a subscriber unit has a processor . the processor provides an output phase signal corresponding to a selected output digital frequency . a tuning register buffers the phase signal . a lookup table has two sets of predefined stored values pertaining to the amplitude of a signal for a single quadrant . the predefined stored values comprise coarse angle approximations and fine angle approximations . a sine and cosine generator receives the phase signal and generates sine and cosine waveforms utilizing amplitude values obtained from the lookup table . the phase signal includes phase data and specifies the quadrant and the algebraic sign of the phase data . the sine and cosine generator accessing the lookup table differently depending upon the quadrant and sine of the phase data , such that the lookup table provides an amplitude value from the sets of predefined stored values based on the phase data . a modulator combines the sine and cosine waveforms to produce the selected output digital frequency and modulates digital frequency .