IPS panel

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IPS (In-plane switching) is a screen technology used for liquid crystal displays (LCDs). It was designed to solve the main limitations of the twisted nematic field effect (TN) matrix LCDs in the late 1980s, such as relatively high response time, strong viewing angle dependence and low-quality color reproduction. In-plane switching involves arranging and switching the molecules of the liquid crystal (LC) layer between the glass substrates. This is done in a plane parallel to these glass plates.

History[edit]

The TN method was the only viable technology for active matrix TFT LCDs in the late 1980s and early 1990s. Early panels showed gray inversion from up to down, and had a high response time (lower is better, for example for the same kind of transition, 1ms is visually better than 5ms). In the mid-1990s new technologies were developed—typically IPS and VA (Vertical Alignment)—that could resolve these weaknesses and were applied to large monitor panels.

One approach patented in 1974 was to use inter-digital electrodes on one glass substrate only to produce an electric field essentially parallel to the glass substrates.[1][2] However, the inventor was not yet able to implement such IPS-LCDs superior to TN displays.

After thorough analysis, details of advantageous molecular arrangements were filed in Germany by Guenter Baur et al. and patented in various countries incl. USA on 9 January 1990.[3][4] 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. A leader in this field was Katsumi Kondo, who worked at the Hitachi Research Center in Japan.[5]

Later, LG and other South Korean, Japanese and Taiwanese LCD manufacturers adapted IPS technology as well.

Today, IPS technology is widely used in panels for TVs, tablet computers and smartphones.

Hitachi IPS technology development[6][7]
Name Nickname Year Advantage Transmittance/
contrast ratio
Remarks
Super TFT IPS 1996 Wide viewing angle 100/100
Base level
Most panels also support true 8-bit per channel color. 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Super-IPS S-IPS 1998 Color shift free 100/137 IPS has since been superseded by S-IPS (Super-IPS, Hitachi Ltd. in 1998), which has all the benefits of IPS technology with the addition of improved pixel refresh timing.
Advanced Super-IPS AS-IPS 2002 High transmittance 130/250 AS-IPS, also developed by Hitachi Ltd. in 2002, improves substantially on the contrast ratio of traditional S-IPS panels to the point where they are second only to some S-PVAs.
IPS-Provectus IPS-Pro 2004 High contrast ratio 137/313 The latest panel from IPS Alpha Technology with a wider color gamut and contrast ratio matching PVA and ASV displays without off-angle glowing.
IPS alpha IPS-Pro 2008 High contrast ratio Next generation of IPS-Pro
IPS alpha next gen IPS-Pro 2010 High contrast ratio Technology transfer from Hitachi to Panasonic
LG IPS technology development
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 5ms.[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.[8]

Technology[edit]

Schematic diagram IPS LC display

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° 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. Because they are in the same plane and on only one glass plate, they generate an electric field 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 electrical 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 & e2 and a corresponding electrical field E is generated, which 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. As both electrodes are on the same substrate, they take more space than electrodes of TN matrices. This also reduces contrast and brightness.[9]

Super-IPS was later introduced with even better response times and color reproduction.[10]

This pixel layout is found in S-IPS LCDs. A chevron shape is used to widen the viewing cone.

Advantages[edit]

  • IPS panels display consistent, accurate color from all viewing angles[11] A state-of-the-art (2014) comparison of IPS vs. TN panels concerning color consistency under different viewing angles can be seen on the website of Japan Display Inc.[12]
  • Unlike TN LCDs, IPS panels do not lighten or show tailing when touched. This is important for touch-screen devices, such as smartphones and tablets.[9]
  • 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.[9]

Disadvantages[edit]

  • IPS panels require up to 15% more power than TN displays.
  • IPS panels are more expensive to produce than TN displays.

Super PLS[edit]

In 2012, Samsung Electronics 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 in the past AMOLED panels 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.[13]

Samsung claimed the following benefits of Super PLS (commonly referred to as just "PLS") over IPS:[14]

  • Further improvement in viewing angle
  • 10 percent increase in brightness
  • Up to 15 percent decrease in production costs
  • Increased image quality
  • Flexible panel

Manufacturers[edit]

See also[edit]

References[edit]

  1. ^ "Bibliographic data: US3834794 (A) ― 1974-09-10". Espacenet.com. Retrieved 9 October 2013. 
  2. ^ U.S. Patent 3,834,794: R. Soref, Liquid crystal electric field sensing measurement and display device, filed 28 June 1973.
  3. ^ "Bibliographic data: US5576867 (A) ― 1996-11-19". Espacenet.com. Retrieved 9 October 2013. 
  4. ^ 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 9 January 1990.
  5. ^ "2014 SID Honors and Awards". SID informationdisplay.org. Retrieved 4 July 2014. 
  6. ^ IPS-Pro (Evolving IPS technology)
  7. ^ http://www.barco.be/barcoview/downloads/IPS-Pro_LCD_technology.pdf
  8. ^ tech2 News Staff. "LG Announces Super High Resolution AH-IPS Displays". Tech2.in.com. Retrieved 2013-07-21. 
  9. ^ a b c Baker, Simon (30 April 2011). "Panel Technologies: TN Film, MVA, PVA and IPS Explained". Tftcentral.co.uk. Retrieved 13 January 2012. [unreliable source?]
  10. ^ "LCD Panel Technology Explained". PChardwarehelp.com. Retrieved 13 January 2012. [unreliable source?]
  11. ^ Comparisons done by LG Display
  12. ^ Visual comparison of IPS and TN done by Japan Display Inc.
  13. ^ "Samsung Adopts IPS instead of AMOLED: Why?". seoul.co.kr. Retrieved 9 November 2012. 
  14. ^ "Samsung PLS improves on IPS displays like iPad's, costs less". electronista.com. Retrieved 30 October 2012. 
  15. ^ Cross, Jason (March 18, 2012). "Digital Displays Explained". TechHive. PC World. p. 4. Retrieved 9 October 2013. 

External links[edit]

Media related to IPS panel at Wikimedia Commons