The set-top box ( Set-Top Box ) technology is the crucial technology in information appliance. So far the functions of set-top boxes from a multiple frequency tuner and decoder jumped for the movie, multimedia events, news, online database of a control terminal. Therefore, how to extend the functions of set-top boxes, improve quality, reduce the production cost, optimize the product structure, to the development of interactive TV network has important significance.
Function
( 1) can indicate to the user the indoor equipment, CATV network and program resource state; can use user television screen display services and providers of information sent messages and menus.
( 2) the selection information of the user is transmitted to the service center or information providers.
( 4) has the bidirectional communication capacity, can realize the television shopping, distance education and VOD.
( 5) can be connected with the household computer.
( 6) can carry out signal transmission, modulation and demodulation, can deal with ATM protocol.
( 7) capable of monitoring equipment, signal transmission properties of remote sensing and feedback.
The principle structure
With the open structure of the ITV set-top box is of a simple structure, low cost of equipment. It consists of a cheap microprocessor control special VLSI chip, providing the above functions, and complete response to query, routing, decoding, decompression and treatment and control of the work. It is mainly composed of a microprocessor, a digital modulator, ATM processing unit ( ADSL ), image decompressing device, audio decompressor, NTSC / PAL / SECAM RGB encoder, decoder, a remote control interface ( ROM ), read-only memory, random access memory ( RAM ) and the expansion interface.
The set-top box is not only a tuner, and a video server remote control unit. Through the ATM network system, set-top boxes and video server are connected, and the video server are bidirectional, full duplex digital communications.
( 2) Digital Tuner Receiver Microprocessor instructions, acquisition of signal transmission at the desired frequency, bandwidth, modulation mode and needed to decode the digital information. The resulting digital stream includes a plurality of processes or threads, after primary treatment, and then transmitted to the ATM processing device.
The ATM processor will the selected data into the video stream, an audio stream and the data stream for. The video stream to the image decompressing device for processing, audio stream to audio decompressor for processing, data stream is transmitted to a control system. At the same time, the ATM processor also collects the transmission in the relevant error state, and when necessary, send this information to the control system, so that with the end device contact amendments.
( 4) open image decompressing device is a specially designed programmable digital image processing chip. It is loaded for image processing some of the basic fixed algorithm, and from the control system receives special image decompression algorithm. When the ATM processor from digital information into the image decompressing device, you can use the firmware, previously compressed video data.
Then, the decompressed video data is transmitted to the NTSC / PAL / SECAM decoder. Similarly, audio decompressor can also from the control system receives the decompression algorithm. From the ATM processor receives the compressed sound data after decompression, then become a modulated or unmodulated stereo signal, and transmitted to the TV.
