What Is LCD???
• A liquid crystal display (LCD) is a thin, flat panel used for
electronically displaying information such as text, images, and
• 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
• 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%
History and Development of LCDs
• Discovery of liquid crystals
• Friedrich Reinitzer discovers liquid crystals
• Otto Lehmann publishes work on liquid crystals
• Richard Williams and George Heilmeier suggest using
liquid crystals for making a display device
• First operational LCD created by RCA using Dynamic Scattering Method
• First LCD using Twisted Nematics (TN) produced
History and Development of LCDs (cntd)
• First commercial LCDs came into existence. The technology was first
used in the quartz watch and in early calculator displays.
• Early use of colour LCDs for digital cameras and computer monitors
• Technological improvements led to larger LCDs suitable for home theatre
• 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.
Types of LCDs
• Passive vs Active Matrix
• 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
• 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
• There is no switching device.
• Pixels are addressed one at a time by row and
• Only used in low-resolution displays (such as watch,
• Slow response time, poor contrast
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
• 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
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
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.
ADVANTAGES OF LCD
Produces very bright images due to high peak intensity. Very
suitable for environments that are brightly lit .
Produce considerably lower electric, magnetic and
electromagnetic fields than CRTs.
No geometric distortion at the native resolution. Minor
distortion can occur for other resolutions.
Energy efficient. Consume less than 1/3 the power of a
comparable CRT. Consume less electricity than a CRT and
produce little heat.
Take up about 40% less desk space. LCDs are thin and
Screen Shape Completely flat screen.
At 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 LCD
Aspect Ratio The aspect ratio and resolution are fixed.
Not proficient at producing black and very dark grays. In a
"standard" configuration, not appropriate for use in dimly lit and
Contrast Lower contrast than CRTs due to a poor black-level.
Considerably more expensive purchase price than comparable
CRTs . (Cheaper lifetime cost: lasts about 13,000 - 15,000 more
hours than a typical CRT.)
Slow response times and scan rate conversion result in severe
motion artifacts and image degradation for moving or rapidly
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.
Restricted viewing angles. Viewing angles affect the brightness,
contrast and colors shown. Wide angles can lead to contrast and