Cs. Koukourlis et al., A GENERAL-PURPOSE DIFFERENTIAL DIGITAL MODULATOR IMPLEMENTATION INCORPORATING A DIRECT DIGITAL SYNTHESIS METHOD, IEEE transactions on broadcasting, 39(4), 1993, pp. 383-389
A highly versatile digital modulator is described which uses a direct
digital synthesis method to perform signal modulation. In contrast to
the customary methods of implementing I-Q modulation schemes utilizing
in-phase and quadrature branches, this design approach is based on di
rectly accessing any of the digitally stored carrier modulating symbol
s according to the information bearing input signals. Apart from the D
igital-to-Analog Converter, all the previous stages are digital. To de
monstrate the concept, a differential 16-QAM modulator was implemented
and is presented in the material that follows. The technique describe
d, lends itself to VLSI implementation. It can be considered as a digi
tal implementation of a digital modulator.