Speciality of IPS LCD displays - eZoneToday


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Thursday, 13 October 2016

Speciality of IPS LCD displays

IPS LCD Display is one of leading display technology used in smartphones and other handheld devices.

Many Leading Mobile Phones like
iPhone7 use an IPS display
Content Highlights
  • What is LCD and How it works 
  • How LCD panel is wired 
  • Twisted nematic LCD 
  • Different Layers of LCD pannel
  • TFT display and its shortcomings 
  • IPS Display technology 
  • Advantages and Disadvantages of IPS LCD display technology in comparison with TFT,LED etc..

Before going into IPS LCD displays,let us have look at basic operation of LCDs. Liquid crystals (LCs) are matter in a state which has properties between those of conventional liquids and those of solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. When electricity is passed through, this crystals scatter light is different directions. This basic property of Liquid Crystals is exploited in Liquid Crystal Displays.

Basic unit of a LCD display system is a liquid crystal cell consists of a thin layer (about 10 u m) of a liquid crystal sandwiched between two glass sheets with transparent electrodes deposited on their inside faces. With both glass sheets transparent, the cell is known as transmittive type cell. When one glass is transparent and the other has a reflective coating, the cell is called reflective type. The LCD does not produce any light of its own. It depends entirely on light falling on it from an external source for producing viewable light.

Twisted nematic LCD

A nematic liquid crystal is a transparent or translucent liquid that causes the polarization of light waves(focusing of light in a plane) to change as the light pass through it.The extend of polarization depends on the intensity of applied electric field.
Twisted Nematics, a particular nematic substance is twisted naturally. When a known voltage is applied to the substance, it gets untwisted in varying degrees according to our requirement. This in turn is useful in controlling the passage of light. The relatively inexpensive twisted nematic display is the most common consumer display type.

How LCD works
Different Layers of an LCD unit
An LCD unit has two polarized glass pieces(F). The glass which does not have a polarized film on it must be rubbed with a special polymer to form microscopic grooves in the surface(B&E). Grooves are on the same direction as the polarizing film. Nematic crystal layer(D) is sandwiched between electrodes. The grooves will cause the first layer of molecules to align with the filter’s(polarizer) orientation. Two grooved glasses are at right angle to each other. Till the uppermost layer is at a 90-degree angle to the bottom, each successive layer of TN molecules will keep on twisting. The first filter will naturally be polarized as the light strikes it at the beginning. Thus the light passes through each layer and is guided on to the next with the help of molecules. When this happens, the molecules tend to change the plane of vibration of the light to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. The light is only allowed an entrance if the second polarized glass filter is same as the final layer. Take a look at the figure given above. Please note two polarizers are at right angle to each other.

The main principle behind liquid crystal molecules is that when an electric field is applied across them, they tend to untwist. This causes a change in the light angle passing through them. This causes a change in the angle of the top polarizing filter with respect to it. So little light is allowed to pass through that particular area of LCD. Thus that area becomes darker comparing to others.

Colour LCDs are those that can display pictures in colours. In addition to above layers, there must be three sub-pixels with red, green and blue colour filters to create each colour pixel.

LCD panel wiring

The liquid crystal displays used in calculators and other devices with similarly simple displays have direct-driven image elements, and therefore a voltage can be easily applied across just one segment of these types of displays without interfering with the other segments.
LCD pannel wiring
Direct driven LCD pannel

This would be impractical for a large display, because it would have a large number of (color) picture elements (pixels), and thus it would require millions of connections, both top and bottom for each one of the three colors (red, green and blue) of every pixel. To avoid this issue, the pixels are addressed in rows and columns, reducing the connection count from millions down to thousands. The column and row wires attach to transistor switches, one for each pixel. The one-way current passing characteristic of the transistor prevents the charge that is being applied to each pixel from being drained between refreshes to a display's image. Each pixel is a small capacitor with a layer of insulating liquid crystal sandwiched between transparent conductive layers.

TFT Displays

TFT Displays uses TN(Twisted nematic technology) The circuit layout process of a TFT-LCD is same as that explained above. However, rather than fabricating the transistors from silicon, that is formed into a silicon wafer, they are made from a thin film of silicon that is deposited on a glass panel. Transistors take up only a small fraction of the area of each pixel and the rest of the silicon film is etched away to allow light to easily pass through it.

Disadvantage of of TFT displays

Since TFT display uses TN technology,it has got disadvantages of TN displays.TN displays suffer from limited viewing angles. Colors will shift when viewed off-perpendicular
Also, most TN panels represent colors using only six bits per RGB color, or 18 bit in total, and are unable to display the 16.7 million color shades (24-bit true-color) that are available from graphics cards. Instead, these panels display interpolated 24-bit color using a method that combines adjacent pixels to simulate the desired shade. This disadvantages lead to the invention of IPS Technology.

IPS Display Technology

IPS (In-Plane Switching) displays provide consistent, accurate color from all viewing angles without blur or grayscale inversion. IPS displays show clear images with stable response time, and no halo effect is produced when touched.

Working of IPS Display
Working of IPS Display
What is an ips display?:Each pixel within an IPS type TFT consists of three sub-pixels (Red, Green and Blue). Each sub-pixel has a pair of electrodes to control the twisting of the Liquid Crystals. Unlike TN type TFTs where the electrodes are on opposing plates, the electrodes in an IPS TFT are on only one of the glass plates (i.e. in the same plane). When voltage is applied to the electrodes, all the Liquid Crystal molecules align in parallel with that plane and allow light to pass through to the polarizers and RGB color filters. In effect, TN displays force the Liquid Crystal molecules perpendicular to the glass which blocks some light from coming out at wide angles, while IPS displays keep the Liquid Crystal molecules in line to allow light through at all angles.
All modern mobiles phones from iPhones,samsung,LG etc.. are using IPS LCD displays.Many varaints of IPS displays are available in market.LG is one of the largest supplier of IPS displays.

Advantages of IPS Display

  • IPS panels display consistent, accurate colour from all viewing angles
  • Unlike TFT- TN LCDs, IPS panels do not lighten or show tailing when touched (halo effect). This is important for touch-screen devices, such as smartphones and tablets 
  • IPS panels offer clear images and stable response time .

Disadvantages of IPS Display

  • IPS panels require up to 15% more power than TN panels.
  • IPS panels are more expensive to produce than TN panels.
  • IPS panels have longer response time than TN panels.
All modern mobiles phones from iPhones,samsung,LG etc.. are using hd ips display.LG is one of the largest supplier of IPS screen displays.Are you planning to buy a IPS display laptop or full HD IPS display smartphone,then do some research ,because many varaints of IPS display monitors are available in market.Choose your product based on the price and affordability.

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