SETUP BOX
A set-top box is a receiver and decoder digital device for satellite TV. A satellite TV system is a digital TV transmission system that compresses and codes the TV signals to limit the bandwidth and minimize the error. To reproduce the received TV signals a sophisticated application-specific system-on-chip (SoC) is required. A set-top box contain these kind of SOCs which act as an interfacing device between the antenna system and TV display set. A simplified block diagram of the set-top box is shown in Fig.5.21
The first stage of the set-top box is the RF module which receives television signals from a dish antenna via co-axial cable. The RF module consists of a low noise amplifier which reduces the noise and amplifies the signal. The signal is given to a quadrature down converter which is used to reduce the error rate from the signal.
The quadrature down converter converts the incoming RF signal into two components in-phase and quadrature components. These I and Q components are given to ADC to convert into digital signals. The demodulator is a sophisticated 11-chip that recovers the data stream and performs error correction.
This feeds the MPEG decoder, which incorporates the MPEG-2 video decoder. This video decoder decompresses the digital data stream which has been compressed by the transmitter before transmission. This video decompression restores the picture PE quality of the original video signal.
Graphics processor provides additional control such as brightness, contrast, sharpness, etc. The audio processor facilitates the interface for stereophonic or 5.1-channel audio output. This unit also includes circuitry to handle the user interface, a wireless network connection, and a wide range of interfaces, such as USB.
HIGH DEFINITION TV(HDTV)
Definition: usually an aspect ratio of 16: 9The viewer of HDTV feels as if they are part of the scene they are watching.
HDTV and digital TV are not the same thing - HDTV is one format of original digital TV.
FEATURES OF HD TV
1. Wider screen.
2. The high aspect ratio is 16: 9.
3. This permits high viewing angle Peripheral viewing.
4. Resolution is high.
5. Double horizontal lines for the sharpest picture.
6. It produces very high-quality pictures.
7. The quality of sound is excellent.
1. Wide Screen Mode: It allows you to watch 4:3 normal broadcasts in widescreen mode (16:9 aspect ratio).
2. High Aspect Ratio: Standard television has a 4:3 aspect ratio - it is four units wide by three units high. HDTV has a 16:9 aspect ratio, more like a movie screen.
3. Viewing Angle is High: This permits a high viewing angle.
4. High Resolution: The lowest standard resolution (SDTV) will be about the same as analog TV and will go up 704x480 pixels. The highest HDTV resolution is 1920×1080 pixels. For 4K ultra HD smart TV which produces images at a resolution of 3840×2160 pixels. This resolution is four times higher than standard HDTVs.
5. Double Horizontal Lines for Sharpest Picture: The sharpest picture is due to the enhanced number of horizontal lines from 625 to 1250 (or) 525 to 1120 in America.
6. Very High-Quality Picture: It delivers superb picture quality from any video source. It produces high-quality crystal clear pictures.
7. Digital quality of Sound: The quality of sound is excellent. HDTV produces a rich, deep, and digital quality 10.1 channel sound.
8. Frame Rate: A set's frame rate describes how many times it creates a complete picture on the screen every second.
WORKING PRINCIPLE OF LCD
An LCD element consists of two major components; a layer of liquid crystal sandwiched between two finely grooved surfaces with their grooves perpendicular to each other and two optical polarizing filters perpendicular to each other. The liquid crystal consists of long-rod-like molecules that are in their natural state and arrange themselves with their axes roughly parallel to each other.
By flowing the liquid crystal over the finely grooved surface it is possible to control the alignment of the molecules as they follow the alignment of the grooves. The molecules at the two surfaces are aligned perpendicular to each other and those at the intermediate layers are twisted by Intermediate angles. Natural light waves are oriented at random angles and flow along various planes from the light source.
An optical polarizing filter or polarizer can isolate a single plane of light from the collection. The filter acts as a net of finely parallel lines blocking all light except those flowing in a plane parallel to the lines. The light in this condition is said to be polarized. A second polarizer whose lines are perpendicular to the first would block all the polarized light.
The container with grooved surfaces is placed in between two perpendicular polarizing filters. However in this case the liquid crystal material placed in between twists the plane of light by 90° passes through the material due to its molecular alignments. The light now is parallel to the second filter and comes wholly through it to the eye of the observer This constitutes a light pixel on the screen.
TYPES OF LED'S
Liquid Crystal Display (LCD) is a passive device which means that it does not produce any light( because LCDs are not self-emitting like LEDs) to display characters, images, video, and animations. But internal construction of LCD, simply allows the light to travel through it in order to produce any characters, images, videos, and animations.
Liquid crystals are used as displays in many modern equipment such as TV receivers, watches, calculators, mobile phones, etc. LCDs are very popular as display units because of their low power consumption compared to LEDs, Matter has three states which are gasses, solids, and liquids. Liquid crystals have been considered as the fourth state of matter. Crystal is a solid form but liquid crystal material exists in liquid forms.
Based on Construction LCD Displays are classified into Two Types:
Dynamic Scattering Type LCD: In liquid crystals, the molecules are oriented in definite crystal patterns when unexcited. When an electric field is applied to the liquid crystal, the molecules tend to disordered state, and the liquid crystal scatters light. This phenomenon is called dynamic scattering. Dynamic scattering type LCD produces a white display on a dark background.
2. Field Effect Type LCD: The construction of a field effect LCD display is similar to that of the dynamic scattering type, with the exception of two polarizing optical filters. Field effect type LCD produces a dark display on a white background.
