CRT TECHNOLOGY

CRT : DEFINITION

• A CRT is a glass tube that is narrow

at one end and opens to a flat screen
at the other end.

CRT : STRUCTURE

• Narrow end of CRT contains

– a single electron gun for single-color

monitor

– Three electron guns for a color monitor

—one each for three primary colors: red,
green, and yellow.

• The display screen is covered with

tiny phosphor dots.

CRT : PRINCIPLE

• CRT display works on :

Electron emission
Electrons are emitted from the Cathode

tube.

Phosphorescence
It is the emission of visible light, when

electron beam strikes Phosphor
material.

CRT : WORKING

• Cathode
• Grid
• Focusing anode
• Accelerating anode
• Aquadag coating

CRT DISPLAY:ADVANTAGES

• Offers greater resolution .
• Widest viewing angle when

compared to any other technology.

• It is cheap as compared to

LCD,PLASMA displays.

CRT DISPLAY:DISADVANTAGES

• Thickness is much larger as compared to

LCD, PLASMA display.

• Cannot be used for smaller displays
like watches.
• View area is less than the offered monitor

size.

• It is more heavier.

LED TECHNOLOGY

Working of LED

• A light emitting diode is composed of a

semiconductor diode. A semiconductor is a
material that can conduct electricity. A
semiconductor diode is composed of a
semiconductive crystal that has added
impurities in order to create a positive and
negative side; since current flows in one
direction through the diode. A region is
then created in between the positive and
negative zones, called a PN junction, which
is where the action takes place within the
diode; in our case it emits light.

Structure and symbol of LED

LED packages for single element

LEDs

Metal can to-5

type

Epoxy
type

Advantages of LEDs

• Efficiency: An incandescent light requires much

more energy to properly heat the filament in order
to generate light. The light produced by an LED is a
cool light. More light is produced per watt in an LED
than an incandescent.

• Color: LEDs do not require filters, like colored bulbs,

in order to create a specific colored light. Color is
produced based on the material of the
semiconductor.

• Size: LEDs come in many different sizes since they

are not constrained to creating a vacuum in which
to house the filament. LEDs can be smaller than 2
mm.

• On/Off Time: LEDs are very fast devices, having

turn ON/OFF time of less than 1ns.

• Cycling: In applications that are cycled between on

and off frequently, like an outdoor solar light, LEDs
are ideal since they won't burn out quickly.

Cont’d

• Lifetime: The lifetime of the LED greatly exceeds

its incandescent, and even its fluorescent
counterparts. An average lifetime of an
incandescent light is 1,000-2,000 hrs. The LED,
on the other hand, has a typical lifetime of
35,000-50,000 hrs.

• Light Dispersement: An LED is designed to focus

its light, so where an incandescent or fluorescent
may seem brighter since the light radiates in all
directions, the LED light can be directed to a
specific location without the use of an external
reflector.

• Ecologically Friendly: LEDs are more efficient than

others, as stated above; so they conserve
electricity, especially if they are solar powered.

Different material used for

doping

• Ga As --- red
• Ga As P -- red or yellow
• Ga P – red or green

LCD TECHNOLOGY

LCD : DEFINITION

 A liquid crystal display is a thin,

flat display device made up of any
number of pixels arrayed in front of a
light source or reflector. It uses very
small amounts of electric power, and
is suitable for use in battery-powered
electronic devices

LCD : PRINCIPLE

• Liquid crystals are organic compounds,

whose macroscopic behavior resemble

that of liquid but shows physical

properties of crystals

• They have characteristics like: rod-like

molecular structure, rigidness of the long

axis, and strong dipoles and/or easily

polarizable constituents.

CHARACTERISTICS :

LCD : CONSTRUCTION

• Each pixel of an LCD consists of a

layer of molecules aligned between
two transparent electrodes.

• Orientation of the liquid crystal

molecules is determined by the
alignment at the surfaces.

LCD : CONSTRUCTION

A subpixel of a color LCD

LCD : WORKING

• Before applying Electric field, the

molecules arrange themselves in a

helical structure, or twist.

• When a voltage is applied across the

electrodes, a torque acts to align the

liquid crystal molecules parallel to

the electric field , distorting the

helical structure .

• This reduces the rotation of the

polarization of the incident light.

LCD : CLASSIFICATION

• Transmissive displays:
It is illuminated from the back by a

backlight and viewed from the

opposite side (front).Ex :Computer

display.

• Reflective displays:
It is illuminated by external light

reflected by a diffusing reflector

behind the display. Ex: Calculator.

LCD : USES

• LCDs with a small number of

segments, are used in digital
watches and pocket calculators

• Small monochrome displays in

personal organizers, or older laptop
screens

• High-resolution color displays such as

modern LCD computer monitors and
televisions

Features

• Electric field reqd to activate LCD is

of the order of 10

4

V/cm. (=10V when

NLC is 10u thick)

• NLC material possess high resistivity

10

10

ohm. So the current reqd for

scattering light in NLC material is
very marginal.

• Power requirement is 10uW/cm
• Slow device (on/off time upto few

ms)

Printers and plotters

• Printer - A device that prints text or

illustrations on paper.

• Plotters - These printers use a pen

to draw the image on the paper.

Classification

• Impact and non impact
• Fully formed character and dot

matrix printer

• Character at a time and line at a time

printer

Types

• DOT Matrix Printer - Type of printer that employs

movable print heads with pins or wires that shoot and
strike the ribbon placing a dot on the paper with
hundreds of dots forming images or text.

• Inkjet Printer - Printer developed by Canon which

forms letters and images on the paper by spraying
small streams of quick-drying ink. The ink is stored in
a disposable ink cartridge.

• Laser Printer - Laser printers are Printer that uses

laser technology to print images on the paper. The
laser recreates the image on a negatively charged
drum which will then collect ink that is positively
charged to attract to the areas of the image. The
Paper is then negatively charged therefore the
positively charged ink is attracted to the paper and
then is fused onto the paper.

Cont’d

• Thermal printer - A printer that uses heated

pins to "burn" images onto heat-sensitive paper.
The pins are electrically heated and brought into
contact with the specially treated paper easily,
instead of with great impact. The coating on the
paper discolors when heated in this way. These
printers, used in calculators and many fax
machines, are inexpensive, but produce low-
quality, low resolution print. They are however,
quiet and fast as they print.