LIQUID CRYSTAL DISPLAY (LCD)

What Is LCD???• A liquid crystal display (LCD) is a thin, flat panel used for

electronically displaying information such as text, images, and moving pictures.

• It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of a light source(backlight) or reflector to produce images in color or monochrome.

• Its uses include computer monitors ,televisions , instrument panels, and devices ranging from aircraft cockpit displays, to every-day consumer devices such as clocks , calculators, and telephones.

3

LCD Overview

• LCDs are a type of light modulating display device. LCD technology does not directly emit light in order to create visualizations, it rather modifies the transmission of light to represent images.– On the other hand Plasma displays, CRT and OLED devices are all

light emitting display devices.• LCDs are rapidly becoming the most popular display device available.

– 2006 - Nearly 33% of all TVs sold in North America were LCDs– 2007 - Expected to surpass 50%

4

History and Development of LCDs• Discovery of liquid crystals

– 1888• Friedrich Reinitzer discovers liquid crystals

– 1904• Otto Lehmann publishes work on liquid crystals

• Innovation– 1963

• Richard Williams and George Heilmeier suggest using liquid crystals for making a display device

– 1968• First operational LCD created by RCA using Dynamic Scattering Method

(DSM)– 1971

• First LCD using Twisted Nematics (TN) produced

5

History and Development of LCDs (cntd)• Applications

– 1970’s• First commercial LCDs came into existence. The technology was first

used in the quartz watch and in early calculator displays.– 1990’s

• Early use of colour LCDs for digital cameras and computer monitors – 2000’s

• Technological improvements led to larger LCDs suitable for home theatre use.

• Full HD 1080p displays produced• Currently the largest LCD panel is 108”

Liquid Crystal Displays

Liquid crystal display (LCD) is a flat electronic display panel used as a visual display aid. It uses liquid crystals to create visual effects on screen. Liquid crystal is a state of matter between solids and liquids. LCDs do not generate light on their own but rely on sunlight or room light to generate images with help of liquid crystal.

How LCD Works

8

Types of LCDs• Passive vs Active Matrix

– Passive• Each pixel must retain it’s state without a steady electric charge• Scanned one pixel at a time• Poor contrast, and very slow response times

– Active• Electric charged is stored between refreshes• Scanned one row at a time

PASSIVE MATRIX LCD DISPLAY

• Uses a grid of vertical and horizontal conductors comprised of Indium Tin Oxide (ITO) to create an image

• There is no switching device.• Pixels are addressed one at a time by row and

column matrix• Only used in low-resolution displays (such as watch,

calculator)• Slow response time, poor contrast

9

10

PASSIVE MATRIX LCD DISPLAY

PASSIVE MATRIX LCD DISPLAY

• It is based on Thin Film Transistor (TFT) Technology• Switching element at each pixel. Individual pixels

isolated from each other. Thin Film Transistors most commonly used.

• Each row line is activated sequentially• Used in computer displays• A switching device and a storage capacitor are

integrated at the each cross point of the electrodes

11

12

ACTIVE MATRIX LCD DISPLAY

PROBLEMS FACED IN PASSIVE DISPLAY

• Crosstalk occurs when neighboring pixel voltages affect each other, reducing the gray scale, contrast, and viewing angle.

• Submarining occurs when slow-to-respond LC materials cannot respond quickly enough and the picture can disappear temporarily.

• One Solution: placing a switch at each pixel, such as a transistor or diode --> pixel matrix becomes “active.”

13

PROBLEMS SOLVED BY ACTIVE DISPLAY

• Pixel isolation eliminates crosstalk • Isolation from the column line permits the pixel

capacitor to remain charged, so that faster responding liquid crystals can be used. • Due to switching action of transistors,only the desired

pixel recieve a charge ,improving image quality over a passive matrix.

14

ADVANTAGES OF LCDBrightness Produces very bright images due to high peak intensity. Very

suitable for environments that are brightly lit .

Emissions Produce considerably lower electric, magnetic and electromagnetic fields than CRTs.

Geometric Distortion

No geometric distortion at the native resolution. Minor distortion can occur for other resolutions.

Power Consumption

Energy efficient. Consume less than 1/3 the power of a comparable CRT. Consume less electricity than a CRT and produce little heat.

Physical Aspects Take up about 40% less desk space. LCDs are thin and compact.

Screen Shape Completely flat screen.

SharpnessAt the native resolution, the image is perfectly sharp. Adjustments are required at all other resolutions which can result in measurable degradation to the image.

DISADVANTAGES OF LCDAspect Ratio The aspect ratio and resolution are fixed.

Black-LevelNot proficient at producing black and very dark grays. In a "standard" configuration, not appropriate for use in dimly lit and dark conditions.

Contrast Lower contrast than CRTs due to a poor black-level.

CostConsiderably more expensive purchase price than comparable CRTs . (Cheaper lifetime cost: lasts about 13,000 - 15,000 more hours than a typical CRT.)

Motion Artifacts

Slow response times and scan rate conversion result in severe motion artifacts and image degradation for moving or rapidly changing images.

Resolution

Works best at the native resolution. The native resolution can not be changed. All other resolutions require adjusting procedures which can cause considerable deterioration of the image.

Viewing Angle

Restricted viewing angles. Viewing angles affect the brightness, contrast and colors shown. Wide angles can lead to contrast and color reversal.

THANK YOU

BYAVI DHRUV - 15

AAKASH GOYAL – 16HOZEFA JARWALA - 17

JAI KABRA – 18