LIQUID CRYSTAL TELEVISION (AUDIO AND VIDEO SYSTEM). PRESENTED BY:- PATEL PURTI B. (130630111018)

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 picture.

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 nematic. 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: Light can be polarized. Liquid crystals can transmit and change polarized light. The structure of liquid crystals can be changed by electric current. Availability of transparent substances that can conduct electricity.

LCD MATRIX TYPES AND OPERATION. The two types of LCDs have either passive or active matrix patterns. 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 oxide. 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 screen. 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 panel

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 and Radiation Emission 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 PC’s. 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 milliseconds.

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 colors. 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 past.

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 computer. 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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