LIQUID CRYSTAL AND DISPLAY APPLICATIONS

MONIKAM.SC. APPLIED PHYSICS

Topic: Display Applications

What is LCD??

Liquid crystal display (LCD) is a thin, flat panel used for electronically displaying

information such as text, images, and moving pictures.

LCD does not directly emit light in order to create visualizations, it rather modifies the transmission of light to represent images.

Light EMITTING Display DeviceLight MODULATING Display Devices.

Plasma displays, CRT and OLED devices

How this Stuff Works??

Working…No Voltage applied across the pixel

Molecules twist to align the rubbing of the glass plates.Light entering 1st polarizer is twisted and can exit the 2nd

polarizerPixel is ON

Voltage applied across the pixelMolecules untwisted to align with electric field.Light entering 1st polarizer cannot exit the 2nd polarizerPixel is OFF

Color Display Each pixel has three sub-pixels: Red, Green and

Blue.Different intensities of the sub-pixels give

perception of whole spectrum of colors.If each red ,green and blue sub-pixel can display

256 different intensity of their respective color , then each pixel can produce a possible palette of 16.8 million (256*256*256) colors

Types of LCD Passive Matrix Active Matrix

Passive Matrix Liquid Crystal Display

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

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 Only used in low-resolution displays (such as watch, calculator)

Cross talk 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.”

Passive Matrix Display Problems

Active Matrix Liquid Crystal Display

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

each other. Each row line is activated sequentially (Scanned one row at a

time) Used in computer displays A switching device and a storage capacitor are integrated at

the each cross point of the electrodes.

Advantage of Active Matrix Display

• Higher sizes• Higher contrast• Higher gray scale• Higher resolution• Higher viewing angle• Faster response.• Better control of the color

Smaller size —LCDs occupy approximately 60 percent less space than CRT displays.

Lower power consumption—LCDs typically consume about half the power and emit much less heat than CRT displays.

Lighter weight —LCDs weigh approximately 70 percent less than CRT displays of comparable size.

No electromagnetic fields —LCDs do not emit electromagnetic fields and are not susceptible to them. Thus, they are suitable for use in areas where CRTs cannot be used.

Longer life —LCDs have a longer useful life than CRTs.

Advantage Of LCD Over CRT

Disadvantages of LCDAspect Ratio aspect ratio and resolution are fixed.

Black-Level Not 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.

Motion Artifacts

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

Resolution procedures which can cause considerable deterioration of the image.

Viewing Angle

Restricted viewing angles. Viewing angles affect the brightness, contrast and colors shown.

Bibliography

http://bootstrike.com/Articles/LCDvsCRT

http://www.explainstuff.com/lcdtv.html

http://www.slideshare.net/

https://www.youtube.com/watch?v=Bf3547WB5qs Liquid Crystal Displays: Fundamental Physics and Technology by

Robert H. Chen

Thank You