Direct digital frequency synthesizer for use in a subscriber unit of a wireless digital communication system

Claim 1

A digital frequency synthesizer for use in a subscriber unit of a wireless digital communication system comprising: a processor, for providing an output phase signal corresponding to a selected output digital frequency; means for buffering said phase signal; lookup table means comprising a memory device having two sets of predefined stored values pertaining to the amplitude of a signal for a single quadrant, wherein said predefined stored values comprise coarse angle approximations and fine angle approximations; signal generator means for receiving said phase signal and generating sine and cosine waveforms utilizing amplitude values obtained from said lookup table means, wherein said phase signal includes phase data and specifies the quadrant and the algebraic sign of the phase data; said signal generator means accessing said lookup table means differently depending upon the quadrant and sign of the phase data such that the lookup table means provides an amplitude value from said sets of predefined stored values based upon the phase data; means for combining the sine and cosine waveforms to produce said selected output digital frequency; and means for modulating said digital frequency.