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Set-top boxes may be associated with these major categories.
(1) Broadcast TV Set-top Boxes - (a.k.a. Thin Boxes) - A more primitive set-top box with no back channel (return path.) These might come with interface ports, some memory and some processing power.
(2) Enhanced TV Set-top Boxes - (May be known as: Smart TV Set-top Box, Thick Boxes) - These have a back channel (return path), often through a phone line. These may be capable of Video on Demand, e-commerce, Internet browsing, e-mail communications, chat and more.
(3) Advanced Set-top Boxes - (a.k.a. Advanced digital Set-top boxes, Smart TV Set-top Box, Thick Boxes, All-in-one Set Top Box, Media Center) - A fully integrated set-top box. These have good processors, memory, middleware, software applications and optional hard-drives. They're often used with high-speed (broadband) connections. Features could include high-speed Internet access, Interactive TV, digital video recording & gaming. Instead of this, a "sidecar" (below) might be used in tandem with the set top box and/or TV. Advanced set-top boxes are more likely to be integrated with DVRs and high-definition TV. See Media Centers.
(4) Sidecar - This type of set-top box provides an additional transport stream of data from the network operator to compliment the main stream. With Charter Communications’, the BMC-8000 (Broadband Media Center) is/was a sidecar box that works in tandem with the Motorola DCT-2000. A fully integrated unit would not require a Sidecar.
(5) Hybrid Digital Cable Box – A Hybrid Digital Cable Box is a specialized cable TV set-top box with high end functions. Motorola Broadband’s DCP501 home theater system is/was an example (depending on when you read this.) It has/had a DVD player and high-end stereo output. This term may be antiquated. See Home Media Centers.
(6) Over-the-top Boxes - Electronic device manufacturers are providing DVD players, video game consoles and TVs with built-in wireless connectivity. These devices piggy back on an existing wireless network and pull content from the Internet and deliver it to the TV set. Typically these devices need no additional wires, hardware or advanced knowledge in how to operate. Content suited for TV can be delivered via the Internet.
Modern day set-top boxes generally are digital devices that communicate using computer language. In the past when the set-top box functions were built in to another device, such as a TV, it might have been referred to as a device with a “built-in”. Now-a-days the phrase “built-in” has been superceeded by the phrase "integrated". Now a TV with set-top box functionality built into it is more often called an "Integrated TV". If it's a digital TV, it would be known as an "Integrated Digital TV" (iDTV). just because a TV has set-top box functions built in to it, that doesn't mean it's a digital TV. In that case it's just an analog TV with set-top box functions built into it.
A set-top box is a computerized device that processes digital information. Set-top boxes (STB) come in many forms and can have a variety of functions. Digital Media Adapters, Digital Media Receivers, Windows Media Extender and most video game consoles are also examples of set-top boxes. Currently the type of TV set-top box most widely used is one which receives encoded/compressed digital signals from the signal source (perhaps your cable or telco TV provider's headend) and decodes/decompresses those signals, converting them into analog signals that your analog (SDTV) television can understand. The STB accepts commands from the user (often via the use of remote devices such as a remote control) and transmits these commands back to the network operator through some sort of return path. Most set-top boxes deployed today have return path capability for two-way communication.
STBs can make it possible to receive and display TV signals, connect to networks, play games via a game console, surf the Internet, interact with Interactive Program Guides (IPGs), virtual channels, electronic storefronts, walled gardens, send e-mail, and videoconference. Many STBs are able to communicate in real time with devices such as camcorders, DVD and CD players, portable media devices and music keyboards. Some have huge hard-drives and smart card slots to put your smart card into for purchases and identification.
Generally put, to provide interactive services, the set-top box might need some or all of the below:
(1) A network that offers the potential for interactivity.
(2) The network interface - This connects the STB to a network which makes it possible to communicate with the servers.
(3) A tuner is electronics that 'catch' the incoming signal.
(4) The decoder - In order to save storage space, disk bandwidth, and network bandwidth, programming is usually encoded (compressed) before being sent over the network to the STB. Thus, the end-user (subscriber) needs a decoder to decode (uncompress among other things) the incoming stream's data before it can be viewable on the TV. This is part of what a modem does. The decoding process may be known as (or include) Demodulation (Heavy Lifting.) It could include Demultiplexing. (MPEG-4) compression technology utilizes up to 40 percent less network bandwidth than the MPEG-2 compression used in most systems to date.
(5) The buffer - Due to delay jitters in the network, the exact arrival time of a video stream often cannot be determined. In order to guarantee continuous and consistent playback for the viewer, the video and/or data stream(s) may be received one or even a few seconds before it's actually seen by the end-user. This way if there are fluctuations in the transport time of the streams to that receiver (aka set-top box, decoder), the viewer won't know the difference as their buffer has a bit of time to spare.
(6) Synchronization software/hardware - Video and audio streams must be synchronized with each other before viewing. Other streams may be added including those related to enhancements (such as metadata.)
(10) Any additional software and/or hardware.
(11) A return path (back channel).
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The working phase of the digital television set-box is roughly as follows:
1. The R.F.head receives the high frequency signal from cable network, finish the signal channel to decode through QAM demodulator, isolate the sound, video and other data information to flow from the carrier. Generally sound, video flowing and some data information while conveying and flowing.The digital television set-box is the integration products of computer and television in view of function, the set-box includes the following levels:
( 1) Physical layer and connecting layer: Including high-frequency tuner, QPSK, QAM, OFDM, VSB demodulation, the convolution is decoded, de-interleaving, a Saloman of Reed decodes, solve energy dispersal.
( 2) Transport layer: Including demultiplexing, it divides transport stream into video, audio frequency and data packet.
( 3) Program layer: Including MPEG- 2 video decoding. MPEG/AC- 3 audio decoding.
( 4) User level: Including serving information, the electronic listing, graphical user interface (GUI) ,The browser, remote control, conditional acceptance, the data are decoded.
( 5) Output interface: Look at the audio interface including dividing simulation, the figure looks at the audio interface, data interface, the keyboard, the mouse,etc..
2.Set-box critical technology of the digital television
The top box of digital machine embodies a concentrated reflection of the multimedia, computer, data compressed encoding, adds the descrambling algorithm, adds decoding algorithm, communication skill and network state-of-the-art, so the technological content is very high, the critical technology that it involves is mainly as follows,
( 1) Multiplex and decompression technique: After the digitization of analog signal. The information volume is increased severely, data compaction is essential. MPEG- 2 video compression standard adopts in the digital television extensively, suitable for the image quality of many kinds of sharpness:
MPEG- 4 adopt on the basis of compressed coded method of target, it cut different target apart into, deal with respectively picture and video, not only raise the compression ratio of the data, still can realize a lot of mutual functions based on content, have offered the broader platform for compressed encoding of multimedia data.
It is employed extensively that technical with large-scale integrated-circuit technique and embedded system, the hardware implementation of the top box of digital machine adopt the special purpose chip or digital signal processing (DSP more, DigitalSignalProcessing) The chip, integrate CPU kernel and MPEG-2, MPEG4 transport stream NULL, DVB common descrambler, MPEG audio frequency video decoder and NTSC/PAL Coder, form the key chip of STB. In order to realizing demultiplexing in real time and real time data information processing.
( 2) Demodulation of data of descenting and signal channel decode technology: The data after compressing can't be transmitted on the signal channel directly, need to carry on channel coding and modulate. Usually transmissive digital television and value-added service in cable television network, adopt more QAM (QuadratureAmplitudeModulation)s Modulation mode and RS (ReeDSOlomon) Error correction coding.
( 3) The machine format modulation code of up run: In the interactive application, generally adopt 3 ways, namely adopt the telephone line to convey the upstream data. Adopt Ethernet to convey the upstream data and convey the upstream data through the wired network. Because upstream data should be few much to data of descenting, so use more OP-SK (QuadraturePhaseShiftKeying)s Or 160AM way is modulated.
( 4) The network browses through technology: In order to realize the real network browses through, the Cable News Network connects with Internet except considering the up run and data of descenting, must also consider that operate IP (InternetProtocol) on it .