A General Purpose Differential Digital Modulator Implementation Incorporating a Direct Digital Synthesis Method

A highly versatile digital modulator is described hich uses a direct digital synthesis method to perform signal modulation. In contrast to the customary methods of implementing l-Q modulation schemes utilizing in-phase and quadrature branches, this design approach is based on directly accessing any of the digitally stored carrier modulating symbols according to the information bearing input signals. Apart from the Digital-to-Analog Converter, all the previous stages are digital. To demonstrate the concept, a differential 16-QAM modulator as implemented and is presented in the material that follos. The technique described, lends itself to VLSI implementation. It can be considered as a digital implementation of a digital modulator.