 the polarizer A. In the ON state, a sufficient voltage is applied between electrodes e1 and e2, a corresponding electric field E is generated realigns the LC molecules as shown on the right of the diagram. Here, light L2 can pass through the polarizer A.
In practice, other schemes of implementation exist which have a different structure of the LC molecules - for example without any twist in the OFF state. To achieve a wider viewing angle and faster response speed requires using a compensatory film and complicated multi-domain technology to divide pixels into parts. As both electrodes are on the same substrate, they take more space than electrodes of TN matrices. This also reduces contrast and brightness.
Super-IPS was later introduced with even better response times and color reproduction.
- IPS panels display consistent and accurate color from all viewing angles.
- Unlike TN LCDs, IPS panels do not lighten or show tailing when touched. This is important for touchscreen devices, such as smartphones and tablets.
- IPS panels can process high speed signals without data loss by using copper wiring with low resistance values.
- IPS Panels offer clear images and stable response time.
- IPS panels have slower response times and are therefore more prone to the ghosting effect.
- IPS panels require up to 15% more power consumption than TN displays.
Super PLS 
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Samsung Electronics in 2010 introduced technology named Super PLS (Plane-to-Line Switching) with the intent of superseding conventional IPS. It seems that Samsung adopted PLS panels instead of AMOLED panels because AMOLED panels had in the past had difficulties in realizing full HD resolution on mobile devices. PLS technology was Samsung’s wide-viewing angle LCD technology, and it is known as a similar technology to LG’s IPS technology.
Samsung claims the following benefits of Super PLS (commonly referred to as just "PLS") over IPS: 
- Further improvement in viewing angle
- 10 percent increase in brightness
- Up to 15 percent decrease in production costs
- Increased image quality
- Flexible panel
See also 
- U.S. Patent 3,834,794: R. Soref, Liquid crystal electric field sensing measurement and display device, filed June 28, 1973.
- U.S. Patent 5,576,867: G. Baur, W. Fehrenbach, B. Staudacher, F. Windscheid, R. Kiefer, Liquid crystal switching elements having a parallel electric field and beta o which is not 0 or 90 degrees, filed Jan 9, 1990.
- "LCD TVs, LED TVs and WHAT more to come!". 4 December 2010. Retrieved 13 January 2012.
- Baker, Simon (30 April 2011). "Panel Technologies: TN Film, MVA, PVA and IPS Explained". Retrieved 13 January 2012.
- "LCD Panel Technology Explained". Retrieved 13 January 2012.
- "Samsung Adopts IPS instead of AMOLED: Why?". Retrieved 9 November 2012.
- "Samsung PLS improves on IPS displays like iPad's, costs less". Retrieved 30 October 2012.
- "Digital Displays Explained". Retrieved 19 November 2012.
Media related to IPS panel at Wikimedia Commons