NAME: VIPUL KUMAR MISHRA (014) NIKHIL ANANDE (005) ENROLMENT NUMBER: 130950111014 130950111005 DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING, ITM UNIVERSE, VADODARA. 5Th Semester. SUBJECT : AUDIO AND VIDEO SYSTEMS (2151101)

LCD And PLASMA Televisions

LCD DISPLAY HISTORY OF LIQUID CRYSTALS And ITS Application In LCD First discovered in 1888 by an Austrian botanist – Freidrich Reinitzer. He melted a curious cholesterol – like substance (cholesteryl benzoate), it first became a cloudy liquid and then cleared up as its temperature rose. Upon cooling, the liquid turned blue before finally crystallizing. The first experimental LCD was made in 1968 (after 80 years of discovering the first liquid crystal substance).

WHAT ARE LIQUID CRYSTALS? Liquid crystals are matter in such a state that has properties in between those of conventional liquids and those of solids crystals. So, liquid crystals do not directly melt to the liquid phase but first pass through a Para crystalline stage. Liquid crystal materials generally have several common characteristics. Among these are a rod-like molecular structure, rigidness of the long axis, and are strong dipoles. SOLID LIQUID CRYSTAL LIQUID LIQUID LIQUID CRYSTAL

TYPES OF LIQUID CRYSTAL Broadly, liquid crystals can be classified into – thermotropic and lyotropic. Further, thermotropic types have various sub phases like – nematic phase, smectic phase and choelsteric phase.

OVERVIEW OF LIQUID CRYSTAL PHASES

CREATING AN LCD LCDs work using these four major concepts or ideas : Light can be polarized. Liquid crystals can transmit and change polarized light. The above mentioned fact can be realised by changing the structure of liquid crystals by applying an electric field. Availability of transparent substances that can conduct electricity.

LIGHT AND POLARIZATION Light can be represented as a transverse electromagnetic wave made up of mutually perpendicular, fluctuating electric and magnetic fields. Ordinary white light is made up of waves that fluctuate at all possible angles – this is non polarized light whereas a polarized light will consist of electric field (or magnetic field) oscillating in any particular direction – may be vertical (vertical polarization), may be horizontal (horizontal polarization), or may be diagonal ( diagonal polarization) or any possible single direction.

HOW POLARIZATION IS ACHIEVED? Polarization is achieved using Polarizers. A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations.

HOW LCD WORKS? Lets consider a LCD Screen! And Suppose that we zoom into it……

What will you observe?? Three Of These Grouped Together makes up one picture element called as pixel in short.

... And When you Split Up These PIXELS You will see : A Backlight Three Colour Filters, and Polarizers.

What happens when light passes through first polarizer which is a horizontal polarizer? Now, What happens when the light leaves the backlight source… ? It travels in different planes including – Horizontal and Vertical.

No light will reach the colour filter – it will remain black!!! This is where liquid crystals come into play!! What happens when light passes through Second polarizer which is a vertical polarizer? No light will reach the colour filter – it will remain black!!!

… Lets have a close look at one of these liquid crystals. It consist of : Transparent electrode at front and back. Itched glass on the front and the back. … Lets have a close look at one of these liquid crystals.

The itched glasses in the front and back forces the liquid crystals to orient themselves in a predictable fashion which are otherwise randomly oriented. Light naturally follows the path of oriented molecules. So that any light travelling along the horizontal planes exits along the vertical plane. RANDOM ORIENTATION

Now, as the role of itched glass is to orient molecules in a predictable fashion.. The role of glass electrode is to pass an electric field to make the molecules of liquid crystal align themselves in the direction of electric flow… Now, since there is no twisting of light.. No light will flow out of the liquid crystal.

… Now lets place these liquid crystals back into the pixels.

However, if we turn on the electrode!! As we saw before, due to re alignment of LC molecules , Light is no longer twisted AND the untwisted light stops at the vertical polarizer.

… But by adjusting the amount of electricity between the electrodes we can control how much light reaches each colour filter!! And that’s how it is decided, what colour is seen on the screen.

We generally talk about colour on the display in terms of how bright RED, BLUE and GREEN are in each pixel from 0 to 255. If All three numbers are ZERO then, colour on the display appears BLACK.

If all the numbers are 255 then the colour which appears on the screen in white.

As you increase the amount of RED, GREEN and BLUE you will see different colours appear on the screen.

… And this is how a LCD works. The monitor adjusts the amount of electricity flowing through each liquid crystal one by one, row by row around 60 times per second to get the full picture. … And this is how a LCD works.

PLASMA DISPLAYS

What is a plasma? How is plasma created? It is a fourth state of matter and is the most abundant form of ordinary matter in the Universe . All the stars including sun is made up of plasma. A plasma can be created by heating a gas or subjecting it to a strong electromagnetic field. This decreases or increases the number of electrons, creating positive or negative charged particles called ions, and is accompanied by the dissociation of molecular bonds, if present .

A plasma display is a computer video display in which each pixel on the screen is illuminated by a tiny bit of plasma or charged gas, somewhat like a tiny neon light. Plasma displays are thinner than cathode ray tube ( CRT ) displays and brighter than liquid crystal displays ( LCD ). A plasma display panel (PDP) is a type of flat panel display common to large TV displays 30 inches (76 cm) or larger.

They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent lamps.

PRINCIPLE OF PLASMA DISPLAY PANELS In plasma display panels the light of each picture element is emitted from plasma created by an electric discharge. The dimensions of the discharge are in the 100 micro-meters range at a pressure of a few hundred torrs, and the voltage applied between electrodes is in the 100-200 V range.

GENERAL CHARACTERISTICS Plasma displays are bright (1,000 lux or higher for the module). They have a wide color range. They can be produced in fairly large sizes up to 3.8 meters (150 in) diagonally. They have a very low-luminance "dark-room" black level compared with the lighter grey of the unilluminated parts of an LCD screen (i.e. the blacks are blacker on plasmas and greyer on LCDs). The display panel itself is about 6 cm (2.4 in) thick, generally the device's total thickness (including electronics) to be less than 10 cm (3.9 in). Power consumption is 400 watts for a 127 cm (50 in) screen. 200 to 310 watts for a 127 cm (50 in) display when set to cinema mode. Most screens are set to "shop" mode by default, which draws at least twice the power (around 500–700 watts) of a "home" setting of less extreme brightness.

WORKING OF A PLASMA DISPLAY

ADVANANTAGES Picture Quality:   Picture Quality: Capable of producing deeper blacks allowing for superior contrast ratio. Wider viewing angles than those of LCD; images do not suffer from degradation at high angles like LCDs. Less visible motion blur, very high refresh rates and a faster response time, contributing to superior performance when displaying content.

DISADVANTAGES Use more electrical power, on average, than an LCD TV. Does not work well at high altitudes above 2 km due to pressure differential between the gases inside the screen and the air pressure at altitude. It may cause a buzzing noise. For those who wish to listen to AM radio, or are amateur radio operators (hams) or shortwave listeners (SWL), the radio frequency interference (RFI) from these devices can be irritating or disabling.

Thank You