G. H. Raisoni College of Engineering
An Autonomous Institution under UGC Act 1965 |Accredited by NBA & NAAC ‘A’ Grade
ELECTRONICS AND TELECOMMUNICATION
“Activity Based Learning”
3rdyear / 5th semester.
Section: ‘C ’.
Prof. K.A. Kalbande
Roll No. 30. Ashish Pandey
Today the abbreviation “HD” is known almost to everyone. And it’s clear why: the
notion “high definition” is applied to everything more or less associated with video
production or playback – smartphones, camcorders, monitors, glasses, etc. But most
often we hear about high-definition television, or HDTV. Let’s figure out what it is and
find answers to the most popular questions about HDTV.
HDTV, standing for high-definition television, is a new means of television broadcasting
and the machines that take advantage of it. HDTV broadcasts video digitally (in contrast
to the common analog formats PAL, NTSC, and SECAM) and of higher 720 pixels or 1080
HDTV (high definition television) is a television display technology that provides
picture quality similar to 35 mm. movies with sound quality similar to that of today's
compact disc. Some television stations have begun transmitting HDTV broadcasts to
users on a limited number of channels. HDTV generally uses digital rather than analog
signal transmission. However, in Japan, the first analog HDTV program was broadcast
on June 3, 1989. The first image to appear was the Statue of Liberty and the New York
Harbor. It required a 20 Mhz channel, which is why analog HDTV broadcasting is not
feasible in most countries.
HDTV and standard definition television (SDTV) are the two categories of display
formats for digital television (DTV) transmissions, which are becoming the standard.
HDTV provides a higher quality display with a vertical resolution display from 720p to
1080i. The p stands for progressive scanning, which means that each scan includes every
line for a complete picture, and the i stands for interlaced scanning which means that
each scan includes alternate lines for half a picture. These rates translate into a frame
rate of up to 60 frames per second, twice that of conventional television. One of HDTV's
most prominent features is its wider aspect ratio (the width to height ratio of the
screen) of 16:9, a development based on research showing that the viewer's experience
is enhanced by screens that are wider. HDTV pixel numbers range from one to two
million, compared to SDTV's range of 300,000 to one million. New television sets will be
either HDTV-capable or SDTV-capable, with receivers that can convert the signal to
their native display format. In terms of audio quality, HDTV receives, reproduces, and
outputs Dolby Digital 5.1. In the United States, the FCC has assigned broadcast channels
for DTV transmissions. In SDTV formats, DTV makes it possible to use the designated
channels for multiple signals at current quality levels instead of single signals at HDTV
levels, which would allow more programming with the same bandwidth usage.
Commercial and public broadcast stations are currently deciding exactly how they will
implement their use of HDTV. HDTV uses the MPEG-2 file format and compression
The video from the camera consists of the R, G, and B signals that are converted to the
luminance and chrominance signals. These are digitized by A/D converters. The
luminance sampling rate is 14.3 MHz, and the chroma sampling rate is 7.15 MHz. The
resulting signals are serialized and sent to a data compressor. The purpose of this
device is to reduce the number of bits needed to represent the video data and therefore
permit higher transmission rates in a limited-bandwidth channel. MPEG-2 is the data
compression method used in HDTV. The MPEG-2 data compressor processes the data
according to an algorithm that effectively reduces any redundancy in the video signal.
For example, if the picture is one-half light blue sky, the pixel values will be the same for
many lines. All this data can be reduced to one pixel value transmitted for a known
number of times. The algorithm also uses fewer bits to encode the color than to encode
the brightness because the human eye is much more sensitive to brightness than to
color. The MPEG-2 encoder captures and compares successive frames of video and
compares them to detect the redundancy so that only differences between successive
frames are transmitted. The signal is next sent to a data randomizer. The randomizer
scrambles or randomizes the signal. This is done to ensure that random data is
transmitted even when no video is present or when the video is a constant value for
many scan lines. This permits clock recovery at the receiver. 8.4 MHz Camera ADC
MPEG-2 data compression Sync Header Audio source Other audio sources 8-Level signal
Balanced modulator Carrier generator Local oscillator Power amplifier Antenna Serial
video data Packetizer Packetizer MPX Frame formatter SB filter Data scrambler ADC AC-
3 data compression Trellis encoder Reed-Solomon error detection MPX DAC Up
converter (mixer) Figure 23-27 HDTV transmitter. 32 Chapter 23 Next the random
serial signal is passed through a Reed-Solomon (RS) error detection and correction
circuit. This circuit adds extra bits to the data stream so that transmission errors can be
detected at the receiver and corrected. This ensures high reliability in signal
transmission even under severe noise conditions. In HDTV, the RS encoder adds 20
parity bytes per block of data that can provide correction for up to 10 byte errors per
block. The signal is next fed to a trellis encoder. This circuit further modifies the data to
permit error correction at the receiver. Trellis encoding is widely used in modems.
Trellis coding is not used in the cable TV version of HDTV. The audio portion of the
HDTV signal is also digital. It provides for compact disk (CD) quality audio. The audio
system can accommodate up to six audio channels, permitting monophonic sound,
stereo, and multichannel surround sound. The channel arrangement is flexible to permit
different systems. For example, one channel could be used for a second language
transmission or closed captioning. Each audio channel is sampled at a 48-kbps rate,
ensuring that audio signals up to about 24 kHz are accurately captured and transmitted.
Each audio sample is converted to an 18-bit digital word. The audio information is time-
multiplexed and transmitted as a serial bit stream at a frequency of A data compression
technique designated AC-3 is used to speed up audio transmission.
An HDTV receiver picks up the composite signal and then demodulates and decodes the
signal into the original video and audio information. A simplified receiver block diagram is
shown in Fig. 23-30. The tuner and IF systems are similar to those in a standard TV receiver.
From there the 8-VSB signal is demodulated (using a synchronous detector) into the original
bit stream. A balanced modulator is used along with a carrier signal that is phase-locked to
the pilot carrier to ensure accurate demodulation. A clock recovery circuit regenerates the
clock signal that times all the remaining digital operations. The signal then passes through
an NTSC filter that is designed to filter out any one channel or adjacent channel interference
from standard TV stations. The signal is also passed through an equalizer circuit that adjusts
the signal to correct for amplitude and phase variations encountered during transmission.
The signals are demultiplexed into the video and audio bit streams. Next, the trellis decoder
and RS decoder ensure that any received errors caused by noise are corrected. The signal is
descrambled and decompressed. The video signal is then converted back to the digital
signals that will drive the D/A converters that, in turn, drive the red, green, and blue
electron guns in the CRT. The audio signal is also demultiplexed and fed to AC-3 decoders.
The resulting digital signals are fed to D/A converters that create the analog audio for each
of the six audio channels.
The development of HDTV is in its very final stages, with implementation slated for 2006.
Issues that will have to be worked out include compression, bandwidth allocation,
development of accepted standards in resolution and aspect ratio, and finally widespread
conversion throughout the United States. By the time that conversion takes place, consumers
will have had to chose one of a number of varying options in order to take advantage of
HDTV. At base terms, what sets HDTV apart from the current television system is that it has:
Much more sharpness and clarity
5.1 channel CD-quality Dolby Digital (AC-3) surround sound
Digitally transmitted signals - eliminating snow, double images, and picture sparkles.
With all the hype surrounding it, much like the conversion from black and white to color
television, if HDTV is to be considered successful when implemented, it will have brought
the nation a stunning leap in their television experience with unparalleled image quality,
vastly improved sound, and a new reliability that makes the current NTSC system pale in