From LinuxTVWiki

Revision as of 23:39, 18 December 2007 by CityK (Talk | contribs)
Jump to: navigation, search

A Demodulator (short Demod) recovers (demodulates) the original information from the received and downconverted RF signal -- a tuner acquires the RF signal and converts it to an intermediate frequency (IF) which is then passed onto the demodulator for processing. The type of demodulator IC used for this task of information recovery is specific and dependent upon the nature of the signal transmission scheme involved.

In the case of analog TV, the IF inputted into the demodulator contains the composite signal that was originally modulated onto the RF carrier. After recovery, the demodulator outputs a CVSB signal, which will then need to be digitized through sampling techniques performed by a A/V decoder.

In the case of digital TV transmission schemes, the IF inputted into the demodulator contains a MPEG2 Transport Stream (TS) that was originally modulated onto the RF carrier. In the process of recovering that TS, digital demodulators will perform Forward Error Correction (Convolutional Viterbi- and Block-Reed-Solomon-Decoding). This whole process is sometimes referred to as RF-to-bits, for, unlike the case with analog IF demodulators, the recovered signal outputted from the digital demodulator is already a digital bit stream; specifically a TS. The TS will in turn be sent to a decoder in order to display (and, depending upon what format the underlying video content contained within the TS was encoded with, this could be a MPEG2 or MPEG4 decoder ... and either hardware or software based).

Also see

Personal tools