| 摘要 |
PROBLEM TO BE SOLVED: To provide a digital modulator which mainly receives and demodulates a 16-QAM signal, in which an A/D converting part is composed by one, and which also automatically cancels a DC offset and performs data demodulation. SOLUTION: The A/D converting part 1 performs under-sampling of an intermediate frequency signal IF of a QAM wave to convert the signal IF into a digital signal, a quadrature detecting part 2 performs digital detection, an LPF 3 of a route Nyquist characteristic subsequently extracts a required low- pass component, and an AFC 4 corrects a carrier frequency. A 1st phase error calculating part 5 calculates a phase error from the output of the AFC 4, a 1st phase correcting part 7 performs phase correction of the output of the AFC 4 with the calculation results, an offset cancel level calculating part 9 calculates a DC offset level, and adders 10 and 11 subsequently add the calculated data to the output of the AFC 4 and cancel the DC offset. A 2nd phase error calculating part 12 further calculates a phase error about the canceled signal, and an area deciding part 18 decodes the data on the basis of a signal whose phase is corrected by a 2nd phase correcting part 13. |
