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Digital TV Set-top Box
Nov 13, 2018

The digital TV set-top box is composed of a high frequency head, a QAM demodulator, a TS stream demultiplexer, an MPEG-2 decoder, a PAUNTSC video encoder, an embedded CPU system and a peripheral interface, a CA module, and an uplink data modulator.

The working process of the digital TV set-top box is roughly as follows: the tuner receives the high-frequency signal from the cable network, completes the channel decoding through the QAM demodulator, and separates the transport stream threshold containing the audio, video and other data information from the carrier. The transport stream generally contains multiple audio and video streams and some data information. The demultiplexer is used to distinguish different programs, extract corresponding audio, video streams and data streams, and send MPEG-2 decoder and corresponding parsing software to complete the restoration of digital information. For pay TV, the conditional receiving module performs descrambling on the audio and video streams, and uses a smart card containing the identification user and the billing function to ensure that the legitimate user can watch normally. The MPEG-2 decoder performs decompression of audio and video signals, restores analog audio and video signals through video encoder and audio D/A conversion, displays high quality images on a conventional color television, and provides multi-channel stereo programs. .

The digital TV set-top box is a fusion of computer and TV, but the structure is different from the two. From the perspective of signal processing and application operation, the set-top box contains the following levels:

(1) Physical layer and connection layer: including high frequency tuner, QPSK, QAM, OFDM, VSB demodulation, convolutional decoding, deinterleaving, Reed-Solomon decoding, solution energy diffusion.

(2) Transport layer: including demultiplexing, which divides the transport stream into video, audio and data packets.

(3) Program layer: including MPEG-2 video decoding. MPEG/AC-3 audio decoding.

(4) User layer: including service information, electronic program table, graphical user interface (GUI), browser, remote control, conditional access, data decoding.

(5) Output interface: including analog audio and video interface, digital video and audio interface, data interface, keyboard, mouse, etc.


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