To make the output useful, the sign

To make the output useful, the signal must be converted from phase information into a sinusoidal value. Because phase information maps directly into amplitude, a ROM LUT converts the phase information into amplitude. To do this, the digital phase information is used to address a sine ROM LUT. Although the NCO contains a 32-bit phase accumulator, the output of the NCO is truncated to 12 bits. Using the full resolution of the phase accumulator is impractical and unnecessary because this would require a look-up table of 232 entries. It is only necessary to have sufficient phase resolution in the LUTs so that the dc error of the output waveform is dominated by the quantization error in the DAC. This requires the look-up table to have two more bits of phase resolution than the 10-bit DAC.