liquid crystal television

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Transcript liquid crystal television

INTRODUCTION: Liquid Crystal Display(LCD) was the first to emerge
as an alternative and initially found applications in
computer monitors, laptops and as indicators in watches
and various equipments.
 In a LCD display, the screen consists of a liquid crystal
solution in-between two clear glass panels.
 An electric current passed through the solution causes
the crystal to act like a shutter, either blocking the
incident light or allowing it to pass through.
 This phenomena is used to cause light and dark areas
on the LCD screen which when regulated results in
LCD TECHNOLOGY: Liquid Crystals. In solids, molecules always maintain
their orientation and stay in the same position with
respect to each other.
 In liquids, molecules change their orientation and
move anywhere in the liquid.
 However, there are some substances where the
molecules tend to maintain their orientation like in
solids but move around to different locations as in
liquids. These are called as liquid crystals.
 LIQUID CRYSTAL TYPE. Most liquid crystals
have rod shaped molecules and are classified as
Thermotropic or Lyotropic.
 Thermotropic liquid crystals can be either Isotropic or
 While molecules in isotropic liquid crystals are
random in their arrangement but in nematic type these
have a definite order or pattern.
 Their pattern can be changed on application of
magnetic or electric charge across them and this forms
the basis of LCD display.
 CREATING AN LCD. The four factors that enable
making of LCD panels are:
i. Light can be polarized.
ii. Liquid crystals can transmit and change polarized
iii. The structure of liquid crystals can be changed by
electric current.
iv. Availability of transparent substances that can
conduct electricity.
 The two types of LCDs have either passive or active matrix
 Passive Matrix. All LCD display consists of millions of
tiny sub-areas called pixels as in CRT screens.
 In the passive matrix, a simple grid is used to supply
charge to a particular pixel in the display.
 However, the process of creating a grid is quite complex
and starts with two layers called substrates which are made
from a transparent conductive material, usually indium-tin
 One substrate is for columns and the other for rows.
 The rows and columns are connected to integrated circuits
that control the charge when sent down a particular column
and row.
 The liquid crystal material is sandwiched between the
chosen glass substrates and a polarizing film is added to the
other side of each substrate.
 Slow Response Time. The passive matrix system has a
significant drawback called ‘Slow Response Time’.
 This refers to the LCD’s ability to refresh the displayed
image i.e., to remove it quickly after it gets displayed.
 If the action is slow, ghost images will be shown on the
 Non-Precise voltage control. Another Drawback is due to
non-precise voltage control that hinders the passive matrix’s
ability to influence only one pixel at a time.
 The result is that when voltage is applied to
untwist one pixel, the pixels around it also
partially untwist making the appear fuzzy and
lacking in contrast.
 Thus passive matrix is not suitable where signal
changes are very fast as in television.
 Active Matrix. To overcome the drawbacks
stated above, the active matrix display uses thin
film transistors(TFT) for delivery of charge.
 Thin film transistors are tiny switching transistors
cum capacitors.
 For control the charge delivery, the TFT’s are
arranged in a similar matrix on the substrate and
exercise precise control
Advantages of LCDs
• Physical Size
– Compact and Lightweight
– Space saving
– Can be mounted on a wall or
Advantages of LCDs
• Display Size
– Available at comparable in screen size as
traditional CRT
– Shown on the next slide, a 12.1" LCD
display (left) has only a slightly smaller
viewing area than a typical 14" CRT
monitor. Newer, larger LCD monitors are
also appearing that have 15", 17", and even
larger screen sizes that are comparable to
the largest CRT monitors. (One thing to
note is that LCD monitors are typically
sized by their actual viewable diagonal
measurement, but CRTs typically are not.)
Advantages of LCDs
• Power Consumption
– Does not emit Radiation
– Not subject to Electromagnetic Interference
Advantages of CRT
• Response Time
– Faster response time. Critical to people
who watch videos or play games on their
– The fastest LCD’s offer a response time of
about 25 milliseconds as apposed to CRT’s
that have a response time of about 13
Disadvantages of LCDs
• Resolution
• Displays Native Resolutions (Resolution
that it displays best)
• Viewing Angle
• Smaller, needed to be viewed more
directly from the front.
• From the side the images on an LCD
screen can seem to disappear, or invert
• Newer displays that are coming out have
a wider viewing angle so this is not as
much of an issue as it has been in the
Disadvantages of LCDs
• Price
– Upfront cost it is more costly but long-term
cost but will conserve energy in the long run.
– The energy savings may not be much for an
individual use, but for a corporate office where
50 displays or more are in use, the energy
savings might be more of an issue.
Disadvantages of LCDs
• Installation
– Need a plug interface to connect to the
– Some require a special digital plug-interface in
order to work .
– Problem: is that this plug is not available on
most computers, so another video card or
adapter must be purchased to plug these LCD
monitors into the computer.
Disadvantages of LCDs
• Response Time
– It is much slower. The delay can cause a
ghosting effect on images it displays.
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