A DTV receiver is a
set-top box
A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of sign ...
that permits the reception of
digital television
Digital television (DTV) is the transmission of television signals using digital encoding, in contrast to the earlier analog television technology which used analog signals. At the time of its development it was considered an innovative advanc ...
. Its components are very similar to a desktop PC. The DTV receiver is a vital link in the chain of television system. The goal of a broadcasting system is to concentrate the hardware requirements at the source to simplify the receivers and makes it as inexpensive as possible.
It is usually connected to the TV set or incorporated in the TV set. The main features of a DTV receiver may be classified as follows:
*decodes the incoming digital signal;
*verifies access rights and security levels;
*displays cinema quality pictures on the TV set;
*outputs digital surround sound;
*processes and renders Internet and interactive TV services.
Overview
The tuner in the box receives a digital signal from a
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
, a
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
, or terrestrial network and isolates a particular channel. The signal is then forwarded to a demodulator and converted to binary format. Once in binary format, the demodulator will check for error and forward the binary signal to a demultiplexer that will extract audio, video, and data from the binary stream.
Once the demultiplexer has finished with the signal, the decoders will transform the digital bits into a format suitable for viewing on the television set.
As the architecture of a DTV receiver can vary in function of the network operator or the set-box manufacturer, we have chosen to divide the physical components into the following categories:
*system board,
*tuner,
*modulator and demodulator,
*demultiplexer and decryptor,
*decoders,
*graphics processor,
*CPU and memory,
*storage devices,
*physical interfaces,
*physical characteristics.
Architecture
System board
All the main hardware components of the receiver are connected to the system board. Buses are used to carry the digital TV information between the hardware components.
DTV Tuner
The
ATSC tuner
An ATSC (Advanced Television Systems Committee) tuner, often called an ATSC receiver or HDTV tuner, is a type of television tuner that allows reception of digital television (DTV) television channels that use ATSC standards, as transmitted by te ...
module is available for accessing QAM-, OFDM, and QPSK-based networks. In addition to receiving inputs from digital networks, most tuners are also capable of tuning analog broadcasts. Tuners can be divided into three broad categories:
*Broadcast In-band (IB) Tuner. Once the signal arrives from the physical transmission media, the IB tuner will isolate a physical from a multiplex of channels and convert to baseband. The term baseband is used to describe a single channel or digital signal, extracted from broadband signal which is a stream of multiple channels.
*Out Of Band (OOB) Tuner. This type of tuner facilitates the transfer of data between the head-end systems and the set-box. They are widely used in cable set-top boxes for providing subscribers with medley of interactive services. Implementations of the OOB tuner tend to operate within 100 to 350 MHz frequency band.
*Return Path Tuner. This tuner allows a subscriber to activate the return of path and send data back to the interactive services provider. Implementations of this tuner tend to operate within the 5 to 60 MHz frequency band.
Modulator and demodulator
The function of the demodulator is to convert the analog signal to a digital bitstream. Then, it checks for errors and forward the bitstream to the demultiplexer.
The modulator reverses the actions of a demodulator and its function is to deliver a signal to the return path tuner.
Demultiplexer and decryptor
The technology used in DTV television is
MPEG-2
MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic video coding format, coding of moving pictures and associated audio information". It describes a combination of Lossy compression, lossy video compression and ...
. The demultiplexer selects particular packets, decrypts, and forwards to a specific decoder.
Decoders
A DTV receiver will normally contain three separate decoders for converting the
digital bit-stream back into a format that can be heard and viewed by the subscriber.
A video decoder It transforms video packets into a sequence of pictures, which are displayed by the TV monitor.
An audio decoder It decompresses the audio bit-stream. Different audio modes are usually supported by the DTV receiver: mono and dual channel, stereo, and joint stereo.
A data decoder.
Graphics Processor
The main purpose of a graphics processor is to render a range of Internet file formats and proprietary interactive TV file formats.
Central processing unit
The CPU, like in a desktop PC, is the brain of the DTV receiver. Functions provided by a CPU include:
*initializes the various hardware components;
*processes a range of Internet and interactive TV applications;
*monitors and manages hardware interrupts;
*fetches data and instructions from memory;
*runs various programs.
Memory
As a computer, a DTV receiver needs memory to store and manipulates instructions. Most elements within the receiver require memory to perform various tasks: The graphics engine, video decoder...
See also
*
Analog television
Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, instantaneous phase and frequency, ...
*
ATSC standards
*
Broadcast television system
Broadcast television systems (or terrestrial television systems outside the US and Canada) are the encoding or formatting systems for the transmission and reception of terrestrial television signals.
Analog television systems were standardized by ...
s
*
Common Interface
In Digital Video Broadcasting, the Common Interface (also called DVB-CI) is a technology which allows decryption of pay TV channels. Pay TV stations want to choose which encryption method to use. The Common Interface allows TV manufacturers to ...
*
Digital radio
Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services.
Types
In digital broadcasting syst ...
including digital television broadcasting
*
Digital Video Broadcasting
Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) ...
*
Digital Video Broadcasting - Terrestrial
*
DMB-T/H,
China's
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
digital television standard
*
Digital terrestrial television
Digital terrestrial television (DTTV or DTT, or DTTB with "broadcasting") is a technology for terrestrial television in which land-based (terrestrial) television stations broadcast television content by radio waves to televisions in consumers' ...
(DTT or DTTV)
*
High-definition television
High-definition television (HD or HDTV) describes a television system which provides a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936; in more recent times, it refers to the g ...
*
Interactive television
Interactive television is a form of media convergence, adding data services to traditional television technology. It has included on-demand delivery of content, online shopping, and viewer polls. Interactive TV is an example of how new information ...
Notes
References
{{No footnotes, date=November 2009
*Gerard O'Driscoll, ''The essential Guide to Digital Set-Boxes and Interactive TV'', reprinted April 2000
*Jerry whitaker, ''Television Receivers'', 2001
Digital television
Set-top box