A GENERAL-PURPOSE DIFFERENTIAL DIGITAL MODULATOR IMPLEMENTATION INCORPORATING A DIRECT DIGITAL SYNTHESIS METHOD

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.