Digital modulator and baseband signal generator for digital modulator

摘要

A digital modulator includes a signal source for a digital baseband signal and a signal source for carrier phase information. The digital baseband signal is converted into amplitude information of an I phase, a Q phase, an I' phase and a Q' phase by a mapping circuit. The carrier phase information is converted into four phase information with phases shifted by shift registers to be out of phase by &pgr;/4 from each other. The digital modulator includes four ROM, each ROM outputting a multiplication result of the corresponding amplitude information and carrier signal based on the corresponding one of the four amplitude information as a higher order address and the corresponding one of the four phase information as a lower order address. These outputs are added to each other in a digital manner and then converted into an analog signal which is supplied as a modulated signal.