What is Digital tv system ?
A Digital TV (DTV) system consists of two main components viz. the digital tv transmitter and receiver. These components work together to deliver digital television (tv) signals. This system offers high quality and more efficient broadcasting in comparison to traditional analog TV system. Let us explore the basics of dtv using block diagram of each.
The evolution of Digital TV is to replace NTSC system and to provide improvement in the picture and sound quality. It is also referred as HDTV (High Definition Television). DTV employs scanning concept to paint a picture on the CRT. DTV screen is made of thousands of tiny dots of light referred as pixels. The greater the pixels better is the resolution and quality of the picture. The format of DTV screen is defined in terms of (Number of pixels/horizontal line) by (Number of vertical pixels).
The DTV uses progressive line scanning rather than interlaced scanning used by NTSC analog TV version. This is the major difference between them. This format is compliant to computer screens and hence such monitors can be used to display DTV formats. Let us understand DTV Transmitter and receiver modules.
Digital tv Transmitter
The figure-1 depicts digital tv transmitter block diagram. The video and audio signals are processed by this DTV Transmitter.
• Video signal from the camera consisting of R,G and B signals are converted to luminance and
chrominance form. These signals are digitized using A/D converter.
• The resulting signal is serialized and passed to the data compressor . The purpose of data compression is to reduce number of bits required to represent the video data. This way higher transmission rate is obtained in limited bandwidth. MPEG2 is used as data compression method.
• The signal is next passed through the data randomizer. This data randomizer randomizes the data signal. This helps in clock recovery at the receiver.
• The random signal is passed to the RS encoder which adds 20 parity bytes per block of data. This helps in correcting 10 bytes of error per block.
• The signal is next provided to the Trellis Encoder. It modifies the data which helps in error correction at the receiver. This is passed to the packetizer which helps in packaging the video along with the audio as per the DTV packet format mentioned in fig.2.
Audio signal is passed from A/D converter and processed as per AC-3 data compression before being packetized.
As shown in figure-2, DTV packet consists of total 188 bits of data including both video plus audio as well as 4 bytes used for synchronization and header. The header part helps in identifying number of packet, its sequence and video format.
Now, packets are assembled into frames of data representing one frame of video. The frame consists of 626 packets which are transmitted sequentially. The final signal is given to the modulator. DTV uses 8-VSB modulation technique. Some systems even employ 16 level VSB modulation technique.
Digital tv Receiver block diagram
The figure-3 depicts digital tv (dtv) receiver block diagram. DTV receiver does reverse of what has been carried out in the DTV transmission. The main function of DTV receiver is to pick up the composite signal and demodulates and decodes the signal into original audio and video formats. The tuning and IF portions are similar to standard TV receiver.
As mentioned 8 level VSB signal is demodulated using synchronous detector into original bit streams. After equalization bits are processed for error correction using trellis and RS decoder. The signal is demultiplexed into audio and video formats and feed to CRT for display.
ATSC 3.0 Latest Digital TV (DTV) Standard
This ATSC 3.0 tutorial covers basics of ATSC 3.0 TV technology including features. It mentions ATSC 3.0 protocol stack, ATSC 3.0 Physical layer,
ATSC 3.0 Frame structure and ATSC 3.0 advantages or benefits.
Follow ATSC 3.0 tutorial➤.
Conclusion : Digital TV system offers various benefits such as high picture and sound quality, interactive features, more efficient usage of spectrum compared to analog TV system. The digital elevision broadcasting is used widely across many parts of the world.
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