Transcript Liquid crystals

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
zoom
we
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.
Now, What happens when
the light leaves the backlight
source… ?
It travels in different planes
including – Horizontal and
Vertical.
What happens when light
passes through first polarizer
which is a horizontal polarizer?
What happens when light passes
through Second polarizer which is a
vertical polarizer?
No light will reach the colour
filter – it will remain black!!!
This is where liquid
crystals come into play!!
… 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.
The itched glasses in the front and back
forces the liquid crystals to orient
themselves in a predictable fashion
which are otherwise randomly
oriented.
RANDOM ORIENTATION
Light naturally follows the path
of oriented molecules.
So that any light travelling along
the horizontal planes exits along
the vertical plane.
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.
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?
• 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.
How is plasma created?
• 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:
•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.