Pick   To:       This article introduces the DMB-T standard definition receiver set-top box built with LGS8222 , which has the characteristics of superior performance, simple structure and low cost.
Overview
Digital Terrestrial Television Broadcasting (DTTB) since November 1998 launch in North America and Europe, many countries have entered the business in the operational phase. There are currently three international standards for digital TV (DTV) terrestrial transmission, namely: the American ATSC system using 8-VSB modulation , the European DVB-T system using COFDM modulation, and the Japanese ISDB-T system using BST-OFDM . On the basis of fully absorbing the advantages of these three terrestrial transmission standards, the Digital TV Technology Research Center of Tsinghua University introduced new technological achievements in the field of communication, and proposed a new type of ground with independent intellectual property rights in China for the specific requirements of television broadcasting Digital Multimedia / TV Broadcast Transmission Standard (Terrestrial Digital MulTImedia / TV BroadcasTIng, DMB-T) scheme. It uses time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) modulation method, which is unique and effective in system frame structure, synchronization, channel estimation, guard interval, symbol mapping, error correction coding and system implementation. The technical solution has great improvements in anti-multichannel noise, multipath, Doppler fading, clock recovery, transmission efficiency, etc. The latest generation of dedicated chip models for receivers launched by the Digital TV Technology Research Center of Tsinghua University for the DMB-T solution is LGS8222 . This article will briefly introduce the solution of using LGS8222 to build a standard definition set-top box that meets the DMB-T protocol standard definition.
system introduction
As shown in Figure 1 , the main components of the DMB-T standard definition set-top box include: high-frequency head, DMB-T channel demodulation chip, MPEG-2 decoding chip, power supply unit, various peripheral memories and amplifiers. Standard definition set built demultiplexer, MPEG-2 decoders and PAL / NTSC encoder, and an infrared remote control interface of the 81MHz CPU. The system uses 16MB of SDRAM as the memory shared by MPEG and CPU , and 4MB of Flash memory as the program memory. The input of the set-top box is a radio frequency signal conforming to the DMB-T specification, and the output is an audio and video signal. In order to facilitate vehicle installation , the power input of the set-top box is DC 12V , and the total power consumption of the system is 8W . In order to facilitate monitoring of reception performance, the set-top box also provides an error indication signal.
Figure 1 DMB-T set - top box block diagram
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Figure 2 LGS-8222 system block diagram
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Picture 3 Â DMB-T standard definition set-top box
The key parts of the block diagram are briefly described below.
Tuner
The high frequency head used by DMB-T is similar to the high frequency head of DVB-T system. All high frequency heads that support DVB-T can be used in DMB-T set-top boxes. Thomson, Sharp tuner related functions are used Thomson's DTT7578 / 7579 (vertical / horizontal) in the present embodiment. It is a high-frequency head developed by Thomson for digital terrestrial television broadcasting. Its operating frequency range is V- segment (177 ~ 227MHz) and U- segment (470 ~ 860MHz) , and its output is an intermediate frequency of 36MHz . Inside the tuner there are two levels of AGC -RF AGC and intermediate frequency AGC , the total gain of the two levels of AGC is 90dB . DTT7578 / 7579 uses a single power supply, and the various voltages required are provided by the internal DC / DC converter. The control of the high frequency head is realized through the I2C bus.
DMB-T channel decoding chip
LGS-8222 is a digital television technology, Tsinghua University Research Center latest channel monolithic meet specification receiving DMB-T demodulator chip, which has good reception performance in a variety of complex situations, the function block diagram shown in Figure 2 . LGS8222 has a built-in high-performance A / D converter. The A / D converter performs digital-to-analog conversion on the input analog intermediate frequency signal, then synchronizes, equalizes, and corrects the signal, and finally outputs the MPEG-2 code stream.
The main characteristics of the LGS-8222 chip are as follows:
MPEG-2 decoder chip
STI5518 is a powerful and low-cost new MPEG-2 decoder launched by ST . It is an upgraded product of the company's set-top box back-end decoder STI5500 (OMEGA) . STi5518 retains all the features of STi5500 and adds support for Dolby Digital and MP3 audio decoding. Since additional logic circuits have been added to facilitate the connection of hard drives, this device has become an ideal component for emerging "converged" products that can provide functions such as pause of live TV and playback of recorded TV programs. STi5518 integrates on one chip: a transmission signal separator module, an ST2032 -bit CPU , an audio / video MPEG-2 decoder, display and graphics functions, a digital video encoder and system peripherals. STi5518 can be seamlessly combined with LGS8222 to realize DMB-T receiver set-top box.
Conclusion
The DMB - T SD receiver set-top box built with LGS8222 has the characteristics of simple system, low power consumption (the entire set-top box power consumption is about 8W) , and low cost. It provides a strong guarantee for the development of terrestrial digital multimedia broadcasting services. Figure 3 is a photo of the DMB-T standard definition set-top box built with LGS8222 . â–
references:
1. Â LGS-8222 Manual
2. Â Â Â Â Â Â Â STi5518 Manual
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