| 摘要 |
A demodulator suitable for implementation in a single chip for demodulating digital video broadcast signals comprising data modulated on a multiplicity of spaced carrier frequencies, wherein an input broadcast signal is converted to a frequency sufficiently low to enable analog digital conversion 20 of the signal, conversion means 22 for converting the broadcast signal to a series of digital samples in complex format, transform means 24 for analysing the digital sample values to provide a series of data symbol values for each carrier frequency and signal processing means including channel equalisation means 32 for receiving the signal values and providing an output for decoding, automatic frequency control means 38 for controlling the frequencies of the digital sampling signals applied to said transform means, and timing synchronisation means 26 for synchronising the transform means with the symbol periods of the broadcast signal, including correlation means for receiving said digital signal values and comprising delay means having a time period equal to the active symbol period, and multiplier means for receiving the digital signal values and a version thereof delayed by said delay means, to form a complex product signal, and means for processing the complex product signal to derive timing synchronisation pulses, wherein the timing synchronisation means is operable in an initial hunt mode for analysing said digital sample values over a relatively wide timing range to establish synchronisation, and then operable in a zoom mode for analysing the digital sample values over a relatively narrow range about the synchronisation point.
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